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Title: SPATIO-TEMPORAL ANALYSIS OF YIELD VARIABILITY FOR A CORN-SOYBEAN FIELD IN IOWA

Author
item BAKHSH, A - IOWA STATE UNIVERISTY
item Jaynes, Dan
item Colvin, Thomas
item KANWAR, R S - IOWA STATE UNIVERSITY

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2000
Publication Date: 1/31/2000
Citation: Bakhsh, A., Jaynes, D.B., Colvin, T.S., Kanwar, R. 2000. Spatio-temporal analysis of yield variability for a corn-soybean field in Iowa. Transactions of the ASAE. 43(1):31-38.

Interpretive Summary: Recent research in agriculture has been targeted at evaluating and developing the concept of precision farming. The concept of precision farming is that agricultural inputs such as seed, fertilizer, and herbicides need to be applied at variable rates across a field rather than uniformly as currently practiced. It is thought that variable application of inputs will maximize yield and/or economic returns while minimizing detrimental affects on water and soil resources. Before these concepts can be successfully adopted by farmers, we need to understand how yields vary across fields, what factors are determining these yield patterns, and how and if they will respond to management. In a three year study, we showed that yield patterns within a 60 acre field changed from year to year and that there was little similarity among yearly patterns. Even after applying sophisticated statistical analyzes we were unable to determine the underlying factors controlling the observed yield patterns. If the lack of repeatable yield patterns is typical for most fields, we will need to rethink how (and if) precision farming practices can improve farming efficiency. These findings are of great importance not only to agricultural scientists investigating precision farming technologies, but also to producers, crop consultants, and industries who are interested in pursuing precision farming technologies and practices.

Technical Abstract: Spatio-temporal analyses of yield variability are required to delineate areas of stable yield patterns for application of precision farming techniques. Spatial structure and temporal stability patterns were studied using 1995-97 yield data for the 25-ha field located near Story City, Iowa. Corn was grown during 1995-96, and soybean for 1997. The yield data were collected on nine east-west transects, consisting of 25 yield blocks per transect. In order to compare yield variability among different crops and years, data were detrended by the median polishing technique. The trend surface accounted for the large-scale deterministic structure induced by treatments and landscape effects. After removal of the trend, the resulting yield residuals were used in the analysis of the small-scale stochastic variability by variography. The variogram analysis showed strong spatial structure for the yield residuals. The spatial correlation lengths were found to vary from about 40 m for corn to about 90 m for soybean. The range parameter of the variograms showed a correlation coefficient of -0.95 with the cumulative growing season rainfall.