Nitrogen fixation and transfer in vetch and vetch-oats mixtures
1991
Papastylianou, I. | Danso, S.K.A.
15N-labelled organic matter and ammonium sulphate fertilizer (20 and 60 kg N ha-1) were applied as 15N sources to estimate N2 fixed in field-grown pure vetch (Vicia sativa L.) and vetch grown in two mixtures with oats (Avena sativa). The decline in 15N enrichment in the soil during the seven sequential harvests and deduced from the atom % 15N excess values in the oats reference crop was significantly slower in the organic matter labelled plots than with the 15N-labelled ammonium sulphate plots. Total N uptake patterns of oats and vetch differed markedly for the last two or three harvests. Also, estimates of N2 fixed (Ndfa) in vetch differed with the 15N source. The mean % Ndfa (or total Ndfa) at 106 days after emergence was 76% (95 kg N ha-1) with the ploughed-in organic matter, 45% (61 kg N ha-1) or 41% (41 kg N ha-1) when 20 or 60 kg N ha-1, respectively, of 15N-labelled ammonium sulphate was applied. Estimates of N transferred from the legume to the cereal were similarly influence by the 15N source. Little (maximum 5 kg N ha-1) or no N transfer from vetch to oats was detected, using the organic matter labelled plots. in contrast, several significant values (up to 29 kg N ha-1) of N transferred were estimated using the inorganic 15N-labelled plots. With the greater effects of fast 15N:14N ratio decline in soil on reference crop errors, we estimate that the values of N2 fixed and of N transferred under the more stable 15N:14N conditions, i.e. with 15N-labelled organic incorporated into soil, should be the most accurate. Thus, vetch derived on the average, over 70% of its N from fixation, while N transfer from vetch to oats was not significant.
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