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Calculating Manure Application Rates and Fertilizer Requirements

Important Terms

Table 6.1.1 Key Terms and Definitions

Term Definition

N-Based Application A manure application rate calculated to meet the nitrogen (N) requirements of the crop. P-Based Application A manure application rate calculated to meet the phosphorus (P) requirements of the crop.

Reference Nutrient

The ‘nutrient’ on which the manure application rate was based or developed (e.g., nitrogen, phosphorus). Threshold Application Rate

A simple calculation to determine whether the eligible land base will be sufficient to accommodate the total annual manure collected.

One of the most critical tasks in manure nutrient management planning is determining the appropriate manure application rates to get the desired crop productivity. It is also necessary in certain scenarios to determine fertilizer application rates to meet any nutrient requirements not met through manure application. These activities involve using information discussed in earlier chapters, including:

available land base • soil nutrient profile • crop nutrient requirements • nutrient content of manure • application method and conditions •

This chapter will work through the procedure for calculating manure application rates and determining fertilizer requirements. A hypothetical case study will be used to illustrate and reinforce the principles in each step.

Calculating Manure Application Rates

Calculating manure application rates involves four steps:

Estimate available nutrient content of manure 1. Determine crop nutrient requirements 2.

Determine basis for application rate calculation 3. Calculate manure application rate 4.

If manure is sampled during loading or application use “book values” or historical information on bulk density and manure nutrient content to calculate manure application rates. Once bulk density and manure analysis information is available repeat the calculations using this information to determine the correct manure and nutrient application rates and determine whether additional fertilizer is required.

Once the application rate has been determined, estimate the amount of nutrients that will become available in that year plus subsequent years, from that application. If a whole farm nutrient management plan is being developed determine whether additional area is required to apply all of the manure at agronomic rates.

Large surpluses of manure may suggest a need to:

Build cooperative relationships with surrounding •

landowners to secure additional land for manure application. Consider alternative treatment measures, such as •

solid-liquid separation technologies or composting to increase the distance manure can be transported economically. Develop marketing options for the manure produced. •