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Micronutrients: Effective Measurement and Use of Manganese


This article is the second in a two part series on the micronutrient manganese. See the February/March issue of Organic Farmer magazine for additional information on manganese.

A close reading of the information provided in Part 1 of this article series and elsewhere should make it evident that testing for manganese levels can be measured and reported with great variance from lab to lab. Consequently, the required numbers can be very different on other tests than those that are being discussed here.

The guidelines used below for manganese needs and recommendations are based on tests for evaluating soils analyzed by using the originally established needs for the Albrecht system. Some may object and question why one would report numbers that are not of universal application. When numbers vary so greatly, nothing is meaningful unless it can be based on a foundation that is solid enough to report what field testing shows to be actually needed.


Manganese Deficiencies

What should growers look for to help identify when manganese is deficient (less than 40 ppm on the true Albrecht system tests) and limiting for the crop being grown on such soils? Numbers reported by other soil laboratories are not comparable according to those who have tried to do so. This is just to caution that pushing up the numbers on other soil tests to match what is shown as the measured need for crop examples used here may result in the overuse of manganese.

But when this specific test is performed, 40 ppm is the minimum recommended. Soybeans will begin to show mild symptoms of manganese deficiency in mature leaves later in the season at 37 to 38 ppm. Levels of 30 ppm or so begin to show results of shorter stalks of corn, though less yield and stalk size should be expected to result long before that. This makes manganese deficiency especially important for attaining the highest tonnages of corn silage.

Once other obvious deficiencies have been eliminated, wheat yields tend to respond well as manganese builds to the higher levels in any soil. For example, soils with similar fertility that have 40 ppm manganese will not produce the yield that those same soils provide at 80 ppm manganese. In fact, when manganese is truly the most limiting factor for high-yielding wheat soils, the yields will continue to increase on those soils until 200 to 250 ppm available manganese is reached when this specific type of testing is performed. Caution is extremely necessary here as almost any textbook will report that 200 ppm manganese is toxic to growing plants. Obviously, the tests being used are not the same as the one advocated here for determining manganese availability.

Tree crops, especially nut trees, respond very well to manganese with best results on soils where manganese is above 120 ppm. Walnuts are especially sensitive to manganese deficiency. Consequently, though normally not specifically recognized as the problem, soils that test below 40 ppm using this particular type of testing for manganese are generally classified as being unfit for walnut production.

The guidelines given here for manganese are specific to this type of testing, and using them is not advised for any other laboratory’s manganese test. But these numbers are being provided here to show there is a basic foundation to explain what can be expected when manganese is properly measured and applied for crop production.

Anything less than 40 ppm on the test we use means the full benefits from adequate manganese will not be realized for whatever crop. Although on soils with more than 5% organic matter, resulting deficiencies may not be as evident, and optimum results will still not be attained until any manganese deficiency is corrected.

In addition, keep in mind that a true manganese deficiency of below 40 ppm may be the case, and manganese still may not give the expected response when applied and even brought up to above the deficiency level. That is why so many “research” plots concerning manganese use fail to provide any benefits. If any of the primary or secondary elements are seriously deficient, correcting them will take precedence over the manganese level.

For example, a serious problem with newly planted almond trees is breakage during high winds. Some growers have corrected that problem by adding sufficient amounts of manganese. Many others try it without the same satisfactory results. That is because there are three elements involved here that provide for increased wood strength of which manganese is usually found to be correctly ranked as the second or third most important.

Adequate potassium is always of primary importance for wood strength. Manganese is second if it is below 40 ppm. Sufficient copper, which will be considered next in this series, is the other needed element and is necessary to help provide strength and resilience to the limbs.

Without an adequate uptake of manganese, weaker wood will always be the result. But soils can have good to excellent manganese levels and still the trees or other crops that grow there can be deficient in manganese. This becomes a serious problem when soils are too high in potassium (generally on lighter soils where too much compost has been applied) or too high in sodium (a problem for many soils, especially in the Western U.S.)
In fact, in any combination where potassium and sodium added together exceeds 10% of total soil saturation, manganese uptake begins to be blocked. The higher that percentage goes above 10%, the worse this problem becomes for the growth of any crop.

Note that the soil test may show to have plenty of manganese, but remember that, in this case, manganese is still there and in the correctly available form. That is because potassium and sodium do not tie up the manganese. Between the two when their levels of soil saturation is too high (10% on the Albrecht test), then, the uptake of sufficient manganese is blocked out. There is so much available potassium or sodium there that sufficient manganese just cannot get into the plants.


Having Sufficient Manganese

Why be concerned about having sufficient manganese in the soil? What are the benefits to farmers and growers when manganese-deficient soil is adequately corrected?

First, sufficient manganese (above 40 ppm) is necessary for quicker seed germination. Accordingly, enough manganese will cause the plants to grow off faster. Manganese is needed to determine the number of seed to be produced and to hold the blooms and seed or fruit in place. So, adequate manganese is needed from start to finish in terms of crop production.

What levels are needed? 40 ppm is the minimum. 80 ppm is considered as good. 125 ppm is considered the low side of excellent and 200 to 250 the high side, depending on crop sensitivity. In any case, it is best to build the level up in increments, even if the cost to do so is not considered as being a problem.

The guidelines for application rates on manganese is a maximum of 200 pounds of 28% manganese sulfate per acre even when severe deficiencies will not be corrected by that amount.

There is yet another problem that growers may have in trying to determine when there is sufficient manganese for the crop. This has to do with using a leaf analysis to determine if plants have sufficient or insufficient manganese.

One good example is when the Albrecht analysis shows manganese as even slightly deficient, common scab can be a problem for potatoes. Yet, in too many cases, the leaf analysis shows the level of manganese to be adequate, even when the soil test still shows manganese as deficient in the soil. Which should be believed? The fact that this problem is never solved until adequate manganese is present in those soils should help show which is correct!

Keep in mind that many potato growers use a metallic manganese based foliar to treat for disease. This can greatly skew the levels shown from the leaf test. But this is not the entire story. Potatoes have been used as an example here due to their extreme sensitivity to manganese deficiency. And at times, even those who have not used a foliar manganese can have leaf tests that show manganese as “too high” when, in actuality, the soils are still too deficient to correctly supply plant needs.

We find this consistently tends to be the case with leaf testing for most micronutrients, not just manganese, as compared to the levels shown to be required on the soil test to properly solve each deficiency. Such deviations can also be a serious problem when considering needs for other manganese-sensitive crops such as wheat, grapes and all types of trees, but especially English walnuts and black walnuts.

There is still another precaution that should be considered when using a leaf analysis for evaluating available levels of manganese for crop production. Even leaving dust on the leaves can cause manganese levels to appear to be too high in the plant. A good way to detect this is when iron and aluminum are also shown to be extremely high on the same analysis. When that happens, test again with clean plant tissue to be sure.

Another factor that is essential for manganese uptake is that a sufficient supply of calcium must be present in the soil. This is not determined by the fact that the soil has an adequate to high pH. There is only one way to tell when soils have at least the minimum level of available calcium to take up sufficient manganese for the crop: the soil needs calcium levels to be built up to and then maintained at between 60% to 70% base saturation before plants can most efficiently utilize available manganese from the soil. (CAUTION: Some labs may test as much as 4% lower while others show as much as 12% higher soil calcium saturation than the numbers determined by the Albrecht system testing procedures.)

Perhaps an additional word of caution should be given here, for even soils that may initially have an adequate amount of manganese can develop a deficiency problem if an excessive amount of unneeded lime is applied. An excess can cause manganese to go from adequate to deficient over the next one to three cropping seasons.

This can happen when any material containing a sufficient amount of calcium is applied on soils that barely have enough manganese (with even worse results when the soil is already deficient in manganese), because when calcium is applied, as it becomes available over the next one to three years, it will begin to tie up plant-available manganese in that soil. If the soil has enough manganese to stand the amount of calcium applied, manganese will not become a problem there as a result of applying needed lime.

This is one reason why in some areas potato growers can apply calcium limestone and have no problem with common scab, but in other areas no one will dare apply it. And due to soils needing calcium for adequate uptake of all the other nutrients (including N-P-K) if the problem is not solved, crop production will not only suffer but may even decline in terms of yield and certainly in terms of food quality.

