Proceedings of the South & East African combined agricultural, cotton, entomological and mycological conference held at Nairobi, August, 1926

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Monograph

Identifikator:: 1738588467

URN:: urn:nbn:de:zbw-retromon-115043

Document type:: Monograph

Title:: Proceedings of the South & East African combined agricultural, cotton, entomological and mycological conference held at Nairobi, August, 1926

Place of publication:: Nairobi

Publisher:: East African Standard

Year of publication:: 1926

Scope:: VI, 337 Seiten; Ill.

Digitisation:: 2020

Collection:: Economics Books

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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part II. Agriculture

Collection:: Economics Books

. [PART 11, The coffee plantations are mainly situated on the soils derived from the Laikipian lavas. These have weathered into steeply sloped ridges upon which coffee has been planted. On such slopes the possibility of surface erosion is evident; however, in newly established plantations the danger is small. The soil possesses a wonderful crumb structure, which allows water to be absorbed most freely. Practically no water collects on the surface and, thus, there is practically no run off to cause wash. Unless kept cleanly cultivated coffee plantations are very readily overgrown by weeds. The continuous clean cultivation demanded breaks down the erumbs to a fine condition, rather like that of fine sand, which does not allow of rapid absorption of water. Surface water collects and wash becomes alarming. It is of interest to note that, in native shambas, even though the slope may, and often is, greater than in most coffee shambas, the wash is negligible. ~~ Under native agriculture, the soil is forced to carry more than one crop; maize is inter-planted with pulse crops, sweet potatoes, and other low growing crops. Continuous cultivation is impossible and the mechanical destruction of the crumbs does not occur. Instead of removing or burning the crop residues, the greater part is dug into the soil, maintaining the supply of humus, which being freshly produced, re-cements the soil particles, encouraging the regeneration of the crumbs. In order to prevent wash on newly prepared slopes, stops of grass or rushes are placed across the slope. A system of green manuring, primitive it is true, is practised, the plant being a lush growing labiate. These native methods of agriculture are not possible in coffee plantations or on other European farms. The intermingling of crops is not an economical practice. Other means of preventing wash have to be employed. The commonest of the methods consists in cultivating roughly along the contour lines so as to form shallow terraces on which the coffee grows, and in the planting of low growing plants as hedges across the slope. Neither of these methods can restore to the soil its highly absorbent nature, upon which the complete prevention of wash depends. The regeneration of the crumb structure is essential. The cementing colloids in the Laikipian soils are ferric hydroxide and ferric humate. The first acts as a permanent cement and is probably derived from the latter. The particles are tenaciously cemented together, but when broken apart the re-cementation by ferric hydroxide per se is a very slow process. Humic acid, capable of forming ferric humate, is necessary to bring about the regeneration of the crumbs. Under the continuous cultivation the soils receive the aeration is most thorough; the greater part of the humus capable of reacting with the iron compounds of the soil has been oxidised and lost to the soil. The cultivations, necessary to keep the plantations free from weeds, at the same time are rapidly decreasing the water absorbing powers of the soil. It is essential, if wash is to be properly prevented, and the absorbent qualities improved, that organic manures, which will provide the fresh reacting humus. be used in conjunction with contour cultivation. Another factor, that seems connected with the continuous cultivation in coffee plantations, is a decrease in the water retaining power. Soils that carried a heavy virgin growth of forest, now, under coffee, are unable to meet the water requirements of the crop. What the cause for this decrease may be is at present a matter of mere conjecture, and will early be made the subject of investigation. 29

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