Diverse fertility building leys in arable rotations

Summary

The results of a three year study in the UK suggest that there are several advantages to more complex mixtures;
• Greater resilience to variable conditions
• Combine early and late weed suppression • Slower decomposition on incorporation
• Extends forage availability for key insect pollinators
• Generally achieve higher forage yields
• Potential for higher subsequent crop yields.
Practical recommendation
• There are a number of plant characteristics that have an impact on nitrogen release and mobilisation, namely C:N ratio, lignin and polyphenol content which result in slower N release and lower N losses or better N utilisation.
• Including grass species in the mix takes up the N fixed by the legumes and reduces the free N in the soil; the rhizobia bacteria respond to the low soil N, resulting in higher N fixation and greater biomass. Moreover the higher C:N ratio prolongs the release of N to subsequent crops. The balance of grass and legumes is important.
• The annual N accumulation of ley mixtures decreases after two years, although there may be other advantages from longer leys such as weed control.
• In terms of forage yield including a 3rd or 4th legume is generally advantageous.
• The best multifunctional mixtures contain one or more species of Black Medic, Lucerne and Red Clover, plus other legumes according to the circumstances.