<<

NebGuide

Nebraska Extension Research-Based Information That You Can Use G2295 · Index: Crops, Crop Production/Field Crops November 2017

Nutrient Management in Sam E. Wortman, Assistant Professor–­Environmental Charles S. Wortmann, Extension Specialist Ashley Linville Pine, Former M.S. Graduate Student Charles A. Shapiro, Soils Specialist–­Crop Nutrition Ashley A. Thompson, Post-­Doctoral Research Associate Richard S. Little, Research Technologist

Compost (left) and cover crops (right) are potentially complementary components of a successful organic management plan.

This NebGuide addresses in organic farming age and animal material applications to maintain or and considers sources, availability, and cycling of . improve soil ,” but minimize “contamination of crops, soil, or water by nutrients, pathogenic organisms, Maintaining or enhancing long-­term soil productiv- heavy metals, or residues of prohibited substances.” Any ity is a key provision of the National Organic Program soil-­applied product, including or , must (NOP) regulation § 205.203, which states that the producer be produced in compliance with NOP regulations. must (a) select and implement practices “that maintain or The National Organic Standards Board (NOSB) improve the physical, chemical, and biological condition of periodically revises the NOP list of allowed or prohibited soil and minimize soil ,” (b) “manage crop nutrients substances by considering the need for the product and the and through rotations, cover crops, and the impact it may have on health and the environment. application of plant and animal materials,” and (c) “man- The Organic Materials Review Institute (OMRI) reviews

1 manufacturer claims for specific products annually to Table 1. Critical values for four diverse field crops determine whether they meet NOP requirements. OMRI common to Nebraska (based on soil samples taken to an 8-­ maintains an extensive, up-­to-­date list of approved sub- inch depth). Values are derived from EC155, Nutrient Man- agement for Agronomic Crops in Nebraska stances available at www​.omri​.org. When a specific fer- Crop tilizer or amendment is not OMRI-­listed, should consult their third-­party certifying agency prior to appli- Soil property Corn Dry beans Potato P (ppm) >16–­24 1 >10 2 >25 1 cation to ensure compliance. The use of organic materials, K (ppm) >125–­150 >125 >125 , cover crops, and crop rotations according to SO -­S (ppm) >6–­8 3 * >8 National Organic Program standards are addressed in this 4 Zn (ppm) >0.8 >1.5 >1.0 NebGuide. 1. Bray-­1 P values; 2. Olsen-­P values; dry bean production regions in Nebraska have Nutrient management on organic should high pH, calcareous soils where Olsen-­P test is more appropriate (however, values can be economically meet crop nutrient needs and avoid soil multiplied by 1.5 to estimate Bray-­1 values); 3. Only applicable for sandy soil with very low ; * = not limiting in soils of typical production regions nutrient depletion, while maintaining or improving soil productivity without excessive nutrient losses. Soil nutrient availability is dependent on diverse soil chemical, physi- cal, and biological properties, their interactions, and their organic cropping systems in Nebraska. Iron deficiency is interaction with the . While measurements commonly associated with calcareous soils with pH > 7.2. can be made for many soil properties, crop performance Alkaline soils on organic farms can be acidified over time is the best indicator of soil productivity. Farmers typically by applying OMRI-­approved mineral (e.g., of manage to minimize soil physical and chemical constraints ) or acidic (e.g., pine needles). to sustainable productivity through practices such as: Applying agricultural lime to raise soil pH is allowed in organic production. Beef feedlot has a lim- • Applying organic materials such as manure, , ing effect, typically the equivalent of about 60 pounds of and biofertilizers to supply nutrients and maintain soil agricultural lime per ton of manure dry weight. However, organic matter most other manures and composts, and biological nitro- • Growing cover crops to cycle soil nutrients and biolog- gen fixation, have a net acidifying effect. Plant and soil ically fix atmospheric testing laboratories commonly do recommend nutrient application rates, but Nebraska Extension EC155, Nutrient • Diversifying crop rotations for more efficient recovery Management for Agronomic Crops in Nebraska is especially and physiological use of valuable for interpretation of soil test results and determi- nation of nutrient and lime application rates. Critical levels for soil nutrient availability represent Soil and plant tissue analysis thresholds above which no increase is expected due to Most crop essential soil nutrients are adequately sup- application of the nutrient, although application of organic plied by agricultural soils in Nebraska. Application of nitro- materials may have other positive effects on the crop. See gen and is most common for high crop produc- Table 1 for a sample of critical soil test values for several tivity in Nebraska. Deficiencies of , sulfur (with essential plant nutrients for common field crops in Nebras- sandy soil), iron (with calcareous soil), and can occur ka. These values can be used as a starting point for making and require attention in some fields. Yield increases due to annual decisions about nutrient sources and application application of other nutrients are rare in Nebraska. Manage- rates; however, developing a long-­term nutrient manage- ment to avoid acidic soil conditions (Nebraska Extension ment plan and proactive (instead of reactive) management NebGuides G1503 and G1504) and soil aggregation, and to of soil fertility is advised for organic farms. avoid compaction (NebGuide G896) are also important for Soil -­nitrogen is highly variable throughout ensuring sufficient nutrient availability to crops. a field and over time is not always a reliable predictor of Soil sampling every four years is advised to test for need. Many farmers use a late-­spring soil nitrate soil organic matter, pH, and availabilities of phosphorus, test to determine sidedress application rates in corn, but potassium, and zinc, as as other properties of interest. sidedress fertilizer applications are rare in organic - Soil sampling practices and methods, such as grid versus ing. Crop nitrogen demand and annual removal should management zone sampling, are addressed in NebGuide guide fertilizer or amendment application rates in organic G1740. Soil pH 6 is the desired minimum pH for most farming, but rates can be reduced if nitrate is detected in

