Photo: Palden Jenkins
Green manures are crops that are grown to build soil fertility and soil structure. We use green manures in many ways and consider them to be the key to organic production at Northdown.
We operate a stockless system (i.e no farm animals apart from 3 chickens for our own eggs) so can't rely on manure and can't leave land in grass and clover for grazing. We make compost on the farm and buy more in but try to create as closed a system as possible. We have 3 tried and tested strategies:
1. 1 year ley. This fits in the rotation after 3 years vegetables and before potatoes. We generally use a mixture of ryegrass (for soil structure and smothering weeds) and legumes: red clover, crimson clover and tares to fix nitrogen. The crop is established in August/September or March/April depending on when the previous crops are cleared, it will then be in the ground between 12-18months before ploughing the following February/March for potatoes.
2. Catch crops. These are short term green manures that fit between vegetable crops. After onions and garlic we can sow, in August, red and crimson clovers to grow over winter to precede the next year's cabbage and broccoli. This particularly benefits the later plantings as the clovers will have had a chance to fix useful amounts of nitrogen in the spring. After crops such as potatoes we use rye and tares that can be sown as late as October. In summer, any time there is an 8 week gap between crops we can sow phacelia or buckwheat that are great attractants for beneficial insects.
3. Inter crops: Here, by sowing the green manure under the market crop, the crop and green manure occupy the same time and space. Once sweetcorn is well established we can drill white clover and yellow trefoil. By autumn this forms a thick mat under the corn, we leave the dead corn stalks standing over winter (to the delight of the sky larks) then plough in May ready for winter leeks planted in July. We also use clover and trefoil in the paths between courgettes, squash and pumpkins so when the crop finishes at the end of September half the land is already down to clovers effectively achieving 21 months fertility building before the following potato crop.
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