Cover crops and smother crops are commonly used as green manure after they have
served their purpose.
Legumes are the most commonly used green manure crops as they provide the
biggest increase in soil nitrogen.
Examples—Crops used for Green Manure:
atropurpureum), sunflower, sunn hemp (Crotalaria spp.) and velvet beans.
- two or more of these crops, or different varieties of the same crop, are often planted
together. This spreads the risk of one failing and also increases the range of - sometimes these crops are planted together with a food crop, such as siratro with
millet. Siratro can fix Nitrogen, which it passes on to the companion millet.
The mulch is placed on the soil surface where it forms a kind of cover or protection.
Mulching of a soil surface can improve the fertility of the soil, reduce weed growth and
water loss and increase crop yields in almost all farming systems, although the effect is
often more dramatic in dry regions than in humid ones.
The mulch itself can be almost any material, biodegradable or otherwise: crop
residues (stems, leaves, harvested pods etc.), grass cuttings, branches or young trees,
pulled up or hoed weeds, leaves, sawdust and even jute, or plastic sheeting. The
prunings of crops such as bananas, oil palm, tea and coffee can also be used as mulch.
Old carpets work well, on a small scale, if they are made of natural material.
Green manure crops can also act as a mulch. They can be either pulled up, hoed or
cut down and then left on the soil surface to act as the mulch. They can be ploughed in
after some time, and so complete their dual-purpose role of green manure and mulch.
Advantages of Mulch
- The soil is protected—from drying out, and consequent loss by wind erosion, from
heavy rain—and loss by water erosion—and—from high temperatures; - As the mulch rots down into the soil it provides nutrients for subsequent crops;
- More rain water is able to filter into the soil due to reduced evaporation and runoff;
- Weed growth is reduced; this can compensate for the fact that mulching needs more
labour than burning; - The soil retains more moisture because evaporation is reduced;
- It is claimed that nitrogen fixation can be increased by free-living soil bacteria, and
also that the effect of fertilisers can be improved.
Disadvantages of Mulch
- The spread of diseases and/or insect pests can be increased if infected or infested
plants are used as mulch. In theory at least this disadvantage can be eliminated if
Alfalfa, cassia species, clovers, cowpeas, lupin, mustard, rye, siratro (Macroptilium
70 TONY WINCH
e Mulch
benefits.