Erosion is the loss of soil particles, often due to wind or water.  Ammonium N (NH₄⁺) is a cation, and thus is readily adsorbed onto the soil CEC.  This holds the ammonium N in a readily-available form which is not susceptible to leaching or denitrification.  However, since most of the CEC is in the clay fraction of the soil, and since this is the fraction that is most susceptible to detachment and erosion, there can be a significant loss of available N when erosion occurs.  Similarly, P is held mainly in insoluble forms in the soil, thus making erosion the predominant mechanism for P loss.  When the eroded soil enters water, the dilution effect will solubize some of the P, which can lead to eutrophication.

Runoff represents a loss of nutrients dissolved in water that drains off a field.  P is commonly lost through runoff.  The capacity for a soil to fix P is very large; however, it is not infinite.  It is possible to add enough P to use up most of the available Fe and Al (which bind it to soil particles), at least in the surface soil.  When this happens, the soil is said to be saturated with P.  Thus, additional P is not fixed, and it remains soluble and can be lost with runoff.  This becomes very important when large amounts of P are added to the soil surface.  The surface layer of soil can become saturated very quickly, and then when there is runoff over the surface, it interacts with this saturated surface soil layer and picks up significant amounts of soluble P and transports it off the field.  If this runoff goes into a water body, the P is immediately available to cause eutrophication.  In very sandy soils with little natural Fe and Al, there is little capacity to hold the P, and thus it becomes saturated more quickly.  In these soils, soluble P loss is an even greater concern, and even P leaching can be significant.

Volatilization is the loss of nutrients in the gas form.  Urea nitrogen (found in urea fertilizer, UAN solution fertilizer, and manure) is unique in that the available ammonium N (NH₄⁺) from urea can be rapidly converted to ammonia (NH₃), which is a gas.  If this reaction occurs on the soil surface, the ammonia is lost into the atmosphere.  Losses of over 1/3 of the N from urea can occur within one week of surface application of a urea-containing material.  Tillage or ½ inch of rain, which incorporates the urea, will minimize this loss.  The sooner tillage or rain occurs after application, the smaller the losses will be; thus immediate incorporation or timing application just before rain are important to reducing this loss.  Other common N sources, such as ammonium sulfate and ammonium nitrate, are not susceptible to volatilization loss.  Also, urease inhibitors have been developed as an additive to urea to effectively reduce this loss when incorporation is not possible.  Volatilization can represent a significant loss to the crop and the ammonia that goes into the atmosphere represents a significant potential pollution problem.

Denitrification is the loss of gaseous forms of N due to anaerobic conditions, like when soils become saturated with water.  This is especially a problem in poorly-drained soils.  Denitrification occurs when all organisms in a saturated soil begin to run out of oxygen.  Some of these organisms have developed the ability to extract the oxygens from nitrate (NO₃^-) to survive.  In the process, the N from the nitrate is released as either dinitrogen (N₂) or nitrous oxide (N₂O), both of which are gases which are unavailable to plants.  Nitrous oxides are greenhouse gases with serious environmental implications.

Leaching is similar to runoff in that nutrients in the soil solution leave with water.  Most N sources are rapidly converted to nitrate N (NO₃^-) by bacteria in the soil.  This is an important process because nitrate is the most common form of N taken up by plants.  However, since nitrate is an anion (has a negative charge), it is not held by the soil CEC.  Therefore, if water percolates through the soil, it can easily carry significant amounts of nitrate with it.  If the nitrate is leached below the rooting zone of the crop, it is no longer available, and if it leaches to the groundwater, it represents a pollution problem with public health implications.  This is especially a problem on well-drained soils.

Nitrogen is a very dynamic element in the soil.  It is constantly changing forms and is very mobile.  As soon as N is applied to the soils, it begins to change and move.  Unfortunately, while some of these changes result in greater availability of the N to the plant, many of these forms can be lost from the system.  These losses not only represent a loss from potential uptake by the crop, but the N that is lost can end up creating environmental problems.  One of the most important management factors to minimize these losses is to time the application of N as close to the time of crop uptake as possible, thus reducing the time that the N is exposed to losses.

