Green Manure

From Antivist

Green manures are crops grown solely for the improvement of the soil. When sown toward the close of the season, either alone or among other crops as these are approaching maturity they are often called cover crops because they are intended to cover the ground during winter and thus prevent loss of plant food through washing over the surface ('sheet erosion') or by seepage to lower levels and drainage. In the latter case they are always plowed under in early spring before they have made much growth. Otherwise they might become woody they might decay slowly and thus, for a time be a detriment to the soil.

Plants used for green manures are of two classes; nitrogen gatherers, those that work over atmospheric nitrogen from the air in the soil, and nitrogen consumers. Those that cannot perform this function. But use what nitrogenous compounds are already in the soil. The former are generally the most important because they increase the supply of this important element of plant growth. The most expensive to buy and the one most easily lost from the soil.

The principal nitrogen gathering crops are clovers, vetches, peas, cowpeas, and soy beans. The consumer crops are buckwheat, rye, cowhorn, common turnips and dwarf essex rape. Often these crops are sown together to perform both functions at the same time. One favorite combination is rye and winter vetch. Another is buckwheat and crimson clover. Sometimes all four are sowed together in July, after an early vegetable crop has been harvested. Buckwheat plants are killed by the first frost, and winter will kill crimson clover. The vegetable matter these crops develop will be just as good as if alive when turned under. Rye and vetch will probably live through the winter, must be dug or plowed under before they get 8" high or the job will be difficult and the effecs may not be as good as if the plants were more succulent.

When fresh or rotted manure is available, it is highly advantageous to apply liberally just before a cover crop or a green manure crop is turned under because the bacteria these contain will help break down the buried plants and thus make their plant food material more quickly available to the succeeding crops.

For best results, the soil temperature should be at least 65 degrees and have moist conditions following plowing under for best decomposition.

Choice of the green manure or cover crop will depend on whether or not an increased supply of nitrates is desired in the soil. For summer sue cowpeas, soy beans, velvet beans, and summer vetch. For fall and winter, use crimson clover, hairy or winter vetch, and Canada field peas.

Sweet clover has notable value as a green manure, especially on heavy soils because of its deep rooting habit and the abundance of its foliage. However if the soil is acid it may fail unless lime or superphosphate is applied shortly before seeding. Also it may fail if 'unscarified' (machine scratched) seed is sown late - after the ground has become dry in spring. Such seed gives best results when sown in late fall or on the snow during winter. In these cases, the plants et an earlier start than the weeds which they choke out. Scarified seed cannot be safely used in this way because it germinates too early.


Mulch is an application of manure, or any other loose material such as leaves spread upon the soil surface to protect the roots of newly planted trees, shrubs, tender plants. Today, it is extended to include earth kept loose by surface tillage to check evaporation.

You can use buckwheat hulls, shredded corn stover, chopped straw, or granulated peat moss. For mulching trees, and berry plants, coarser material may be used - marsh hay, straw, leaves, and corn stalks.

Also used is black paper spread upon the ground between or through which young plants may be grown. It sheds water into the soil, conserves water in the soil by checking evaporation, increases germination, greatly reduce or even eliminate weedings and cultivation, increase soil temperature, hasten maturity, increase yields, and produce larger high quality, and cleaner crops.

Paper should not be used on low value crops. It usually eliminates weeds in the covered area, and thus conserves the moisture and fertility they would use. It also cuts down the cost of cultivation.

Mulching gardens with straw or other litter such as hay or manure is a practical way to increase yields and produce vegetables of the best quality. The benefits are greatest with long-season crops and in dry years. Though straw mulches have increased the yields of nearly all vegetables, their use is not recommended with early short-season crops such as leaf lettuce, peas, spinach, seeded onions, cauliflower, and early cabbage. With root crops such as carrots, beets, and parsnips their use does not appear advantageous and with transplanted onions is of doubtful value. The difficulties of applying straw more than offset the advantage which most of these crops might gain. Straw mulching has been found desirable with all long season crops except sweet corn. Straw should not be applied until the plants are well established. A mulch of 2" to 4" is adequate. Deeper is unnecessary and undesirable.

Between 10 and 15 tons of straw are needed for mulching an acre, or about 500 pounds foro 2,000 square feet.

At the end of the season, straw mulches should be removed and burned because of the unfavorable effect upon the soil when such a large amount of dry organic matter is plowed under. This isi most serious with un-irrigated or sandy soils.

With potatoes, the straw mulch should be applied before the plants come through the soil. With other crops, such as tomatoes, eggplants, and other transplanted vegetables, before transplanting or after the plants are established, preferable at the latter time.

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