Biological N 2-fixation by three tropical forage legumes and its transfer to Brachiaria humidicola in mixed swards
A study was conducted (a) to determine the biological N 2-fixation (BNF) by three tropical pasture legumes ( Centrosema pubescens, Stylosanthes hamata and Pueraria phaseoloides) grown in monoculture and associated with the grass Brachiaria humidicola; and (b) to assess the potential transfer of fixe...
Saved in:
Published in | Soil biology & biochemistry Vol. 29; no. 5; pp. 999 - 1004 |
---|---|
Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
Elsevier Ltd
01.05.1997
|
Online Access | Get full text |
Cover
Loading…
Summary: | A study was conducted (a) to determine the biological N
2-fixation (BNF) by three tropical pasture legumes (
Centrosema pubescens, Stylosanthes hamata and
Pueraria phaseoloides) grown in monoculture and associated with the grass
Brachiaria humidicola; and (b) to assess the potential transfer of fixed N from the legume to the companion grass. To calculate the proportion of N in the legume derived from air, the
15N isotope dilution technique was used. The fertilizer (ammonium sulfate 10% enriched with
15N) was applied in seven split doses during the growing season. Aboveground biomass of the grass and the legumes in monocrop and in mixture were determined twice a year, after 3 months of regrowth, and samples were analyzed for total N and
15N. Over the two evaluation periods, the association
B. humidicola/C. pubescens was the most stable, with a proportion of 20–30% of the legume in the mixture. As the sole crop,
B. humidicola had the highest production of shoot biomass (972 g m
−2) among all treatments during the first regrowth period (middle of the rainy season). Total shoot biomass in the associations ranged from 574 (
B. humidicola/C. pubescens) to 807 g m
−2 (
B. humidicola/S. hamata). Dry matter production for the second evaluation (end of the rainy season) showed the same trend, but lower yields were obtained due to soil drying conditions. The N content in the shoot biomass was always higher in the legumes than in grass. However,
B. humidicola in monoculture showed the highest total N accumulation (18.1 g m
−2) due to its higher growth rate. Legumes in monocrop had a very significant proportion of N derived from BNF (47–69%), with
C. pubescens as the better N
2-fixing legume (51–69%). A higher contribution from BNF also was observed in the legumes when mixed with the grass (57–76%). No clear transfer of N from the legume to the companion grass was observed, since the
15N in
B. humidicola was always higher in the mixed swards. This grass appeared to have a different pattern of N uptake, obtaining a very significant amount of unlabeled N from outside the marked plots. |
---|---|
ISSN: | 0038-0717 1879-3428 |
DOI: | 10.1016/S0038-0717(96)00230-1 |