Foliar applications of fertilizers to cotton have been shown to be a means of supplementing soil applied fertilizers. Consistent results have been observed in correcting micronutrient (zinc and iron) deficiencies. From a conceptual standpoint, foliar applications of major elements (nitrogen or phosphorus) should enhance a soil fertility program. Environmental changes that increase water availability or solar radiation may serve to increase crop yield potential, and fertility may become limiting. Under these conditions, foliar fertilization could prove beneficial; however, studies on Texas High Plains cotton have been inconclusive.

A field study was initiated at the Texas Tech University farm at Lubbock in 1990. Fertilizer was applied to the entire site following soil test recommendations, for a total of 90 lbs N/a and 35 lbs P₂O₅/a. Paymaster variety HS-26 was planted on May 12. Six treatments were established: untreated check, three commercial foliar products, and two rates of soluble urea. The commercial products were applied following label rates and timing. Urea was applied at 2.5 lbs N/a at 62, 77, 91, and 104 days after planting (DAP), another urea treatment was applied at 5 lbs N/a at 77 and 91 DAP and again at 10 lbs N/a at 104 DAP.

Treatments were arranged in a randomized complete block design with six replications. Normal cultural practices including irrigation scheduling were followed. Ten plants were collected from each plot at 53, 67, 81, 94, and 115 DAP. Conventional plant maps were developed. Each plant was then divided into three nodal horizons: less than node 10, nodes 10 through 13, and nodes greater than 13. Leaf area and dry weights were determined by horizon. Final lint harvest was on November 14.

Plant maps indicated that between 81 and 94 DAP a significant boll shed of first and second position fruit occurred, with nodes 10 through 13 most severely impacted. This boll shed appeared to be the result of both decreased heat unit accumulation and reduced solar radiation during the month of July. During the study period, the bottom horizon lost an average of 1.6 fruit, while the node 10-13 horizon lost an average of 2.6 fruit. Leaf nitrogen values for the bottom horizon decreased at a relatively constant rate with time, which is considered normal. For nodes 10-13, leaf nitrogen changed little between 81 and 94 DAP, then decreased at 115 DAP. This suggests that fruit losses were not a result of an imbalance in the source/sink relationships for nitrogen, but rather were in response to a carbohydrate stress imposed upon the plants during the month of July.

Lint yields averaged about 430 lbs/a over the entire study. Statistical analysis of lint and seed yields indicated that there were no significant differences between treatments. Weather conditions appeared to be the yield limiting factor in this study.