Soil zinc and its uptake by plants. II. Soil chemistry in relation to prediction of availability

Abstract

Representatives of nine soil groups were extracted with reagents that have been used to predict zinc deficiency. The amounts of soil zinc removed were discussed in terms of specific and non-specific bonding in relation to the reagent used. The desorption of natural zinc was also described in terms of the quantity/intensity (Q/I) relation and an equilibrium zinc concentration (ZnQ) at natural pH. The ZnQ values varied from 1 to 4 µgI. for the alkaline soils and 8-190 pg/l. for the acidic soils. The Q/I ratio was derived by radioisotopic and chemical isotherm procedures. Log Q/I (I = total soluble zinc) approximated closely a linear relation of unit slope with pH. This was ascnbed to a common reation of zinc with all soils by specific sorption dominated by ZnOHA ions such that Q/I¿ = constant where I' = (ZnOH+aq). Deviations from this relation are discussed. The relations between soil and plant (clover and wheat) variables were studied by simple and multiple regression analysis. Single values of intensity variables, and, to a lesser extent, Q/I variables, correlated well with plant data but not the quantity variables. The improved correlations of Q variables when combined with Q/I variables accorded with published work. The problem of predicting zinc availability on alkaline soils which are dominated by very high Q/I values, is discussed.