Green manures and cover crops

 Vegetable fertilizers are crops that are not intended for sale; rather they serve to protect and to amend the soil. It is mainly grasses and legumes that are incorporated into the soil after having been mown to increase fertility. The basic idea of ​​the fertilizing action of green manure is as follows:


Many legumes (beans, peas, soybeans, alfalfa, clover, etc.) have the extraordinary ability to capture (fix) nitrogen in the air and bring it back to the ground. When such a culture is incorporated into the garden, a new supply of nitrogen becomes available for other crops. When cereals (oats, rye, wheat, etc.) are mixed with legumes, crop residues provide not only nitrogen but also carbonaceous organic matter. Green manure can therefore be considered as an amendment to the same as compost and manure.


The important advantage of vegetable fertilizers is that the raw material that sett to manufacture the amendment is on-site and requires no other handling than sowing, crushing, and incorporating the crop into the soil. The disadvantage is that green manure occupies the space of a paying culture during its growth, which can vary from six weeks to a full season, depending on the species chosen. To this, it is often necessary to add two weeks of latency after burying to allow microorganisms to properly decompose the fertilizer green and make nitrogen available to plants.


Inorganic market gardening, the fertilization of crops with green manure is very recommended. It is an economical and efficient way to apply nitrogen to the field, especially if it is compared to one that involves large amounts of compost and manure over a large area. It is also a way to fertilize your crops with nitrogen without adding phosphorus. However, the use of green manures to fertilize small surfaces is far from being ideal. The succession of crops leaves little time to their establishment and the idea of ​​leaving several plots fallow is contrary to optimal use of a cultivated surface. Without a grinder, their Burying with the tiller is also very problematic.


That said, we still use legumes and grasses in our gardens, and this, pom different reasons, but rather we call them "Cover crops". This is how we integrate the benefits of their use in our intensive production system.


Add nitrogen as a supplement

Although we value more compost crop fertilization in our gardens, we do not give up the idea of ​​benefiting from the action fertilizer of legumes. For us, the challenge is to find "holes" in crop planning that would allow us to plant a fertilizer green before a crop (what is called a "fertilizer stealthy green ”). Fertilizing legumes that we prefer are the feed peas and the common vetch. In both cases, we mix them with oats so that they stick to them. and are supplemented during growth.


To benefit from the fertilizing action of green manure of legumes, it is necessary to take into account the following two aspects:


~ First, the best time to bury its green manure is just before its flowering. This is when the plant has stored its maximum nitrogen and that the contribution to the ground is the most significant. Of more, at this stage, the green manure is still young and tender, which facilitates and accelerates its composition for the next crop.


~ Second, be aware that legumes do not automatically fix nitrogen. air. These are bacteria of the genus "rhizobium" which form nodules on the roots of plants and which allow this exchange to take place. On the other hand, it is possible that these bacteria are not present in soils where legumes do not have pushed for some time. In all the case, it is a good business to inoculate his seeds with the right rhizobia. To ensure that the rhizobia fix as much nitrogen as possible, the seeds must be of each species of legumes receive their inoculant. It is simply a small powder that is mixed with seeds with water. Make sure you use products that meet the standards of organic certification.


Add organic matter

As I just mentioned, it is advantageous to incorporate green manure into the soil when it is still young and green. In doing so, little remains a residual organic matter in the soil after decomposition.


To obtain a good quantity of organic matter from green manure, it is necessary to incorporate in the soil mature and very fibrous plants which will be fairly resistant to decomposition. Dense fall rye or a sorghum hybrid are two good examples. Such cultures produce a lot of biomass and the work of drilling that their roots allow is very positive for a soil structure. On the other hand, you should know that to break down such fertilizers green, microorganisms will need nitrogen, which they will draw from the ground. The strategy of using green manure to incorporate a large amount of carbon residue can therefore cause a decrease in nitrogen available for the next crop.


In our gardens, we mainly rely on compost (a compost rich in moss peat) to add organic matter to the ground. The only green manures that are tough enough to add organic matter to our soil significantly are those we sow in the end seasonal, to cover the ground before winter.