Effect of the soil Ca/Mg, Ca/K and Mg/K ratios on sweet sorghum production

Abstract

A experiment was carried out in greenhouse conditions, in pots containing 25l of soil, to study the sorghum (Sorghum bicolor) response to magnesium with and without liming and potassium fertilization. Soil samples were taken at plant emergence and analysis of K, Ca and Mg were performed to determine the effect of four Mg doses as sulphate, two potassium doses as chloride and two calcium doses as calcite limestone upon the soil Ca/Mg, Ca/K and Mg/K ratios. At boot stage sorghum leaves were sampled for foliar diagnosis, and at harvest stalk and grain yields were evaluated. The results didn't show any difference in sorghum stalk yields when the magnesium level in the soil ranged from 0,15 to 0,52 meq/cm³, but when the Mg/K and Ca/K ratios in the soil were lower than 0.6 and 7.4 respectively, there was a decrease in sweet sorghum stalk yields, as a function of the lower Mg and Ca uptake. There was not any effect of the Ca/Mg ratio on sorghum yields. There was an increase in grain yields due to Mg application only in the absence of potassium in one of the soils.