2 Table 2. A phosphorus (P) budget example for a four-­year organic where animal manure was applied to meet crop nitrogen demand, resulting in high phosphorus application and accumulation over time P content Rate Total P content Crop Total P Total P Crop Inputs of inputs (dry) P input of crop* yield removed† balance % tons/ac lb/ac % lb/ac lb/ac lb/ac

Soybean None 0.659 1,775 12 -­12

Corn Manure 0.6 15 180 0.317 5,850 19 161 None 0.659 1,775 12 -­12

Wheat Manure 0.6 10 120 0.435 2,810 12 108 4-­yr total 245

*Based on values from NRCS Plant Nutrient Content Database. All P values are for elemental P and not for P2O5; † Total P removed = (% P content of grain) x (grain yield)

soil samples taken to the rooting depth (2–­4 feet for most crops but contributes to phosphorus loss in runoff and ero- crops; see EC155 for interpretation of deep soil nitrate val- sion and contamination of water bodies. Therefore, manure ues in agronomic crops) and when a is the preced- nitrogen needs to be complemented by biological nitrogen ing crop (see section below for further information). fixation or other nitrogen sources in organic systems. In addition to increased productivity, using organic A nutrient budget can be a useful tool for long-­term materials to fertilize crops can improve broader measures accounting of phosphorus addition via manure (or other of soil “quality” or “health.” Changes to soil physical and fertilizer source) and removal via harvested crops (see ex- biological properties that may result from long-­term or- ample in Table 2). This approach to nutrient management ganic nutrient management include reduced bulk density, can help to ensure organic farmers do not unsustainably increased aggregate size and stability, increased water in- mine inherent soil nutrient reserves, and on the other end filtration, and increased water-­holding capacity; increased of the extreme, do not build up soil nutrient levels of high microbial biomass, diversity, and respiration; and increased risk for environmental contamination. nitrogen mineralization potential, reduced The National Organic Program restricts the use of ma- and soil crusting, and increased sequestra- nure on crops for human consumption. Raw manure must tion (NebGuide G2283). Soil physical and biological tests be applied more than 120 days before if the edible are available at some soil testing labs. Other “soil health” portion of the crop will be in direct contact with soil, and do-­it-­yourself procedures also are available, including the 90 days before harvest if the edible portion of the crop will USDA NRCS Soil Quality Test Kit (https://​www​.nrcs​.usda​ not be in direct contact with soil. These restrictions do not .gov​/wps​/portal​/nrcs​/detail​/soils​/health​/assessment​/​?cid​=​ apply for composted manure and for crops not intended for nrcs142p2​_053873). human consumption; however, if the farm is Good Agri- Plant tissue analysis every three to five years to di- cultural Practices (GAPs) certified https://( ​www​.ams​.usda​ agnose potential nutrient deficiencies of perennial crops, .gov​/services​/auditing​/gap​-­­ghp), it is important to consult such as fruit tree crops, is advised. See New State with the certification agency for recent guidelines prior to University Cooperative Extension Service Guide A-­123, any manure applications. Sampling for Plant Tissue Analysis, for crop-­specific sam- Typical nutrient concentration estimates for different pling techniques. manure sources are available (Table 3), but actual nutrient content varies with the methods of manure storage and handling, ration, animal maturity, and weather Nutrient sources conditions. Thus, manure samples should be analyzed for Manure nutrient content before application (NebGuide G1450). Manure application equipment should be calibrated to Manure application is often valuable to organic pro- ensure the desired rate of nutrient application (NebGuide duction. However, applying manure to meet all of the crop G1335). nitrogen demand can lead to excessive soil phosphorus Manure nitrogen is primarily in organic and ammoni- because crops remove more nitrogen than phosphorus. um forms. -­nitrogen is immediately available The excessive soil phosphorus is not likely to be harmful to to the crop for uptake if it is not lost to volatilization as

