Comparing copper requirements of canola, albus lupin, durum wheat and spring wheat grown on alkaline soils

The copper (Cu) requirements of spring wheat (Triticum aestivum L.), the major crop for alkaline soils in south-western Australia, is well known. The Cu requirements of canola (Brassica napus L.), albus lupin (Lupinus albus L.) and durum wheat (Triticum durum L.), alternative crops for these soils, are not known. A glasshouse experiment, using 2 alkaline soils from south-western Australia, compared the yield and Cu content response to applications of Cu to canola, albus lupin, durum wheat and spring wheat. The Cu was applied either just before 45-days incubation in moist soil at 20°C (incubated Cu), or just before sowing after the incubation treatment (current Cu). Comparative Cu requirements were determined from yields of 45-day-old dried shoots for: (i) Cu already present in the soil (indigenous soil Cu); (ii) the amount of applied Cu required to produce the same percentage of the maximum (relative) yield of dried shoots; and (iii) the Cu content of dried shoots (Cu concentration multiplied by yield of dried shoots). The concentration of Cu in youngest tissue and in dried rest of shoots was used to determine critical Cu concentrations in tissue. Albus lupin used indigenous Cu so effectively it only showed a 10% yield increase to applied Cu. Canola used indigenous Cu more effectively than durum wheat, which was followed by spring wheat. Relative to spring wheat, durum wheat was about 15% less effective at using incubated and current Cu to produce dried shoots and canola was about 47% more effective. Therefore, to produce the same percentage of the maximum (relative) yield as spring wheat, durum wheat required about 15% more incubated and current Cu and canola required about 50% less Cu. As determined using Cu content in shoots, canola and durum wheat were about 45% more effective than spring wheat at increasing Cu content in shoots and albus lupin was about 80% more effective. Evidently, all 3 species took up more copper than spring wheat. Durum wheat did not use this Cu to produce more shoot yield than spring wheat, whereas canola did. The critical Cu concentration in the youngest tissue (mg Cu/kg), associated with 90% of the relative yield, was: 1.5 for spring wheat; 1.7 for durum wheat; 1.0 for albus lupin; and 2.2 for canola. Corresponding values (mg Cu/kg) for rest of dried shoots were: 2.5 for spring wheat; 3.2 for durum wheat; 1.3 for albus lupin; and 2.7 for canola.