Management to minimize P loss is a compromise.  Incorporating the P positions it so that surface runoff and erosion will not have access to the added P, thus reducing the potential for loss.  Also, the mixing that occurs spreads the P out, so it contacts more soil and the soil does not saturate as rapidly.  However, tillage to incorporate P usually increases the potential for erosion, which is the major loss mechanism for P.  The ideal is to place the P below the soil surface in a way that minimizes soil and residue disturbance.  Direct injection of manure or fertilizer P can be very effective at reducing P loss.  Finally, timing can help.  Most P sources are highly soluble when first applied.  If a runoff or erosion event occurs immediately following application, loss can be very high.  However, with time the P reacts with the soil and becomes less soluble.  Thus, timing P applications when it is less likely that there will be significant runoff or erosion events can reduce losses.  Finally, soil properties which control water movement can play a very important role.  If a soil is compacted or crusted, or has a low amount of residue cover, then more water will runoff, increasing the potential for P loss.  Managing soil drainage can have a similar impact.

The NRCS 590 Standard establishes criteria for nutrient management elements of comprehensive nutrient management plans (CNMPs) for Concentrated Animal Feeding Operations (CAFOs) and other farms receiving state or federal cost-sharing for Best Management Practices (BMPs).

Guidelines of the 590 include:

• Account for nutrients from all sources
• Plan manure application based on crop nutrient needs
• Apply P runoff and N leaching guidelines (such as NY P Runoff Index and Nitrate Leaching Index)
• Apply appropriate manure application setbacks
• Follow Land Grant University Guideline

A Mass Nutrient Balance can be described as the difference between total amount of nutrients imported onto the farm and nutrients exported via milk, meat, crops, manure, etc.  Zero or negative balances are not sustainable, as all biologic systems have inherent losses.  Due to differences in NPK ratios of manure versus crop NPK needs, it is difficult to achieve acceptable balances simultaneously on dairy and livestock farms; balancing field applications for N with manure will increase soil P and K over time.

Most manures contain approximately three times as much N as P.  Thus, applying manure to meet crop N needs will result in overapplication of P and K.  Unused P can be lost due to leaching, erosion, and runoff, and can contaminate groundwater and cause eutrophication.  Meanwhile, applying manure to meet crop P needs runs the risk of underapplying N, resulting in deficiencies for the growing crop and a poor yield.  It requires more land, as smaller manure applications will be utilized on each field, and requires supplemental N in some form, which can be expensive.

For example, compare nutrient content of poultry and dairy manure to crop needs:

When applied to meet N needs (left), both poultry and dairy manure provide much more P and K than needed.

When applied to meet P needs (right), both poultry and dairy manure fail to provide adequate N.

Manure contains organic N and inorganic N.  The latter can be lost as ammonia if manure is not incorporated.  Because of these losses, more manure needs to be applied to achieve the same available N.  This will result in larger P and K applications as well, leading to more rapid P and K soil test increases over time.  Surface application of nutrients also leaves them exposed to erosion and runoff events, potentially increasing losses to the environment.  While tillage reduces surface exposure of nutrients, it can increase erosion rates.  Many farms are limited in the acreage available over which to spread manure.  Overapplying manure leads to nutrient excesses and environmental losses.  It may become necessary to export manure nutrients in another way.

The largest amount of nutrients imported by dairy and livestock farms tends to be from feed imports.  Better forage quality and matching diets with animal needs can improve animal nutrient use efficiency, reducing nutrients in manure and thus reducing feed nutrient imports, improving the farm's nutrient balance.

Environmentally-sensitive areas are areas that have the largest potential to lose nutrients and cause offsite environmental impacts.  These areas should be managed carefully to minimize such offsite environmental impacts.  Impacts include things like loss of plant and animal species, growth of undesirable plant and animal species, poor drinking water quality (taste, odor), loss of a fishery, etc.

Examples of environmentally-sensitive areas include:

Locating facilities and fields on maps enhances communication between the planner, producer, farm staff, and custom applicators.

Identifying environmentally-sensitive areas allows for careful management of nutrients to minimize offsite environmental impacts.

The crop rotation drives fertility guidelines, especially N.

Expected yields drive fertility guidelines, especially N, and help with overall assessment of forage production.

Soil tests drive P, K, Mg, etc. guidelines and manure application rates.  Plant analyses help determine the nutrient removal of plants, and can assist in diagnoses of plant nutrient status.  Water analyses determine the level of nutrients in the water, which can indicate potential excesses (i.e. losses) in existence.

Quantifying nutrients from all sources available assists in the proper allocation of them across the farm, and informs the user whether export of manure nutrients is needed.  Nutrient sources include manure, compost, biosolids, fertilizer, legume N, residual manure N, etc.

A field-specific nutrient budget is the amount of each nutrient required for optimum yield.  Estimates of nutrient additions from all sources and nutrient losses are made, and then nutrient additions are adjusted to meet crop needs and to not exceed other environmental goals.

