Organic matter is essential for plantain cultivation . External sources of mulch can consist of elephant grass (Pennisetum purpureum), which is rich in potassium, or cassava peelings, wood shavings, palm bunch refuse, dried weeds, kitchen refuse, and so on. Collecting and transporting mulch are expensive in time and labor. The most convenient source consists of plants growing inside the plantain fields if they produce a great deal of organic matter without competing with the plantains.
Suitable mulch material can be obtained from trees which were slashed when the fields were cleared and which are growing again; or from a deep-rooted legume shrub called Flemingia congesta or F. macrophylla. F. congesta is seed drilled in the middle of the 3 m plantain alley. It can be difficult to establish, but from the second year onwards it grows vigorously. It can reach a height of approximately 2.5 to 3 m if left unpruned, but in the field it is cut back 4 times a year to a height of about 1.5 m.
The pruning’s are spread over the soil. Flemingia is not fertilized as it benefits from fixed nitrogen and leached fertilizers applied to the plantains. Grass growing between the plantains is not suitable as a mulch source because it competes with the plantains.
Organic matter is essential for plantain cultivation if the field is to be very productive for a long time. A high level of organic matter in the soil is beneficial because it stimulates root development, improves soil drainage, de- creases soil temperature fluctuations, and increases soil porosity and biological life.
Organic matter decays under the influence of microorganisms in the soil, heavy rainfall and high soil temperature. The amount of organic matter will gradually decrease once the field has been cleared and cause a decrease in yield. Therefore newly established plantains which receive only fertilizer will produce a high yield only in the first year. In the second year the yield will drop because the organic matter will have decomposed.
To compensate for this continuous decrease in the amount of organic matter, the field needs mulch from plants and/or manure from animals. There are many sources of mulch. It can be either carried into the field or produced between the plants; but to be effective, it should cover the soil completely. Once the field is mulched, weeds are controlled and the topsoil is protected against heavy rainfall and intense sun- shine. Poultry, pigs and cows produce suitable manure which is applied only at the base of the mat.