Wheat response to alternative crops on a duplex soil

Rates of crop growth (including the root system), water extraction from specific soil layers, leaf water potential and crop nitrogen content were measured in a field experiment of wheat (Triticum aestivum L.) grown after alternative crops. The previous crops of lupin (Lupinus angustifolius L.), faba bean (Vicia faba L.), chickpea (Cicer arietinum L.), vetch (Vicia sativa L.), canola (Brassica napus L.), and Indian mustard (Brassica juncea L.) all showed a 'break crop' effect compared with wheat after wheat. In addition, the legumes lupin, faba bean, chickpea and vetch stimulated biomass production of successive wheat crops via increased nitrogen supply. When the previous crop was lupin, wheat root length density at depth in a duplex soil tended to be increased and post-anthesis water uptake by wheat was enhanced. Wheat after lupin resulted in a 42-76% higher yield than wheat after the other legumes, a 37-68% higher yield than wheat after the non-legumes and a 131% higher yield than wheat after wheat. Wheat yields did not relate to previous crop root depth, but correlated well with residue nitrogen from the various alternative crops.