Soil samples and yield data were collected from 32 to 41 center-pivot systems annually in a 4-year (1985-1988) on-farm irrigation study and are reported in this paper. Irrigation reduced annual yield variability in both solid and skip row cotton and tended to stabilize lint yields at a higher level. Average yearly response to irrigation was 199 and 147 lb lint/land acre for solid planted and skip row planted cotton, respectively.

Yields were significantly correlated with soil test phosphorus levels at 0-6, 6-12, and 12-18 inch soil depths in non-irrigated solid cotton and at 0-6 and 6-12 inch depths in irrigated skip row cotton. Soil test potassium levels were significantly correlated with yields at all three soil sample depths in non-irrigated solid planted and both solid and skip row planted cotton when irrigated.

Soil test phosphorus values had less influence on lint yields with soil sample depth on non-irrigated solid cotton and yields were higher at the middle range of soil test phosphorus levels in irrigated skip row cotton. Soil test potassium values had more influence on yield with soil sample depth for both non-irrigated solid and irrigated skip row cotton. Lint yields were more influenced by subsoil test levels of soil potassium than soil test phosphorus levels for this four-year on-farm irrigation study.