|Bakhsh, A. - IOWA STATE UNIVERSITY|
|Kanwar, R. - IOWA STATE UNIVERSITY|
Submitted to: ASAE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: July 16, 1998
Publication Date: N/A
Technical Abstract: Spatiotemporal stability analyses are required to delineate areas of stable yield patterns for the application of precision farming management techniques. Spatial structure and temporal stability patterns were studied using 1995-1997 yield data for a field located near Story City, Iowa. Corn was grown during 1995-1996, and soybean during 1997. Yield was measured on 9 east-west transects, consisting of 25 yield blocks per transect. In order to compare the yield variability among different crops and years, data were detrended by median polishing. The resulting yield residuals were used in the subsequent spatial analysis. The trend surface analysis generated from the median polished data showed apparent large scale deterministic structure. The microsale stochastic structure was studied by variography. The variogram analysis showed strong spatial structure for the yield data. Spatial correlations were found to vary from about 40 m for corn to about 90 m for soybean. The total variance of 1995 corn yield was partitioned as 56% by trend, 37% by small scale stochastic structure, and 7% as an interaction of both. Yield variance of 1996 corn was partitioned as 80% trend and 20% small scale stochastic structure. Contrary to corn years, the total yield variance for soybean in 1997 was partitioned as 25% trend, and 75% small scale stochastic structure. The lack of temporal stability resulting from trend surface, variance, and correlation matrix analyses, showed that yield variability is not only controlled by intrinsic soil properties but also by extrinsic factors such as climatic and management.