Hi All, another Autumn drilling focused post today, looking to provoke thought and opinion about the best approaches for drilling and establishing your winter crops. As the title suggests I will be looking at the increasingly popular approach of increasing genetic diversity and crop resilience through the use of species mixtures, colloquially known as "plant teams", with a particular focus on the combination of a cereal/grain legume bi-crop. Whilst using intra-species variety blends could be considered intercropping it is the interspecies combination, seeking to maximise on complementary traits between two grain crops to enhance productivity through greater resource use efficiency that we will look at in this post.
The reasons behind why to intercrop are well studied with numerous agronomic benefits from increased agro-biodiversity to enhanced weed control, disease reduction and more effectively utilise resources for crop growth, particular around light capture and for nutrient uptake. More simply it can be considered a way to spread risk and hedge bets under uncertain seasonal climatic conditions, with water availability of increasing concern in a climate that appears to be getting a lot drier at least in the spring months. Intercropping also enables the farmer to make selections of the best combination of traits to maximise in-field crop performance, being able to make best use of a wider range of traits than are available through standard monocropping and in lieu of targeted organic and low-input breeding programmes that would help make current species better adapted to organic environments.
So, in terms of practical considerations, the first would be which species to team up and then which varieties. The classic example is wheat and beans although oats and beans should work equally as well and used to be a traditional practice in Scotland. The reason a cereal and beans seem to work well is that not only do they have several complementary traits but also certain deficiencies as monocrops that can be to some degree addressed when grown simultaneously. The most obvious issue is the open canopy and slow establishment of the beans that can lead to poorer weed suppression, with a faster growing, more closed canopy of a cereal helping to smother the weeds whilst the beans establish. The cereal is also generally more "hungry" when it comes to nutrients, particularly nitrogen, so reducing seed rates and including with a legume can help to reduce overall nitrogen requirements of the crop with the cereal also acting as a catch crop which should encourage the beans to fix more atmospheric nitrogen. Nitrogen fixation is a resource heavy process for a legume and it won't necessarily provide the resources to the N-fixing bacteria if it isn't required. Another reason for combining the two crops is that the root architecture and depth of the two species will differ, creating a rhizosphere niche with the deeper bean root helping soil structure and the complementarity leading to enhanced nutrient and water acquisition, offering a buffering capacity against drought. The differing root exudates will also encourage more diverse microbial communities.
Alongside species selection should be a consideration of the end market and whether separation is required or even possible. It may be that the bi-crop can be sold together as feed but if wanting to sell the cereal at a milling premium, separation will be required. If the crop has performed poorly there could also be the emergency option of wholecropping but again make sure there is somewhere to sell this if not being used on farm.
Seed rates is another important consideration. The first decision should be which crop is the focus? It may be that higher seed rates for this species are used but if both grains are equally prized an approach that ranges between 50-75% of the mono-cropped seed rate should be most effective, giving 100-150% of standard monocropped seed rates. The reduction in seed rate within species helps to reduce that competition, whilst an overall higher seed rate provides insurance, and hopefully maximises on the complementary traits for optimum performance.
Spatial arrangement is perhaps less of consideration purely because it is less possible to control it but there are farmers able to inter row drill or sow alternate rows. The usual approach would be fully mixed rows of each species, but broadcasting is also possible. There is research that shows differing arrangements offer different benefits, particularly for pest and disease reduction, whether that be through dilution effect or barrier effect would depend on the spatial layout. If looking to maximise the resource use efficiency it would seem logical to take a fully mixed approach, but alternate rows may provide something of an "edge effect" reducing competition around each row.
Bi-cropping may not always out yield a monocrop alternative but the theory would be longer term yields would hopefully be more stable especially for a "boom or bust" crop like beans. Finding ways to increase the number of legumes in the rotation can be expected to improve soil fertility and health with obvious rotational benefits. With increasing demand for homegrown protein sources, and a bean price currently around the £600 a tonne mark, it makes sense on economic as well as agronomic and environmental levels.
Andrew has recently returned from a fact-finding mission to Denmark, to investigate a bean toasting machine that will be on trial at Godminster. Look out for his write-up on this experience.