Biological nitrogen fixation in field pea and vetch: contribution from above and belowground structures to the partial N balance.

Abstract

Abstract Purpose The inclusion of winter legumes during fallow periods allows the addition of N to the system through biological N fixation (BNF), which will depend on management practices and crop species (for grain production or a cover crop). The objectives of this study were to evaluate the BNF and biomass and N accumulation in pea and vetch crops growing under field conditions and to study the impact of including belowground structures in the partial N balance of both crops. Methods Biomass, BNF and N uptake, including belowground structures (determined in field monoliths to 0.3m depth), were quantified in a two-year field study evaluating two genotypes (semi-leafless and conventional-leaved) in field pea, and contrasting sowing dates in vetch. Results Belowground BNF inputs improved the partial N balances and averaged 1 and 4 kg N ha− 1 in field pea and vetch, respectively. The partial N balance in field pea was negative in most cases (average − 7 kg N ha− 1), determined to a greater extent by a high NHI, while in vetch net N inputs increased with the delay of sowing date (from 60 to 295 kg N ha− 1). Conclusions In field pea, the different genotypes exerted minor effects on biomass and %Ndfa, whereas in vetch sowing dates had a strong impact on these variables. BNF-derived N at full bloom in vetch proved to be higher when delaying sowing dates, despite plants reaching lower total biomass with a higher partial N balance.