Pasture responses to traces of zinc in phosphate fertilizers

Abstract

The effect of zinc present as a contaminant in commercial superphosphate was compared with the zinc in zinc sulphate (ZnSO4.7H2O) in its effect on subterranean clover grown on a deficient light soil (Kojonup sand) in the field. A dressing of 55 grams of zinc an acre, applied as a contaminant in superphosphate, increased the yield of subterranean clover in the pear of application from 2300 to 3200 lb of dry matter an acre. The total uptake of zinc in the tops was increased from 11 to 19 grams of zinc an acre. The proportion of the contaminant zinc absorbed from superphosphate was at least equal to that absorbed from a dressing of ZnSO4.7H2O. These results are discussed in relation to the zinc contents of superphosphate and of various compounds used in phosphatic fertilizers. The evidence indicates that the amount of zinc contaminant applied in the present experiment could be contained in dressings of even less than 2 cwt an acre of superphosphate.