COMPARISON OF ADJUVANT EFFECTS ON COTTON LEAF POTASSIUM CONCENTRATIONAND LINT YIELD

Visual mid-season potassium (K) deficiencies in cotton (Gossypium hirs utum L.) have recently been reported in many parts of the Cotton Belt. Foliar K sprays are sometimes used to correct these mid-season defici encies. However, little is known about the uptake of K by leaves, whet her spray adjuvants or surfactants facilitate movement of K into leave s, 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 fiel d experiments (one K concentration time-course study and two foliar-ap plied 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 mon itored at 0, 2, 4, 6, 24, and 48 h after application. The KNO3 solutio ns were applied alone or with either Tween 20 (a commonly used laborat ory 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 conc entration 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 KN O3 without adjuvant had higher K concentration (13.7 g/kg) than the wa ter and check treatments (12.8 g/kg). Petiole K averaged 47 g/kg and w as 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. Fo r 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 include d. Tn both years, foliar-applied K increased leaf blade K concentratio n 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 grea ter lint yield.