I worked for a few years in Northern Cameroon. There are no commercial
soil test labs in that area. I do not believe it would currently be
economically feasible for farmers to send soil samples to any labs within
the region. In addition, to most subsistence farmers in the savannah
region (and the vast majority of farmers are at the subsistance level),
money is almost a non-existant commodity.
To understand why farmers use chemical inputs, like fertilizers, it is
important to try and understand the crop growing/marketing systems which
exist in the region. When a farmer grows a cash crop (cotton, for example)
the state company in charge of that crop supplies the farmer with chemicals
(fertilizers and sprays), seed, and some technical assistance. When it is
time for the farmer to sell the crop he/she must sell to the company. The
price of advanced purchases is subtracted from the market value of the
crop. There is very little choice in this marketing system.
Regarding compost, mulch, and manure - basically, there are no "left-overs"
in cropping systems in the savannah region. Plant material is either used
as a human or animal food source (i.e., young legume leaves are cooked in
sauces, plant material after harvest is fed as hay) or used in contruction
(sorgum, millet and corn stalks are used for fences and reinforcing huts).
Manure is gathered and used for fuel. Literally, nothing is left in a
field after harvest.
In much of the savannah region, the non-cropping season is too dry to grow
any field crops. So a green manure crop grown during the off-season simply
does not work. And I can not see the possibility of a farmer growing a
crop during the cropping season simply to plow it down. Life is lived too
much from season to season. The more critical situation is how to live
from one year to the next without consuming next years seed.
Also, even though occupations tend to be defined by tribes (Fulani are
herders, Mafa are farmers), there is co-existance between the tribes on the
same soil. This means the herders keep out of the fields until after
harvest. At that time, the herds move in and eat any crop remains. Meat,
milk, and blood is then available on the local market.
These are all my impressions of how life is lived on the savannah of
Northern Cameroon. It has been a few years since I was there, but the
images are certainly etched very clearly in my mind. Thank you for
bringing them to the forefront again.
**********************************************************************
>>I read with great interest in what you wrote about developing nations.
>>I have some questions that I hope are not too stupid. I am trying to
>>learn more about the soil and soils quality in different regions. If
>>these farmers are planting in savannah, isn't the soil quality fairly
>>high in fertility? Why, instead of using chemical fertilizers, can't some
>>inexpensive soil testing be done, and more natural methods of retaining
>>soil quality, such as the use of compost and mulches be used? If they are
>>clearing 10-20 ha, are they raising any livestock on this land. What is
>>being doine with all the animal manure, plus all the cleared *debris*
>>(for lack of a better word)? There is some pretty marginal land in the US
>>that is managed for gardens year after rear, by the above methods.
>>
>>My lack of knowledge may be very evident with these questions. I feel
>>that the way livestock is being raised here leaves a lot to be desired,
>>and hate to see our less than sustainable methods being exported
>>exclusively to third world nations. If you have any books or other
>>references that you would recommend I read, please tell me. I guess I
>>mainly don't understand why these people would be having to abandon their
>>land after three years from lack of fertility, when there is knowledge
>>that I would think would prevent that.
>>
>>Thank you for your time and expertise.
>>
>>Ann Wells, DVM
>>
>>
>
>The Savannas of West and Central Africa are largely characterized by soils
>with low cation exchange capacity, due to coarse texture in many places and
>a clay fraction dominated by kaolinite, which is considered a low activitit=
y
>clay. There are exceptions, of course, such as the more fertile loess soil=
s
>of Northern Nigeria. That means that the soil is able to hold a limited
>amount of nutrients relative to more fertile soils. Hence organic matter
>plays a very crucial role in plant nutrition since it also is a store of
>nutrients and in low CEC soils, comprises a large percentage of exchange
>capacity. During the cropping phase, tillage results in a rapid breakdown
>of organic matter through microbial action. This benefits the first crops,
>which are able to utilize the nutrients released from this decomposition.
>But with successive seasons the organic matter and thus nutrients in the
>soil decline and crop productivity declines as well. Once the land is
>abandoned to natural fallow, the organic matter is restored with the natura=
l
>vegetation.
>
>Your question about compost and mulches is very pertinent, because they can
>be used to maintain productivity. The problem is where to obtain sufficien=
t
>quantity of organic matter to accomplish this on a field scale.
>Undoubtedly, better use could be made of the organic resources they have,
>but for most crop farmers, this would not serve for much beyond the kitchen
>gardens. You have to understand that in much of sub-Saharan Africa, you do
>not have mixed livestock/crop farming, like we know it in Europe and North
>America. Traditionally, livestock and crop farming tend to be separated
>along ethnic lines, with tribes such as the Fulani and Massai living as
>herdmen concentrating on cattle rearing, while other groups being sedentary
>crop farmers. Although Africa is changing, the distinctions generally hold=
.
>Crop farmers often have a few small livestock, such as chickens and goats,
>but these roam freely or are tethered in the field, so that collection of
>manure is not convenient, and at any rate would not be sufficient to sustai=
n
>production.
>
>The Western solution to restoring organic matter was to introduce leguminou=
s
>cover crops as green manures. That has generally not been adopted by
>low-resource farmers. Farmers generally are not willing to plant a crop
>simply to restore the soil, with no other benefit. To me, it makes sense
>that so long as they don't have traction and must rely on manual labor for
>tillage it will not be an option. Recently, there has been some interest i=
n
>the slash mulch, a modified cover crop system with velvet bean that has bee=
n
>developed in Central America. Velvet bean is an annual legume which
>produces a lot of N-rich vegetation. The problem is that velvet bean can
>become a very competitive weed and may not fit in cropping systems where
>there are two crops a year.
>
>One of the most promising alternatives is alley cropping, where fast-growin=
g
>leguminous trees are planted in rows about 4-5 meters apart and are pruned
>regularly to provide nitrogen rich mulch for crops which are grown between
>the rows of trees. There has been a lot of research on this during the las=
t
>10 years and most of it has been positive. One of the first trials was
>established in 1978 in Nigeria and continues to support a crop of maize and
>a crop of cowpeas each year. It is still in the testing phase on farm in
>Africa and adoption is limited. It is being adopted by some farmers in
>Haiti and apparently in the Philippines and Indonesia. Although there are
>some problems to work out, I believe that it is one of the most promising
>alternatives for sustaining crop yields of low resource farmers.
>
>
>References on tropical soils:
>
>Sanchez, P.A. 1976. Properties and Management of Soils of the Tropics.
>Wiley-Interscience, NY.
>
>Kowal, J.M. and A.K. Kassam. 1978. Agricultural Ecology of Savanna: A
>study of West Africa. Clarendon Press, Oxford.
>
>Jones, M.J. and A. Wild. Soils of the West African Savanna. Commonwealth
>Agricultural Bureau, Commonwealth Bureau of Soils Tech. Comm. No. 55
>Dennis A. Shannon
>Department of Agronomy and Soils
>202 Funchess Hall
>Auburn University, Alabama 36849-5412
>
>Telephone: 334-844-3963
>Facsimile: 334-844-3945
>
>E-mail: dshannon@ag.auburn.edu
Carol A. Miles, Ph.D.
Washington State University
Extension Agricultural Systems
360 NW North Street
Chehalis, WA 98532
PHONE 360-740-1295 FAX 360-740-1475
milesc@wsu.edu