Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/1998
Publication Date: N/A
Interpretive Summary: The Missouri Management Systems Evaluation Area (MSEA) project was initiated in 1990 to investigate how farming systems using different chemical and conservation best management practices impact ground and surface water quality on claypan soils, which have a subsurface layer high in clay content. The research objective was to use soil water collection devices called lysimeters to evaluate the impact of different farming systems on water, nitrate, and atrazine movement through the root zone. Claypan soils crack upon drying developing pathways for the rapid downward movement of water and agricultural chemicals. Three different farming systems varying in the type of tillage practice, N fertilizer rate, herbicide rate, and crop rotation were evaluated for a three-year period (1991-1994). Farming system differences did not have much impact on the amount of water that leached into the lysimeters nor the magnitude of the nitrate and atrazine concentrations. Water flow was influenced more by th hydrological properties of the soil above each of the lysimeters. Soil cracks, old filled-in cracks, and biopores were observed during lysimeter installation, providing pathways for water to quickly move to the bottom of the root-zone. The type and number of these pathways varied considerably among the instrumented sites which caused very large differences in leaching between plot replicates for each farming system. Herbicide leaching appeared to be slightly reduced with over-the-row banding, but adoption of this practice will remain low on claypan soils because cultivation is required for good weed control. More research to identify alternative farming systems that minimize chemical leaching to ground water on claypan soils will be planned and undertaken.
Technical Abstract: The research objective was to evaluate the impact of ridge and mulch tillage farming systems on root-zone water quality on claypan soils. The experiment was conducted in north-central Missouri on a Mexico silt loam soil (fine, montmorillonitic, mesic Udollic Ochraqualf) characterized by a pronounced Bt horizon. Zero-tension pan lysimeters installed at a 91-cm depth were used to monitor nitrate-nitrogen (NO3-N) and herbicide concentrations in three farming systems: 1) a high chemical input system with mulch-till in a corn-soybean rotation (MTH); 2) a reduced chemical input system with mulch-till in a corn-soybean-wheat rotation (MTL); and 3) a reduced chemical input system with ridge-till in a corn-soybean rotation (RTL). Farming systems were replicated three times with lysimeters installed on two of three replications. By band applying herbicide over crop rows, the herbicide mass applied to the MTL and RLT systems was half that applied to the MTH system. Only marginal benefits to root-zone water quality could be attributed to the reduced input farming systems. Leachate water flow and chemical concentrations were influenced more by intrinsic, site-specific soil hydrology properties and year-to-year variations in rainfall intensity and timing than by farming system. For example, in one MTH plot, maximum NO3-N and atrazine concentrations in leachate were 42 ppm and 100 ppb, respectively, while concentrations in the other replicate were less than 7 ppm and 2 ppb, respectively. Atrazine concentration and leachate volume following chemical application were strongly correlated (r=0.63) for these two farming systems. While herbicide mass is reduced with banding, adoption of this management practice will remain low on claypan soils because of increased risk for yield loss.