Nutrient Management

The purpose of your Nutrient Management Plan is to outline how to best utilize your on-farm nutrients, while also minimizing your impacts to resources such as water, soil, and air. The information in the Plan provides you with the knowledge and guidelines to properly manage nutrients via application to fields, crop management, and resource protection. It is your responsibility to follow all guidelines and management practices laid forth to ensure proper functioning and success of your nutrient management plan.

The following nutrient management guidelines are based off of the Washington State NRCS 590 Nutrient Management Specification (Feb, 2014 from the WA NRCS Field Office Technical Guide). The specifications focuses on the proper placement, timing, source, and rate of nutrient application to prevent impact to resources, and is the foundation of a DNMP.

Nutrient Management Requirements of Your DNMP

Nutrient Value of Manure

Properly utilized manure can be considered a beneficial resource that produces economic returns. Efficient use of animal manure in crop production can result in substantial savings in net energy consumption, higher crop yields, and improved soil tilth. Where application of liquid or solid manure is on pastureland, the final objective is to use the nutrients to grow forage while also timing the application to avoid rejection of the forage by livestock.

The most obvious benefit of applying manure to the land is the fertilizer value. Manure adds organic matter to the soil, improving soil structure, infiltration and general tilth. Soil erosion is generally reduced and the moisture holding capacity is increased. Another benefit is that organically bound nitrogen and phosphorus are released slowly by the action of microorganisms, which conserve these elements and make them available throughout the growing season as they are needed by growing plants.

Nitrogen, phosphorus and potassium are the major nutrients in manure. Phosphorus is rapidly absorbed in the soil and is not subject to significant leaching. It does, however, readily move with sediment and surface runoff into water bodies. Potassium, although absorbed in soil less than phosphorus, is not generally considered a pollutant in surface or subsurface waters. Nitrogen, however, is a more mobile element. In the nitrate (NO3) form, it dissolves readily in water and leaches easily through the soil. As ammonia (NH3), it volatilizes into the atmosphere. And as ammonium (NH4), it dissolves in water and can runoff off of the soil surface into water bodies. All three of these pollutants can impact resources and therefore need to managed appropriately to minimize pollution via runoff and leaching to water.

The actual nutrient ratio and concentration of N, P, and K of manure will vary by farm and season due to changes in animal diet, biological processes during storage, manure processing (i.e., composting, solid separation, digestion, etc.), holding time, and dilution from rainwater and/or washwater. The more water used, the more dilute the nutrients per unit of volume will be. Frequent testing is recommended to determine the change throughout the season. 

Crop Nutrient Requirements

For information on individual crop nutrient needs, please select the appropriate fertilizer guide in the Publications section.

Crop nutrient requirements are affected by a variety of factors including crop type, soil type, nutrient availability, yield, soil moisture, irrigation practices, soil temperature, etc. Additionally, plant growth, and subsequent nutrient need, is not uniform during the growing cycle. Plants tend to have a greater nutrient need and uptake early in the growth cycle, which levels off during late growth, and ceases after harvest. Timing of manure application needs to be considered when looking at timing of crop needs. In general, early application of manure nutrients to soils will aid in the availability of nutrients to crops during the early stages of growth, which is the time of increased nutrient need. Applying manure before planting or peak growing stages gives plants the best chance to use the nutrients. Applying manure at the end of the growth cycle, or after harvest is not beneficial and typically leads to losses via runoff and/or leaching.

One of the primary nutrients crops need is nitrogen (N). There are two types of N in manure, organic and inorganic. The organic (slow release) form of nitrogen slowly mineralizes, providing plant-available N months and even years after application, while inorganic (fast release) forms consist primarily of ammonium-N and are quickly converted to plant available forms of N such as nitrate. Unfortunately, inorganic forms are highly susceptible to loss through ammonia volatilization during storage and field application, and nitrate leaching during fall/winter rains. Promptly incorporating manure into the soil, and matching crop needs to nutrients applied, can reduce these inorganic N losses.

