Abstract
All the exchangeable K values were significantly inter-related and their precision in predicting foliar K was in the following decreasing order: 0·01M CaCl2 > 0.13M NH4Cl > 0.05M HCl + 0.13M H2SO4 > HOAc + NaOAc > 0.1M HNO3 > 0.1M NH4OAc. The N and K fertilizer effects on extractable K values were significant at the 0·l per cent probability level. The equilibrium activity ratio (AReK) and its logarithmic form, pK-0.5p(Ca + Mg), were well correlated and each accounted for about 62 per cent of the total foliar K variability. The activity ratio, aK/[a(Ca+Mg)]½ , based on equilibrium of the soil without addition of KCl accounted for about 71 per cent of the observed variation in foliar K, whereas about 36, 62 and 70 per cent of the total foliar K variability was accounted for by, respectively, PBCK,-?Kº, and b-index. Although ratios of exchangeable cations were related significantly to foliar K, they were not, however, superior to measures of exchangeable K insofar as determining the probability of crop responses was concerned.