3 Table 3. Typical nutrient content of different solid manure Table 4. Estimated first-­season availability (%) of manure sources ammonium-­nitrogen and organic-­nitrogen Nutrient composition Ammonium-­N % ammonium-­N (NH -­N) available this year1 Solid Dry Ammonium-­N Organic-­N P2O5 K2O 4 manure matter Incorporation Solid Liquid (<50 °F) Liquid (>50 °F) % Immediately 95% 95% 95% (lb of nutrient per ton of manure) 1 day after 50% 70% 70% Beef (dirt lot) 67 2 22 23 30 2 days after 25% 55% 45% Beef (paved 29 5 9 9 13 3 days after 15% 45% 40% lot) 7+ days after 0% 40% 0% Beef (bedded 30 1 17 11 14 pack barn) 1. Applied preplant and incorporated via or rainfall event greater than ½ inch. Swine (hoop 40 6 20 15 18 barns)‡ Dairy 46 —­ 14 11 16 (scraped input, organic farmers must be proactive and plan crop ro- earthen) lots) tations and nutrient inputs well in advance to synchronize Broiler (house 69 15 60 27 33 ) nutrient availability with crop demand. Layer 41 18 19 55 32 70 —­ 44 15 30 Compost (house litter) Source: NebGuide G1335, Determining Crop Available Nutrients from Manure. Dashes Composting processes organic waste into material indicate reliable numbers are not available for this manure. of higher nutrient concentration, and reduces the bulk of organic materials through carbohydrate and water loss during decomposition (NebGuide G1315). Compost is of- . Ammonium-­nitrogen availability depends on if ten easier to handle than the bulk organic material, and the the manure is injected or surface-­applied, the time before composting process kills some pathogens and weed . incorporation if surface-­applied, temperature, and pre- Compost has less odor and fewer microbial pathogens, cipitation or events (Table 4). Manure organic with less risk of microbial contamination of fresh produce nitrogen must be mineralized to ammonium before it can than with raw manure. There are fewer NOP restrictions on be used by . Estimated organic nitrogen availability the use of compost in edible crops, but composted animal from applied manures, municipal and composts manures must be applied to soil prior to planting to miti- is 40-20-10-5 percent for the first, second, third, and fourth gate pathogen risks. For GAPs-­certified growers, composts crop following application. An exception is 15-20-10-5 for must meet Safety Modernization Act standards. composted feedlot manure. If manure is applied for a fall- Nitrogen mineralization for finished composts with a sown crop such as winter , the first year availability is carbon:nitrogen ratio (C:N) less than 20:1 occurs readily 28 rather than 40%. with much of the organic nitrogen released to the first crop Instead of depending on manure to meet annual crop following application. Composts with C:N greater than nitrogen demand, organic farmers should build diverse fer- 30:1 will result in net immobilization of soil nitrogen with tility strategies into their farm system plan. A conventional reduced nitrogen availability to the first crop following crop may receive the majority of nitrogen from mineral application. Nearly all of the nitrate and ammonium in the applied prior to the growing season. However, an compost will be available to the plants the first season after organic crop should receive nitrogen from a greater num- application, but only 15 percent of the organic nitrogen ber of sources at a greater number of intervals to ensure in the compost may be available during that season if the regular mineralization of organic nitrogen. For example, 40 C:N is high. Organic N availability estimates for years two percent of nitrogen may be supplied by fall-­applied manure through four are the same as for manure (15, 7, and 4 per- followed by mineralization until nitrogen uptake by the cent, respectively). following crop ceases; 20 percent may be available from a In addition to supplying nitrogen, compost is an preceding summer legume ; and 40 percent may important source of other macro-­ and . As be available from mineralization of soil organic matter and with other organic materials, compost application can im- ammonium-­nitrogen deposition from the air. Because the prove soil organic matter content, cation exchange capacity, timing of nitrogen availability varies by crop and nutrient soil porosity, aggregate stability, and water-­holding capac-