Recommendations of nutrient rate, timing, form, and method of application should be made, keeping in mind how they affect nutrient availability and risk of environmental loss.  This step includes identification of periods of excess water where runoff, erosion, and leaching may occur.  Nutrient applications should be avoided during these times.

Review and modify the plan as needed, at least annually.  These updates are needed to reflect actual application rates, timing, method, rotation shifts, purchase of new land, and other changes that could impact management in the next year.

Manure quantities and analyses are needed to properly allocate manure to cropland on an annual basis.  Manure production can be measured based on the size of the storage, from records of how many loads of manure of a given size are hauled each year, or from animal inventories and production levels on the farm.

Animal excretion plus other additions to process wastewater uses estimates of per-animal excretion to estimate total manure production.  To use these factors, you need to determine the number of animal units (AU) that are producing manure and the number of days in the manure collection period.  You may need to divide the animals into groups based on different size, age, storage or handling systems, etc.

Animal unit calculation:

• For growing animals, use the average weight during the collection period.
• For example: hogs growing from 45 lb to 245 lb would have an average weight of 145 lb.  With 500 pigs: AU = 500 x 145 / 1000 = 72.5 AU
• Use the table (on the next page) to determine daily manure production rates.
• Finishing pigs produce 11 gal manure/AU/day.  Thus for these pigs: 72.5 AU x 11 gal/AU/day = 797.5 gal/day
• This number is multiplied by the number of days that manure is collected.
• If manure is collected and spread every 4 months (120 days): 120 days x 797.5 gal/day = 95,700 gal to spread every 4 months
• Any additions to the manure, such as rainwater, washwater, bedding, etc. should be added to this total for the collection period.

Load records and manure spreader calibration calculates manure production based on what has been spread.  There are three methods used to do this.

3. Method 3: counting loads

• Works for solid, semi-solid, and liquid manures.
• Requires knowledge of field size and average manure load (tons/load or gal/load).  Apply manure evenly to the whole field, count the loads applied, and calculate rate per acre.

Calibrating manure spreader using weights (image source)

Size, type, and number of animals affect the amount of manure generated (refer to PO 54).  Land base and weather determine accessibility in various times of the year.  If machinery cannot get onto fields to spread manure, extra storage capacity is necessary.  In addition, equipment and labor force might restrict the ability to apply manure in a short timeframe.

If an agronomic soil test is done, manure or biosolids can be added in amounts where expected plant P uptake and removal is equal to the P that will be added.

Soil test P levels in surface soil can be used to determine whether or not the recommendation should be P-based.  If soil P test levels are below the critical level, then manure and biosolids applications can be N-based.  If soil test levels exceed the critical value, then recommendations are P-based.  A second higher critical value precludes manure or biosolids application.

A P index can be developed for fields, which integrates factors relating to potential P loss to evaluate the relative risk of P application to a field.  These include the P that might be transported from manure or biosolids and soil, the potential to transport that P to a body of water, how much rainfall might occur, and whether or not best management practices are in place.  The amount of manure or biosolids that can be applied is a function of the P index value.  If it is low enough, manure or biosolid application rates can be N-based.

The P index is an indicator of potential P loss, designed to identify fields at high risk for P runoff by combining sources of P (soil, fertilizer, manure) with factors contributing to runoff (distance to streams, erosion, flooding frequency, drainage, etc).

The four score management categories are: low, medium, high, and very high.  Actual scores will differ for states in the Northeast (and nationally), but management guidance in each for the four categories will be the same.  State-specific P index calculations can be obtained from the local Land Grant University.

For example: NY P index scores, vulnerability rankings, and management implications

A greater application rate increases the P index score, as there is more P that can potentially saturate the soil surface and be lost.  Incorporation of manure reduces the P index score.  Application in summer is less risky (lower score) than in early spring, as the soil is warmer and not as subject to runoff.  Applying manure close to streams carries greater risk (higher score), as there is an increased likelihood that runoff will get into the stream.  Last, reducing erosion through soil conservation practices will reduce the P index score.

To determine crop removal, multiply yield (in lb) by the Dry Matter (DM) content times the P content of the DM.

• For example: 20 tons of silage yield at 35% DM and 0.62% P₂O₅.
• Crop P removal = 20 tons x 2000 lb/ton x 0.35 x 0.0062 = 87 lb P₂O₅ (or 4.35 lb P₂O₅/ton silage)

The chart below gives P removal estimates of common field crops.

The nitrate Leaching Index is an indicator of the potential for nitrate to reach groundwater.  The current LI rates leaching potential based on soil hydrologic group and precipitation data.

