Kravchenko, A. N., G. P. Robertson, K. D. Thelen, and R. R. Harwood. 2005. Management, topographical, and weather effects on spatial variability of crop grain yields. Agronomy Journal 97:514-523.
The quantitative characterization of spatiotemporal variability in crop grain yields is an important component for successful precision-agriculture applications. The objective of this study was to analyze and quantify effects of management practices, topographical features, and weather conditions on spatial variability of crop yields. A one-factor randomized complete block design experiment with six replications was established at the Long Term Ecological Research site in southwest Michigan in 1988. The treatments used in this study were two treatments with conventional chemical inputs (chisel plow and no-till) and two organic-based chisel-plowed treatments with a winter leguminous cover crop (low chemical input and zero chemical input). The data consisted of corn (Zea mays L.), soybean [Glycine max (L.) Merr.], wheat (Triticum aestivum L.) yields collected via combine monitors from 1996 to 2001. We observed that stressful conditions, regardless of the stress origin, were associated with increase in the overall yield variability (coefficient of variation) as well as the small-scale yield variability (variogram values at short lag distances and variogram slopes near the origin) with yields probably being more sensitive to the small-scale variations in growth conditions due to soil and microtopographical differences. Coefficients of variation were as high as 45% in years with low precipitation and as low as 14% in years with above-average precipitation. During the years with low precipitation, both the coefficients of variation and the small-scale variability were often significantly higher in the zero chemical input treatment than in the treatments that received fertilizer inputs. The coefficients of variation and the small-scale variability parameters also tended to be higher in corn stressed by antagonism from previous wheat crop in the no-till treatment.
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