. [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. 
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