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 fertilizat ion on soil chemical and physical properties is needed in order to ass ess the contributions of these practices to sustainable land managemen t, especially in warm, subhumid climates where organic matter is quick ly oxidized. Soil properties were evaluated after 16 years of corn (Ze a mays L.)/cotton (Gossypium hirsutum L.) production under conventiona l-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, hypert hermic Typic Ochraqualf) soil in south Texas (USA). Tillage systems si gnificantly 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 ot her 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 treatmen ts, while plots with the high N rate exhibited 8% more residue than wi th low N fertilization. In the 0- to 50-mm surface layer, organic C, t otal N, and extractable P were approximately 64, 78, and 110% higher w ith 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 cat ion exchange capacity (CEC) and soil pH as compared with MB, CH, and C T 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 tre atments. Higher levels of soil organic C, total N, and extractable P a nd lower concentrations of NO3- were directly related to surface accum ulation 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 Sci ence B.V.