Lateral variability in soil properties may influence the efficacy/dissipation of herbicides applied to soil. The spatial distribution of relevant soil properties is an important component of precision herbicide management. Scientists at the USDA-ARS Southern Weed Science Laboratory (SWSL) in Stoneville have initiated investigations characterizing the spatial variability of soil properties at two MSEA sites (Deep Hollow and Beasley). At each site, approximately 100 A of land under cotton production were surveyed and marked off in a rectangular grid with mesh points at 200-ft intervals. Soil samples were collected and soil biological, chemical, and physical properties were measured. Satellite global positioning technology (GPS) is being used to locate the mesh points on the grids so that the areas can be mapped. The information provided here can be used for determining pesticide and fertilizer application rates.

A subset of the previously described areas at Beasley and Deep Hollow were selected based upon soil characteristics. Locations were chosen so that major representative soil series were included. Beginning at herbicide application, surface and subsurface soil samples were collected from these locations various times during the season. These samples are being processed for analysis of fluometuron (Cotoran) (Beasley and Deep Hollow) and norflurazon (Zorial) (Deep Hollow). These data will be used to evaluate effects of best-management practices and soil characteristics on herbicide dissipation.

Variability in soils may also affect the distribution of weeds. Scientists in the USDA-ARS Application and Production Technology Research Unit (APTRU) and SWSL in Stoneville have used GPS to map the distribution of some weed species at Deep Hollow. The weed maps can then be used for site-specific herbicide applications. These data can also be used to evaluate effects of BMPs on weed shifts and weed population dynamics.

Sensor sprayer technology is another aspect of precision management, which is currently being investigated at the Deep Hollow MSEA site by APTRU. A hooded sprayer with sensors was used to apply post-emergence herbicides such as glyphosate (Roundup) only where weeds were present. Ultra-low volume (ULV) application technology can reduce herbicide consumption while increasing efficacy of weed control. Research using ULV is being planned pending EPA approval.