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Precision and Accuracy in a Nutrient Management Plan utilizing Liquid Manure Application: Expectations and Reality

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  032158,  2003 ASAE Annual Meeting . (doi: 10.13031/2013.14023) @2003
Authors:   Ted L. Funk, Matthew J. Robert, Yuanhui Zhang, and Randolph E. Fonner
Keywords:   manure application, nutrient management plans

Manure application on land for the purpose of fertilizing crops is a process plagued with uncertainties (errors) in the calculations, equipment calibrations, performance of the application process and yield of the crop. One errorpropagation algorithm for combining the component uncertainties arising from each step of the process is proposed. The largest uncertainties with either a nitrogen based or phosphorus based application approach are the crop yield and on-farm manure sampling, followed by mineralization rates (nitrogen) and laboratory analysis (nitrogen and phosphorus). For examples and estimates given in the paper, overall process uncertainties are on the order of 32-34 percent.

It is suggested that, for nitrogen based plans where crop yield is expected to be nitrogen limited, producers might increase their calculated manure application rates by an amount dictated by a practical confidence level desired and the errorpropagation algorithm. Phosphorus-based manure applications do not need greater manure application rates, since phosphorus is much less mobile than nitrogen and soil levels of phosphorus increase and decrease more slowly with phosphorus additions.

Writers of nutrient management plans need to understand the magnitudes of uncertainties in order to efficiently target areas in which the process may be improved. Regulatory personnel inspecting nutrient management plans should be aware of the component uncertainties in manure utilization on cropland and the effect of combining those errors, and judge discrepancies between planned applications and actual records of manure spreading according to realistic expectations.

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