Subsurface drip irrigation and conservation tillage are tools for improving water management for cotton (Gossypium hirsutum L.). In previous research with cotton grown with no tillage over subsurface drip laterals, excessive soil compaction near the soil surface occurred. We hypothesized that loosening this compacted surface soil would improve cotton productivity. We tested this hypothesis by conducting a 2-year field experiment to determine the effect of three levels of soil loosening (no tillage, shallow in-row tillage with a rigid shank, and shallow tillage with a stubble mulch plow to loosen the entire surface layer of soil) and two drip lateral spacings (under every row and in every other row middle; 1-m and 2-m spacings, respectively) on early-season physiological parameters and productivity of cotton. The subsurface drip irrigation system had been used for 7 years before initiating this experiment. Early-season cotton leaf gas exchange, leaf nutrient concentrations, yield, and fiber quality were measured. The tillage implements loosened the soil as expected (as determined with a cone penetrometer), but the level of soil loosening had almost no effect on leaf gas exchange and leaf nutrient status. Similarly, tillage and lateral spacing did not affect cotton yield and quality. Yields were not high (mean yield of 1215 kg/hain 1998 and 700 kg/hain 1999) but were not atypical for irrigated yields in this region during those years. Conservation tillage methods that include shallow tillage over drip laterals on compacted SE coastal plain soils did not improve cotton productivity.
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