4 ity, although the magnitude of improvements will depend per and transfer these to plant roots, but these are typically on current soil organic matter levels (NebGuide G2283). abundant in Nebraska agricultural soils. Humic acid is Similarly, soil biological properties, including microbial important to plant growth but is already abundant in most biomass, microbial enzymatic activity, and po- soils. A soil with 3 percent organic matter may have as tential are often increased following compost application. much as 10–­15 tons of humic acid in the surface soil layer; Despite the many benefits of compost, raw manure is still thus, adding a few more ounces per acre is unlikely to popular because of the added cost of composting and the enhance crop growth and yield. nitrogen volatilization loss that occurs during composting. While biofertilizers may be beneficial in some situ- ations, it is important to note that biofertilizers, unlike chemical fertilizers, are not regulated. Product labels Other products for nutrient supply often lack detailed information about the ingredients. If For organic production of agronomic crops, manure, they contain living organisms, the shelf life is often short. compost, and are the main sources of Given the number of products on the market with unprov- added nutrients. However, other organic products are used en claims of crop and soil benefits, growers are urged to to enhance nutrient availability for high-­value crops (Table include a non-­treated check or control in the field when 4) with varying nutrient composition and mineralization using biofertilizers to test the claims of soil or crop bene- rates. As with manure and compost, the nutrient miner- fits and evaluate their cost-­effectiveness. See the Nebraska alization rates of such products are largely driven by the Extension “Grower’s Guide to On-­Farm Research” (http://​ C:N. Use of these products for lower value commodities is cropwatch​.unl​.edu​/nofrnzmag) for tips on conducting limited due to high purchase and shipping costs. Given the simple, but effective and scientifically valid, experiments on low nutritional content of compost, manure, and organic your own farm. Evaluations of many biofertilizers and oth- products on a mass basis (relative to fertilizer), economic er nontraditional soil additives are documented but others feasibility of application decreases as distance from the are too short lived to be evaluated well (http://​extension​ source increases. .agron​.iastate​.edu​/compendium​/index​.aspx).