Yet the issue of adequate manganese in the soil can be overcome by applying a sufficient amount of the correct type of manganese. That needed amount should be based on a detailed soil analysis which can accurately determine the desired level in the soil. The test should be such that it can accurately determine how much manganese is required to overcome any tie-up from added calcium as well. Whether already deficient, or for a potential decrease in manganese due to liming or other sources of calcium (such as poultry manure), only the use of true manganese sulfate should be considered for adding to the soil to sufficiently build up the manganese level to solve that need.

From the tests we use, the need for manganese will be reflected and solved based on the use of one pound of actual manganese for every pound shown to be lacking. If that does not happen in the next twelve months after an initial application, someone is likely providing the wrong advice or recommending the wrong product.

Some soils do not even build well using manganese sulfate. In a very few cases it has been necessary to apply the needed amount for two or three years in a row to reach the desired minimum level. Because of its physiological make-up, a crop which can also help to measurably increase manganese availability in the soil is rice.

Just keep in mind that the primary elements, N-P-K, truly are primary in terms of getting enough nutrients there to grow the crop. But when any one of these three are over-applied, providing more than the soil can tolerate, those same elements can cause a whole new set of problems, not just for the crops mentioned in this article but for all types of crops and growing plants.

For example, as discussed already in regard to manganese, potassium or sodium alone, or any combination of the two, totaling more than 10% will begin to block the uptake of manganese. Normally, available soil boron will begin to be tied up when potassium remains above 7.5% saturation in any soil during the growing season. Excessive phosphate reduces zinc availability and uptake in crops. And excessive nitrogen ties up available copper, which is the next micronutrient that will be considered in this series about the need for trace elements.

Understanding the Economics of Organic Seed Production


Organic seed production is a developing industry and viable economic opportunity for organic growers. To help growers manage the uncertainties and risks inherent to seed production, and to help growers earn more profit, Organic Seed Alliance (OSA) recently published an online toolkit to assist organic seed growers and seed enterprises. The toolkit serves as the first of its kind to focus on organic seed production specifically, offering support in the form of budgeting spreadsheets, inventory management, and foundation and stock seed planning.

Seed production can be deeply rewarding work. However, turning a passion for seeds into a viable livelihood is a challenge that even experienced seed growers struggle to overcome. That’s why this entire toolkit was developed in partnership with agricultural economists at Highland Economics— experienced professionals who understand the importance of a farm budget and production plan.


Tracking Expenses and Budgets

The first tool in the Seed Economics Toolkit is a spreadsheet that helps growers track the costs associated with producing seed crops. Enterprise budgets provide a snapshot of costs associated with a crop for a single year and do not make predictions or forecasts for future years. However, they can be used to provide guidance for growers who are considering investments in new equipment and scaling up.


Stock and Foundation Seed Production

Common questions around foundation, stock and production seed include: How much foundation seed do I need to ensure I have enough stock seed? How much stock seed should I produce every third year for my production seed? This second spreadsheet helps guide decisions around how much and how often to produce foundation, stock, and production seed based on your operation, desired inventory, longevity of the seed and estimated yield.


Tracking Labor

Tracking on-farm labor can be confusing and overwhelming, but it is also extremely important for growers trying to get a handle on their operation costs. A third piece of this toolkit is designed as a guide for tracking your operation each day, including a form designed for routine activities over the course of many days (such as watering in a greenhouse or screening a large seed lot) for tracking labor in seed production.


Getting Seed Contracts

Success in seed production contracts requires careful management of the grower-buyer relationship and an understanding of the terms of the contract. Learning from others’ experience can save many headaches and ensure a successful grower-buyer relationship. Over the years, experienced seed growers and buyers have shared their experiences and advice in workshops and webinars at the Organic Seed Growers Conference and other online networking events. Several of these webinars also offer contact information and guidance on how to reach out to seed companies when seeking contracts (all of these webinars are provided as part of the Seed Economics Toolkit at the link at the end of the article.)

Growing seed on contract for a seed company takes some of the sales-related risks out of seed production, but finding the opportunity to grow on contract can also be a hurdle as it is not always clear how to connect with a seed company to acquire contracts. Seed companies and growers alike report that they most often make new relationships by networking at conferences, such as the Organic Seed Growers Conference, and other regional events. Many seed growers also cold call companies to see if they’re looking to contract with new growers.

As an organization that strives to create networking opportunities for seed growers, OSA developed an online registry called the Organic Seed Producers Directory to connect seed growers with seed companies. It includes a user profile that shares each grower’s location, scale and crop expertise. In this way, the directory can be searched by seed companies seeking new growers and for producers to connect with one another as well.

If you are an organic seed grower who would like to join this directory, create a profile today to start connecting with seed companies and other growers at: seedalliance.org/directory/.


Seed Company Advice

Prices for wholesale production vary widely by crop, variety and scale as well as terms of the contract. The roles and expectations of the producer also influence the pricing in a production contract and understanding the expectations of the seed company is very important as it significantly influences the risks and costs of production. While prices vary widely from company to company and depend on a multitude of factors, it is also helpful to have some ballpark idea of average wholesale prices to help in negotiating contracts and using the enterprise budgeting tool to project profit potential.

OSA surveyed nine seed companies to solicit feedback on best practices for engaging in contract seed production and to inquire about average contract prices for specific crops to help growers develop production plans (these prices are listed in the online toolkit at the link at the end of the article.) Contract prices often varied widely between companies and within a given crop by each company. Commonly mentioned determinants of prices included production scale; variety type (high or low yielding, ease of production); roles of producer, such as need for rogueing or finished quality seed cleaning; seed quality, such as germination rate and disease testing; and whether the crop is an open-pollinated or hybrid variety.

Below is a summary of best practices shared by seed companies:
The best time to contact seed companies to inquire about contract opportunities is between September and January when companies are preparing for the following year’s production.

Communication is critical to maintaining a good contract relationship. Most companies request an update on the crop status two to three times throughout the growing season. Photos of the crop and updates on any off types are very helpful.

Timely delivery of clean seed is important as it helps the company prepare for the following year’s sales.

If you are new to contract production, start small and try crops that you are familiar with growing. Try a test plot the first year if it is a new crop you are unfamiliar with so you can determine if you can grow it in your location. Also, plan for how you will harvest and handle the finished seed crop.

Keep good records on your costs of production, including your time, so that you are able to engage in informed negotiations on price.

Share your production information with the company and ask them to share what they know about the crop. Seed companies want to learn from your experience and also help you succeed. It takes an open exchange of information to ensure everyone’s success. If you need help, ask!

To access the Seed Economics Toolkit, visit seedalliance.org/publications/seed-economics-toolkit/.

Biosolarization and Cover Crop Impact on Weeds and Soilborne Pathogens

Soils contain a lot of good things, but they are also reservoirs for weeds, pathogens and nematodes, which, if left uncontrolled, can devastate crop yields. If soilborne pests rise to economically damaging levels, it becomes necessary for growers to use soil disinfestation techniques to kill soilborne organisms.

Most conventional growers use fumigants for soil disinfestation. Fumigation is unavailable to organic growers leaving organic growers few options for controlling soilborne pests. However, over the past couple of decades, there has been substantial research into organic soil disinfestation techniques due to increasing regulations for conventional fumigants. Researchers at California Polytechnic State University, San Luis Obispo recently conducted research on soil solarization and biosolarization, two organic soil disinfestation techniques, on organic strawberry production at the Cal Poly Organic Farm in San Luis Obispo, California.

Strawberries in May (peak production period for San Luis Obispo) of non-solarized (left) and solarized plots (right) (all photos courtesy A.M. Tubeileh.)

Soil Solarization

Solarization involves placing clear, thin (25 to 50μm), low-density polyethylene tarps over irrigated soil to increase soil temperatures to lethal levels for pathogens, pests and weeds. In general, temperatures generated during soil solarization range from 104 to 158 degrees F. The tarp is left on the soil for four to eight weeks, depending on the soil temperatures generated during solarization. The efficacy of solarization is primarily based on ambient air/soil temperatures and intensity of solar radiation. In most cases, solarization should raise the ambient soil temperature between 10 and 20 degrees C (18 to 36 degrees F) in the top six inches of the soil. Solarization is most effective when used during the summer when solar radiation is high in sunny, warm climates. Costs of solarization vary depending on plastic prices, but in general, the plastic costs in between $150 to $300 per acre. The best plastics are clear/transparent, one to three millimeters thick and UV-inhibited to prevent breakdown in sunlight.

