|Tour Stop #2: Upland Water Quality and Conservation Tillage|
S. Smith, Jr J. D. Schreiber R. F. Cullum
In an effort to reduce runoff and erosion and the resulting contamination/sedimentation of water bodies surrounding agricultural areas, researchers have increasingly advocated the adoption of conservation tillage practices on land subject to erosion, e.g., uplands of north Mississippi. Other best management practices (BMPS) for improving surface water quality include terracing, contouring, vegetative filter strips, grassed waterways, constructed wetlands, crop rotation, and selective agrichemical application, timing, and formulation. However, some of these surface water quality BMPs have the potential for increased infiltration and ground water contamination.
Research is ongoing on the sloping loessial fragipan (restrictive layer) soils of north Mississippi to determine the effects of selected BMPs on both surface and shallow ground water quality as well as sediment transport. Movement of agrochemicals through the fragipan into more porous Coastal Plain sands below could result in contamination of permanent ground water used for drinking.
Following are some findings of our current research: Herbicide losses in runoff from upland soybeans were about the same for both notill (NT) and conventional tillage (CT). In upland corn, however, we found reductions in water phase runoff losses of herbicides from NT and reduced-till (RT) compared to CT. We attribute these reductions to reductions in runoff volumes in NT and RT corn (high residue crop). No such reductions in runoff volumes occurred in NT soybeans (medium residue crop). For both crops, NT facilitated greater herbicide leaching to perched shallow ground water, probably due to macropore flow. However, herbicides were not detectable by crop harvest. Total nutrient yields in runoff from upland soybeans were dramatically reduced under NT, however, shallow ground water N03-N concentrations were essentially the same for both NT and CT and generally less that the water quality standard of 10ppm. In both NT and CT upland soybeans and upland corn, annual NO3-N concentrations were similar at the fragipan surface to those at deeper depths down to 5m and annual mean NO3-N values were <10 ppm for all depths.
Key Words:Runoff, Shallow ground water, Nutrients, Pesticides, Tillage, Water movement
Publications:Cullum, R. F., Schreiber, J. D., Smith, S. Jr., and Grissinger, E. H. Shallow ground water and surface runoff instrumentation for small watersheds. Applied Engr. Agdc. 8(4):449-453. 1992. Schreiber, J. D., Smith, S., and Cullum, R. F. 1993. Pesticides and nutrients in southern U. S. shallow groundwater and surface runoff. Water Sci. Technol. 28:583-588
Smith, S., Jr. Effects of tillage on pesticide concentrations in shallow ground water and surface runoff from fragipan soils in north Mississippi, USA. 2nd USA/CIS Joint International Conf. Environ. Hydrol. & Hydrogeol. Yoram Eckstein and Alexander Zaporozec (eds.). WEF, Alexander, VA. Pp. 79-91. 1993.
Smith, S., Jr., Cullum, R. F., and Schreiber, J. D. Pesticides in runoff and shallow groundwater from upland corn production in north Mississippi, USA. Second International Conf. on Groundwater Ecol. TSP94- 1. Jack Stanford & Maurice Vallett (eds.). AWRA, Herdon, VA Pp.247-258. 1994.
Smith, S., Jr., Schreiber, J. D., and Cullum, R. F. Upland soybean production: Surface and shallow groundwater quality as affected by tillage and herbicide use. Trans. ASAE 38(4):1061-1068. 1995.
Cullum, R. F. Smith, S., Jr., and Schreiber, J. D. Agricultural transport in corn on fragipan soils in northern Mississippi. Proc. Miss. Water Resources Conference 1995. Pp. 107-112. 1995.
Schreiber, J. D., Smith, S. Jr., and Cooper, C. M. The occurrence, distribution, and remediation of transient pollution events in agricultural and sivilcultural environments. Water Sci. Technol. 33:17-26. 1996.