Caracterización del potasio en algunos suelos de Chanchamayo, selva alta del Perú

Abstract

The forms and availability of potassium for sorghum (Sorghum vulgare L.) were determined in 31 soil horizons from the orders Entisol, Inceptisol, Ultisol and Vertisol from the tropical humid region of Perk. Available K was also extracted with 2, 4, 6 and 8N sulfuric acid; 0.5 N hydrochloric acid; N sodium acetate, and N ammonium acetate. Total K ranged from 1761 to 4548 ppm with the acid, the sandy soils having the lower amounts. No relationship was found between soluble K and the other forms. However, the ratio fixed/exchangeable K was a good index to group the soils This ratio was higher in the more acid soils. Exchangeable K was directly related to clay content and inversely related to the degree of weathering of the soils. Sulfuric and hydrochloric acid extracted from 30% to 50% more K than ammonium acetate (exchangeable K), except in those soils with 2:1 expandible clays. Sodium acetate extracted only 20% to 65%of the exchangeable K. The decrease in exchangeable K with cropping explains from 80% to 100% the uptake of K by plants in soils having more than 70% base saturation, while it only explains 50% of K uptake in soils having less than 50% base saturation. A tentative critical level for deficient soils is proposed at 0.15 meq K/100 g soil.