The level of N₂-fixation of different genotypes of winter pea in comparison to spring pea in pure and mixed stands

Abstract

In contrast to the common spring pea (SP), little is known about the capacity of winter peas (WP) for sym­biotic N₂ fixation in pure and mixed stands. Therefore, seven WP genotypes and one semi-leafless SP in pure stands and two mixtures with cereals (25% (Mix1) or 50% (Mix2) of the pea pure stand sowing density) were examined in field experiments on two sites. The amount of fixed N₂ at flowering and at mature harvest was assessed applying the extended total-N-difference method. At flowering and at grain harvest the N₂ fixation for the five frost-resistant WP genotypes (52 and 85 kg ha^–1, respectively) was generally higher than for SP (17 and 42 kg ha^–1, respectively). This was traced back to the earlier N₂ fixation of WP and a usually higher above-ground biomass (144 and 75 kg ha^–1, respectively) and presumably higher below-ground biomass as compared with SP. Furthermore, average inorganic N in soil at mature harvest in pure stands was higher under WP (69 kg ha^–1) than under SP (36 kg ha^–1), while for any other treatment similar values on a lower level were estimated. Results show that WP may better contribute to the N supply within crop rotations than SP.