Page 223 - Nutrient Management Planning Guide

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Chapter 6.1

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A useful online calculator is available on Ropin’ the Web, to estimate crop uptake and or removal for several crops at various yields. To access this calculator, visit Ropin’ the Web and select the “Calculators” tab from the horizontal toolbar on the homepage. The calculator is called “Grains, Forage and Straw Nutrient Use”.

Summary of crop available nutrient content for the solid and liquid manure sources in the year of application:

Source

Crop Available N

Crop Available P

Crop Available K

Liquid 2.4 g/L 0.7 g/L 3.9 g/L Solid 3.3 kg/t 1.6 kg/t 6.2 kg/t

It may be necessary to convert units appearing on the lab report, depending on testing facility and the units used in subsequent calculations. Many of the common conversions were presented in Table 4.3.3 (Chapter 4.3).

Determine Crop Nutrient Requirements

Use fertilizer recommendations generated by a testing facility based on representative soil samples to determine crop nutrient requirements. Remember that lab recommendations for P and K are reported as kg or lb of P

2

O

5

and K

2

O, respectively, which is not useful when applying manure. Available P and K content of manure must be converted to available P

2

O

5

and K

2

O in order to calculate manure application rate using fertilizer recommendations.

To convert P to P

2

O

5

, and K to K

2

O, use the following equations:

P

2

O

5

= P × 2.29

K

2

O = K × 1.20

For situations where, for one reason or another, soil testing on an annual basis is either not possible or practical, an alternative strategy will need to be used. In order of preference, some alternatives are:

Use fertilizer recommendations from comparable •

soil analysis results. This could include past recommendations for that field or recommendations for neighbouring fields under similar management. Use historical application rates, provided historical •

yield, quality (e.g., protein) and production factors (e.g., lodging, maturity) suggest that these rates were appropriate. Apply manure nutrients so as to replace nutrients •

removed by the crop at expected yields

(Appendix 6). Information on historical yields can help estimate crop nutrient removal. Note that none of these approaches are acceptable substitutes for soil testing in the long term but may be reasonable compromises if annual sampling of all fields is not possible. Remember that for a field to be eligible to receive manure AOPA requires soil analysis from within the last 3 years.