To N-fertilize cereal-legume intercrops or not? (ReMIX Practice abstract)

Summary

Outcome
Intercropping cereal-legume usually results in a higher cereal grain protein concentration compared to sole crop cereal, and the greatest benefit is always obtained without N-fertilizer.
Practical recommendations
• The efficiency of synthetic N-fertilizer is generally high (> 75% of N applied). It always increases the proportion of cereal in an intercrop with legumes, regardless of the sowing density and pedoclimatic conditions.
• The efficiency of organic N-fertilizer is always low (< 20%), so it is not relevant to apply in organic farming.
• For winter intercrops (e.g. wheat-winter pea), the N fertilization must be adapted and based on the: i) proportion of species observed in March, ii) grain yield targeted, and iii) proportion of the two species expected at harvest. To increase cereal grain yield, N-fertilizer could be applied during stem elongation (40-80 kg N/ha), while to increase the cereal grain protein concentration, it should be applied at earing (30-50 kg N/ha).
• For spring intercrops (e.g. spring barley-spring pea), no N fertilization is generally required, except to ensure a high proportion of cereal grains at harvest by applying N-fertilizer at the end of tillering (30-60 kg N/ha).
Practical testing/ Farmers’ experiences
Farmers should try different N fertilization rates and/or times, for example, in strips across a field, to visually compare the effect of N fertilization on yield, species proportion and cereal grain protein concentration. Start with a small number of rates and/or times (including no fertilizer) and repeat the test for more than a year to improve know-how.