Comparing copper requirements of field pea and wheat grown on alkaline soils

Copper (Cu) is a common deficiency of spring wheat (Triticum aestivum L.), the major crop grown in south-western Australia. The Cu requirements of wheat are well known for soils in the region, but are not known for field pea (Pisum sativum L.) grown in rotation with wheat on alkaline soils in the region. The Cu requirements of field pea and spring wheat were compared in a glasshouse experiment, using 2 alkaline soils from south-western Australia. The Cu was either incubated in moist soil at 22°C for 100 days before sowing (incubated Cu) or applied just before sowing (current Cu). Comparative Cu requirements were determined from yields of 43-day-old dried shoots for: (i) Cu already present in the soil (indigenous Cu); (ii) the amount of added 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 critical concentrations of Cu in youngest mature growth and in dried shoots were also determined. As determined from yield of shoots, both species used indigenous Cu about equally effectively. Compared with spring wheat, field pea was about 12% less effective at using current and incubated Cu to produce dried shoots. It was about 15% less effective at using current and incubated Cu to increase Cu content in dried shoots. Relative to current Cu, the effectiveness of incubated Cu declined by about 60% for both wheat and field pea in both soils. The critical Cu concentration in the youngest tissue, associated with 90% of the relative yield, was 1.4 mg Cu/kg for spring wheat and 2.0 mg Cu/kg for field pea. The critical value for the rest of the dried shoots was about 3.0 mg Cu/kg for both species.