Effects of timing of foliar zinc fertilizer on yield components of soyabeans

Abstract

The effects of foliar applications of zinc sulfate heptahydrate on the yield components of six soybean varieties were studied at Trangie, New South Wales, on a zincdeficient soil. Zinc was applied at 0.9 kg/ha four, six and both four and six weeks after sowing and the plants were compared with unsprayed plots. Visual zinc deficiency symptoms appeared in unsprayed plots of Forrest, Dare, Dodds and Bragg from five weeks after sowing and zinc application increased yields and foliar zinc concentrations in all these varieties. Lee and Ruse did not show zinc deficiency symptoms and did not respond to the zinc treatments. The single zinc application six weeks after sowing was slightly more effective than that at four weeks, and the double spray gave additional benefit to Forrest, Dare and Dodds. Forrest was the most responsive variety with zinc applications increasing yields from 920 to 3220 kg/ha through increases in pods/m2, seeds/pod and seed weight. Yield of Dodds increased from 1835 to 2699 kg/ha in response to zinc by the production of more podslm2 and more seeds/pod, while yield responses of Dare (1783 to 2934 kg/ha) and Bragg (1801 to 2292, kg/ha) were due to increases in podslm2 alone.