Crop performance, biological N fixation and pre-crop effect of pea ideotypes in an organic farming system

Pea ( Pisum sativum L.) is a valuable grain legume in organic crop rotations. Pea rotations provide nitrogen (N) to the system through N fixation and produce animal feed or human food. Because of the high susceptibility of pea to pests, diseases and weeds and due to low profitability, especially in organic systems, pea cropping intensity decreased in the last 15 years in Austria. Therefore, it is important to find strategies for improving pea cropping systems in organic systems, by increasing yields and providing a positive N balance. The objective of this study was to compare pea genotypes of selected field and fodder pea in pure and mixed pea stands for biomass performance, biological N fixation and pre-crop effect under dry site conditions in a 2-year study in Eastern Austria. Pea N fixation was estimated using the extended N-difference method, with oat as the reference crop. The highest grain yield was found for the leafed field pea, with 2.5 Mg dry mass (DM) ha −1 , followed by the semi-leafless field pea with 2.1 Mg DM ha −1 and the pea-mixtures with 2.2 Mg DM ha −1 . The field pea cultivars yielded more than the fodder pea cultivars with 1.6 Mg DM ha −1 . The average N concentration in pea grains was 3.6 mg g −1 . The fodder pea type contained 3.8 mg g −1 , significantly more N ( p < 0.0001) than the semi-leafless and leafed field pea. Pea N fixation ranged from 53 to 75 kg N ha −1 , corresponding to 42–50% of N derived from the atmosphere (% N dfa ). No differences in N fixation were found among cultivars, types and field/fodder pea. The fodder pea exported less N from the field because of their lower grain yield. Therefore, the N balance (N-input − N-output) of fodder pea was positive, with + 3.4 kg N ha −1 compared to the negative N balance of − 0.6 to − 3.6 kg N ha −1 for the leafed field pea types. These differences were not reflected in the following winter wheat crop, where the DM grain yield was 3.6–3.9 Mg ha −1 with no differences between cultivars and ideotypes. The results demonstrate that leafed field pea could have a sufficient grain yield and fodder pea could produce high N concentration in the grains. Because there are no differences regarding the effect of pea types on the yield of the following crop, it can be concluded that all tested pea types are suitable for successful organic pea production under dry site conditions. While there were no negative effects on the subsequent crop, the different ideotypes and mixtures may be selected based on different management goals.