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CURRENT AND PLANNED CROP PRODUCTION AND ROTATION

The first step in balancing crop needs and nutrient application is knowing what your crop needs are. This is largely based on crop type and yield. Crop needs will vary depending on variety and yields.

 

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CONSIDERATIONS FOR MAKING EFFECTIVE NUTRIENT MANAGEMENT DECISIONS  

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 a Nutrient Management 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.

 

One of the most important processes for limiting resource pollution is assessing and mitigating the risks associated with manure application. WCD has developed an Application Risk Management (ARM) System designed to be used in conjunction with your NMP to guide you through the process of properly assessing and avoiding the risks associated with manure application. The ARM system takes into account your individual field risk levels and limitations and helps you determine when it is safe to apply manure without causing runoff or resource pollution issues. The system gives you more responsibility and flexibility on application dates, while also reducing your pollution potential, when followed properly. Strict adherence to guidelines and criteria is required to insure you do not increase your risk of runoff and have an unwanted discharge.

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Your Nutrient Management Plan was developed based on requirements of the current NRCS 590 standard and all applicable federal, state, and local regulations and ordinances. Any changes in these requirements may necessitate a revision of your Plan.

 

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Nutrient Value of Manure

Properly utilized agricultural wastes can be considered a natural 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.

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Nitrogen, phosphorus and potassium are the major nutrients in manure. Phosphorus is rapidly absorbed in the soil and is not subject to significant leaching. Potassium, although absorbed less than phosphorus, is not generally considered a pollutant in surface and subsurface waters. Nitrogen, however, is a more mobile element. In the nitrate form it leaches easily through the soil. Of the three major nutrients, nitrogen has the greatest potential to pollute water; therefore, it is the limiting factor which determines the amount of manure that can be safely applied and utilized by growing plants.

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The actual nutrient content of manure is subject to change due to such processes as storage, mineralization, volatilization, denitrification and leaching. In addition, the amount of water added to the manure storage (i.e., runoff, rainwater, washwater, etc.) affects the nutrient value of liquid manure on a per gallon basis. The more water used, the more dilute the nutrients will be.

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.

 

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Crop Nutrient Requirement Guidelines

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. 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 just before planting or at peak growing stages gives plants the best chance to use the nutrients. It also reduces the chance of nutrient runoff.

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One of the primary nutrients crops need is nitrogen. 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 immediately plant available. Unfortunately, inorganic forms are highly susceptible to loss through ammonia volatilization during storage and field application. 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 year of application. 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 or transformed or utilized by soil microbes. Nitrogen that is expected to be available to the plant has value as a fertilizer. The nitrogen which is lost to the environment, or which is not available to the crop in the year it is needed or subsequent years, does not have value.

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Phosphorus and Potassium in manure are mostly present in the inorganic form. This means that P and K are similar to commercial fertilizer in that they are readily available for plant uptake.

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Crop nutrient requirements for optimum crop growth are dependent upon adequate supplies of crop nutrients. The total nutrient removal by a crop depends on the yield; higher yields will mean greater amounts of nutrients removed by the crop. When manure is applied based on how much plant available nitrogen it contains, the total N applied is actually much higher. Plant available nitrogen is subject to application losses such as volatilization and is generally available for crop uptake for a limited time, while organic N is converted to plant available nitrogen slowly and is available over a longer time period.   

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The optimum nitrogen 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.

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Nutrient Testing

The second step in balancing crop needs is knowing the nutrient content of your soil and the nutrient value of your manure. In order to apply your nutrients at agronomic rates, accurate and up-to-date manure and soil records should be kept.

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Soil tests help you determine the current nutrient content of your soil and allow you to calculate the nutrient needs required to meet agronomic crop needs. It is recommended that you follow PNW land grant university soil testing protocols.
The fall nitrate test allows you to determine how well you balanced nutrients for the year and may give you an idea where you can improve your nutrient application rates the following year.

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Manure testing records are necessary for knowing the current nutrient content of your manure and how that matches your crops agronomic needs. Matching crop needs to nutrient availability is necessary to reduce excess application, which can increase your potential for leaching and/or runoff events. 

