IMPACTS OF AGRICULTURAL MANAGEMENT-PRACTICES ON SOYBEAN AND CORN CROPS EVIDENT IN GROUND-TRUTH DATA AND THEMATIC MAPPER VEGETATION INDEXES

Vegetation indices from Landsat-5 Thematic Mapper (TM) observations on single dates in August 1988, a drought year, and August 1989, a year with wet early season conditions, were used to study the impact of agr icultural management and cultural practices on soybean (Glycine max) a nd corn (Zea mays) crop growth and yield. Management and cultural prac tices studied included date of planting, tillage, soil association, dr ainage, plant density, and stress factors. Crop ground-truth informati on consisted of leaf area index, wet biomass, dry biomass, and grain y ield. During both years ground-truth data were collected from at least 50 commercial farms every one to three weeks. Multispectral TM vegeta tion indices were developed using the mid-infrared bands 5 and 7 as we ll as the commonly used near-infrared and red bands. Two mid-infrared vegetation indices proved to be particularly useful in identifying man agement practice impacts on both crops. For both crops, yield and crop growth measurements gave similar trends versus TM vegetation indices. Planting date, plant density, an index of crop stress, and tillage si gnificantly impacted on soybean and corn crop attributes.