ABSTRACT

The selection of management practices that increase organic matter of soil is important in dryland in order to increase soil water holding capacity from precipitation as well as other properties important in soil function. This study investigated plant and weather characteristics and the potential of different soil properties to determine spatial variability in dryland. Soil samples were taken before and after the first summer growing season of the establishment of a field study on 4 ha of total land in Lubbock, TX. The study was established in 2003 as a complete randomized block design with three field replicates of a cotton (Gossypium hirsutum L.) -sorghum (Sorghum bicolor L.) rotation without winter cover crop, a cotton-sorghum rotation with a winter cover crop, and a continuous high biomass crop rotation with haygrazer (Sorghum bicolor L.) and winter cover crop. The winter cover crop was rye (Secale cereale). The crop rotations were under conventional and no-tillage practices. The land revealed a decrease in elevation of 1 m from north to south that affected the spatial variability of clay content and soil nutrients such as phosphorus and potassium. This slope caused nutrients and clay runoff to the south of the field, where they became more concentrated compared to the north. Higher nutrient and clay contents in the south part of the field resulted in higher vegetative indexes compared to the north part. Organic matter reflected the previous cropping history of the plots ranging from 0.3 to 1.10 mg kg^-1 soil. Microbial biomass C reflected the organic matter content of this soil. Microbial biomass C was unaffected by the first tillage practices on the plots whereas alkaline phosphatase activity was significantly decreased by conventional tillage. Plant yields were higher on conventional tillage plots compared to no-tilled plots. This was not in agreement with the higher alkaline phosphatase activity under no-tilled plots, either because the first year under conservation tillage may still have not increased soil water conservation, and/or because the high land variability found did not allow an assessment of tillage impacts on plant yields. At this point of the study, the results provide indications that alkaline phosphatase activity may promise to provide early trends of soil changes in organic matter needed for our future management decisions.