POTASSIUM NUTRITION OF COTTON IN THE USA, WITH PARTICULAR REFERENCE TO FOLIAR FERTILIZATION
Mar 10, 2017

Agronomy & physiology WCRC Agro-Physio-north-america WCRC1
Abstract                                                                         Back to Table of contents

Widespread late-season potassium (K) deficiency in the US Cotton Belt has focused attention on K nutrition of cotton (Gossypium hirsutum L.).  Potassium is required in large amounts by cotton for normal crop growth and fiber development, with a crop containing 112 to 246 kg K ha-1.  Plant uptake of K follows a pattern similar to dry weight accumulation except that K uptake peaks at 2.2 to 5.0 kg ha-1 day-1 a few weeks after the start of flowering.  Cotton is more sensitive to low K availability than most other major field crops, and often shows signs of K deficiency on soils not considered K deficient.  The K-deficiency syndrome appears to be a complex anomaly related to low soil K status, K fixation in the soil, a greater demand for K by modern cultivars, the inability of the root system to supply this, and possible relationships with diseases such as Verticillium wilt.  Preplant soil tests provide a means for estimating overall K fertilizer requirements, whereas petiole analysis has become a valuable diagnostic tool for assessing nutrient status and determining K requirements during the growing season.  There is still some uncertainty about K threshold levels and the validity of petiole diagnosis after peak boll development.  The sufficiency levels of K in petioles for cotton generally range from 4.0% at first flower to 0.25 at first open boll.  Luxury consumption of K can occur in cotton and could possibly perplex tissue diagnostic recommendations.  Foliar applications of K offer the opportunity of countering late-season K deficiencies quickly and efficiently with a resulting improvement in yield and quality.  Significant yield increases from foliar-applied K were obtained in approximately 40% of the field trials in the USA in the past five years, with an overall average increase of about 75 kg lint ha-1.  KNO3 was the preferred formulation with K2SO4 and K2S2O3 being similar in effectiveness, and KCl and K2CO3 having no beneficial effect on yield.  The use of adjuvants with foliar sprays increased the uptake of K but did not increase lint yield.  Additional research is needed to understand the physiology of K utilization in cotton and the specific causes of late-season K deficiency symptoms.

Conclusions

Potassium deficiency has occurred widely across the US Cotton Belt in recent years.  The occurrence of these outbreaks of K deficiency have been somewhat unpredictable and the explanations not clear.  The K-deficiency syndrome appears to be a complex anomaly related to low soil K status, K fixation in the soil, a greater demand for K by modern cultivars, less storage of K prior to flowering by modern cultivars, the inability of the root system to supply the needed K during boll development, and possible relationships with diseases such as Verticillium wilt.  Interest has focused on the possibility of foliar feeding with K to supplement traditional soil application methods.  Foliar applications of K offer the opportunity of correcting these deficiencies quickly and efficiently, especially late in the season when soil application of K may not be effective.  Research during the last five years has shown that foliar-applications of KNO3 can alleviate K deficiency and significantly increase yield and fiber quality. However, results from across the Cotton Belt have been variable and unpredictable, and additional research is needed to fully explain this phenomenon.  There is sufficient evidence that foliar application of KNO3 appears to be a useful production practice for supplementing preplant soil applications of potassium fertilizer especially when K deficiency symptoms occur and soil and petiole tests show a low K status.

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