section 3 : Regional examples

Mulching as traditionally applied by small scale coffee growers in Tanzania

C.G.B. Tibanyenda

Directorate of Meteoorology
P.O. Box3056, Dares Salaam, Tanzania

Abstract

Microclimate management of coffee farming by small holders using organic mulching is dealt with. A review of the commonly used mulch — dried grass and sometimes banana leaves, applied to each or alternate inter-row is made. The marked effect on the climate of the soil enables the farmers to practice intercropping with suitable annual crops during the first few years of the coffee plants, and increased coffee yields thereafter. The gains accrued are mainly due to improved soil and water conservation, and addition of organic matter and nutrients. Both the effects and gains are treated qualitatively due to limited availability of figures.

Introduction

The application of mulch in coffee plots by small holders may date back to the time when coffee was first introduced in East Africa by missionaries from Reunion island between 1883 and 18% (Acland 1973). At the time, the advantages of mulching as we know them today were unknown except probably that of weed control (or suppression). The mulch, most commonly used was, and still is, cut wild grass or sorghum trash. Some few small holders however do produce napier grass for this purpose. In this respect, we shall define mulch as covering of the soil surface with cut grass or crop residue.

The use of mulch in coffee farms has been on the increase over the years especially during the first few years after planting. The enthusiasm however has slackened at times during low coffee prices such as the world economic depression of the late 1920's and early 1930's and also the inter-world-war years. Through experience, farmers know the direct relationship between mulching and better yields, although they might not be fully aware of all the beneficial effects that lead to this relationship.

Materials and their method of application by most farmers in Tanzania will be dealt with briefly in this presentation.

Mulching materials

Mulches are generally divided into two categories, organic and inorganic (Davies 1975). Organic mulches include cut grass (wild or grown), straw, non-synthetic cloth, creeping crops, weed and crop residues. Inorganic mulches though not used by farmers in coffee crops are: ash, water, minerals (sand and stones) and synthetic materials such as opaque or transparent plastics (Stigter 1982).

The most common organic mulches used in coffee plots by farmers are cut grass, sorghum and maize trash. Wild grass is conveniently available for use in areas where there is less demand for land. It is cut at the end of the rains, baled and transported to the farms. A limited number of farmers use sown grass such as napier grass. It has a higher bulk than any other grass: up to 173 tons per hectare of green matter from two cuts per year (Acland 1971). Banana leaves, which are within easy reach when banana trees are interplanted with coffee for shade, are also used. Although it lasts longer than a year, this mulch is generally insufficient by itself.

In areas where maize and sorghum are grown for food, their trash is properly utilized for a mulch. They decompose very quickly but are only readily available at the end of the farming season. Other materials are also used if available, but they are in insufficient quantities to be of noticeable value.

Methods of application

The method of application is dependent on the planting pattern, which is usually by rows but is also influenced by the availability of land for other crops. If the same plot is intended for interplanting with other crops such as maize or beans, mulch is applied to the rows leaving the space between the rows for the annual crops. This practice of intercropping is normally carried out during the first few years of the coffee plants, and is stopped after the first coffee harvest when mulch is applied to the whole field except near the stems to enable easy harvesting.

Mulch is also applied to interrows. This is normally the case in areas where there is high infestation of weeds. Intercropping with annual crops then is generally not practiced but interplanting with banana trees is carried out by some farmers. Others apply mulch to alternate tree rows or alternate interrows. With this practice, intercropping with annual crops is easily carried out, although it would seem that such farmers are faced with non-availability of sufficient materials in the first place. With mulch applied to the whole surface, normally no other farming activity except field works is carried out on the farm. The practice of applying mulch to the whole surface can also be observed in areas where the cultivated land is situated on a sloping terrain, in which case mulching is mainly applied to arrest soil erosion.

Time of application

For a traditional farmer, mulching materials are readily available at the end of the rainy season (wild or grown grass) and after harvesting of the annual crops for trash or crop residue. Unless advised otherwise, the practice is to apply mulch at the end of the rains. This practice is beneficial in areas with heavy rains, e.g., the slopes of Mt. Kilimanjaro where amounts greater than 800 mm usually fall in April and May, and mulch only makes the soil too wet if applied before the rains. Where the rainfall is rather low, mulch gives higher yields if it is applied before the rains start (Acland 1971), this encourages maximum water infiltration.

