Comparison of adjuvant effects on cotton leaf potassium concentration and lint yield¹

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Abstract

Visual mid‐season potassium (K) deficiencies in cotton (Gossypium hirsutum L.) have recently been reported in many parts of the Cotton Belt. Foliar K sprays are sometimes used to correct these mid‐season deficiencies. However, little is known about the uptake of K by leaves, whether spray adjuvants or surfactants facilitate movement of K into leaves, or whether foliar‐applied K plus adjuvants enhance lint yield. The objective of this study was to compare the efficacy of spray adjuvants when mixed with foliar potassium nitrate (KNO₃) solutions. Three field experiments (one K concentration time‐course study and two foliar‐applied K lint yield studies) were conducted. In the time‐course study, plants were sprayed over‐the‐top once during mid‐bloom with a 11.2 kg KNO₃/ha (4.3 kg K/ha). Leaf blade and petiole K concentration were monitored at 0, 2, 4, 6, 24, and 48 h after application. The KNO₃ solutions were applied alone or with either Tween 20 (a commonly used laboratory surfactant), Kinetic, Dyne‐amic, Penetrator Plus, Invade, Plex, or X‐77. Water and an unsprayed check were also evaluated. Applying KNO3 with any of the tested adjuvants resulted in higher leaf blade K concentration at 4 h after application (14.9 g/kg) compared to KNO₃ sprays without an adjuvant (13.0 g/kg). At 24 h, leaf blades treated with KNO₃ without adjuvant had higher K concentration (13.7 g/kg) than the water and check treatments (12.8 g/kg). Petiole K averaged 47 g/kg and was unaffected by the treatments. For the first lint yield study, plots received foliar‐applied KNO₃ (at a seasonal rate of 44.8 kg/ha) with one of four selected adjuvants or a Tween 20 solution without KNO₃. For the second lint yield study, plots received foliar‐applied KNO₃ (at seasonal rates of 0, 22.4, and 44.8 kg/ha) with or without Penetrator Plus. Water as a foliar spray and an unsprayed check were also included. In both years, foliar‐applied K increased leaf blade K concentration but lint yields and fiber properties were not affected. In summary, leaf blade K concentrations increased when adjuvants were added to the foliar‐applied K solutions but these increases did not result in greater lint yield.

Notes

Mention of a trade mark, vendor, or proprietary product does not constitute a guarantee or a warranty of this product by the United States Department of Agriculture and does not imply its approval to the exclusion of other products or vendors that may also be suitable.

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