Potassium Fertilization of Cotton Produced on a Low K Soil with Contrasting Tillage Systems

Abstract

Correcting K deficiency in fast‐fruiting cotton (Gossypium hirsutum L.) cultivars requires information on growth response to available soil K, soil K2O rates, and supplemental foliar K. Field research was initiated in 1991 on a Memphis silt loam soil (fine‐silty, mixed, active, thermic Typic Hapludalf), low in Mehlich I extractable K, to evaluate cotton responses to soil‐and foliar‐applied K for conventional‐tillage (CT) and notillage (NT) production systems in Tennessee. Potassium rates of 0, 30, 60, and 120 lb K2O/acre were soil‐applied to the same plots each year. Foliar treatments included: no‐foliar K, KNO3, and Ca(NO3)2. KNO3 was applied four times per year to supply 4.4 lb K2O/acre per application. Ca(NO3)2 was applied at 1.4 lb N/acre per application, equalling the N applied in the KNO3 foliar applications. Petiole K concentrations were evaluated for each foliar application. Soil samples (0–6 in.) were collected after harvest from the no‐foliar K treatments of each main plot to evaluate Mehlich I extractable soil K. Lint yields were determined by mechanically picking the two center plot rows twice each year. Extractable soil K increased linearly with increased soil K2O rates each year for both tillage systems. Yields in both tillage systems were increased by soil‐ and foliarapplied K. Regression equations expressing yield as a function of K2O rate were developed for KNO3 and no‐foliar K treatments each year for both tillage systems. In 1991 and 1992, the foliar KNO3 treatment increased yields at all soil K2O rates. In 1993, foliar KNO3 increased yields at soil K2O rates up to 94 lb K2O/acre in CT and up to 103 lb K2O/acre in NT. In addition, foliar KNO3 increased yields at soil K2O rates up to 108 lb K2O/acre for the 1994 NT cotton. Relationships found between Mehlich I soil extractable K and soil K2O rates were used to calculate the critical soil extractable K levels for predicting yield response to foliar K. These values ranged from 158 to 161 lb K/acre and correspond to the 160 lb Wacre value used to distinguish between medium and high testing soils in Tennessee. For this soil, foliar K supplemented soil K2O rates and increased yields when extractable K was medium or lower. Moreover, petiole K concentrations indicated plant K was deficient in 1991 and 1992 at all K2O rates and was deficient in 1993 for K2O rates of 60 lb/acre or less. Research Questions Potassium deficiency may limit yields of certain high yielding, fast‐maturing cotton varieties. Information is needed on K fertilizer requirements to correct deficiencies on low testing soils. What are the optimum combinations of soil and foliar K applications on a low extractable K soil for conventional‐ (CT) and no‐tillage (NT) cotton? What is the relationship between soil‐applied and foliar K for increasing lint yields on a low K soil? Literature Summary Visual K deficiency symptoms in cotton have been observed in the new vegetative growth of fast‐fruiting varieties. Deficiencies occur as the boll load is set over a short growth period and when root ...

Potassium Effects on Canopy Light Interception and Earliness of No‐Tillage Cotton

“…This may be a response to residual K carried over from previous years (Table 1). We suspect that three previous years of 16.4 kg K ha-1 yc 1 applied to foliage elevated soil K fertility sufficiently to elicit a canopy response in the fourth year, in the absence of soilapplied K. This is consistent with a companion study by Howard et a!. (1998), in which the greatest yield response to foliar K occurred with no soil-applied K fertilizer.…”

“…Foliar KN0 3 also increased lint yields in both years, but only in the absence of soil-applied K, as reflected in the soil X foliar treatment interactions for yield. In a companion study in which Ca(N0 3 ) 2 was also applied as a foliar treatment, Howard et al (1998) demonstrated that nearly all of the yield response to foliar KN0 3 was attributable to K rather than N. The relative yield response to KN0 3 was somewhat greater in the year of adequate rainfall (58%) than in the drought year of 1993 ( 42% ). In 1993, there was no significant earliness response to K, despite yield responses at both first and second harvest.…”

“…No supplemental irrigation was applied, and no winter cover crop was grown. At the start of this period, the site was found to have low extractable K at the 0-to 15-cm depth (90 kg K ha-1 ) and at the 15-to 30cm depth (49 kg K ha-1 ), using Mehlich I extraction methods (Howard et a!., 1998). A split-plot arrangement of a randomized complete block design with five replications was permanently established on this site in 1991.…”

“…First-harvest yields were generally unaffected. A companion study (Howard et al, 1998) determined that most of this yield response was due to K rather than N. Mitchell et al (1995) also found a yield response to foliar KN0 3 , but no earliness response. Response to foliar K is expected to occur in years of extended growing season in which upper canopy bolls can develop (Oosterhuis, 1993).…”

“…Managing the crop for earliness increases the likelihood that harvest can be completed before a killing frost arrests boll development. Agronomic practices to optimize cotton yields and earliness in regions with short growing seasons include no-tillage and crop nutrient management (Howard et al, 1998;Joham, 1986).…”