Biosolarization, which combines the use of organic soil amendments and soil solarization, has been proven to enhance the results of solarization in numerous field experiments. Organic amendments commonly used are plant residues, animal manure, compost and other high-nitrogen organic materials such as blood meal. Biosolarization is a relatively new area of research and can reduce the time needed for solarization as well as increase solarization’s effectiveness in areas with marginal conditions for solarization. For example, in San Luis Obispo, we are about five miles from the coast, experience frequent, foggy mornings and rarely have temperatures above 90 degrees F. We included biosolarization of cover crop residues in our experiment to see if it would increase the efficacy of solarization in our climate.

The rest of this article will focus on the results from our research. For more information on solarization and biosolarization, including application techniques, please see our previous Organic Farmer article from April/May 2019 or UC extension’s webpage on solarization ipm.ucanr.edu/PMG/PESTNOTES/pn74145.html.


Solarization Research

As part of our research, we conducted lab experiments under simulated solarization conditions assessing the time needed to kill weed seeds at five different temperatures (104, 113, 122, 131 and 140 degrees F). Seeds tested included little mallow, redstem filaree, bristly oxtongue, annual sow thistle, common purslane, common lambsquarters and redroot pigweed. Efficacy of solarization temperatures differed between different species. In general, cool-season annuals annual sow thistle and bristly oxtongue were more susceptible to heat treatments than warm-season annuals such as redroot pigweed. Additionally, hard seeded (thick seed coats) seed were relatively unaffected by heat treatments taking long duration to kill. Time and percent mortality of weed seeds were used to create thermal death models for weed seeds at each temperature (Figure 1). Additionally, models were used to estimate the amount of time needed to kill 90% of seeds for all species tested (Figure 2). Redstem filaree germination rates were unaffected by heat treatments. Additionally, common purslane was unaffected by heat treatments below 113 degrees F or lower and redroot pigweed was unaffected by temperatures of 104 degrees F or below. Results indicated daily temperatures above 122 degrees F are needed for four to eight weeks to achieve adequate weed management via solarization.

Figure 1. Logistic regression models showing how germination rate of different weed species is affected by the duration of exposure to 122 degrees F under laboratory conditions simulating solarization.

We also conducted field experiments on solarization of sudangrass residues in organic strawberry production.

The objectives of our field experiment were:

  • To determine if soil solarization can reduce weed and pathogen pressures and improve plant health and strawberry yields in San Luis Obispo County,
  • To determine if the effect of sudangrass cover crop residues will increase the effects of soil solarization, and
  • To compare the effects of sudangrass residue mulching vs. incorporation on weed populations, pathogen populations and strawberry health and yields.

The experiment was designed so that we had three cover crop treatments: A control, one where sudangrass was left as a surface mulch after mowing, and the other where sudangrass was incorporated into the soil after mowing. Within each cover crop treatment, we solarized half and left the other half non-solarized.

‘Piper’ sudangrass was planted in mid-May using a seed drill. In mid-July, sudangrass was chopped and shredded with a tractor-drawn flail mower and incorporated into the soil in our incorporated treatment. After incorporation, beds were created in all plots except mulched plots. In mulched treatments, sudangrass residue was left on the soil surface and no beds were created. On July 26, solarization plastic was hand-applied onto solarized plots. After applying plastic, fields were irrigated for 72 hours using one line of drip tape till fields reached field capacity. Tarps were left on for five weeks and removed on August 31, 2018. Strawberries were planted in October after doing weed population assessments in our various treatments.

Table 1. The yield in grams per 30 plants from solarized treatments (n=12) and sudangrass treatments (n=8) from March through June.


Maximum soil temperatures in solarized plots were 118 degrees F at a soil depth of two inches and 42 degrees C at a soil depth of 6 inches. On average, temperatures in cover crop mulched plots were 4 to 6 degrees F lower than other solarized plots. Temperatures in all solarized plots were 18 to 30 degrees F higher than non-solarized plots. In initial weed biomass assessments taken six weeks after tarp removal, non-solarized incorporated plots reduced weed biomass by 24.4% compared to the control. Non-solarized mulched plots reduced weed biomass by 95.6% compared to the control. All solarized plots resulted in similar reduction in weed biomass compared to the control with an average reduction of 97.1% ± 0.6%. Efficacy of solarization treatments decreased with time. In final weed biomass assessments taken 15 weeks after tarp removal, the only solarization treatment providing a significant reduction in weed biomass compared to the control was incorporated plots with solarization resulting in 67% lower biomass than the control. Mulched plots without solarization also provided significant control, reducing weed biomass to 84.1% of the control. However, in non-solarized mulched treatments, the sudangrass re-grew after mowing and did not die until the winter.

This led to poor strawberry establishment, although the strawberries later recovered.

Solarization reduced verticillium wilt populations by 80.7% compared to non-solarized plots. Solarized plots had much lower disease incidence throughout the growing season. Non-solarized plots started to experience disease symptoms in April and were not producing fruit by May. Solarized plots experienced almost no disease pressure till late May/June when temperatures warmed. Solarized plants experienced disease pressure from Charcoal Rot, Macrophomina phaesolina, a warm-season pathogen which we theorize was not reduced to the same degree as verticillium wilt populations were. Total plant mortality was significantly higher in non-solarized plots with 35.5% mortality compared to 16.0 % mortality in solarized plots. Additionally, solarized plots had much higher yield than non-solarized plots. The different cover crop treatments did not have a clear effect on reducing verticillium wilt population, disease severity or increasing yields.

Non-solarized (left) and solarized (right) beds of strawberries during June.


Key Takeaways

Solarization provided effective weed management for 3.5 months after tarp removal, reduced verticillium wilt populations, reduced disease severity and increased yield compared to non-solarized plots.

Cover crop treatments did not enhance the effect of solarization. Cover crop treatments did not have a significant effect on verticillium populations or yields. Mulched treatments did reduce weed population and had lower disease severity than other treatments.

Solarization effectively killed mowed sudangrass, preventing it from regrowing. Solarization of mowed cover crops provides a potential mechanism for killing cover crops for organic growers wishing to perform no-till production. However, more research is needed into this topic.

The effectiveness of solarization depends not only on the temperatures you can achieve, but on the disease and weed species present in a field as well. Particularly in areas with cooler climates or frequent foggy/cloudy days during the summer, knowing the temperature thresholds required to kill the pests in your field can be important in determining whether solarization is a viable solution. This is another area where more research can be done. First, develop models to help growers estimate the temperatures they can achieve during solarization. Secondly, models can be used to determine the susceptibility of different pest species to solarization.

USDA National Organic Program Changing Approach to Organic Oversight in India

USDA is increasing its oversight in the Indian organic market to better monitor organic products coming into the United States.

On Jan. 11, 2021, USDA notified India’s Agricultural and Processed Food Products Exports Development Authority (APEDA) that they are ending U.S.-India Organic Recognition. The decision comes as USDA deemed India’s organic control system unable to adequately protect the integrity of the USDA organic seal.

The previous agreement between USDA and APEDA allowed APEDA-accredited certifiers to provide USDA organic certification in India, according to the USDA website (ams.usda.gov/services/organic-certification/international-trade/India).

USDA is altering the agreement so that all India organic products/ingredients across the entire supply chain are to be certified as USDA organic with a USDA National Organic Program (NOP) certificate in order to come to the U.S. starting July 12, 2022. USDA will allow a one-and-a-half-year transition period for India organic suppliers and U.S. buyers in order to help minimize market disruption as a result of the new requirements. During this period, organic operations previously certified by APEDA-accredited certifiers will be allowed to apply for direct certification to NOP by USDA-accredited certifiers.

The exact timeline of the transition period, according to USDA, is as follows:

  • Jan. 11, 2021: APEDA notified of an end to U.S.-India Organic Recognition.
  • March 2021: Certifiers are to report any certification applicants who are currently certified by APEDA in India in the Organic Integrity Database (public data). This will help U.S. buyers verify that a farm or business in India has applied for NOP certification.
  • July 12, 2021: Any India organic business wanting to export to the U.S. must have applied for USDA/NOP certification.
  • July 12, 2022: To export to the U.S., all India organic products/ingredients across the supply chain must be certified USDA organic with a USDA/NOP certificate.

