Thursday, 13 July 2006

Crop Residue Levels Over a 12-yr Period of No-Tilll Cropping Systems in a Semi-Arid Environment.

Dwayne Westfall1, C. Cantero-Martinez2, Gary A. Peterson1, and Lucretia Sherrod3. (1) Colorado State University, 200 West Lake St., Fort Collins, CO 80523, (2) Departamento de Produccion Vegetal y Ciencia Forestal, Universitat de Lleida-IRTA, Rovira Roure, 191, Lleida, Spain, (3) Great Plains Systems Unit, USDA-ARS, Fort Collins, CO 80526

Dryland cropping systems in the semi-arid environment of the West Central Great Plains of the US are subject to soil erosion by wind and water, and have suffered a degrading soil carbon base due to excessive tillage. No-till management and the resultant retention of crop residue on the soil surface has been shown to address some of the adverse effects of cropping in this environment by increasing above-ground biomass production, which in turn reduces runoff, and protects the soil from wind. Long-term studies were conducted to determine the interaction of no-till cropping systems intensification, soils, and climatic gradient on the production, retention and disappearance of crop residue over a 12-yr period. The soil variable was driven by landscape position; summit, side slope and toe slope. Four cropping systems were evaluated ranged in cropping intensity from the traditional winter wheat (Triticum aestivum) -summer fallow (WF) (one crop every two yr) to a continuous cropping (CC) system. The residue base achieved a stead state level in 4-5 yr and generally changed little after this time with the exception of the WF system where there was a trend for the residue levels to decrease after the initial base level was achieved. Cropping intensity increased residue retention; total crop residue retained on the soil surface increased as the proportion of fallow time decreased. Greater residue production and retention occurred on the toeslope soil position because these soils are deeper, have greater water holding capacity, and receive run-on water from upslope positions and thus produce more above-ground biomass. Length of the fallow period affected residue disappearance; more residue was retained before corn planting compared to before wheat planting, because of the shorter fallow period. The fallow period before wheat also included a hot summer fallow period, which favors decomposition. Interestingly, residue loss was greater during the cropping period than during the fallow periods when no crops were grown. Residue levels were generally adequate to control erosion by wind. However, at the high PET site, that also produced the least above-ground biomass, the residue levels were not always adequate for wind erosion control, particularly in the WF system. Residue retention by adoption of no-till management and increased cropping intensity is vital to ensure the sustainability of dryland cropping systems and soil conservation in this semi-arid environment.

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