Comparing responses of grain legumes, wheat and canola to applications of superphosphate

Phosphorus (P) is a major deficiency of soils of south-western Australia (W A). The fertilizer P requirements are not known for grain legumes being eva luated for neutral to alkaline, fine textured soils in WA. To rectify this, glasshouse and field experiments were undertaken to compare the responses of several grain legume species, wheat and canola to applications of single superphosphate and the results are reported in this paper. The glasshouse experiments measured responses of dried tops, harvested at 26 to 42 days af ter sowing, to P that was freshly-applied (current P) and previously-applie d (previous P). Responses in the glasshouse were measured using yield, P co ncentration and P content (P concentration multiplied by yield) of oven dri ed tops of the following: wheat (Triticum aestivum), canola (Brassica napus ), faba bean (Vicia faba), chickpea (Cicer arietinum), lentil (Lens culinar is), field pea (Pisum sativum), albus lupin (Lupinus albus) and narrow leaf lupin (Lupinus angustifolius). Field experiments in 1994 and 1995 compared seed (grain) yield responses of faba bean, chickpea, lentil, albus lupin a nd wheat to applications of current P. The P was banded (drilled) with the seed while sowing at 5 cm depth. Canola and wheat produced very large yield responses to increasing applications of current P. Responses were much sma ller for albus lupin, faba bean and chickpea. Responses for lentil, narrow leaf lupin and held pea, fell in between responses of the small and large s eeded species. Similar trends for responses were obtained as measured using yield, P concentration, or P content. For soils treated with previous P, s imilar trends were observed as for current P, but differences in yield resp onses between species were much less marked and the response curves tended to become more sigmoid. In the field experiments, grain yield responses to current P of albus lupin and chickpea were less than that for wheat. Relati ve to wheat, faba bean was the most responsive grain legume to applications of current P, with lentil producing similar responses to wheat in one expe riment at a newly cleared, P deficient site.