Organic businesses in the U.S. buying from an India organic supplier certified by an APEDA-accredited certifier must communicate with those suppliers about the need to apply for NOP certification to a USDA-accredited certifier by July 12, 2021. USDA states that USDA-accredited certifiers may issue USDA/NOP certification to any organic business verified to fully comply with USDA organic regulations throughout the transition period.

India organic suppliers cannot continue business with U.S. buyers after July 12, 2021 if they do not apply for the NOP certification. The Organic Integrity Database will need to be used by buyers to verify existing certification or a pending application with a USDA-accredited certifier. The database can be accessed at organic.ams.usda.gov/Integrity/.

Organic suppliers in India that are certified by an APEDA-accredited certifier will need to identify USDA-accredited certifiers previously approved under the U.S.-India recognition agreement. To accomplish this, visit apeda.gov.in/apedawebsite/organic/NPOP_certification_bodies.pdf and refer to the “Validity of Current Accreditation” and “Scope of Accreditation” columns. Suppliers that do not apply for certification by July 12, 2021 will be barred from exporting USDA organic products to the U.S.

India suppliers currently accredited by APEDA for USDA certification may apply to the USDA National Organic Program (NOP) for direct accreditation at any time.

How to Help Endangered Pollinators While Also Helping Your Farm


As a result of human activity, the world has lost about half of its insect populations in the last 75 years. Those insect declines are due largely to habitat loss and degradation, pesticides and climate change, said Jessa Kay-Cruz of the Xerces Society for Invertebrate Conservation. Some of those insects can be important pollinators for crop production, such as the monarch butterfly.

“Monarchs across the U.S. are imperiled, though the Western population is worse off than the Eastern population,” said Sarah McKibbin, Restoration Project Manager of Solano Resource Conservation District (RCD).

“Monarchs are completely dependent on milkweed plants,” said McKibbin, who was a speaker for a recent online workshop sponsored by Solano.

The butterflies lay their eggs on milkweed plants. When the eggs hatch, the caterpillars eat only milkweed.

“The toxins in milkweed helps protect them from predators,” she said.

The milkweed flowers provide a nectar source, not only for adult monarchs, but for other pollinators too, such as native bees. “Milkweed is a relatively prolific nectar supplier,” McKibbin said

The monarch caterpillars go through five instar stages (between molts) before forming a chrysalis and attaching it to a milkweed stem. The monarch lifecycle repeats four to five times each spring through fall. The last batch of butterflies that emerge are the ones that migrate from parts of the U.S. and Canada.

Monarch caterpillar on woolypod milkweed, A. eriocarpa .There are multiple native milkweed species available for planting (photo courtesy Brianna Borders/Xerces Society.)

“Western monarchs overwinter along the California coast in Monterey pines and eucalyptus trees,” McKibbin said. “Eastern monarch populations overwinter in Mexico in Oyamel fir trees.”


Monarch Numbers

In the 1980s, there were an estimated 4.5 million monarchs that overwintered along the Pacific Coast. In 2019, the number had dropped to approximately 29,000, and in 2020, the Western Monarch Thanksgiving Count tallied only 1,914 monarchs.

“Western monarchs have declined by over 99%,” McKibbin said. “The Eastern monarchs have ‘only’ declined by 80% in the past 20 years.”

So why are the Western monarchs in such rapid decline? The reasons are many, according to Solano RCD:

  • Loss of overwintering habitat.
  • Development along the Pacific coastline.
  • Decline and aging of pine and eucalyptus groves without regeneration.
  • Breeding habitat loss and degradation.
  • Urban sprawl.
  • Agricultural practices with extensive tilling and pesticide use.
  • Pesticides used for mosquito control.
  • Pesticides used by homeowners and the nursery trade.
  • Widespread pesticide contamination of milkweed.
  • Climate change – causing changes in temperature and rainfall patterns which affects monarch migration and milkweed distribution.
  • Tropical milkweed, which is not native and can harbor a parasite harmful to monarchs.

    Adult monarch on narrow-leaf milkweed, A. fascicuaris . In 2020, the Western Monarch Thanksgiving Count tallied only 1,914 monarchs (photo courtesy Stephanie McKnight/Xerces Society.)

“Good” vs. “Bad” Milkweed

So, what is the difference between milkweed that is harmful to monarchs and milkweed that is beneficial? Tropical or exotic milkweed, Asclpias curassavica, is harmful. It grows north to Mexico but isn’t native to the U.S. or Canada. It’s an attractive plant and easily grown, so it is most often the species offered for sale in nurseries. Tropical milkweed blooms and grows year-round in mild climates – except in the case of rare freeze events. Because of its year-round availability, tropical milkweed convinces the monarch to continue breeding throughout the winter.

Nature didn’t intend for monarchs to breed year-round, and there are several risks involved when they do, according to Monarch Joint Venture (MJV), University of Minnesota. Risks include a higher OE infection rate and frigid temperatures during those rare freezing events. There is also a chance of food shortages when caterpillars eat tropical milkweed to the ground during the winter and there is no native milkweed available because of winter dieback.

When gardeners and growers in the coastal southern U.S. and California plant non-native tropical milkweed, there is another potential risk to the monarch. Milkweed harbors a debilitating parasite, a protozoan called Ophyocystis elektroscirrha (OE). Patches of tropical milkweed growing year-round can foster greater transmission of OE, according to MJV, although another study shows that tropical milkweed can lower OE replication. This is because of elevated levels of cardenolide toxins (a type of heart-arresting steroid) in the plant. But less OE replication still may not be in the monarch’s favor. Instead of dying quickly, butterflies that are moderately infected could potentially spread more disease over a longer life span.

Adult monarchs infected with OE can harbor thousands, even millions, of microscopic spores on their bodies. Infected butterflies scatter the dormant spores onto eggs or milkweed leaves. These in turn are ingested by monarch caterpillars. The spores replicate inside the larvae and pupae. Heavily infested monarchs may not emerge completely from their chrysalis. They either become stuck or are too weak to fully open their wings. Monarchs with milder infections of OE can’t fly as well and don’t live as long as healthy butterflies.

North America’s native milkweeds show dieback in the winter, which stops the winter breeding and resets the population of OE. If you have any tropical milkweed, MJV suggests cutting it back in the fall and winter months and gradually replacing it with native milkweed species. The natives include narrow-leaf milkweed, Asclpias fascicuaris; showy milkweed, A. speciosa; California milkweed, A. Californica; heartleaf milkweed, A. cordifolia; and woolypod milkweed, A. eriocarpa.

Other milkweed notes: “Don’t plant milkweed within five miles of the coast because it can interrupt the monarch’s life cycle,” McKibbin said.

The toxin in milkweed concerns ranchers, but it takes a long ingestion period before it harms cattle. “There are no recent reported deaths of cattle to USDA from milkweed,” McKibbin said.

Incorporating native milkweed species into cover crops can create a habitat for monarchs while reducing the need for broad-spectrum insecticides (photos courtesy Cameron Newell and Jesse Kay-Cruz, Xerces Society.)


Helping Adult Monarchs and Other Pollinators

Besides native milkweed, there are other plantings that farmers can grow to attract monarchs as well as native bees and other pollinators. Plant a variety of nectar sources and plan your flowering selections so they produce year-round bloom.

McKibbin suggests practicing the 10-10-10-10-1 rule:

  • Plant a 10’ X 10’ area (minimum).
  • Include at least 10 native milkweed plants of the same species.
  • Plant a total of at least 10 different plant species.
  • Plant each species in a block at least one square meter in size.
  • Other ways to help pollinators is to shop mindfully − buy organic produce and organic nursery stock.

“Avoid products that contain GMO ingredients, especially corn, wheat, and soy. These are the most common ‘Roundup-ready’ GMO crops that allow farmers to spray entire fields with roundup to kill all plants except their crop, including wild milkweed. Milkweed that would have grown wild in fields and farm edges are collateral damage, so GMO crops are a large contributor to habitat loss in agricultural settings – no milkweed means no monarch caterpillar food,” McKibbin said.

Protect monarch overwintering sites. Volunteer for citizen science projects. Get involved with the Thanksgiving and New Year’s monarch counts. Donate to nonprofits that are helping to protect monarchs and other pollinators. Avoid pesticides, especially systemic insecticides such as neonicotinoids.

