We started our series of articles about cover crops with an overview of one of the three main plant groups we use at Avondale, cereals. It’s time now to take a look at another plant group which offers us a range of beneficial cover crops, the legumes.
A legume is a plant in the family Fabaceae. Legumes are commonly farmed for their edible seeds which are consumed by people and farm animals, and also provide oils. The main legumes that we use as cover crops include bitter lupin, fava bean, vetch, clovers, medics, seredela and lucerne.
Why do we use Legumes as Cover Crops?
As part of our holistic BioLOGIC® approach, Avondale makes use of a uniquely diverse cover cropping system, and legumes play an important role in our cover crop mixes because:
- working in conjunction with the rhizobia bacteria in their root nodules and the mineral molybdenum, legumes bind nitrogen from the atmosphere in the soil, making it available to the vines. Thus, using legumes as cover crops enables the wine farmer to build natural nitrogen in the soil. This means we have no need for chemical nitrogen fertiliser
- legumes are a diverse group, and different species can be matched to different soil types. For instance, we use fine-seeded, drought-resistant medics in the mix for our rocky soils, while deeper-rooted lupin and vetch are sown in the wetter areas where their roots provide natural tillage
- legumes such as the clovers have an extended flowering time and attract useful insects
- legumes with strong, deep tap root systems can be used to break up compacted soil and to bring natural phosphate up to the surface where it is more available to the vines
- after their growing season, legumes create a valuable nitrate-rich biomass and help to build humus in the soil
Avondale’s BioLOGIC® system addresses the complexity of finding balance in the soils by making use of ten different types of cover crop mixes. These mixes are matched to the different soil types found on our farm, and each mix includes at least two different types of legumes which offer multiple benefits to their plant communities. Of course, the greatest benefit is that these legumes are fixing the nitrogen in our soil which our vines will need for sustained growth and healthy, balanced grapes. In our next article in this series, we’ll provide an overview of the brassicas, the third main group of plant used as cover crops.
Left: Root nodules on a legume plant containing nitrogen-fixing rhizobia bacteria
Right: A cross-section of a root nodule of a legume plant. The rust colour indicates the presence of rhizobia bacteria