Biofertilizers Cover crops Biofertilizers are products designed to provide enhanced Cover crops can improve soil physical properties, nu- nutrient availability and uptake, stimulation of crop growth, trient cycling, and soil microbial activity. In addition, cover biological nitrogen fixation, and protection against insect crops can scavenge residual nitrogen mineralized from soil pests and disease. Depending on the purpose, and organic amendments before it is lost to volatilization, products can be applied to soil, seeds, or foliar tissue. Evi- runoff, or . However, like other sources of organic dence to support product claims is often limited or mixed. nitrogen, nitrogen contained in cover crop biomass is not Recent research suggests biofertilizers may be most beneficial entirely available to the next crop. It is important to consid- in soils of low to moderate soil organic matter and nutrient er the C:N of the cover . Species with high C:N availability or with foliar application. In contrast, biofertilizer (>20:1; e.g., grasses) result in net immobilization of soil applications to soils of >3 percent organic matter rarely result nitrogen in the short term, whereas nitrogen will be more in measurable crop or soil benefits. Introduced microorgan- readily available following decomposition of species with isms often fail to compete and survive with already well-­ low C:N (<20:1; e.g., legumes). established and resilient microbial communities. Nitrogen fixation by legume cover crops can be Several common categories of biofertilizers include especially useful for increasing soil nitrogen availability nitrogen-­fixers, phosphorus-­solubilizers, phosphorus-­ and balancing the abundant phosphorus and potassium absorbers, and humic acid. Nitrogen-­fixers such asRhi - supplied through manure or compost application. Legume zobium (in with ), Azospirillum, and cover crops high in nitrogen, such as hairy vetch and Azotobacter convert atmospheric nitrogen into ammonia. field , can provide up to 150 pounds of plant-­available Bacillus and Pseudomonas are examples of microbes found nitrogen per acre to the following crop, depending on the in phosphorus-­solubilizing biofertilizers that lower the soil amount of growth. However, the cover crop needs to be pH to dissolve soil-­bound for plant availability terminated early enough to avoid increased C:N as the and may be most effective for calcareous soils. Arbuscular plant matures, and to allow sufficient time for residue mycorrhizal fungi take up soil phosphorus, zinc, and cop- decomposition, mineralization of organic nitrogen, and

5 Table 5. Nutrient analysis and approximate release speed Table 6. Predicted ammonium-­N (Am-­N) release from cover (time required for mineralization of guaranteed nutrients) crop residues with differing N content and C:N ratios of common products for organic production Cover crop residue total N Predicted Am-­N release

