Green manures



Green manures have been used for thousands of years for mainly vegetable crops; it is a way of replenishing organic matter into the soil, especially soils that have been impoverished by chemical fertilization. It is a sustainable enrichment of soil by incorporating un-decomposed green plant material for the benefit of the soil. You dig it in and let the roots, stems, and leaves decay there.

Some green manures have very deep roots, which reach down into the subsoil and pull up nutrients that would not otherwise be available to most garden plants. The above ground portion of a green manure crop covers the soil, protecting it from erosion and compaction due to heavy rains.

These rapidly growing plants also shade the gro und, which suppresses the growth of winter weeds. Other green manures are nitrogen-fixers. This means that certain bacteria colonize within the plants roots. These microbes have the ability to pull nitrogen out of the air and convert it into a form that they (and your plants) can use:

Increase soil fertility Increase biological activity Nourish subsequent crops Reduce soil erosion Reduce nitrate losses Weed suppressant Soil structure improvement

The Annual Lupin is extensively used as a green manure crop as is Crimson Clover (Trigonella foenum graecum) and Mustard (Sinapsis alba). These will add organic matter to improve the soil as they rot down. One key ingredient in green manure is a legume, which fix nitrogen into the soil. This is a good practise especially in soil where hungry feeders have been grown. When choosing a green manure, look for a plant that germinates easily in your soil and grows quickly, covering the ground. Some manure crops are planted in autumn and turned under in the spring, giving you organic matter quickly. Others grow from spring to spring, giving long-term erosion control.

However, green manure does not give quick results as it is slow to activate - and the reason why it is not often used in ordinary home gardens. It usually takes at the very least six months for the vegetation waste to rot down. When crops are dug into the land in a fresh condition, the soil organisms have to get to work on the green plants and break them down. In doing so they starve the land of nitrogen during the time the waste is being broken down. Therefore green manure method is generally applied on land that is to have a season of rest. There are other factors, which come into play in order that the best results are achieved from green manure. The land should be properly drained so that sufficient air is present; it should be adequately limed so that it is not acid, and the soil should be warm.