Submitted to: Geospatial Information in Agriculture and Forestry International Conference
Publication Type: Abstract Only
Publication Acceptance Date: January 12, 2000
Publication Date: N/A
Technical Abstract: Variation of crop yield across fields has been shown to vary considerably due to soil and nutrient variations. The exact cause of yield variation, however, has proven to be more elusive than simple relationships. We began a study in 1997 to evaluate the soil water use differences across a field in central Iowa relative to soil type and nitrogen management practices. To measure the water use we used Bowen ratio equipment positioned in two soil types with three different nitrogen management practices. Nitrogen management included starter fertilizer only (55 kg/ha), starter plus an amount determined by the late spring nitrate test (90 kg/ha), and non-limiting fertilizer rate (150 kg/ha). The water use measurements were made throughout the growing season from shortly after planting until harvest. In 1997, differences among soil types and nitrogen management became evident just before tasseling and continued through the remainder of fthe season. Low nitrogen availability reduced water use by 40% compared t the other nitrogen treatments. In 1998, a similar response was found among treatments. These data have been used to explain yield differences across the field, and we have begun to relate water use and radiation use efficiency as measures of crop response to soil variation within a field. This approach provides a method for comparing response among soils and nitrogen management that explains the yearly variation more completely.