At Domaine de L’Arlot, when I visited in November a year or two ago, they were in the process of ploughing to oxygenate the soil, although they stopped temporarily as the cold weather had frozen the ground and they were in danger of breaking the plough. Oxygen is a key factor in ploughing, which many consider to be beneficial for the micro-organisms, as Jean-Marc Roulot observes, “the micro-organisms are the identity of the soil.” After the autumn plough these growers leave any grasses which appear to grow undisturbed over the winter. At Domaine de L’Arlot they plough lightly in the spring, not really for the weeds but to turn in the bio-prep. “This is the most important element for us, as it is the first level of exchange between the land and the vine. The soil must be a living place.”
A clean soil can also limit the danger of frost in the late spring. Etienne Grivot advocates hoeing in March/April to minimise the dangers of a strike in May.
Also, by not using herbicides many growers argue that ploughing is the environmentally sound option. But is it? It is time to consider the arguments against ploughing.
Starting with the green and clean argument – one must consider just how environmentally friendly are tractors. Frédéric Mugnier has obviously spent some time researching ploughing as he has developed his own approach and reports that 60% of land producing cereals in Argentina is not ploughed because of the long term depletion of the soil leading to erosion. As well as being considerable cheaper by saving on tractor fuel, it saves on engine emissions making this approach altogether more environmentally sound.
Frédéric ploughs in spring and summer, but he points out that it is superficial. “I don’t like the idea of turning the soil. The soil has a vertical structure. Each layer has its own bacteria, yeasts and insects, which have adapted to that particular layer. Turning it disturbs the wildlife in the soil.”
As farmers will tell you, carbon and nitrogen exist in the soil in a form not immediately accessible to the plant. These elements break down, but it is a slow process particularly below 10 cm beneath the surface. Ploughing speeds up the mineralisation of carbon and nitrogen. Hence it is used by farmers to help make carbon and nitrogen more readily available to the plant. However as Frédéric Mugnier points out, farmers plough deeper and deeper to reach layers where organic material is still available, and when they have exhausted this, they plough deeper still, to a point at which there is no organic material (humous is a complex form of organic material) available. The soil loses its structure and becomes extremely susceptible to erosion.
So Frédéric Mugnier”s solution? “Stop ploughing. This will restructure the soil and assist in the production of humous.” He also advocates leaving organic material such as straw on top of the soil and remarks, “the biological life will return. It is more ecological.” Frédéric prefers to hoe, just to get rid of the weeds. On this point, Jean-Marc Roulot, who ploughs in the autumn, comments that after ploughing he leaves any weeds to grow through the winter to prevent erosion.
What about cutting the laterals and encouraging the roots downwards? Dominic Lafon, who plough with horses remarks, “I am not worried about the laterals. That is stupid. They will not go down. You must get the plant to grow to improve root activity.”
Etienne Grivot is equally unimpressed with this argument, although he adds that it does depend on the rootstock. With most rootstock, the principal root will go out laterally and along this root the second or third offshoot will descend. The rootstock 3309 is particularly lateral in behaviour while Riparia is the most vertical. So, he warns, you could kill your vine. He is sure the vine’s roots are more vulnerable in the winter, so he ploughs only in the spring.
Frédéric Mugnier finds the oxygen argument equally spurious pointing out that if the bacteria are used to living 15 cm beneath the surface, they are well adapted and why should they benefit from the extra oxygen? Again he stresses that “the soil will restructure itself if left alone and the bacteria and worms will re-establish themselves.” When he acquired Clos de la Marachale the soils were very compacted from deep ploughing with tractors. Frédéric used plants, in this case rye grass, to naturally aerate the soil via the channels made by the roots. The roots will grow in winter and then at the end of winter he will bury the grass to prevent it competing with the vines.
So what about the life of the soil? Well there is the strong argument that the tractors will compact the soil and impact on this life. At Domaine de L’Arlot they admit that compaction is a problem particularly with clay dominant soil and carefully control the number and the timing of the passes.
It may be a minor point, but a clean surface loses heat more quickly than a covered one, which is a point in consider in a marginal climate.
So there are certainly a few strong arguments against ploughing. Does ploughing using a horse mitigate some of these problems or does it entail a new set of its own?