Page 224 - Nutrient Management Planning Guide

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Calculating Manure Application Rates and Fertilizer Requirements

Case Study: Determining Crop Nutrient Requirements

Based on the background information provided and results of the soil analysis the testing facility recommended the following fertilizer rates for a field:

Recommendations based on expected moisture conditions during growing season

Dry (130 mm) Average (200 mm) Wet (270 mm)

N P

2

O

5

K

2

O N P

2

O

5

K

2

O N P

2

O

5

K

2

O 22 kg/ha 20 lb/ac

22 kg/ha 20 lb/ac

-

44 kg/ha 40 lb/ac

28 kg/ha 25 lb/ac

-

78 kg/ha 70 lb/ac

39 kg/ha 35 lb/ac

-

Based on long-term weather patterns, expected crop prices and the fact that the manure has only a small cost associated with it (relative to fertilizer), manure application rate to be developed was based on the fertilizer recommendations for wet conditions.

Determine Basis for Application Rate

N-Based Application »

Current practice in Alberta is to base manure application on crop available N, which is the first limiting nutrient in most Alberta cropping scenarios. The impact this practice has on levels of other nutrients in the soil should be considered. By applying manure based on N, other nutrients including P and K will be simultaneously applied at rates that exceed crop removal. This is due to the typical nutrient content of most manure. This has three important implications:

Applying nutrients above their agronomic •

requirement prevents the full economic value of manure to be realized. Research has clearly demonstrated that long- •

term application of P above agronomic rates is contributing to P build-up in surface soil layers to the point that the risk of runoff losses is increased. Loss of P to surface water is a significant environmental concern.

High soil test levels of certain nutrients can impair •

the crop’s ability to take up other essential nutrients (e.g., high soil test P can impair zinc uptake). If manure is to be applied based on N, monitor soil test P levels regularly. Crops generally do not respond to soil test P levels above 112 kg/ha (100 lb/ac) in the top 15 cm of soil and higher levels increase the risk of runoff losses.

Due to equipment limitations it may be necessary to apply more than one-year’s worth of manure, particularly if only small rates of manure application are suggested for a particular field.

P-Based Application »

One way of avoiding nutrient accumulation in soils is to apply manure based on P. At present, however, there is no one single prescribed strategy for applying manure on a P basis. One of the major constraints to P-based application is that current application technologies are not able to consistently apply manure at the low rates that would be required to meet agronomic P requirements for a