“They are the worst,” McKibbin said. “They can affect plants, water and soils for months to years.”

For more information on helping monarchs and other beneficial insects visit the following websites: Solano Resource Conservation District: https://www.solano.org, Xerces Society: https//xerces.org, Monarch Joint Venture: https//monarchjointventure.org.

Monarch chrysalis on narrow-leaf milkweed, A. fascicuaris.Planting milkweed within five miles of the coast can interrupt the monarch’s life cycle, according to McKibbin (photo courtesy Stephanie McKnight/Xerces Society.)

Food Safety Laws and Standard Operating Procedures for Urban Farmers

As urban farming continues to rise in popularity as a way for urban communities to tackle food insecurity and promote food sovereignty, new laws and standard operation procedures are being put into place to ensure food safety of those products. The California Urban Agriculture Food Safety Guide, produced in December 2020 by UC Berkeley, UCCE and Sustainable Economies Law Center, provides a thorough overview of what those urban farmers or gardeners may be subject to.

“For new urban farmers, it outlines relatively new laws that offer new opportunities for urban farmers and gardeners to grow and distribute foods for sale including the Cottage Food Act and the Community Food Producer Act,” said Jennifer Sowerwine, UCCE metropolitan agriculture and food safety specialist at UC Berkeley and lead author of the guide.

“We tried to take complex regulations and put them into a format that will be more accessible for very small-scale growers,” added Rachel Surls, UCCE sustainable food systems advisor and co-author.

The 72-page guide also explains whether or not urban farmers may be subject to the Food Safety Modernization Act (FSMA), and clarifies that all food grown and sold or donated in urban environments should be following the CDFA’s Small Farm Food Safety Guidelines, according to Sowerwine.

“Generally, any farm or organization in California that grows or distributes produce offered for public consumption is subject to these guidelines,” she said. “Therefore, urban farmers, community gardens and backyard gardeners should all read and implement these guidelines before offering food for public consumption, whether by sale or by donation.”

Radishes for sale at an urban farm in Ontario, Calif. The 72-page guide clarifies that all food grown and sold or donated in urban environments should be following the CDFA’s Small Farm Food Safety Guidelines.


Clearing Things Up

The laws and standard operation procedures in the guide were previously difficult to find and navigate. Sowerwine said that this guide provides a “one-stop-shop” for laws that may affect the urban farm as well as best practices for safe growing, distribution and storage of not only fresh produce, but also eggs, chicken and small livestock. It also provides guidelines and resources for safe compost production, application and management.

Surls noted that products produced and distributed by urban farmers have long existed in a “legal gray area” and that new laws like the ones outlined in the guide are clearing things up.

“[Urban farm produce] was not necessarily considered an “approved source” for sale to retail food establishments,” she said. “Two laws cleared that up. Now urban growers are considered “approved source” through a category called “community food producers” established by California state laws AB 1990 and AB 234.”

Sowerwine said that the COVID-19 pandemic has contributed to an increase in household food production as evidenced by the rapid decline in seed supplies, and rising demand in raising chickens in backyards. This has given more incentive for people to not only become urban growers but to also be aware of any laws or acts that may pertain to them.

“Many are sharing foods with their neighbors, donating it to food pantries, aggregating produce into CSA-type boxes, and some are taking advantage of the Community Food Producer Act to sell their products,” Sowerwine said.

Handwashing station at an urban farm in San Diego. CDFA’s Small Farm Food Safety Guidelines dictate that proper hygiene should be followed in every step of the growing process.


Importance of Food Safety

The entire guide is structured around the necessity for food safety in an urban environment. Urban farmers need to adhere to any and all food safety laws that may apply to their operation, namely those relating to soil health and disease prevention in order to grow and sell products.

“Food safety is very important in the urban farming sphere, particularly in relation to urban soils,” Sowerwine said. “It is important before starting to farm to assess your urban soils for any risk of contamination by learning about the prior site use, and if there is elevated risk, then getting a soil test.” The guide outlines testing, remediation and best management practices for urban soils.

Another issue is disease prevention. The guide makes it clear that following standard operating procedures is necessary to ensure that every biosecurity measure is met to reduce any and all incidence, whether that be between animals or zoonotic.

“Even one case of E. coli or Salmonella is too many,” Surls said. “Everyone who produces food for distribution wants it to be healthy for whomever is going to eat it. Growers can face legal liability if someone gets sick from eating what they grew, and of course we want to prevent that from happening.”

Surls said that urban farmers are generally focused on community health and food access, so the incentive for following proper guidelines to keep food production constant is there.
“Everyone wants to be healthy, and following the best practices outlined will help minimize the risk of on-farm or in-garden contamination.”

Vertical urban farm in Los Angeles. Some urban farms, depending on the operation, are fully or partially exempt from certain laws under the Food Safety Modernization Act.


On-Farm Assessment

At the end of the guide, Sowerwine prepared an on-farm food safety assessment for California urban farms. According to Sowerwine, the checklist offers a comprehensive assessment of potential on-farm food safety risks, adapted from USDA guidelines and in compliance with the CDFA Food Safety Guidelines, yet “tailored to smaller-scale operations,” she said.

“It covers the five main areas of potential risk of contamination and how to assess them, including risk from water, animals, soils, surfaces and health and hygiene factors, and best practices to minimize risk as well sample record keeping forms to document best practices,” she said.

Sowerwine noted that even for smaller-scale operations, it can be helpful to walk through the assessment and determine where there may be contamination issues and how to address them.

“And for farms that may have community or student engagement, what kind of signage and training may be beneficial,” she added.

A publication of the full guide is available for free download at anrcatalog.ucanr.edu/pdf/8660.pdf.

Research into Alfalfa Crop Rotation for Organic Tomatoes


The practice of rotating alfalfa with tomatoes was once more popular than it is today, but recent research suggests it offers soil health benefits in organic tomato crops.

Researchers Nicole Tautges, Emily Woodward and Dan Putnam tested a three-year rotation of tomatoes, corn and alfalfa at the UC Davis Russell Ranch Sustainable Agriculture Facility. According to their research, alfalfa benefited tomato yields when in rotation, with fruit yields between 10% to 26% greater following three-year alfalfa as compared to following corn in a two-year tomato-corn rotation.

“This research was motivated by a lot of anecdotal or observational evidence that growers reported seeing on the ground in their crop rotation,” said Tautges, now a researcher with Michael Fields Agricultural Institute in East Troy, Wisc. “A lot of growers would say that they have better soil health and the soil was more workable following alfalfa compared to following other annual crops. They’re seeing yield boosts. They’re seeing decreases in disease and pathogen pressure in the following vegetable crop.”

Tautges said there has been limited research into forages and what exactly the biological and chemical mechanisms were that were driving those comments from growers.

“It’s all qualitative at this point. So, I wanted to take a stab at doing that research,” she said.

Tautges explained they measured a suite of soil health indicators – biological, chemical and physical – in the soil at the end of the alfalfa crop compared to the corn as their annual control. They compared the indicators at the end of each rotation crop with the objective of seeing how the differences persisted in time throughout the rotation. They planted tomatoes after both crops and measured the same indicators in the tomatoes to see how they compared to the findings from the previous crop.

In addition to monitoring the various indicators in the soil, they kept track of yields from the tomato crops and found an increase in tomatoes that followed alfalfa.

“We saw about a 3- to 5-ton-per-acre increase in tomato fruit yields. At times, we did see even up to 10 tons per acre,” she said. She said while there were some individual cases of higher yields, the increase was generally around 10% minimum.

She said they also noticed some other results visually. The plants were greener, bushier and bigger. “There was a real visual difference in the vine health among the systems, and I think that contributed to the stronger yields also.”

Their research findings broke down findings in terms of soil health. The research showed alfalfa enhanced soil microbial biomarkers and the nitrogen uptake of the soil microbial pool after three years compared to the corn. The alfalfa also showed higher levels of mycorrhizal fungi in the soil. The mycorrhizal fungi biomarkers were 45% higher in alfalfa soil than in corn soil.

