Evaluation of Cotton Yield, Quality, and Plant Growth Response to Soil-applied Potassium

The frequency and severity of K deficiency symptoms in crops grown on the clay soils of the Central Blacklands and Gulf Coast regions of Texas have increased in recent years. While drought has contributed to the occurrence, the frequency and widespread geographic nature of the K deficiencies in multiple row crops, especially cotton, is a major concern to producers, scientists and other ag professionals. The objective of this research is to evaluate the effect of K application rates and methods on cotton growth, development, yield and fiber quality. Studies were initiated in 2013 at two field sites, one the Central Blacklands and one in the Gulf Coast region of Texas, with soil test K levels of 60 and 150 ppm, respectively. Five rates of banded liquid K (20, 40, 80, 120, and 160 lb K₂O/A as 0-0-15, KCl) and four rates of granular broadcast K (40, 80, 120, and 160 lb K₂O/A as KCl) were evaluated. The liquid treatments were banded pre-plant approximately 4 in. to the side of the row and 6 in. deep. Granular (dry) treatments were broadcast pre-plant and lightly incorporated. A zero K control was included at both sites. Phosphorus and N were applied according to soil test results for a 2 bale/A (lint) yield goal. In-season plant measurements included stand counts, plant height, nodes to first fruiting branch, and total nodes. Lint yield was determined and samples sent to Cotton Inc. for HVI (quality) analysis.

There was some variation in height and total nodes between differing amounts of K applied, but the biggest visual differences between treatments was in K deficiency symptoms in leaves, with higher rates of K (especially banded) showing fewer symptoms. There was yield response to K application at both locations. Overall, band-applied K treatments performed better than did the broadcast application. Average yield increases for broadcast application were 101 and 80 lb lint/A and for banded application were 296 and 332 lb lint/A in the Blacklands and Gulf Coast region sites, respectively. The highest rates of K application tended to produce the highest yields. The calculated return on investment, which takes into account lint quality parameters, was highest with band applications, and was maximum in the Blacklands and Gulf Coast regions at $166/A (40 lb banded rate) and $221 (120 lb banded rate), respectively. This project will continue in 2014.