Planting of coffee is normally done at the beginning of the main rains. To prevent soil erosion, mulch is sometimes applied only around the stem of the young coffee plant.

Effects of mulching

Soil moisture

Mulching enhances soil moisture status through improved infiltration and reduction in evaporation, the former being more beneficial than the latter according to Webster and Wilson (1971). It is therefore desirable to apply mulch at the beginning of a rainy season in order to aid infiltration, rather than at the end of the rains when it can only reduce the rate of drying out during the following dry season. Pereira and Jones (1954) showed this to be true on coffee in Kenya (Table 1). In fact, mulching alternate rows before the rains gave better yields than mulching all rows after the rains.

Table 1 Yields of clean coffee (after Pereira and Jones 1954;)

Soil temperature

Mulched soil has lower average temperatures and a restricted diurnal temperature range. This effect is of minor importance under tree crops with heavy shade, but even under cocoa Smith (1954) found that mulching reduced average soil temperature slightly and the diurnal range considerably. The lowering of soil temperature reduces losses due to evapotranspiration.

Erosion and soil characteristics

Mulches protect the soil from wind and hail; and prevent breakdown of soil structure by the impact of rainfall, thus decreasing soil erosion and run-off. They also increase earthworm and termite activity which provides many channels for the percolation of water. Through increased infiltration, leaching is promoted thereby reducing soil salinity in the top layers of the soil in saline areas. Decomposition of mulch organic matter thus improves the soil structure.

Weed control

One of the main beneficial effects of mulching is weed control or suppression. It is particularly important in areas with poor rains, as weeds compete with coffee plants for water and nutrients.

Growth and yields

The outcome of the aforementioned effects of mulching together with a few minor ones, combine to give higher yields of the coffee crop. Pereira (1954) quotes field trials in Kenya with large yield increases when an organic mulch was applied before the rains, while Robinson (1964), found that a single annual application of trash mulch to coffee at 18 kg per tree significantly increased yield. High yields are not only realized in coffee but also the annuals (maize and beans) intercropped with it. Better yields of the annual crops, especially beans of the determinate-landraces variety, are realized from nearly-decomposed mulch applied to the surface before it is renewed.

The downward growth of tap roots and the development of the root system as a whole for coffee is increased by mulching (Bull 1963).

Limitations

If the mulching material is to be obtained from grown grass, then land is required for this purpose. This might prove difficult and expensive in areas with high demand for land. Also a lot of labour is involved in cutting and carrying the material from outside the plantation. To a smallholder, it might not be worth the trouble unless the crop sells at a relatively high price especially if the mulch decomposes rapidly.

Concluding remarks

In the tropics, the usual limiting factor for plant growth is moisture. The traditional farmer depends entirely on rainfall as a source of moisture in all agricultural activities. One can say crudely that the more the rainfall the better the yields. However, from time to time, particularly in the recent past, frequent droughts of varying degrees have been experienced in the tropics. This has made it absolutely necessary for the farmer to get the best out of the little rainfall. Incorporating mulching in the farming habits should definitely be encouraged in these areas to maximize the available moisture.

The difficulty with which mulching materials are obtained increases day after day. Firstly, there is no more free land where farmers can go and get wild grass at no expense. Secondly, due to high competition for land and expanding agriculture, proper planning of one's plot is required in order to be able to grow grass for mulching. It is therefore imperative that proper advice is available on the best type of grass to grow to economize on the land, taking into account the yield of mulch and the rapidity with which it decomposes.

References

Acland, J.D. 1971. East African crops. London: Longman.

Bull, RA. 1963. Effects of mulching and irrigation on some East African coffee soils. Turrialba, 13. (Review article)

Davies, J.W. 1975. Mulching effects on plant climate and yield. Technical Note No. 136 (WMO - No.388) Geneva 92 pp.

Hurst, G.W, and R.P. Runney. 1971. Protection of plants against adverse weather. WMO Technical Note No. 118 (WMO-No. 281). Geneva: World Meteorological Organization.

Pereira, B.C. and P.A. Jones. 1984. Field responces by Kenya coffee to fertilizers, manures and mulches. J. Exp. Agric. 22: 23-36.

Stigter, C J. 1983. Mulching as a traditional method of microclimate management. Nat. Agromet Committee of Tanzania, Newsletter No.9. Dar-es-Salaam: Directorate of Meteorology.

 Webster, C.C. and P.N. Wilson. 1971. Agriculture in the tropics. London: Longman.