Evaluation of K Uptake, and Lint Yield Response to Cotton to Foliar K Fertilizer

Research was funded by the Cotton Incorporated Tennessee Support Committee

Nutifafa Adotey, Assistant Professor & Soil and Nutr. Magt Specialist Tyson Raper, Associate Professor & Cotton and Small Grains Specialist Xinhua (Frank) Yin, Professor & Cropping System Scientist, University of Tennessee


Fertilization, especially potassium (K) is essential for quality fiber and optimal lint yield; hence, proper management of fertilizer K is critical to cotton farmers. However, late-season K deficiency in cotton is frequently reported in Tennessee (TN) and across the U.S. Cotton Belt. Some of these reported deficiencies have been observed in fields where soil test K levels are deemed sufficient for optimum yield. Generally, these K deficiencies are more noticeable from flowering through boll set, when the high demand for K exceeds the supply from the soil. The inherently low root density, as well as the slow root and shoot growth during boll development, have been reported as the main cause of the low supply of K. This may partly explain why some cotton plants show deficiency symptoms even in high K testing soils. Foliar application can be a useful means to correct K deficiency especially during the period of peak K demand at boll formation where logistical constraints and field conditions render soil application impractical or ineffective. Studies have evaluated the efficacy of foliar fertilizer application to correct K deficiencies in cotton fields across the U.S. Cotton Belt; however, there are discrepancies on the effectiveness of foliar K fertilization. The timing of foliar application and foliar solution chemistry may partly account for the differences in the performance of foliar K fertilizers. There is limited information comparing the efficacy of foliar fertilizer containing K and B or Zn at the recommended time with early bloom and 2 weeks after. In this project, we are evaluating the effect of foliar application timings and foliar K fertilizers (foliar K containing B and/or Zn) on K uptake, fiber quality, and lint yield.

Materials and Method

A dryland field trial was conducted at the University of Tennessee’s West TN Research and Education Center, Jackson, TN to evaluate the efficacy of foliar K fertilizers containing B and Zn on lint yield. The trial was set up as a randomized complete block design with 13 fertilizer treatment combinations (Table 1) and each treatment was replicated four times. The treatment combination consists of preplant application and foliar application. Three foliar treatments (K only, K+B, K+B+Zn) were applied onto plants grown on plots without (treatments 2 – 4) and with (treatments 5 – 7) preplant boron. In addition, water was applied as a check to evaluate the reliability of the foliar treatments (treatments 8 and 13). The foliar treatments were applied at two timings. The first timing was at pinhead square and early bloom (treatments 2 – 7) while the second timing was at bloom and 2 weeks after bloom (treatments 8 – 13). A control plot with no K and P was also included in the trial. Plots were four rows wide x 40 ft long. Prior to the start of the study, soil samples were collected at only three depths (0-6-, 6-12-, and 12-18-inch depths). The soil samples were analyzed for routine chemical properties. The cotton cultivar, DP 2155 was planted utilizing 38-inch row spacing. At-planting fertilizer consisting of blended ammonium nitrate, diammonium ammonium phosphate, muriate of potash, sulphate of potash, and zinc sulfate (10-90-120-2Zn-13S) was hand-applied onto each plot. In addition, an equivalent amount of 2 lb B per acre was applied onto plots requiring preplant B (treatment 5, 6, 7, 11, 12, 13). Nitrogen fertilizer was applied as a single application of 80 lbs. N/acre using a UAN sprayer fitted with coulters. Foliar treatments were applied at a rate of 3 qt per acre using Spider Lee Sprayer on 71 and 102 days after planting (DAP). Prior to foliar treatment application, a 0.9-foot aboveground plant samples were hand-harvested from each plot prior to foliar application. At the first sampling, four plants from the aboveground samples were separated into leaves and stem, while the aboveground samples for the second sampling were separated into leaves and stem. The tissue samples were analyzed for total nutrient concentration. Standard agronomic and pest management practices were based on University of Tennessee’s recommendations.

Results and Discussion

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