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

The frequency and severity of potassium (K) deficiency symptoms in cotton have increased in some soils in the US Cotton Belt over the past decade or so. Insufficient levels plant available K in these regions are likely decreasing yields and fiber quality and leading to decrease profits for cotton producers.

IPNI-2015-USA-101

22 May 2017

2016 Annual Interpretive Summary


The frequency and severity of potassium (K) deficiency symptoms in cotton have been increasing in some areas of the U.S. Cotton Belt. A recent state level study (TX-56, reported in Better Crops, No. 3, 2016) investigated the impact of multiple rates of broadcast or banded K fertilizer on lint yield, quality, and return on investment (ROI). In 2015, this study was extended across 11 Cotton Belt states with support from multiple sources (Cotton Inc., IPNI, and Fluid Fertilizer Foundation). The major objective of this multi-state study is to evaluate the effect of K fertilizer placement and rate on cotton lint yield, quality, and ROI.

The 2016 study year included 12 states—Alabama, Arizona, Arkansas, Louisiana, Mississippi, Missouri, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, and Virginia—and included eight pre-existing sites and eight new sites. The pre-existing sites maintained the same treatments as in 2015, while the new sites had not been studied yet. Soil samples were collected prior to planting at all sites in increments of 0-6, 6-12, and 12-24 inches, and were subsequently analyzed by the Texas A&M Soil Testing Laboratory. Fertilizer was applied two to four weeks prior to planting. Potassium fertilizer rates were 0, 40, 80, 120, and 160 lb K2O/A; placement comparisons were broadcast incorporated versus banding (6 in. deep, 4 in. to side of row). For the broadcast application, granular KCl was used and for the banded treatment solubilized KCl was used. The need for other nutrients was based on soil test recommendations. A single cotton variety—DeltaPine 1522B2RF—was used at all locations.

As in 2015, lint yield response in 2016 was mixed, with soil K level (Melich III) being an ambiguous predictor of fertilizer response. Of the three new sites that tested below the threshold for soil K (125 ppm), only two sites (Willamson Co., TX and Virginia) reported significant yield response to K rate. With one exception, where soil test K averaged over 150 ppm, there was no significant yield response. The exception—Lubbock, TX—had average soil K levels approaching 300 ppm, but (as in 2015) still showed a significant response to the highest rate of banded K. There are side studies being conducted on soil mineralogy and K extraction methods in an effort to explain these findings.

This project is planned to continue for another year.