clever crop rotation is practised to break the life cycle of pests and diseases. Slugs
love mulches;- Mulch material can interfere with subsequent land preparation, such as by
obstructing ploughs with long woody stems, if the mulch has not become well
rotten and broken down. The mulch may be so dense that it has to be removed from
the field before land preparation can begin. As a result labour input can be higher
than if the crop residues had been removed after harvest and/or burned; - The material which is suitable for mulch often has other valuable uses, such as for
fuel, construction or animal fodder - particularly valuable in dry regions; - Large and bulky volumes are involved. 20 MT/ha or more may be needed to make
a reasonable job of mulching; - In dry areas the breakdown of mulch into the soil can be very slow.
Mulch as Free Fertiliser
Obtaining the appropriate chemical fertiliser is very often a major problem facing food
producers. Even if it is available close enough to be transported to their farm, they often
do not have enough cash or credit. But there is always the possibility of using mulch as
a source of plant nutrients—ie fertiliser.
On the negative side, the demands on labour may be very high, and there may only
be a relatively small gain of nutrients.
Crop residues such as stems and leaves contain 40–90% of the nutrients which crops
remove from the soil. These residues can contain the equivalent of 50 kg/ha or more of
the major plant nutrients, which can be made available to crops which grow later on in
that field if the crop residues are incorporated into the soil and become broken down.
Living Mulch
As well as using dead or inorganic material the mulch can consist of living, growing
(the tick clovers or beggars weeds) growing under rice can dramatically improve crop
growth and may also lengthen the growth period of crops, for the following reasons:
- soil water is conserved;
- soluble nutrients are “locked up” and not lost by leaching;
- weeds are smothered;
- soil temperature fluctuations are reduced.
Mulch—a Summary
The benefits of mulching are greatest in hot, dry regions, and unfortunately it is these
very regions which have the least amount of available mulching material—and where
there are the most pressing needs for mulch material, stems in particular, to be used as
building material, fuel, animal fodder and so on.
In more humid regions where mulching material is more plentiful, increases in yield
may not be so impressive, but the advantages of mulching the land—such as reducing
water erosion and stifling weed growth—almost always outweigh the consequences of
leaving the land bare and exposed to the elements.
Examples: perennial peanuts (Arachis prostrata) under maize, and Desmodium species
GROWING FOOD – THE FOOD PRODUCTION HANDBOOK 71
plants, when they also act as a cover crop, described on page 63.