Soil attributes in a furrow-irrigated bed planting system in northwest Mexico

In the Yaqui valley, northwest Mexico, wheat (Triticum aestivum L.) is grown as a winter crop followed by maize (Zea mays L.) as a summer crop both planted on beds. Straw of both crops is usually burned to facilitate seedbed preparation for the succeeding crop. Soil physical and biological attributes were determined from 1996 to 2000 from a study initiated in 1992 at the CIANO (Centro de Investigaciones Agrícolas del Noroeste) experiment station. The objective was to compare five treatments: (1) conventional tilled bed (CTB)-straw incorporated, and permanent bed (PB) with (2) straw removed, (3) straw partly removed, (4) straw retained, and (5) straw burned — on soil strength, soil structure, and soil microbial biomass carbon (SMB). Seven N treatments were applied to wheat, but for the purpose of this study we chose a subset of three N treatments (0, 150 and 300 kg N ha⁻¹) for measurements. Maize received a uniform application of 150 kg N ha⁻¹ each year. Soil strength decreased as the amount of crop residues applied for each tillage-straw treatment increased. Permanent beds-straw burned treatment had the highest soil strength and CTB-straw incorporated the lowest. The largest soil aggregate fractionation, evaluated with a fractal dimension parameter (D), corresponded to PB-straw burned treatment and the lowest to PB-straw retained treatment. SMB was greater at 0–7 cm than at 7–15 cm depth. As the amount of crop residues increased in each tillage PB-straw treatment, the SMB generally increased. The largest amount of SMB occurred most often on either CTB-straw incorporated or PB-straw retained and the lowest in PB-straw burned treatment. The practice of retaining crop residues as stubble should be adopted in the Yaqui valley since changes resulting from burning crop residues showed the tendency to decrease productivity and soil quality as shown by increased soil strength and soil fractionation, and reduced SMB.