Exchangeable Soil Potassium as Influenced by Seasonal Cropping and Potassium Added in Crop Residues
1967
Grimes, Donald W. | Hanway, John J.
Detailed sampling of soils and crops from three long-term field experiments permitted evaluation of the seasonal depletion of exchangeable soil K and the influence of K added as crop residue. Exchangeable soil K was markedly reduced during the growing season by a growing crop. For corn (Zea mays L.), the regression of the decrease (spring to fall) in exchangeable K (pp2m) on the initial (spring) level of exchangeable K was characterized by a quadratic relationship, Ŷ = −23.5 + 0.62X − 0.00072X² (r² = 0.78**). Increases in the exchangeable K from fall to spring were directly related to K additions in crop residues. Within a single crop rotation, the exchangeable K increased as a result of K additions from corn residues and declined when meadow was grown. When maintained in a field moist condition before the determination of exchangeable K, reduced levels of exchangeable K resulting from cropping were not restored by release of non-exchangeable K. When the exchangeable K was reduced to a very low level, however, nonexchangeable forms of K were released to the exchangeable form to maintain a “minimal” level of exchangeable K.
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