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Diverse fertility building leys in arable rotations
Problem
Leguminous leys are a cornerstone of organic arable systems. However, they do not always deliver reliably, and there is a need to improve their fertility-building capability and resilience. A typical ley of one or two legume and grass species can be vulnerable to failure under unfavourable conditions. Good establishment, weed suppression and controlling the quantity and timing of N release can be especially challenging.
Solution
Different legume species have different growth characteristics and nutrient use profiles. Growing a complex mixture of species can maximise the exploitation of nutrients, aid weed suppression, attract a more diverse range of pollinators and enhance the stability and resilience of the stand. On-farm and field trials (including trials as part of the three year LegLINK project) have evaluated the role of functionally diverse species-rich leys in arable rotations in the UK.
Description
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.