An assessment of nitrogen fixation in 'organically managed' spring-sown lupins and leaching under a following winter cereal

Summary

Three spring-sown species of lupins (Bora, Prima and Wodjil) and peas were compared in terms of N fixation and subsequent leaching under a following winter cereal crop. Although peas out-yielded lupins (5.4 t compared with ca 3.5 t grain, respectively), the yellow lupin (Wodjil) fixed more N than peas (180 compared with 120 kg N ha-1) and all three lupins contained more protein (> 30%) than the peas (22%). Wodjil was the most effective at suppressing weeds, carrying only 12% of the weed burden found in fallow plots, followed by peas (19%). Winter leaching amounted to > 50 kg nitrate-N ha-1 from under the winter cereal, regardless of whether the previous treatment was a legume crop or was left fallow. There were no significant differences in leaching between the three species of lupin. Leachate in the first 350 mm of drainage under the winter cereal exceeded the EU limit on nitrate in drinking water in all treatments. This work is part of a wider collaborative study supported by Defra which covers a range of UK sites.