PART 17.
Two indigenous crotalarias, C. intermedia and an as yet unnamed
species, have proved most promising. These two species are very
widely distributed, growing at all altitudes from 5,000 to 8,000 feet,
so could be used in all coffee plantations. © As compared to Sunn hemp
both are heavier growers and more suitable for green manuring.
For maize and for wheat the problem would seem to be much
simpler. An unexpected difficulty lies in the selectivity of the ordinary
legumes to environment. For example, a variety of cowpea, that at
an altitude of 5,800 feet, gave a yield of about a ton and a half of dry
matter per acre, at an altitude of 6,600 feet on the same type of soil
grew miserably, even though the plants had formed nodules. It is
this selectivity that complicates the search for leguminous green
manures; a legume may be the best for one altitude and fail at another
not far removed.
The crotalarias, mentioned above, are suitable for a large range
of conditions but very little seed is available; the growing seed forms
the favourite food of the caterpillars of a group of blue butterflies.
Many of the legumes widely used for green manurial purposes are
badly attacked by disease and parasitical plants. Of eight varieties of
cowpeas tried so far, two were sensitive to and completely destroyed
by rust and a leaf disease, three produce much seed but little growth
and thus unsuitable for green manuring, one is chlorotic while two are
just suitable. Velvet beans are attacked by a leaf spot fungus and a
species of Orobanche, besides not growing as strongly as some more
resistant legumes.
Several species of Lupin, Dolichos lablab, Phaseolus inamoenus,
certain species of Crotalaria and a cowpea obtained from the Embu
district are, of the legumes tried, the most suitable. All of these will
do well at altitudes from 4,000 to 6,000 feet, while the first two are
suitable up to 7,500 feet. = While ordinary string and runner beans
and field peas do well at altitudes up to 9,000 feet, search is being
made for a crop that will give heavier growth under these conditions.
Arrangements are being made for the establishment of a group of
trial plots at these greater elevations, those at the lesser have already
been arranged, but it will require a little time before sufficient data
can be obtained upon which to base recommendations.
Any strong growing plant, whether leguminous or not, will serve
for the simple addition of humus to the soil. Certain attributes
beyond mere growth are again necessary for the non-leguminous crop.
The psychology of the farmer must be taken into account. If one of
the ordinary cereals be sown and it promises to give a good crop, it is
certain that it will never be treated as a manure. Many of the less
usual crops, such as mustard, may be used but there is a danger of
such a prolific seeder getting out of hand and becoming a weed. It
is essential that the non-leguminous crop plant should not produce
too valuable a crop, should not be too prolific a seeder, nor its seed
be minute. Another desideratum is that it should grow rapidly and
be capable of smothering weeds. Buckwheat appears to be one of the
most suitable. It grows very rapidly, will smother weeds, occupies
the soil for a short time, its seeds are not minute, and it is easily
controlled.
That the weed problem is one to be considered seriously, is shown
by the condition of some of the fields in the maize area, where quick
seeding weeds. capable -of seeding between the last cultivation the

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