Cotton root growth into an acid, fragipan subsoil can be restricted by a number of physicochemical barriers. The foremost of these is a high level of exchangeable or soluble aluminum. A lack of root proliferation into the subsoil limits the amount of soil moisture available to the shoot, resulting in a greater potential for moisture stress to occur. Identification and development of cotton cultivars and genotypes more tolerant to the physicochemical barriers of acid subsoils would integrate well with other practices to ameliorate the problems.

Soil moisture extraction determined by neutron probe, plant height and seedcotton yield were determined for 26 and 18 cultivar/genotypes on an acid, fragipan soil (Gigger silt loam) in 1986 and 1987, respectively. Subsoil moisture extraction was determined by measuring volumetric moisture content with a neutron probe centered at 0.3, 0.6, 0.9 and 1.2 M below the surface in 1986. The same depths were used in 1987 except 0.45 M was substituted for 0.3 M. Moisture determinations were taken four times during the season approximating pre or early square, early bloom, mid to late blooms, and crop maturity.

The cultivars and genotypes that most consistently caused a greater reduction of subsoil moisture in the later part of the season were Deltapine 90, Stoneville 213, LaDASB 12609, and Stoneville 825. Cultivars and genotypes that did not extract as much subsoil moisture were Deltapine 41, Stoneville 112, Coker 201, and Auburn 56. Several, but not all, of the cultivars and genotypes that had the greatest percent reduction in subsoil moisture content had the greatest economic yields. Plant height data indicated that tall (larger) cultivars did not necessarily remove more subsoil moisture than shorter cultivars. Correlation coefficients between percent reduction of original soil moisture content and seedcotton yield were greater in 1987 than in 1986. Yields were significantly and positively correlated with the percent reduction of original soil moisture at crop maturity at depths of 0.9 and 1.2 M (r=0.66 and 0.64, respectively). However, yield and moisture extraction at .45M depth were negatively correlated in 1987. Correlations between percent reduction of original soil moisture values and plant height at the end of season were either not significant or low in each of the years.

The results indicate that genetic variability exists among cotton genotypes in their response to acid, fragipan soils under field conditions and that there is a partial relationship between economic yield and the ability of cultivars/genotypes to extract subsoil moisture from the Gigger of soil.