Provision of mid‐season potassium requirements in cotton with slow release potassium applied pre‐plant

Abstract

Mid‐season development of potassium (K) deficiency in cotton is related to the high K demand during flowering and high rainfall, particularly on sandy soils, removing available K prior to peak demand. Slow‐release K sources have potential for supplying mid‐season K requirements of cotton without having to expend additional labor and fuel applying sidedress or foliar K in mid‐season. The objective of this study was to determine the potential for slow‐release K applied preplant in combination with muriate of potash (KCl) for meeting mid‐season K requirements of cotton. Tests were conducted on ‘Georgia King’ cotton grown on three soil types in the Coastal Plain region of Georgia: 1992–1993 on a Greenville sandy clay loam (Rhodic Kandiudults), 1994 on a Tifton sandy loam (Plinthic Kandiudults), and 1993 on a Lakeland sand (Typic Quartzipsamments). Three K rates were applied (0, 55, and 110 kg K₂O/ha), and two K sources were utilized, KCl (muriate of potash; 0–0‐60) and Multi‐cote 4 slow‐release fertilizer (9–0‐32). Five combinations of the potash sources were applied broadcast pre‐plant and tillivated in: ratios of 1:0, 3:1, 2:2, 1:3, and 0:1 soluble:slow release. Petioles were sampled from first bloom to cutout, and soil samples were taken after harvest; nitrate‐nitrogen (NO₃‐N) and K concentrations were measured. Results varied depending on soil texture. The best yielding treatments on the Lakeland sand were the 55 kg K₂O/ha treatment with either a 2:2 or 0:1 soluble:slow release ratio. The 55 kg K₂O/ha treatment with 0:1 soluble:slow release ratio also had the highest lint percentage. On the Greenville and Tifton soils, the 110 kg K₂O/ha treatment had soil K levels higher than the 55 kg K₂O/ha treatment which was higher than the control. As the slow‐release percentage increased, there was a trend for soil K to increase as well. In general, use of soluble K led to higher petiole K levels early in the season and lower petiole levels in late season as compared to slow release K. Petiole NO₃‐N concentration tended to increase with application of the slow‐release K material, particularly in the early to mid‐sampling periods, due to its 9% nitrogen (N) content. Slow‐release K has the greatest potential for reducing K deficiency and improving cotton yields on soils with high yield potential but with low K‐supplying capacity, either due to low buffering capacity or high leaching losses.