There were differences in nutrients as well. The research states total dissolved nitrogen in the soil solution was more than two times greater following corn than following alfalfa. That dissolved nitrogen represents a pool of potentially leachable nitrogen, the research explains. It also states greater potentially leachable nitrate in the fall lead to greater measured nitrate leaching losses over the winter. According to the research, nitrate leached with winter precipitation was lower following alfalfa compared to conventional corn.
When it comes to nitrogen, Tautges said things get more complicated.

“There should be nitrogen going into the microbial community and there should be nitrogen going into the soil by all of the organic matter decomposition that we’re getting from the alfalfa,” she explained.

Another result from the alfalfa rotation is a change in soil structure. The researched showed alfalfa greatly improved soil aggregation, which Tautges said is an important indicator of soil structure.

“We had hypothesized that alfalfa having a deeper, bigger root system would be punching more holes in the soil and aerating the soil more. Fungi that were being maintained better in the alfalfa system would be leading to better soil aggregation through the compounds fungi secrete,” she explained.

While those factors were leading to improved soil aggregation, one factor of growing alfalfa was having a counter effect. “The haying activities also were increasing bulk density because you’re driving equipment across the field a lot without using any tillage to break it up again.”

The research did find a couple of issues with the alfalfa rotation. Findings indicated the alfalfa tended to deplete soil cations, which left low levels of potassium and calcium fertility for the following tomato crop. However, overall, researchers determined alfalfa benefits biological and physical soil health parameters and tightens nitrogen cycling.

USDA Passes Final Rules on Hemp Growing


Just when you thought you knew all the rules and laws that regulated legal hemp growing in the U.S. at the federal level, the United States Department of Agriculture (USDA) went and made changes to those rules. They didn’t do it to cause headaches, but rather because they listened to what the public had to say and what growers learned during the 2020 growing season.

The regulations that first came out after the 2018 Farm Bill passed into law was an interim final rule. The interim regulations were published on October 31, 2019 and laid out guidelines for hemp growers to legally register, test their plants to stay within the THC limitations and generally stay out of trouble with the law.

On January 15, 2021, the USDA published a final rule. Those updated hemp regulations took effect on March 22, 2021. Below is a general overview of the final federal regulations. Since the law may vary from state to state and within tribal land, be sure to check the regulations within your own state or jurisdiction.

Hemp flowers.


Violation for Too Much THC

As was law before, plants that test too high in tetrahydrocannabinol (THC), a cannabinoid, must be destroyed. The final rule raises the amount from 0.5% to 1%. If plants test at or below the 1% threshold, there is no “negligent violation.” A grower can only receive one such violation in any given growing season.

Scientists estimate there are more than 100 different cannabinoids in hemp. More studies are currently underway. Of those cannabinoids, two are the most well-known. The first is THC. It’s the hallucinogenic, or recreational component in cannabis (marijuana). THC is also found in hemp, but generally in much smaller amounts. The second most recognized is Cannabidiol (CBD), the popular medical cannabinoid in hemp. CBD is also found in cannabis.

Plants over the 1% THC threshold can be destroyed in more ways than before. No longer will a grower be required to use only law enforcement or a Drug Enforcement Administration (DEA) reverse distributor, which is a person or company that reclaims outdated or otherwise unusable drugs and destroys them. Reverse distributors are registered with the DEA.

According to reports submitted by states and tribes in 2020, growers planted 6,166 acres under the 2018 Farm Bill hemp plans and about 730 acres of those had to be destroyed for noncompliance.

A 2019 midwestern hemp crop.


Plant Testing

Since there aren’t enough labs registered with the DEA for the amount of hemp production expected in 2021, the DEA is allowing non-DEA registered labs to test hemp. This is an extension only until January 1, 2022. In the meantime, the DEA is trying to quickly process lab applications to get more testing labs registered.

The timing of plant sample collection has been extended. The interim regulations gave only a 15-day window from testing to harvest. That time frame has been raised to 30 days.

Growers asked for a change in the sampling method. They requested that larger samples be taken from each plant sampled, or that the whole plant be sampled. They also asked that samples be taken from fewer plants.

The final regulations let individual states and tribes set their own policies using a performance-based approach to sampling. These policies must be written into a plan and sent to the USDA for approval. The plan may consider the state’s seed certification programs, the history of grower compliance and other factors as determined by tribe or state.


Tribal Regulations

The rules were a little fuzzy about tribal jurisdiction in the interim regulations. Those initial rules didn’t specifically discuss if a tribe with an approved USDA plan had primary rule of law over hemp production across its entire territory, or only over land in which it had inherent jurisdiction.

Since tribes rule themselves as quasi-sovereign nations, the USDA decided in the final regulations that a tribe may exercise jurisdiction, and therefore regulatory authority, over hemp production in all of its territory no matter the extent of the tribe’s inherent regulatory authority (generally, tribes can’t exercise criminal or civil jurisdiction over non-tribe members.)

Justin Eve believes rules for hemp are being rushed.


A Hemp Researcher’s Perspective

So how do hemp researchers and growers feel about the hemp final regulations? And how do these regulations affect them?

“Working with hemp as a researcher poses unique challenges because of the regulatory factor,” said Sarah Light, UCCE agronomy advisor in Sutter, Yuba and Colusa Counties. “It’s just the nature of working with the crop.”

Light sees the final rule as a positive rather than a negative. “Now that we have the final ruling, we can move ahead. Now we know,” she said. “We’re excited to keep doing research for our growers. We’ll just continue to be in compliance.”


A Hemp Grower’s Perspective

Justin Eve, owner of 7 Generations Producers, is a USDA-certified organic grower. He has a different take on the regulations.

“They’re classifying it and approaching it like some sort of drug,” he said. “It’s a little upsetting to me.

This is an agricultural crop. We already have those regulations in place. We don’t need to recreate the wheel.”

Eve is frustrated with how the USDA and the DEA focus on THC levels within hemp. “It’s such a miniscule aspect to what this crop can be,” he said. “America made its way with hemp.” (The early drafts of the Declaration of Independence and the Bill of Rights were written on hemp paper).

In addition to hemp, Eve also grows moringa and sweet potatoes on 20 acres north of Sacramento, Calif. His background is in bioenergy, plant sciences and soil chemistry. He sees a high level of importance in getting viable hemp genetics that hemp farmers can grow, harvest and make some money on while staying within the legal boundaries of the regulations.

An indoor canopy of hemp plants.

Hemp growers like Eve are banding together to form the Hemp Farmers Guild. The guild is working with the DEA and the USDA to help them understand the growing challenges of hemp from a farmer’s perspective.

So, are the federal agencies listening to hemp growers?

“They are,” Eve said, but added a caveat about the USDA, “They’re not really farmers. They’re not granting us a buffer to make some mistakes as we go along.”

The way the regulations are written makes Eve believe there’s not a lot of wiggle room. “It’s limiting a farmer to harvesting within 30 days. It’s unconstitutional. We just want to grow a good crop and not get arrested for what we thought was legal.

“The limitation on THC is low. The way they’re testing is skewed,” Eve said. If the plants test too high in THC, they must be destroyed; there’s no other path. Eve mentioned a hemp grower in the Merced area that had to destroy a 200-acre, $2 million crop. “It can bankrupt farmers.”

Big companies are hesitant to get involved with the business, according to Eve. But for the industry to flourish, it will take large companies investing in expensive processing facilities.
“The major companies are afraid of backlash from the USDA, the FDA and the DEA,” Eve said.

As for the timing of the final rule, Eve thinks it was rushed. “We should have two more years to figure out a final rule,” he said. He believes that state departments and local ag departments don’t fully understand the USDA regulations. “The head doesn’t know what the tail is doing.

“I think the USDA is heading in the right direction, but up to this point, it’s been too hard,” Eve said.

How Much N Can You Expect from Organic Fertilizers and Compost?

Nitrogen (N) is an essential plant nutrient, providing the building blocks for plant growth and development. The N sources on an organic farm are numerous, including crop residue, compost, fertilizers, soil organic matter and irrigation water (Figure 1). Nitrogen management in organic systems is challenging because complex organic forms of N originating from organic materials need to be mineralized by microbes to become plant-available mineral forms of N: ammonium (NH4+) and nitrate (NO3-). Learning how to predict and monitor N release from soil amendments are important skills useful for selecting amendments and determining application rates and timing to achieve optimum plant health and yield.