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Another important use of your nutrient testing information is calculation of your phosphorous index (P-Index) on a yearly basis. The P-Index is a tool for estimating the potential for off-site movement of P from individual fields. Phosphorous is a powerful pollutant in streams and water bodies and it is vital to keep it out of the ditches and streams on your farm. Each field is typically reviewed for P-Index value. 

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Some interpretation of test results and calculations may need to be conducted on a yearly basis to determine your agronomic application rates and field N and P assessments. Either you or your nutrient consultant can do this. This practice will help you better utilize your on farm nutrients while also reducing the potential for movement of nutrients off of your fields and potentially into critical areas.

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Be sure to maintain records of all manure exports from your farm using the Manure Transfer Agreement forms. This will aid in tracking your nutrient balance.

 

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Agronomic Manure Application Rate

Once you know your crop needs and the nutrient value of your soil and manure, you may balance your manure application at agronomic rates. Agronomic rate is the rate of nutrient application applied to a field so that the amount of a nutrient required by a crop equals the amount available at any given time. Application rates discussed in the following section are based on the estimated nitrogen content and availability of your manure as shown in the your site-specific, Waste Storage Pond calculation sheet. However, this value may vary from the true nitrogen content, so it is recommended that you test your manure at least three times a year (spring, summer and fall) prior to application and adjust application rates accordingly.

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The NRCS Nutrient Specification (590) states the following: At no time should nitrogen application exceed the crop nutrient requirement. Based on our estimates, the nitrogen content in your manure will be determined as a % sufficient or excess of the nitrogen required for crops grown on your farm.  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. There is also an evaluation of whether phosphorous and potassium to meet crop requirements.  

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The nitrogen applications we prescribe follow guidelines from Washington State Fertilizer Guides issued by Washington State University Cooperative Extension, the NRCS Agricultural Waste Management Field Handbook, and values based on data from local sources.

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It is important to realize, however, that estimates of the nitrogen concentration in manure are based on average values and generalized conditions and this will generally be in distinct contrast to the specific situation occurring in the field at any given time. Nutrient management is the practice of adapting each manure application at the time it takes place so that it will match the specific agronomic needs called for in the field.    

 

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Adjusting the Agronomic Manure 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.

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

• Fields where the initial yield estimate was too high (e.g. 23 ton yields of corn were estimated, but 15 tons was closer to the actual yield). 

• Fields in which the yield potential declines due to changes in agronomic practices such as failure to reseed after a grass field becomes dominated by lower yielding species than it was originally seeded with (e.g. a field of orchardgrass taken over by quackgrass), or crop injury due to such factors as soil compaction or the over application of manure. 

• Fields where yield declines are temporary due to natural conditions such as drought and flooding.      

• Fields in which the estimated nitrogen available from soil organic matter is too low.

• Fields in which application losses are lower than estimated.  This can occur due to changes in management practices that increase application efficiency (e.g. irrigation, manure injection).

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

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Examples in which 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:

• Fields in which the initial estimate for nitrogen available from soil organic matter is too high. This can result when knowledge about previous cropping history and manure management practices is incomplete. 

• Nutrient applications that don’t correspond to crop demand. Ideally, nutrients should be applied at a rate corresponding to what the crop will remove in the next one or two months following an application. For grass crops, 4 to 6 nutrient applications spread out over the growing season are advised. Those applying manure in only 1 or 2 applications will see fewer agronomic benefits and are at a greater risk of negatively affecting crop performance and also polluting ground and surface water.        

• Transitory environmental conditions. Heavy rainfall in the late spring can be responsible for high nitrogen losses due to denitrification. In corn fields, when losses of this type occur, PSNT tests are a good tool for determining how much additional nitrogen will be required to cover the deficit.  

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Some other considerations which may alter your N application rate include:
High temperatures, wind, and/or low humidity result in increased nitrogen volatilization and odor. These can be significant any time manure is not incorporated into the soil. Manure should be incorporated as soon as possible after application (within 48 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.

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• High losses of N due to volatilization may occur when manure is applied by a “big gun” to fields in perennial forage crops – especially when the weather is warm and dry. A better alternative for applying manure, where practical, is the use of manure injectors and other equipment that places manure on and/or in the soil and minimizes coating the leaf blade. Some other alternatives that may help reduce volatilization: 

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

  • Avoid manure applications during hot, dry weather.