BARLEY UPTAKE OF N DEPOSITED IN THE RHIZOSPHERE OF ASSOCIATED FIELD PEA

N deposited in the rhizosphere of a legume may contribute to the N-nut rition of an intercropped non-legume. The process of deposition and su bsequent uptake by a neighbouring plant is often termed N-transfer. Th e N-transfer from field pea (Pisum sativum L.) to associated spring ba rley (Hordeum vulgare L.) was determined in three pot experiments usin g a direct split-root N-15-labelling technique. The donor (pea) and re ceiver (barley) plants were grown with their root systems either mixed within the same soil compartment or separated by a 20 mu m mesh bag. Pea-derived N was detected in barley after 4 weeks of growth, but in m ost associations <1% of total pea N was recovered in barley. N-transfe r from barley to pea was not detected when barley was grown as the don or. The amount of pea-derived N in barley increased markedly with time , probably due to the accelerated turnover of root and nodule debris. Separating the root systems reduced the barley recovery of pea-derived N to about half the amount recovered in the association where root sy stems grew in the same compartment. The death of pea, caused by sprayi ng with a herbicide, increased the amount of N recovered in barley, wh ereas shading the pea plant had no effect on the amount of pea-derived N taken up in barley. The N deposited up to 45 days of growth contrib uted <5% of the barley shoot N in most treatments. However, at 70 days , 19% of the N in barley was derived from pea. It is concluded that fi eld pea rhizodeposition of N may be a significant source of N to inter cropped barley, especially at low rates of N-fertilization.