Critical plant and seed concentrations of phosphorus and zinc for predicting response of faba beans (Vicia faba)

Abstract

Faba beans (Vicia faba cv. Fiord) were grown in 1 glasshouse and 3 field experiments to calibrate the critical concentrations of phosphorus (P) and zinc (Zn) in selected plant tissues for vegetative and grain yields. In the field experiments, responses in grain yield to soil-applied P were between 0.5 and 0.8 t/ha (20-25%) at sites with extractable Colwell soil P concentrations of 20 and 23 mg/kg. Similarly, grain yields were increased by 0.6-1.2 t/ha (20-30%) from the application of either soil-applied or foliar Zn. These field responses to Zn only occurred if P fertiliser was applied at sowing. Maximum yields were obtained by either applying about 2 kg Zn/ha to the soil at sowing, or 500 g Zn/ha as a foliar spray, 8 weeks after sowing. In field experiments, critical P concentrations in the youngest open leaf during vegetative growth for prediction of maximum grain yield in the field, remained constant over a 10-week growing period. A critical nutrient range of 0.40-0.41% is proposed. However, critical concentrations of P in whole top for maximum grain yield, declined from 0.40 to 0.27% over the same growing period. For bean seed collected at harvest, a critical concentration of 0.36% P for maximum grain yield was derived. Critical concentrations of Zn during vegetative growth for prediction of maximum grain yield, derived in both glasshouse and field experiments, were very similar in youngest open leaf and whole top, and no significant decline with plant age was observed; a critical nutrient range of 19-24 mg/kg is proposed. For seed collected at harvest, a critical nutrient range for diagnosis of Zn deficiency of 13-15 mg/kg is suggested.