Biological nitrogen fixation in field pea and vetch: Contribution from above and belowground structures to the partial nitrogen balance
Field Crops Research(2024)
Abstract
Context
Including winter legumes during fallow periods in crop rotations may add nitrogen (N) to the agroecosystem through biological N fixation (BNF). This gain will depend on management practices and whether the crop is planted for grain production or as a cover crop. Despite many studies quantified the partial N balance of different legume crops, very few considered the contribution of BNF from belowground structures, which is necessary for more accurate estimations.
Objective
To estimate biomass, N uptake, and BNF in field-grown field pea and vetch, and study the impact of including belowground structures in the partial N balance of both crops.
Methods
A two-year field study evaluating two genotypes of field pea (semi-leafless and conventional-leaved) and vetch was performed under field conditions in the Pampean Region (Argentina). Above and belowground biomass (measured in field monoliths to 0.3 m depth), N uptake and 15N abundance were quantified for determining BNF, and the partial N balance.
Results
The partial N balance of field pea as grain crop was negative in most cases (average −7 kg N ha−1), but, was positive when vetch was evaluated as cover crop (average 51 kg N ha−1). Including belowground components, BNF improved the partial N balance by 1 and 6 kg N ha−1 in field pea and vetch, respectively. In field pea, the proportion of N uptake derived from BNF (%Ndfa) averaged 43 %, and was not affected by genotype or year, whereas for vetch represented 40 and 18 % of total N uptake in 2018 and 2019, respectively. In field pea, belowground BNF averaged 1.2 kg N ha−1, and represented 0.9 % of the total N uptake at maturity. In vetch, belowground BNF averaged 6.3 kg N ha−1 and accounted for 3.8 % of total N uptake at full bloom.
Conclusions
Biomass and the proportion of N derived from BNF were not affected by the different genotypes in field pea, while in vetch, the environmental conditions that increased %Ndfa were more important than those that affected biomass production for increasing the partial N balance.
Implications
Although field pea as a grain crop did not provide a consistent N input to the agrosystem, it arises as a convenient crop in terms of N balance compared to other cash crops. Vetch stands as an attractive cover crop, contributing 46–57 kg N ha−1 and 6–9.5 Mg ha −1 of residues to the agrosystem.
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Key words
Partial N balance,Belowground N,15N natural method,Plant roots,Cover crops
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