Long-term tillage and nitrogen fertilization effects on soil properties of an Alfisol under dryland corn/cotton production

Greater knowledge of the long-term effects of tillage and N fertilization on soil chemical and physical properties is needed in order to assess the contributions of these practices to sustainable land management, especially in warm, subhumid climates where organic matter is quickly oxidized. Soil properties were evaluated after 16 years of corn (Zea mays L.)/cotton (Gossypium hirsutum L.) production under conventional-bedding (CT), moldboard (MB), chisel (CH), minimum tillage (MT), and no-tillage (NT) with low (45 N kg ha(-1)) and high (90 N kg ha(-1)) N fertilization on an Orelia sandy clay loam (fine-loamy, mixed, hyperthermic Typic Ochraqualf) soil in south Texas (USA). Tillage systems significantly affected soil bulk density in the 0- to 200-mm soil depth. No-tillage bulk densities ranged from 5 to 19% higher than for the other tillage treatments while those from MB ranged from 7 to 21% lower. Conservation tillage treatments (NT and MT) resulted in a 30 to 135% increase in surface crop residues compared with other tillage treatments, while plots with the high N rate exhibited 8% more residue than with low N fertilization. In the 0- to 50-mm surface layer, organic C, total N, and extractable P were approximately 64, 78, and 110% higher with NT than with the average of the other tillage treatments. Higher N fertilization increased organic C, total N, and extractable P by 9, 7, and 19%, respectively, in the 200-mm depth. No-tillage decreased cation exchange capacity (CEC) and soil pH as compared with MB, CH, and CT in the 0- to 50-mm soil layer. Residual NO3--N to a depth of 1200 mm under NT and MT was consistently less than with the other tillage treatments. Higher levels of soil organic C, total N, and extractable P and lower concentrations of NO3- were directly related to surface accumulation of crop residues promoted by conservation tillage management. The long-term sustainability for crop production on this soil appeared to be enhanced with reduced tillage management. (C) 1997 Elsevier Science B.V.