Soil K+ to Ca2+ and Mg2+ ratio as well as the total salinity were evaluated in response to potassium fertilizer application onto potato. Potassium was applied at six different rates (0, 60, 120, 240, 480 and 960 kg ha-1 of K2O), as K2SO4, and was placed during planting time in the furrow. Soil from the 0-200 mm layer was collected in the furrow, 20 and 48 days after plant emergence (DAE) to evaluate soil pH, K+, Ca2+ and Mg2+ contents and the total electrical conductivity (EC). A factorial design (6x2), with six K rates and two sampling times was set up in a randomized block design with four replications. The application of K fertilizer increased exchangeable K, did not affect pH and exchangeable Ca and Mg contents, but caused a linear increase of the soil K+/(Ca2++Mg2+)1/2 ratio as well as EC. At 20 DAE, the critical soil K+/(Ca2++Mg2+)1/2ratio and the EC associated with maximum tuber yield (30.5 Mg.ha-1, with 353.4 kg ha-1 of K2O) were 1.79 and 1.6 dS m-1, respectively. The highest soil K+/(Ca2++Mg2+)1/2 ratio and EC were obtained with the highest application of K fertilizer, which led to a reduction in the potato tuber yield.
Solanum tuberosum; potassium; calcium; magnesium; salinity
