Relative effectiveness of soil-applied zinc for four crop species

The yield and zinc content response of canola (Brassica napus L.), albus lupin (Lupinus albus L.), durum wheat (Triticum durum L.) and spring wheat (Triticum aestivum L.) to applications of zinc fertiliser were compared in a glasshouse experiment using 2 alkaline soils from south-western Australia. Five amounts of zinc applied as zinc sulfate were either added just before sowing (current zinc) or incubated in moist soil for 50 days (incubated zinc) before sowing seeds. Comparative zinc requirements were determined from yields of 40-day-old dried shoots for: (i) zinc already present in the soil (indigenous zinc); (ii) the amount of fertiliser zinc required to produce the same percentage of the maximum (relative) yield of dried shoots; and (iii) the zinc content of dried shoots (zinc concentration multiplied by yield of dried shoots). The concentration of zinc in youngest tissue and in dried shoots was used to determine critical concentrations for zinc in tissue. Albus lupin used indigenous, current and incubated zinc more effectively than canola, followed by spring wheat and then durum wheat. Albus lupin and canola were about 30 and 40% more effective at using fertiliser zinc than spring wheat. Durum wheat was about 20% less effective than spring wheat. Relative to current zinc, the effectiveness of incubated zinc declined by about 60% for both spring and durum wheat, and by 50% for canola and albus lupin. The critical zinc concentrations in the youngest tissue, associated with 90% of the relative yield, were (mg zinc/kg): 14 for spring wheat, 20 for durum wheat, 16 for albus lupin and 15 for canola. Corresponding values for dried shoots (mg zinc/kg) were: 32 for spring wheat, 25 for durum wheat, 22 for albus lupin and 23 for canola.