Economically Optimal Compost Rates for Organic Crop Production
- Jeffrey B. Endelman *,
- Jennifer R. Reeve and
- David J. Hole
Current guidelines for the use of compost in organic agriculture are based on nutrient targets, which represent the conditions needed for maximum yield. Due to the high cost of inputs, however, a maximum-yield strategy may be far from economically optimal in some organic cropping systems. In this article we formulate a theory of economically optimal rates (EORs) for compost that incorporates the effects on yield in the years after application. When carryover is neglected, it is well known that the slope of the yield response at the EOR equals the fertilizer/crop price ratio. We show that when carry-over effects are modeled with a decay series, the critical slope is reduced by the sum of the decay series, and this criterion holds for each crop in a rotation. To demonstrate the application of these theoretical results, we used data from a previous study in which the dryland wheat yield response to compost was measured on organic farmland in northern Utah. Since a decay series was not measured, EORs are presented for a range of values of the cumulative carryover, as well as for different compost/wheat price ratios. The EOR for compost sold by one of the region's main composting facilities was predicted to be zero, which highlights the challenging nature of organic fertility management in northern Utah's dryland agriculture. Confidence in the EOR was hindered by our limited understanding of carryover in dryland systems, which should be a priority for future research.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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