Figure 1. An example of N uptake and N supply in an organic tomato field. Field studies occurred in the Sacramento Valley in a silt loam soil with approx. 1% organic matter content, growing fresh market tomato cv Brandywine. Cover crop was an oat legume mix with 3% N that averaged approximately 3 T/A biomass that was incorporated one month before planting. Granular fertilizer was applied at 700 lb./acre. Irrigation water total estimated 3.6 acre-feet with a concentration of 1 ppm NO3-N (Geisseler et al., unpublished).

Soil microbes facilitate N availability in organic systems through organic matter decomposition. Microbes use carbon (C) as their primary energy source. However, to grow, microbes also require N. When compost and fertilizers are added to moist soil, microbes are “fed” and microbial activity is stimulated. With this activity, there is rapid turnover of microbes as well as organic matter decomposition, which become the two main sources of available N for plants. However, as the ratio of C:N in the amendments approaches 20:1, additional N is required to facilitate microbial breakdown. This additional N is taken from the pool of plant-available forms of N in the soil. Because this reduces the amount of N available to plants, it is sometimes referred to as “tying up N” or N immobilization. Because most amendments available to organic farmers are bound in complex molecules containing both C and N, only a portion of the N becomes available to plants in the short term. This begs the question, how much N can you expect from organic fertilizers and compost?


What to Expect

Composts, manures and organic fertilizers are all applied to supplement soil N. The N availability from these materials differs widely, from 90% to tying up N. To better understand this, we mixed common soil amendments with organically-managed field soil and incubated them for 84 days in warm and moist soil (73 degrees F and 60% water holding capacity.) Figure 2 shows how quickly N became available from each material. A negative value indicates N immobilization. Actual N release rates in the field will depend on soil moisture and temperature but will follow a similar pattern.

Figure 2. Predicted N release curves from different amendment types when incorporated into warm, moist soil2.

Our research along with dozens of other studies has found that the C:N ratio and % N of an amendment are good predictors of N availability. The lower the C:N ratio in the material, the more quickly N will be released. As the C:N ratio exceeds 15:1, available N moves closer to 0 due to temporarily tying up N. Such materials should not be applied too close to planting. Especially for compost, it is important to find out the total N and C:N ratio from the supplier to understand whether this material will be contributing N or tying up N in the soil. When C:N ratio is unavailable, the total N concentration is closely related to availability. Generally, as total N increases, availability of N increases (See Figure 3).

Figure 3. Relationship between potentially available N and amendment carbon to nitrogen ratio2.

Among the amendments tested, guano had a very high N content (% N) and a very low C:N ratio which resulted in high N availability (80% to 90% of the total N) and rapid availability—more than 50% of the N was available immediately with an additional 30% to 40% becoming available over 40 days (Figure 2).

On the other hand, composted yard trimmings had low total N content, less than 2%, and a high C:N ratio between 13 to 20, which resulted in slight N immobilization to 4% N release.

Low C:N ratio materials like guano, feather meal and fish emulsion released much of their N in the first week, and almost all their N within three weeks. This quality makes them good sidedress materials. They can also be used to remediate known N deficiency.

Poultry manure composts and granular fertilizers contributed some available N as soon as they were applied, but released their N more slowly. When incorporated into moist soil under warm conditions, they will release more quickly, though still over weeks, not days (See Table 1).

Table 1. Potential N availability from different types of organic amendments under warm, moist conditions. Negative numbers mean the compost tied up soil N2. All % N numbers for solid amendments are on a dry weight basis. Note: Liquid % N is reported on a fresh weight basis and isn’t a good indicator of the release rate. *(See Figure 3)

High C:N materials like plant-based yard trimmings and composts released little to no N. They provide C which supports microbial communities and, over time, improves soil physical structure, but provides little N in the short term. Long-term soil fertility may be improved.

Plant-based liquid fertilizers ranged from 48% to 92% N availability whereas manure-based liquid fertilizers (typically fish) ranged from 83% to 99% N availability after four weeks1,2. Organic liquid fertilizers are suspensions and often include particulate matter with which 8% to 21% of total N content is associated. Without proper filtration, these materials increase the risk of clogging drip emitters. If they are injected before the filter, a significant amount of the N can be removed from the suspension. Regular backflushing may be required to maintain system flow. New technology in liquid organic fertilizer is now providing materials in which N is thoroughly dissolved and does not have the issues just discussed. Coupled with the high cost per unit N, liquid fertilizers are often viewed as an easy way to supplement in-season fertility, but too expensive to provide the bulk of the crop’s N demand.

In all cases, amendment N release is slower in cool weather or dry conditions as microbial activity is decreased. Crops planted in cold temperatures may benefit from starter fertilizers that contain some available N initially − those with a higher amount at day 0 and a steep initial curve (Figure 2). For example, manure-based composts have roughly 15% of their total N available at application, whereas granular fertilizers started with an average of about 22%, or guano at more than 50%.

If only a portion of the total N becomes available, what happens to the rest? The unmineralized organic N becomes part of the soil organic matter pool of N, and will be available in the future as the material is subject to mineralization processes.


How Much N and When?

Crop N demand and yield are very closely linked. The crop N demand includes N requirements to produce the plant material, harvested crop and cull produce. Expected yield is a good starting point for estimating how much N the crop needs. Specific crop N demand guidelines can be found at geisseler.ucdavis.edu/Guidelines/Home.html.

The timing of crop demand depends on the crop. Figure 4 shows the N demand curve for broccoli tomato and strawberry. The steep areas on the curve indicate high N demand and represent times when N should be in high and sufficient supply. The fresh market tomato curve shows that from full bloom to early harvest, tomatoes utilize 73% of the crop’s total N demand. During this period, N uptake rates averaged 3 to 5 pounds N/A/day. Little N was used prior to flowering or once harvest was on-going, in this case of indeterminate tomatoes. Crops with similar growth and fruiting habits form similarly shaped N demand curves, though additional crops can be found at geisseler.ucdavis.edu/Guidelines/N_Uptake.html.

To ensure that sufficient N is available for the period of high N demand, taking a soil test a couple of weeks prior to that period is recommended. Samples taken at this time will reflect current availability from any number of organic sources (fertilizers, compost, cover crop residue, soil organic matter and others). Convert soil test data to lb./A to determine whether the supply will meet the demand. Details on how to take a soil sample can be found at geisseler.ucdavis.edu/Guidelines/Soil_Sampling_Nitrate.pdf.



Supplying a crop with sufficient N is essential for optimum health and production. In organic production, this is very challenging and requires the ability to synthesize hard numbers, educated guesses, and keen observations.

Here are some tips:

  • Establish an N goal for your crop.
  • Identify the C:N ratio or total % N of your amendment to estimate N availability for your amendment (Table 1, Figure 3).
  • Familiarize yourself with the N release pattern from amendments (Figure 2).
  • Learn the N uptake demand for your crop (Figure 4).
  • Monitor N with soil sampling to refine your estimations and confirm sufficient N for your crop.

Organic N management is challenging, so we hope this article will help you navigate this important decision with more confidence and success.

Figure 4. Example of crop N uptake curves of fresh market ‘Brandywine’ tomato and broccoli. Broccoli data is from a conventional field in the Salinas Valley. Yields were 28,000 and 22,000 lb./acre for summer- and winter-seeded broccoli, respectively3. Tomato data is from a fresh-market organic heirloom trial in Yolo County. Total yield was 62,000 lb./acre (unpublished data).

Additional Resources
N dynamics in field-grown organic heirloom tomatoes: ucanr.edu/sites/SFA/files/343252.pdf

Practical Training on N Planning and Management in Organic Production: ccsmallfarms.ucanr.edu/Events_and_trainings/Nitrogen_Planning_and_Management_in_Organic_Production_of_Annual_Crops_915/ 


1 Hartz, T..K., Smith, R., Gaskell, M., 2010. Nitrogen availability from liquid organic fertilizers, HortTechnology 20(1), 169-172.
2 Lazicki, P., Geisseler, D., Lloyd, M., 2020. Nitrogen mineralization from organic amendments is variable but predictable. Journal of Environmental Quality 49, 483-495. Available at: https://acsess.onlinelibrary.wiley.com/doi/epdf/10.1002/jeq2.20030
3 Hartz, T.K., Cahn, M.D., Smith, R.F., 2017. Efficient nitrogen fertility and irrigation management of cool-season vegetables in coastal California. Available at: https://vric.ucdavis.edu/pdf/fertilization/fertilization_EfficientNitrogenManagementforCoolSeasonvegetable2017.pdf

Transforming Agriculture to Mitigate Climate Change and Support Public Health

Many of us spent most of 2020 sheltering at home, doing our part to curb the pandemic we are weathering as a global community. While there is solidarity in the fact that people around the world are modifying their lives to flatten the curve—wearing masks, socially distancing, and working remotely when possible—many of us are eagerly awaiting the vaccine that allows us to emerge from our shelters and breathe a sigh of relief.

