Abstract
Response of potassium (K) correlated with extracted K using five laboratory methods: neutral N NH4OAc pH 7.0; NH4OAc pH 4.8, 0.01M CaCl2, 1N Hot HNO3 and 0.5N NaHCO3 pH 7.0 by sorghum were determined in four selected soils from twenty locations in Kwara State, Nigeria in the green house to ascertain the ideal procedure for routine analysis. Regression equations were derived for each soil between K uptake by sorghum and level of K applied and, by extrapolation, the A-value, which represented the amount of soil K available as applied K, was determined. The data from the five laboratory methods were correlated with A-value, the zero-level K uptake, and with one another. The results showed that 0.01M CaCl2 only, extracted more K than the A-value, which was greater than the K extracted by the other methods. The data of all methods were, however, significantly correlated (p<0.05) with A-value while zero-level K uptake had a highly significant correlation with data of 0.01M CaCl2 (0.99) and low values with that of the other methods. The neutral normal NH4OAc pH 7.0 correlated relatively high and positively with N NH4OAc pH 4.8, 0.01M CaCl2, and 0.5N NaHCO3 pH 7.0, but negatively (-0.60) with 1N Hot HNO3. However, the neutral N NH4OAc pH 7.0; NH4OAc pH 4.8 correlated relatively higher and positively with one another (0.93) although they both extracted unequal amounts of K. Thus, both could be conveniently handled in the routine work in place of hot 1 N HNO3 for the evaluation of K availability indices for sorghum in the region.
Keywords: A-value, available K, extractants, sorghum