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Precision Manure Management: Enhancing Soil Quality & Productivity

September 25, 2009

By Raj Khosla and Jessica Davis

Can we use the principles of precision agriculture to optimize our manure utilization decisions?  Research conducted in Colorado on “Precision fertilizer management” has clearly demonstrated that the best approach for variable rate fertilizer application is the “Variable Yield Goal” (VYG) management strategy. By VYG we mean, that the application of fertilizer is based on a unique yield goal appropriate for each management zone. We cut down fertilizer rates in historically non-productive or less productive areas and reallocate the savings in fertilizers to the historically more productive areas of the field. While such a strategy has multiple benefits and optimizes fertilizer application across the field, its scope is still limited.  The VYG strategy does not address the yield limiting factors in the low producing areas of the field.

Discussions with farmers led to an innovative idea of “precision manure management” to address those low-yielding areas. The big question we had was: Could we strategically apply different rates of manure across a field so that the yields in the low and medium producing areas would be enhanced?  A 3-yr study was recently completed on a heavy textured soil in a furrow-irrigated corn field.  Manure was applied and incorporated in the spring of each year at rates of 10, 20 and 30 tons/acre for low, medium and high productivity zones (VYG strategy) and vice-versa (e.g., 30 tons/acre in the low yielding zone and less in the higher-yielding areas) depending upon the precision manure management strategy.

Our findings indicate improvement in soil organic matter content and reduction in bulk density in the low management zones due to high manure application rates. Interestingly, the precision manure management brought organic matter content of the low productivity areas almost to the levels of the high productivity areas. In addition to soil quality improvement, grain yield response was evaluated. Quite interestingly, in two (2006 and 2008) out of three years, the grain yield responded to variable rate manure application as expected. Grain yield did increase in the low management zones when a higher manure application rate (30 tons/acre) was applied. While the grain yield response corresponded to our expectation, the grain yields were still lower than those observed for the precision N (fertilizer) management strategy for those two years (2006 and 2008). It is interesting to note that in 2007, with above normal precipitation, grain yield levels under precision manure management outperformed yields under precision fertilizer management in all the management zones.

What can we learn from this study? It matters where you apply manure within a field. However, manure alone applied at 30 tons/ac was not sufficient in two out of three years, to completely meet crop nutrient needs. N sidedressing based on either pre-sidedress soil nitrate testing (PSNT) or in-season crop canopy sensing should be coupled with precision manure management to optimize crop nutrition and yield.

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