Soil potassium balance and cumulative cotton response to annual potassium additions on a vermiculitic soil

• Published in: Soil Science Society of America journal Vol. 53; no. 3; pp. 805 - 812
• Main Authors: Cassman, K.G. (Univ. of California, Davis, CA), Roberts, B.A, Kerby, T.A, Bryant, D.C, Higashi, S.L
• Format: Journal Article
• Language: English
• Published: Madison, WI Soil Science Society of America 01-05-1989
• Subjects: Agronomy. Soil science and plant productions; ANALISIS DEL SUELO; ANALYSE DE SOL; Biological and medical sciences; CALIFORNIA; CALIFORNIE; CROP YIELD; ENGRAIS POTASSIQUE; FERTILIDAD DEL SUELO; FERTILITE DU SOL; FERTILIZANTES POTASICOS; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; GOSSYPIUM HIRSUTUM; Nitrogen, phosphorus, potassium fertilizations; NUTRICION DE LAS PLANTAS; NUTRITION DES PLANTES; PLANT NUTRITION; POTASH FERTILIZERS; Potassium fertilization; PROPIEDADES FISICO-QUIMICAS (SUELO); PROPRIETE PHYSICO-CHIMIQUE DU SOL; RENDEMENT DES CULTURES; RENDIMIENTO DE CULTIVOS; SOIL CHEMICOPHYSICAL PROPERTIES; SOIL FERTILITY; SOIL TESTING; Soil-plant relationships. Soil fertility. Fertilization. Amendments; VERMICULITA; VERMICULITE; VERMICULITES; Malvaceae; Nutrition; Potassium fertilization; Saturation; Tropical crop; Fiber crop; Efficiency; Dicotyledones; Angiospermae; Vermiculite; Spermatophyta; Gossypium hirsutum; Potassium
• ISSN: 0361-5995; 1435-0661
• DOI: 10.2136/sssaj1989.03615995005300030030x

Cumulative effects of annual K additions on cotton (Gossypium hirsutum L.) growth and soil K balance were examined in a field study on an irrigated, vermiculitic soil. In each of 3 consecutive yr, cotton ‘Acala SJ2’ was grown with 0, 120, 240, or 480 kg K ha−1 applied to the same treatment plots in a randomized complete block design with 10 replications. The relationship between seed cotton yield and petiole K concentration was similar across years (r2 = 0.61, P < 0.001), but slopes of the yield response to applied K increased each year; 2.6‐fold more seed cotton was obtained per unit K input in 1987 than in 1985. This cumulative response reflected a yield decline without K addition and increasingly higher yield with each additional input of 480 kg K ha−1. Two processes appeared to control this response. First, without K input, NH4‐extractable K+ in surface soil decreased 20% from August 1985 to August 1987. This decrease greatly exceeded the K removal by cotton, and we surmise that an 11% decrease in soil organic C content contributed to this phenomenon. Loss of cation exchange capacity associated with the loss of soil humus may shift K equilibria towards fixation at interlayer sites in vermiculite at the expense of external K pools extracted by NH+4. Second, with high levels of K input, apparent K uptake efficiency from applied K was 50% greater in 1987 than in 1985. Increased efficiency was attributed to the partial saturation of K fixation sites from previous K additions and thus a larger proportion of newly added K remained in plant‐available K pools. At the highest K addition level, 86% of the 1440 kg K ha−1 applied in the 3‐yr period was fixed beyond extraction by NH+4, and plants remained marginally K deficient. The existence of a cumulative response to applied K on vermiculitic soils would have a marked impact on the economics of K fertilization on cotton.