• LI < 2: low risk of nitrate leaching below the root zone
• 2 < LI < 10: intermediate risk of nitrate leaching below the root zone
• LI > 10: high risk of nitrate leaching below the root zone

To meet the N leaching requirements of the NRCS Nutrient Management Standard (590), producers are expected to implement Best Management Practices (BMPs) if the LI score for a field is high, and to consider BMPs if the LI score is intermediate.  Sample BMPs are discussed in PO 61.

NY soil types and hydrologic groups can be obtained from the New York Nitrate Leaching Index (particularly here and here.

• Unless the NY P Index identifies the need for P-based fertility management, manure and fertilizer application rates should be based on Cornell guidelines for meeting crop N needs.
• For corn, pre-plant (other than starter fertilizer) and early post-plant broadcast applications of commercial N without the use of nitrification inhibitors are not recommended.
• Sidedress applications should be made after the corn has at least four true leaves.
• For row and cereal crops, including corn, maintain starter fertilizer N rates below 50 lb/acre actual N under normal conditions.
• Manure and fertilizer applications should be adjusted based on information provided in "Nitrogen Recommendations for Field Crops in New York."
• Evaluate the need for sidedress N applications based on PSNT or other soil nitrogen tests.
• Sod crops should not be incorporated in the fall.  Chemical sod killing may be carried out when the soil temperature at the 4-inch depth is approaching 45°F.
• Minimize fall and/or winter manure application on good grass and/or legume sod fields that are to be rotated the following spring.
• Appropriate ammonia conservation is encouraged.  Losses can either be reduced by immediately incorporating manure, or eliminated by directly injecting manure as a sidedress application to growing crops.
• Plant winter hardy cover crops whenever possible, especially when fall manure is applied (e.g. rye, winter wheat, or interseed ryegrass in the summer).
• Manure may be applied in the fall where there is a growing crop.  Judicious amounts of manure can be applied to or in conjunction with perennial crops or winter hardy cover crops.  Applications should generally not exceed 50 lb/acre of first year available N, or 50% of the expected N needs of next year's crop.
• Frost incorporation/injection is acceptable when soil conditions are suitable, but winter applications should be made in accordance with the NY Phosphorus Index.
• Manure N application on legumes is acceptable to satisfy agronomic requirements when legumes represent less than 50% of the stand.  When legumes represent more than 50% of the stand, manure application should be limited to no more than 150 lb available N/acre.
• Do not spread manure less than 100 ft from wellheads and springs.

Manure treatment and incorporation are two main ways to reduce odor.

Manure incorporation is one way to reduce air emissions of ammonia from fields.

Improved calf care includes prevention of contamination of new calves with adult manure, prevention of calfhood diseases such as BVD, scours, and other health protocols.  This reduces the likelihood of pathogens being present in manure, and produces high-quality animals.

Herd management factors that reduce pathogen loading include cleanliness, treatment and prevention of disease, and proper nutrition.

Cold temperatures inhibit and kill pathogens, which often require moderate or near-body temperatures to survive.

Extended storage kills pathogens over time (approximately one year).  In addition, the ability to store manure for extended periods allows application of manure based on crop needs rather than storage capacity, reducing the volume of manure spread at one time.

Methane digestion treatments kill many pathogenic bacteria.

Composting greatly reduces pathogenic bacterial numbers, as they cannot survive more than one year, and are often killed by the heat produced.

• Nutrient Management Planning requires knowledge and accounting for all nutrient sources.  Manure application must be based on crop nutrient needs, taking into account that manure nutrients and crop needs do not always match perfectly.  Runoff and leaching of P and NO₃^- must be managed: depending on Phosphorus Index and Nitrate Leaching Index scores, BMPs may need to be implemented.  Appropriate manure application setbacks should be utilized, and manure should be stored, applied, and managed in a way that reduces nutrient loss.  Land Grant University guidelines should be adhered to.
• Crop nutrient requirements are best calculated using projected yields, crop rotation, field history and information, and data such as soil test results and PSNTs.
• The NRCS 590 Nutrient Management Standard provides guidelines for planning.
• Proper storage, treatment, and application of manure can reduce the risk of nutrient runoff, pathogen spread, and loss of air and water quality.  Environmentally-sensitive areas should be identified and BMPs implemented when managing these areas.
• Whole-farm nutrient management involves all aspects of the operation: inputs (animal feed, fertilizer, etc) and outputs (milk, meat, crops, etc) must be considered, as should the impacts each has on the other.  Precision feeding can reduce the amount and type of nutrients excreted in the manure, and proper application of that manure can improve crop yields and nutrient quality, while preventing environmental contamination.