|Crop production has become more costly over the years. Improved tillage practice recommendations and implementation of site-specific crop management (SSM) can help farmers achieve soil conservation, better yields, input optimization and consequent savings. Southeastern Coastal Plain soils are highly weathered soils that typically have been intensely cropped under conventional tillage practices and are susceptible to erosion, runoff and degradation. Understanding tillage practices, topography and spatial variability impacts on soil physical properties is important for aiding in the development of management practice recommendations and implementation of SSM. In order to assess management practices and landscape variability effects on soil physical properties,
total carbon (TC), particle size distribution (PSD), bulk density (Db), aggregate stability (AS), infiltration rate (IR), hydraulic conductivity of saturated soil (Ksat) and water retention (WR) were measured in 2006 in a 9 ha field in the central Alabama Coastal Plain. Based on the local soil properties, the field was divided into three management zones (MZ) corresponding to summit (Z1), backslope (Z2) and toeslope (Z3). Four tillage systems treatments [conventional system with (CTM) or without (CT) 10 Mg ha-1 yr-1 of dairy manure, and conservation system with (NTM) or without (NT) 10 Mg ha-1 yr-1 of dairy manure] were established in a corn (Zea mays L.)-cotton (Gossypium hirsutum L.) rotation in 2000 at the research site after 30 years of cotton monoculture under conventional tillage. Overall, conservation system significantly improved TC, IR, AS, Ksat and WR in the top 5cm of this soil, compared to conventional system. Conservation system improved WR at higher suctions (300, 500 and 1000cm H2O), and conventional system improved WR at lower suctions (0 and 20cm H2O). Trends of TC and Db values were very similar. Impacts of tillage system on soil properties had no clear trend at 5-10 and 10-15cm of depth. Manure additions significantly improved TC, Db and WR in the top 5cm for conservation and conventional systems, and at 5-10cm of depth for conventional system. Differences among MZ were significant only for Db, WR, Ksat and IR. Overall, WR was greater at Z1 and Ksat at Z2. Infiltration rate, AS and Db trends among MZ varied according to tillage system. Response of IR and AS to the conservation system were greater in Z2 than the other MZ. We conclude that six years of conservation tillage and manure additions was enough time to improve most of the soil properties measured only in the top 5cm of these soils. Except for WR at higher suctions, soil physical properties at the 5-15cm layer were generally improved by the conventional system. Perhaps a longer period of time is needed to observe significant changes in soil physical properties at lower depths. Regarding differences among MZ, erosion and depositional processes associated with tillage system were the most important factors affecting the spatial variability of soil physical properties on this landscape.
Results of this research can help farmers, extension personnel and consultants to decide about the suitability of management practices for conditions similar to the southeastern Coastal Plain soils studied here. In addition, observed differences in soil properties through the landscape positions could be used as complementary information to support SSM decisions. However, longer term research is needed to better describe observed impacts on this landscape.