Effects of spatial variability of nitrogen supply on environmentally acceptable nitrogen application rates to arable crops.

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Abstract
A model based on a form-quadrant representation of N fertilizer experiments is presented. Calculations showed that spatial variability of mineral N in soil led to higher 'economic optimum' fertilizer rates and rates of Environmentally Acceptable Production (EAP) decreased. Without spatial variability a positive difference of 13 kg/ha was found between the N fertilizer rates for EAP and Maximum Economic Yield (MEY) even when the strictest environmental standard was applied (soil mineral N content at harvest not exceeding 34 kg/ha). At standard levels of variability there was a negative difference of 16 kg/ha, and at doubled variability the difference was 156 kg/ha. An N residue rate of 45 kg/ha at harvest could be met at standard varibility but not at doubled variability. The model showed that higher degrees of 'luxury consumption' and improved synchronization of N mineralization and crop demand had a positive effect on the difference between EAP and MEY. It was concluded that the degree of spatial variability in N supply must be taken into account for environmental and production targets. (Abstract retrieved from CAB Abstracts by CABI’s permission)

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