Selection of cover crops
Cover crops are plants which are grown to cover and protect the
soil. They help add fertility, improve soil structure and water retention and
have a lot of practical benefits such as animal fodder, food and added farm
income.
Cover crops can be used in a variety of ways in agricultural
systems:
1. Interplanted or relay-planted
with maize or other grain crops
2. Planted alone in the cropping
cycle
3. Planted under trees in orchards
or plantations
4. Planted as a fallow crop when the
land is being rested
Note: For suggested species suitable to the above
systems (1-4), please refer to accompanying table under systems
applicable.
Cover crops offer farmers the following benefits:
1. Improved soil fertility through the addition of
significant amounts of nutrients (more than 200 kg N/ha)
2. Suppressed weed growth
3. Reduced labor demands in soil preparation and in weeding
4. Reduced cost of inputs such as fertilizers, herbicides and
hired labor
5. Improved soil structure: cover crops can provide up to 30
tons of organic matter per hectare. Improved soil structure means a better
medium for plant growth; in addition, it improves the soil's ability to retain
moisture during dry periods.
6. Soil and water conservation: cover crops help reduce erosion
by protecting the soil surface for extended periods of time.
7. Rehabilitation of degraded marginal lands
8. Additional benefits: human food, animal forage, fuelwood and
an added source of income
There are many plants which can be used for cover crops,
depending on local conditions (rainfall, soils, local farming practices) and the
objectives of farmers. However, most of the cover crops belong to the family of
plants known as Leguminosae (beans).
The following general characteristics are considered important
in selecting plants for use as effective cover crops:
1. Rapid, prolific growth habit
2. Ability to fix significant amounts of nitrogen
3. Tolerance to a wide range of soil conditions (poor fertility,
texture or structural qualities, extremes in pH, etc.)
4. Good drought tolerance. This is an especially important
factor since most of the green manures are grown during the dry season.
5. Seed availability or the ability of the plant to produce its
own seed locally
6. Shade resistance, since cover crops are frequently
interplanted grown in relay with taller grain crops or trees
7. Proven pest resistance
8. Easy to control. Cover crops must be readily removed from the
farm when the time comes for land clearing.
Potential problems with cover crops:
1. Cover crops can be difficult to establish and
farmers often perceive them to require extra work. Some farmers have been
concerned that cover crops might compete with their staple crops.
2. Some cover crop species can be very aggressive and may be
difficult to eliminate from the farm
3. Cover crops can become an alternate host to pests which
attack food crops.
4. Rats and snakes may hide in the dense foliage of cover
crops.
In general, the most popular cover crops are indeterminate
(continuously produce flowers and pods), single-season legume species. However,
perennial species can be of great value under certain circumstances; determinate
bean species and even tuber crops such as camote can be used as effective cover
crops. Some of the cover crops which have been used successfully by farmers are
shown in Table 9.
There are many other species of plants which have been used
traditionally by farmers to serve the same purpose as the above-mentioned cover
crops. Many of them are as yet undocumented. Additionally, there are other
plants which could also be used. Cover crops are gaining attention from farmers
and agricultural scientists and they deserve much more field trials and
research.
TABLE 9. SELECTED COVER CROPS.
