Page 229 - Nutrient Management Planning Guide

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Chapter 6.1

Calculating Amounts of Residual N and P Applied

There can be substantial excess application of certain nutrients depending on whether application rate is P-based or N-based. After calculating a target application rate, calculate the rates at which other nutrients will be applied.

Portions of residual organic N and P applied will become available in subsequent years. These will not be reflected in subsequent soil tests, but will impact fertilizer requirements.

Determining Application Rates of Other Manure Nutrients

Using the calculated application rates for solid and liquid manure from scenario 1 of the previous example, where manure application was based on a one-year supply of available N: Solid application rate = 23.6 t/ha Liquid Application rate = 32,500 L/ha

Available N applied in both situations = 78 kg/ha

The resulting application rates for total and available P and P

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5

are:

Liquid manure

Total P applied (kg/ha) = 32,500 L/ha ÷ 1,000 × 1.0 kg/1,000 L

Total P applied (kg/ha) = 32.6 kg/ha Total P

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5

applied (kg/ha) = 32.6 kg/ha × 2.29 Total P

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5

applied (kg/ha) = 74.7 kg/ha

By using the factors presented earlier (Estimated crop available P in: year 1 = Total P x 0.7, year 2 = Total P x 0.2, and year 3 = Total P x 0.16), this translates to the following nutrient applied by the liquid manure application:

Year 1 Year 2 Year 3 kg/ha kg/ha kg/ha

Retained NH

4

-N applied

61.8 N/A N/A

Available organic N

16.3 7.4 3.7

Total crop available N

78 7.4 3.7

Available P 22.8 6.5 2.0 Available P

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5

52.2 14.9 4.6

Solid manure

Total P applied (kg/ha) = 23.6 t/ha × 2.3 kg/t Total P applied (kg/ha) = 54.3 kg/ha Total P

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5

applied (kg/ha) = 54.3 kg/ha × 2.29 Total P

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5

applied (kg/ha) = 124.3 kg/ha By using the factors presented earlier (Estimated crop available P in: year 1 = Total P x 0.7, year 2 = Total P x 0.2, and year 3 = Total P x 0.16), this translates to the following nutrient applied by the solid manure application:

Year 1 Year 2 Year 3 kg/ha kg/ha kg/ha

Retained NH

4

-N applied

40.1 n/a n/a

Available organic N

37.2 17.8 8.9

Total crop available N

78 17.8 8.9

Available P 38.0 10.9 3.3 Available P

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5

87.0 24.9 7.5

The rate at which other nutrients were applied can also be calculated, provided the concentrations of these in the manure were analyzed and reported, the application rate and availability estimates (if applicable) are known.

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