Abstract

ZUNIGA-ESTRADA, Lamberto et al. Effects of potassium application in vertisols on quantity/intensity (Q/I) relationships. Terra Latinoam [online]. 2010, vol.28, n.4, pp.319-325. ISSN 2395-8030.

In order to understand the dynamics of K fertilizer in the soil-plant system under laboratory conditions, the present study focused on the ability of a Vertisol to supply K to the soil solution because K is considered a relatively immobile element in the soil. Chemical analyses were performed to determine the effects of fertilizers on the behavior of soluble and exchangeable K. Five treatments with 0, 62, 125, 375 and 750 mg K kg-1 soil were used and, as a K source, KCl grade reagent was used (Merck®). The treated soils were placed in glass beakers, and soil moisture was maintained at field capacity with distilled water, then incubated at 32 °C for 20 days in a forced air oven. In the treated incubated soils, exchangeablE K was determined with AcONH4 1N; soluble K was extracted with CaCl₂ 0.01 M and the values of parameters generated on the quantity/intensity (Q/I) curve were estimated. In the treatments 0 and 750 mg de K kg of soil, exchangeable K ranged from 0.37 to 0.76 cmol(+) kg^-1 and soluble K from 0.08 to 0.23 meq L^-1 respectively. The K ionic radius activity values (AR°K), which represents K in the soil solutions, increased with K fertilization, from 0.0004 to 0.0017 (mol L-1)1/2 in the 0 and 750 mg K kg-1 treatments, respectively. The magnitude of AR°_K (0.01 to 0.006 (mol L-1)1/2) in the 125, 375 y 750 mg K kg^-1 treatments, suggest that the K adsorption is adequate for plant uptake but to maintain K constant in soil solutions periodical fertilization is needed. Exchangeable K values correlated (R = 0.85) with the AR°_K values.

Keywords : exchangeable K; soluble K; parameters of quantity-intensity.