Soil management and landscape variability impacts on field-scale cotton and corn productivity

Conservation systems may alleviate water stress, increase crop productivity and improve soil quality. However, soil management effects have rarely been assessed taking into consideration spatial variability interactions at the field-scale. We evaluated the impacts of soil management practices, soil properties, and landscape attributes on yield, soil water content (0--30-cm), stomatal conductance, leaf canopy temperature and leaf-N content of cotton ( Gossypium hirsutum L.) and corn (Zea mays L.) grown on a 9 ha field (Typic and Aquic Paleudults) in east-central AL. Yields were evaluated during 2001--2003, and soil-plant responses in 2001--2002. Treatments were established in a randomized complete block design (RCB) with 6 replicates in strips traversing the landscape in a corn-cotton rotation. Treatments were a conventional system with or without dairy manure (CT manure or CT), and a conservation system with and without manure (NT manure or NT). Conventional systems consisted of chisel plowing/disking + in-row subsoiling; without cover crops. The conservation systems include no surface tillage with in-row subsoiling and winter cover crops. A detailed soil survey (1:6000), terrain attributes, and soil electrical conductivity (EC) maps were used to delineate management zones (MZ) using cluster analysis. Mixed models accounting for spatial correlation were used to analyze treatment effects on whole field response variables (P ≤ 0.05). In cotton, neither manure nor treatment x year interactions affected overall productivity or soil-crop water relationships. Overall 2001--2002, conservation systems had greater soil water content (0.140 vs. 0.119 m 3 m-3), higher stomatal conductance (0.45 vs. 0.33 mol m-2 s-1) and lower canopy temperature (31.8 vs. 32.9°C) compared with conventional systems. Data suggested a better partitioning of evapotranspiration and greater water infiltration with conservation systems compared to conventional systems; thus, less crop water stress. Averaged over years, conservation systems improved seed cotton yield 14% compared with conventional systems (2710 kg ha-1 vs. 2380 kg ha-1 respectively). In corn, no manure effects were found. Conservation systems had slightly greater stomatal conductance, higher leaf-N and lower temperature during silking only in 2002 (dry year). Conservation systems had greater grain yield than conventional systems in 2002 (8.88 vs. 6.71 Mg ha-1) and 2003 (13.04 vs. 12.33 Mg ha-1); no differences existed in 2001 (9.85 Mg ha -1). Soil organic C, EC, clay content (0--30-cm), slope and elevation, had the highest correlation with yield in both crops. Both crops had equal or higher yield in conservation systems compared with conventional systems in all year x MZ combinations. We found that fewer and simpler MZ may be needed for conservation systems than for conventional systems. The aggregate of data suggests for degraded soils in warm humid climates, conservation systems including no-tillage and high-residue producing cover crops minimize drought risk, improve crop productivity and yield stability, and increase C storage.