Legume LINK: Managing Legume Mixtures – Pros and Cons
Legume LINK is a major new research project which started in 2009 to investigate the potential of a wide range of legumes as fertility building crops in arable systems. A selection of legumes was combined into species mixtures and these are currently being trialled at various sites across the UK in a participatory farm-based approach. Dr. Thomas Döring (Organic Research Centre) described ‘first impressions' from preliminary data collected in year one. There was much interested debate in the open discussion from growers and researchers alike, including the optimisation of legume mixes to different regions of the country and their role in weed suppression.
Legumes, such as clover, fix atmospheric nitrogen through a symbiotic relationship with bacteria known as rhizobia which are found in their root nodules. These plants can, therefore, be used to replenish depleted soil nitrogen and reduce the need for artificial inputs. In arable systems, drilling legumes as a break crop can increase soil fertility in rotations with cereals, thereby building stability.
Legume LINK studies the growth characteristics of an array of legume species as monocultures at research hubs. Mixes of legumes are also grown at a number of participatory farms throughout the UK in order to assess their performance across a climatic gradient on a range of soils, rotational and management conditions. Early results from the trials were presented, showing the variability between individual legume species with respect to establishment and weed suppression, and contrasting this with an ‘all species mix'.
The rationale behind combining species in mixes was explained in relation to the modification of C:N ratios and staggered release of nitrogen to subsequent crops following ploughing. The potential to model and create ‘tailor made' legume mixes suited to different regions of the country was raised during discussions with enthusiastic interest from growers.Interactions between establishment rates of various legume species and weed suppression received considerable debate due to marked differences between trial sites. Faster establishing legume species seem generally to be better at suppressing early weeds, although it was noted that soil type and sowing depth are likely to influence the identity of the ‘best' species at diverse locations.
A number of related topics for future research were suggested, such as the impact of alternating legume species on pest and disease levels. It was emphasised that the current research was at a ‘proof of concept' stage, but with further funding validation of results taking into account the effect of legume mixes on following crops is an ideal next step.