Precision Manure Management Across Site Specific Management Zones.

Management zones based on soil color images have been proven to accurately quantify spatial variability in soils and classify field into (high, medium, and low) productivity potential zones. Previous studies have shown that variable rate Nitrogen (N) fertilization across management zones has increased grain yield, N use efficiency, and net $ returns while reducing environmentally sensitive nutrients into soil on a field-scale basis. However, farmers are concerned that this approach does not improve yield in low productivity zones. Farmers hypothesized that use of manure in low productivity zones could enhance soil quality, water holding capacity, increase organic matter content, improve other soil properties, and would enhance grain yield and net $ return of these areas. The objective of this study was to assess the potential of precision manure management across management zones to improve soil properties and grain yield of low productivity zones. The study took place over three years in irrigated corn fields of Colorado. Results of this study indicate that in two out of three years grain yield responded to variable rate manure application as expected. However, grain yields were still lower than those observed for the precision inorganic fertilizer management strategy. Perhaps, manure alone is not sufficient to meet the complete crop nutritional needs.  This conclusion leads to a new strategy that would use precision manure management in conjunction with in-season inorganic N fertilization to meet the peak crop demand.