EVALUATION OF THE NITROGEN CONTRIBUTION OF LEGUMES TO SUBSEQUENT CEREALS

The effects of a preceding (1986/87) season's crop of vetch (Vicia sativa) or oats (Avena sativa), either singly or as two different mixtures, on the nitrogen uptake and growth of a succeeding barley crop (Hordeum vulgare) were examined in Cyprus in 1987/88, on field plots previously labelled (1984/85) with N-15 enriched organic matter. Grain as well as the vegetative material were harvested before planting the barley. Barley after vetch accumulated 61 % more nitrogen than barley after oats, while, for the mixtures, the nitrogen yields in the succeeding barley crop did not differ significantly from those of barley grown after oats. The N-15 enrichment in barley indicated that fixed N2 from vetch contributed little nitrogen to the available soil nitrogen pool and to the nitrogen in barley. Most of the increased assimilation of nitrogen in barley following vetch (compared to barley after oats) was attributable to a greater availability of soil nitrogen arising from the lower soil nitrogen uptake by the preceding vetch than oats. The dry matter yield of barley following vetch was 84 % higher than for barley after oats, while barley after the vetch-oats mixtures yielded 38-54 % higher than barley following oats. It was concluded that greater nitrogen availability to the cereal following the legume was not the sole cause of the dry matter yield responses observed.