PART II. 
But little is known of the soils derived from the Kapitian and 
Doinyan series. Both are heavy clays and are dark coloured. From 
a cursory examination it would appear that these soils are well supplied 
with organic matter. In the virgin state these soils are apt to crack 
badly but, under cultivation, the soils derived from the Kapitian lavas, 
and probably those of Doinyan origin, improve in condition, they lose 
their compactness and become mellow and friable. Observations on 
these soils under cultivation have not been continued long enough for 
data regarding their behaviour to be obtained. 
The soils of the Rift Valley proper, derived from formations of 
varying age, are very interesting in their behaviour. The area around 
Nakuru has been under cultivation for a sufficient period for 
peculiarities in property to become marked. The soils vary consider- 
ably in character from sandy loams to silts and clay loams. The main 
crop, practically the only crop, has been maize year after year 
continuously.  Ploughing and the various cultivations demanded by 
the growing of maize have been to the same depth season after season. 
In the sandy and silty soils a plough-sole pan has formed, which pan 
is overlain by a structureless soil apt to run into a hard surface after 
rain. The more clayey soils also form a pan but not so markedly as 
the lighter soils nor has the surface soil become broken down; at the 
same time the zone of wetness during which these soils can safely 
be tilled has become considerably reduced. On large farms, where it 
is impossible to complete the ploughing in a few days, this condition 
has made the preparation of a good seed bed extremely difficult, 
clodding has come to be regarded as a necessary evil. 
In the system of farming practised the maize stalks are burnt in 
the field; weeds are likewise burnt. No, or at the best very little, 
organic matter is added to the soil in the form of crop residues with 
the result that the humus content has decreased considerably, leadin 
to loss of structure. A rotation of crops, in which one erop would be 
used as green manure, is required, but, until it can be proved that 
such a rotation does not lead to a monetary loss, not over a period of 
years but over the period of the rotation, it will be extremely difficult 
to persuade farmers to follow a rotation. Another difficulty in this 
area is that pure arable farming only is practised; mixed farming is 
not suited to the conditions. Any minor crop grown in the rotation, 
mn place of maize, would have to be saleable and to produce a nett 
return equal to that from maize. Such a crop is not easy to find; 
experiments are in progress. 
The selection of green manure crops suitable for the two present 
two-staple crops, coffee and maize, are problems that give more 
difficulty than would be expected. For coffee a low growing non- 
climbing plant that can easily be controlled is required. Buckwheat 
is an admirable non-leguminous crop for such purposes; the selection 
of a legume is giving trouble. Sweet clover meets all the require- 
ments, but on the coffee soils it fails, notwithstanding the facet that 
lucerne can be grown successfully. Careful examination of the roots 
of several species of Melilotus has failed to discover any plant carrying 
nodules. The pulse crops producing a heavy growth, such as cowpeas, 
the running beans, varieties of Phaseolus lunatus, ete., are unsuited 
4s green manures for coffee on account of their climbing propensities. 
Search has been made amongst the various erect native legumes 
33