It is important to note that due to the slow release organic form and potential losses of the inorganic form, not all of the N in manure is available to crops during the first year of application. That is why you apply more total N than is immediately needed. Typically 50-70% of applied nitrogen is available in the first year and 10-20% remains in the soil the second year. The remainder is volatilized as ammonia, transformed, mineralized, and/or utilized by soil microbes.  

The optimum nitrogen application rate is strongly related to the soils' capacity to supply nitrogen, which is dependent on the amount of organic matter, drainage capability, rainfall, soil temperature, mineralization potential, leaching potential and denitrification potential. Higher yielding fields don't necessarily require higher nitrogen fertilizer rates, just more accurate application timing. There is an excellent relationship between relative yield and the total N available to the crop, which is the nitrogen the soil supplies plus the manure nutrients. In some cases, more than half of the nitrogen supplied from the crop originated from the nutrients in the soil known as organic N.

Phosphorus (P) and potassium (K) in manure are mostly present in inorganic forms and are similar to commercial fertilizer in that they are readily available for plant uptake. For P, plants will take up only the amount needed for growth. The rest remains in the soil and either builds up over time, or is lost via sediment or runoff. On the other hand, plants such as grass, will take up K in luxury amounts, meaning they take up K in amounts beyond that needed for optimal growth. This will show up in plant tissue tests and can be harmful to animals. Depending on crop, when manure is applied at N rates, P and K are typically over supplied. This means that annual soil tests and tissue sampling should be conducted to determine P and K rates on your farm, and properly mitigated if too high.   

Agronomic Manure Application Rate

Once you know your crop needs and the nutrient value of your soil and manure, you can balance your manure application at agronomic rates. Agronomic rate is the rate of nutrients applied to a field so that the amount of a nutrient required by a crop equals the amount available at any given time. 

Agronomic Rate (gal/acre or ton/acre) = Amount of Plant Available Nutrient Needed (lb/acre) / Estimated Plant Available Nutrient in Manure (lb/1000gal or lb/ton)

Agronomic rate should be calculated for each of the major nutrients (N, P, K) on an annual and individual application basis. However, due to the nutrient balance of manure, N is typically the primary nutrient used in calculating agronomic rate (unless you are required to apply at P rates). At no time should nitrogen application exceed the crop nutrient requirement. Nitrogen is considered to be the most environmentally sensitive nutrient in our area and should not be applied in excess of what is necessary to satisfy crop demand. Nutrient management is the practice of adapting each manure application so that it will match the specific agronomic needs at that given time.   

Adjusting the Agronomic Application Rate

The application rate is made with consideration for both nitrogen available in manure and nitrogen available to plants from the soil. Total nutrient quantities applied must not exceed the amount that can be used by the crop being grown. Liquid manure must be applied at a rate that is compatible with the infiltration characteristics of the soil to avoid standing water, leaching to groundwater, and runoff events. Additionally, rates and quantities must be carefully controlled on sites that have a high water table. In most cases, the maximum nitrogen application rate will be sufficient to meet crop requirements; however, there are some situations in which the rate may either be too high and will need to be revised downward, or too low and will need to be increased.

Examples in which the maximum nitrogen application rate may be too high include:

In all these cases of high nitrogen, readjust your nitrogen application rate the following year based on projected changes and your fall soil nitrate test or complete soil analysis.

In some situations the maximum nitrogen application rate may not be enough. Some of these situations will call for changes in agronomic practices, while others will require revising the application rate upward, either temporarily or permanently.  These are some examples:

Some other considerations which may alter your N application rate include:

High temperatures, wind, and/or low humidity result in increased nitrogen volatilization. These losses can be significant any time manure is not incorporated into the soil. Manure should be incorporated as soon as possible after application (within 24 hours) by irrigating established forage crops or by tilling manure into the fields to be planted with an annual crop or reseeded to grass.  The use of manure injection, where practical, is a better choice than “big gun” liquid manure application.

o  Dilute manure with water during summer months to reduce the nitrogen concentration and the % solids and increase the depth of infiltration into the soil.

o  Avoid manure applications during hot, dry, and/or windy weather.