This study was carried out to evaluate the effect of soil K+ (Ca2++Mg2+ )-0.5 ratio on sugarcane yield response probability to potassium fertilizer. Results of 106 experiments of potassium fertilizer on sugarcane and their soil exchangeable K+, Ca2+ and Mg2+ were studied, evaluating the K+ (Ca2++Mg2+ )-0.5 ratio in each experiment. The statistical method of logistic regression was used, carried out through CATMOD procedure of Statistical Analysis System. There was no difference of behavior of this ratio between plant cane and ratoons; therefore this characteristic was not significant during the adjustment of the statistical model. Soil K+ (Ca2++Mg2+ )-0.5 ratio affected sugarcane yield response likelihood. The increase of K+ (Ca2++Mg2+ )-0.5 ratio decreased the yield response probability. The K+ (Ca2++Mg2+ )-0.5 ratio was classified as low (<0.2547), medium (0.2547 to 0.3349) and high (>0.3349). The soil K+ (Ca2++Mg2+ )-0.5 ratio should be used as another criterion to guide the potassium fertilizer recommendation to sugarcane crops.
Saccharum officinarum; mineral nutrients; nutrient uptake; yields
