Potassium movement in soils as related to potassium chloride application

In recently fertilized soils, plants uptake nutrients mainly from around the granules, but little is known about the chemical composition of these zones. This study aimed to evaluate the K concentration gradient as well as the electrolyte concentration around KCl granules applied at different rates to five soils varying in clay (95 to 569 g kg-1) and organic matter (13 to 54 g kg-1) contents. Treatments consisted of four KCl rates (0, 50, 100, and 200 kg ha-1 K2O). These quantities were obtained by simulating a KCl application to 357 m² ha-1 of soil (broadcast over the soil surface in a band of 2.5 cm in rows spaced 0.7 m apart). Each experimental unit consisted of two joined PVC tubes (diameter 7.0 cm, length x 9.0 cm) filled with soil. KCl granules were uniformly broadcasted between two round filter paper sheets (diameter 7.0 cm), which were placed on the junction of the two tubes. The K concentration gradient of the soils was quantified based on the exchangeable K concentration at different distances from the point of application. K diffusion varied with the soil type, increased with the KCl rate and was lowest in the soil with the highest sand and lowest organic matter contents. After seven days, K diffusion in the soils was highest in an Inceptisol (8.4 cm) and lowest in an Oxisol (6.4 cm). K concentration in the first soil centimeter closest to the fertilizer varied from 9,800 to 16,475 mg kg-1; four centimeters further, it varied from 244 to 2,254 mg kg-1. The electrical conductivity did not attain detrimental values for seed germination of moderately salt-tolerant species, even in the centimeter closest to the fertilizer. A movement of K was observed after few days in the soils, but the maximum diffusion at each KCl rate did not correlate with any soil attribute.

diffusive flux; exchangeable K; electrical conductivity; KCl

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