Application of DRAINMOD-Ks-STMAX to Predict Deep Chiseling Effects on a Drained Southern Alluvial Soil

Deep chiseling in heavy drained soils can help increase infiltration and hence reduce erosion, potentially enhancing growth by reducing excess water in the root zone and reducing nutrient losses through the reduction of runoff to surface waters. The goals of this study were to apply DRAINMOD-Ks-STMAX, a modified form of the water management model, DRAINMOD 1) to predict the effects of deep chiseling on hydrology for a subsurface drained plot and 2) to determine the frequency and timing of deep chiseling. Data from a subsurface drained plot at Ben Hur Research site near Baton Rouge, Louisiana, were used. Simulation results indicated that deep chiseling a Commerce silt loam, a southern alluvial soil, increased cumulative infiltration (CI) by 16% and reduced cumulative sub-surface drainage (CSD) and cumulative surface runoff (CRO) by 26% and 37%, respectively, between 28 September 1995 and 21 November 1996. Between 22 November 1996 and 22 November 1997, it increased CI and CSD by 9% and 17%, respectively, and reduced CRO by 22%. Vertical saturated hydraulic conductivity (Ks) had decreased by 99%, from a maximum initial value immediately after deep chiseling, by the time 150 cm of rain had fallen (approximately 12 months) since deep chiseling. For high rainfall states like Louisiana, with average annual rainfall often exceeding 150 cm, this translates to deep chiseling once every year whereas in drier states deep chiseling can be done once every two to three years depending on the amount of rainfall. Depending on the cumulative amount of rainfall at planting, producers can lose 85% or more of the maximum deep chiseling benefits due to reduced Ks. Because of great rainfall variability in Louisiana and other southern states, it is advisable for farmers to deep chisel their fields just prior to the planting season. Results of this model simulation study indicate that DRAINMOD-Ks-STMAX can be used as a cost-effective (saving time and money) tool to predict the effects of deep chiseling in poorly drained soils with subsurface drainage and potentially open ditch drainage, and to advise farmers on the frequency and timing of deep chiseling based on science. However, the model needs to be tested for longer time periods and under different climatic conditions and soil types before it can be recommended for general application for the purposes listed above.