Residual values of zinc sulfate and acidifying (elemental) sulfur for rice on the alkaline Cununurra soils of the Ord Irrigation Area, Western Australia

Abstract

The residual values of zinc sulfate and acidifying (elemental) sulfur (S) for rice on Cununurra clay were investigated at Kimberley Research Station, near Kununurra in the Ord Irrigation Area, Western Australia. Successive crops were grown on 2 sites showing different degrees of zinc (Zn) deficiency according to visual symptoms. Despite the marked response to Zn fertiliser shown by the first crop of IR665-24-1 rice on the more deficient site (previously fallow for 12 months) there was no significant yield response to applied Zn in the third crop. On the less Zn deficient site (previously under weeds for several years), IR661-1-170-1-3 rice showed no response to Zn fertiliser although transient symptoms occurred in the first and second crops. Continuous cropping per se apparently reduced the severity of Zn deficiency on both sites, thus negating attempts to estimate the residual value of Zn fertiliser. The 2 sites were not distinguishable by the EDTAammonium carbonate soil test for Zn. Extractable Zn increased with increasing level of Zn fertiliser, but plant response was not related to extractable Zn. Application of elemental S (1-4 t ha-1) had no effect on extractable Zn levels before sowing of rice. Increased rice yields due to acidifying S were confirmed, but the residual effects did not extend beyond the fourth crop. In each of the 3 seasons following S application, the yield of IR661-1-170-1-3 increased by 0.3-0.6 t ha-1 but, at current prices, the use of S as a soil ameliorant for rice in the Ord Irrigation Area would be uneconomic.