Measurement and simulation of mulch and tillage effects on soil water conservation

In dryland farming areas with little or no summer rains and only a short wet season during the fallow season, successful farming depends on efficient soil water conservation. Potential practices for efficient water conservation through residue and tillage management can be best understood by measuring and modeling the processes which contribute to water losses and gains. Thus, the objectives of this study were: (1) develop a simulation technique to estimate water and energy budget components and their associated soil moisture and temperature conditions and verify the model by measured field data from heavily instrumented tilled and untilled residue treated fields, (2) substantiate the simulation of soil water storage charge and evaporation using soil moisture data from adjacent non-simulated plots, and (3) assess the relative effect of residue-tillage treatments on long-term cumulative evaporation and soil water storage change.; Simulation procedures were used to evaluate energy and water budget components as influenced by residue and tillage management practices under dryland conditions of the eastern Washington Palouse region. The simulation procedure utilized measured soil hydraulic properties, residue characteristics, and weather data as the input.; Verification of model performance consisted of comparing model prediction of net radiation, soil temperature, moisture content and evaporation with field measured data. The agreement between measured and predicted parameters was good. Average cumulative evaporation over high and low residue levels for each tillage treatment was 130, 121 and 129 mm for chisel, roto-till and no-till respectively. The only treatment with noticeable evaporation reduction relative to other treatments, was the roto-till treatment. Supplementary analysis and comparison of observed evaporation data from non-simulated plots substantiated these results. Total observed cumulative evaporation for the roto-till treatment averaged over the three residue levels was 15% and 19% less than for chisel and no-till, respectively.; The results showed that a finely pulverized soil surface by a roto-till significantly affect not only soil temperature and moisture, but reduced cumulative evaporation more than any other treatments regardless of residue level. The combined residue treatment is less effective for long dry periods than tillage treatment. (Abstract shortened with permission of author.)...