But, is a vaccine the ultimate solution to our public health crisis? While there is no denying we need to address the immediate threat of covid-19, this pandemic is itself a symptom of a challenge that will not be solved by modern medicine. That challenge is climate change, fueled by the loss of natural habitats and biodiversity. If we ignore this broader issue, we face a world where we will likely be challenged by one pandemic after another.

Humans are disrupting natural systems and this is a primary factor in the spread of infectious diseases. As our planet warms and more natural habitats are lost, many species are expanding out of their natural ranges and moving towards the poles¹. As a result, they come into contact with species they would not normally be interacting with, which creates opportunities for pathogens to infect novel hosts, including humans. We have seen these dynamics play out with Ebola, Zika, Hantavirus, and other diseases around the globe²,³. To reduce the risk of infectious disease spread, we need to address the major sources of greenhouse gas emissions and the human activities that threaten natural habitats and biodiversity.

Modern-day agriculture is a major contributor to climate change. The International Panel on Climate Change estimates that direct agricultural greenhouse gas emissions account for over 10% of total anthropogenic (human caused) greenhouse gas emissions⁴.

Agricultural systems that rely on synthetic inputs to compensate for low biodiversity contribute substantially to the emission of three key greenhouse gases: carbon dioxide, nitrous oxide and methane. Field operations and the production of synthetic fertilizers and other inputs are largely responsible for agricultural carbon dioxide emissions, and the use of synthetic fertilizers and livestock production are the main sources of agricultural nitrous oxide and methane emissions, respectively⁴,⁵,⁶.

In the U.S., most livestock are raised in large confinement facilities, rather than on pasture where they have the potential to help build healthy soils that store, or sequester, carbon. Moreover, confined animal operations negatively impact air and water quality, and create prime conditions for infectious disease spread that could spill over to humans⁷.

Agriculture is also the main driver of deforestation, the largest cause of habitat loss worldwide⁸. In particular, large-scale beef production causes massive deforestation, particularly in the tropics⁹. Forests, especially tropical forests, store large amounts of carbon in the soil and in their biomass. When a forest is destroyed, the potential for carbon storage is lost, and if the forest is removed through burning, carbon stored in the vegetation is released to the atmosphere, accelerating global warming. Land-use changes associated with the expansion of large-scale, industrial agricultural systems erode valuable biodiversity and result in simplified landscapes that are more susceptible to outbreaks of agricultural pests and diseases. To compensate, these simplified systems become increasingly reliant on synthetic inputs.

When a forest is destroyed, the potential for carbon storage is lost, and if the forest is removed through burning, carbon stored in the vegetation is released to the atmosphere, accelerating global warming.

Being Part of the Solution

While agriculture is fueling climate change and habitat loss, it can be transformed to become part of the solution. By adopting a systems-based, ecological approach to producing food, agriculture can help reduce negative climate impacts, conserve biodiversity and support human health. Organic agriculture provides this ecological framework for food production and is grounded in measurable standards for biodiversity and soil health, which are the foundations of a healthy farming system, and ultimately a healthy society.

By focusing on soil health building practices, organic agriculture has the potential to play a large role in mitigating climate change by reducing greenhouse gas emissions and sequestering carbon. Organic producers are prohibited from using synthetic fertilizers, the largest source of agricultural nitrous oxide emissions. By building healthy soils that host a diversity of beneficial organisms and support vigorous crop growth, organic producers enhance their system’s resilience to a changing climate. Healthy soils not only increase crop resilience to stressful conditions, they also play a critical role in regulating the global climate by converting organic residues into stable organic matter and storing atmospheric carbon dioxide in the soil¹⁰.

To protect these vital services, the USDA National Organic Program (NOP) Standards mandate the use of best conservation management practices such as diversified crop rotations, intercropping and cover cropping to build soil organic carbon and protect soil health. Diversified crop rotations and intercrops add diversity to farming systems across space and time, which help break pest and disease cycles and increases the abundance and diversity of beneficial soil organisms¹¹. Planting cover crop mixtures with deep root systems can reduce soil erosion and break up compacted soil, store carbon deep into the soil profile and increase the water holding capacity of soils, making the system more resilient to extreme weather events such as heavy rains or floods¹².

While each of these diversification practices individually helps pull carbon out of the atmosphere and builds resilience, the true potential for climate change mitigation and adaptation comes from combining these practices through diversification strategies such as conservation agriculture, agroforestry and integrated crop-livestock systems. For example, reintegrating crops and livestock using advanced grazing management has the potential to sequester enough soil organic carbon to offset the associated enteric methane and manure greenhouse gas emissions¹³. There is also evidence that by improving forage quality, these systems can reduce methane emissions from livestock by almost a third. Managed rotational grazing systems also enhance nutrient cycling and reduce the need to import nutrients in the form of fertilizers or livestock feed.

By building biodiversity into the farming system, best organic management practices also have the potential to support more abundant and diverse communities of animals compared to simplified, input-intensive farming systems. Implementing diversification practices such as wildflower strips, hedgerows and diversified crop rotations can enhance the abundance of wild insect species that support pollination, pest control, nutrient cycling and other important ecosystem services¹⁴. Organic systems that incorporate high agrobiodiversity can also support wildlife-friendly approaches to farming where the goal is to integrate wildlife conservation with production. By planting and preserving habitat for wildlife, such as hedgerows or riparian forest buffers, organic farms can serve as wildlife corridors that connect parcels of natural habitat and provide refuge from synthetic chemical inputs that may be present in the broader landscape.


The Path Forward

To protect public health, we need to adopt and promote sustainable food production practices that safeguard our natural systems and conserve biodiversity. Organic agriculture has great potential to sequester carbon, mitigate greenhouse gas emissions, and build resilience to a changing climate and protect biodiversity. To realize this potential, the public sector must significantly and rapidly increase its investment in organic research, extension and education, and prioritize research topics that help producers address the climate crisis by reducing net greenhouse gas emissions and adapting their operations to shifting weather patterns.

Some current policy proposals, for example, seek to pay farmers for sequestering carbon in their soils; however, to expand these programs, we need additional research on how much carbon is retained in organically managed soils and for how long. We also need to develop more accurate tools to fully understand organic agriculture’s climate mitigation potential. For example, different tools to measure soil carbon sequestration can yield different results on the same field. Furthermore, soil carbon is extremely variable across different soil types, depths, climate conditions and time periods. Even in apparently uniform fields, soil carbon content can vary by as much as five-fold¹⁵. This is one aspect of climate mitigation within agriculture that needs more research so we can better evaluate the climate benefits of various agricultural practices.

Additionally, both USDA and Congress can do more to promote the transition to organic production systems and improve access for organic producers to federal conservation programs. Many of these programs pay farmers and ranchers for implementing advanced grazing management systems, resource-conserving crop rotations and cover crops as well as for protecting wildlife habitat. These programs and the practices they support represent tried and true solutions that not only have climate benefits, but also protect our natural resources, improve air and water quality, and support biodiversity.

Organic and conservation agriculture with their manifold environmental benefits can help farmers and ranchers build resilience into their operations, actively contribute to climate change mitigation and transform our food production system to one that benefits our health and the health of our planet. We cannot afford to stall action on climate change any longer. If we are to limit the likelihood of future pandemics and other catastrophic events driven by a changing climate, we must prioritize and support systems-based, ecological solutions that protect our food systems, the environment and public health.

Cover cropping builds soil organic carbon and protects soil health, and can also provide a food source for pollinators.



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The Organic Farming Research Foundation (OFRF) is a non-profit foundation that works to foster the improvement and widespread adoption of organic farming systems. OFRF cultivates organic research, education and federal policies that bring more farmers and acreage into organic production.