Effects of zinc and iron fertilizers on a disorder in rice on the calcareous soils of the Ord Irrigation Area, Western Australia

Abstract

A field experiment was conducted at Kimberley Research Station near Kununurra, Western Australia to study the effects of urea and ammonium sulphate fertilizers, previous cropping history and method of sowing on the incidence of a long-standing disorder in rice on the calcareous soils of the Ord Irrigation Area, and to determine whether the disorder could be ameliorated by means of zinc and iron fertilizers. Symptoms of the disorder resembling those of zinc deficiency appeared within four weeks after seedling emergence in plots not treated with zinc. The mean concentration of zinc in the tops of affected plants sampled at 2, 7 and 11 weeks was 18 p.p.m. The combination of fallow land, urea and water-sowing resulted in the most severe symptoms. Where 20 kg Zn ha-1 was applied as zinc sulphate, the zinc concentration in the plant tops averaged 66 p.p.m. over the three sampling dates, and zinc deficiency symptoms did not develop. Other symptoms resembling those of iron deficiency also occurred, especially when the level of applied zinc was 20 kg ha-1. The application of both zinc sulphate and ferrous sulphate fertilizers resulted in a significant increase in the grain yield of IR665-24-1 rice. Overall there was no response to zinc sulphate above the level of 10 kg zinc ha-1. The curve of best fit for the overall response to ferrous sulphate was parabolic with a maximum near 240 kg ha-1 ferrous sulphate. The mean yield from plots that received three foliar sprays of 0.1 per cent ferrous sulphate was not significantly different from that of plots fertilized with 200 kg ha-1 ferrous sulphate. There was no significant interaction between zinc and iron.