Diverse fertility building leys in arable rotations


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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.
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.
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.
Soil quality and fertility, Nutrient management, Pest and disease control, Weed management
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