% N % P2O5 % K2O Release 4 weeks 10 weeks speed % N in DM lb N/ton in DM lb PAN/ton DM Nitrogen 1 20 <0 0 Alfalfa meal 2 1 2 2–­6 months 1.5 30 3 9 meal 12 1 1 6–­8 weeks 2 40 7 14 Cottonseed cake 7 2 1 12–­16 weeks 2.5 50 12 20 meal 13 0 0 6–­9 months 3 60 19 28 10 5 0 6–­8 weeks 3.5 70 28 37 5 1 1 <4 weeks Source: Pacific Northwest Extension PNW 636,Estimating Plant-­Available Nitrogen Soybean meal 7 2 1 8–­12 weeks Release from Cover Crops. Phosphate Bonemeal (raw) 4 20 0 8–­12 weeks Rock phosphate 0 20 0 6–­12 months Potassium subsequent crops due to biological nitrogen fixation and 0 1 6 6–­12 months less nitrogen immobilization compared with a non-­legume Kelp meal 1 0.1 4 2–­6 months as the preceding crop (Table 6). However, the nitrogen credit for forage legumes is greater than for grain or vegeta- ble legumes because most of the nitrogen (whether scav- soil water recharge (farmers in western Nebraska should enged from the soil or biologically fixed) is removed during carefully consider trade-­offs between cover crop nitrogen harvest of the grain. contributions and soil water use during fallow periods). To In contrast, forage legumes contribute nitrogen from this end, it is recommended that legume cover crops are vegetative biomass, which can be comparable to cover terminated at the flowering stage and at least one to two crop nitrogen contribution if the forage has time to regrow weeks prior to planting. between the last cutting and termination. and other When using cover crops in nitrogen management, it non-­legume crops in rotation can be useful for building is important to consider the total nitrogen content of the soil organic matter–­an important reservoir of nutrients cover crop residue. If a cover crop has 3 percent nitrogen in organic farming (G2283). Root architecture is import- concentration at the time of termination, the resulting ant to sustainable crop rotation. Deep-­rooted crops like soil input is 60 pounds of organic nitrogen per ton of dry can scavenge immobile nutrients like phosphorus matter. Subsequent ammonium-­nitrogen release from that and leached nutrients like nitrate-­nitrogen from deep soil organic nitrogen is estimated to be 19 pounds of nitrogen layers, which may be released near the soil surface with per ton after four weeks and 28 pounds of nitrogen per ton decomposition of the crop residue for availability to subse- after 10 weeks(Table 5). Thus, if a grower can produce 3 quent crops in rotation. tons of dry matter per acre of a 3 percent nitrogen cover crop, approximately 84 pounds of plant-­available nitrogen Conclusions per acre could be mineralized within 10 weeks after termi- nation. Combined with other organic amendments to meet Nutrient management on organic farms requires plant phosphorus, potassium, and demand, long-­term planning and a diverse combination of cultural cover crops can be a sustainable and cost-­effective nutrient practices and inputs. There are an increasing number of source for organic production. commercially-­available organic fertilizers and biofertiliz- ers, but the most profitable organic farms typically source nutrients on or very near the farm by using organic wastes, Crop rotation scavenging residual soil nutrients, and biological fixation of Crop rotation can contribute to improved soil physical nitrogen. When off-­farm or manufactured fertilizer inputs properties, pest management, nutrient availability, nutrient are necessary, it is essential to verify that the product is use efficiency, and . Legumes in the rotation (e.g., allowed in organic production by consulting the OMRI list beans, alfalfa, or ) can result in a nitrogen credit for or the certifying agency.

6 Table 7. Nitrogen credit to subsequent crop following legume Resources N Fertilizer Credit (lb/acre) The cited Nebraska Extension publications are available at: http://​ extensionpubs​.unl​.edu/. Legume Medium and fine Sandy soils textured soils Flynn, R., S.T. Ball, and R.D. Baker. 2004. Sampling for Plant Tissue Analysis Guide A-­123. New Mexico State University. http://​aces​ Soybean 45 35 .nmsu​.edu​/pubs​/​_a​/A123​.pdf Dry bean 25 25 Sullivan, D.M., and N.D. Andrews. 2012. Estimating plant-­available Alfalfa (70–­100% stand, 150 100 nitrogen release from cover crops. PNW 636: A Pacific >4 plants/ft2) Northwest Extension Publication. Oregon State University, Alfalfa (30–­69% stand, 120 70 Washington State University, University of Idaho. https://​ 1.5–­4 plants/ft2) catalog​.extension​.oregonstate​.edu​/sites​/catalog​/files​/project​/pdf​ Alfalfa (0–­29% stand, 90 40 <1.5 plants/ft2) /pnw636​.pdf\ Sweet clover and red clover 80% of credit allowed for alfalfa

Source: Nebraska Extension EC117, Fertilizer Suggestions for Corn.

This publication has been peer reviewed. Extension is a Division of the Institute of and Natural Resources at the University of Nebraska Extension publications are available online Nebraska–­Lincoln cooperating with the Counties and the United States Department of Agriculture. at http://​extension​.unl​.edu​/publications. University of Nebraska–­Lincoln Extension educational programs abide with the nondiscrimination policies of the University of Nebraska–­Lincoln and the United States Department of Agriculture. © 2017, The Board of Regents of the University of Nebraska on behalf of the University of Nebraska–­ Lincoln Extension. All rights reserved.

7