USING SOIL ATTRIBUTES AND GIS FOR INTERPRETATION OF SPATIAL VARIABILITY IN YIELD

Abstract

Precision farming application requires better understanding of variability in yield patterns in order todetermine the cause-effect relationships. This field study was conducted to investigate the relationship between soilattributes and corn (Zea mays L.)-soybean (Glycine max L.) yield variability using four years (1995-98) yield data from a22-ha field located in central Iowa. Corn was grown in this field during 1995, 1996, and 1998, and soybean was grown in1997. Yield data were collected on nine east-west transects, consisting of 25-yield blocks per transect. To compare yieldvariability among crops and years, yield data were normalized based on N-fertilizer treatments. The soil attributes of bulkdensity, cone index, organic matter, aggregate uniformity coefficient, and plasticity index were determined from datacollected at 42 soil sampling sites in the field. Correlation and stepwise regression analyses over all soil types in the fieldrevealed that Tilth Index, based upon soil attributes, did not show a significant relationship with the yield data for anyyear and may need modifications. The regression analysis showed a significant relationship of soil attributes to yield datafor areas of the field with Harps and Ottosen soils. From a geographic information system (GIS) analysis performed withARC/INFO, it was concluded that yield may be influenced partly by management practices and partly by topography forOkoboji and Ottosen soils. Map overlay analysis showed that areas of lower yield for corn, at higher elevation, in thevicinity of Ottosen and Okoboji soils were consistent from year to year; whereas, areas of higher yield were variable.From GIS and statistical analyses, it was concluded that interaction of soil type and topography influenced yieldvariability of this field. These results suggest that map overlay analysis of yield data and soil attributes over longerduration can be a useful approach to delineate subareas within a field for site specific agricultural inputs by defining theappropriate yield classes.