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RA 00110.pdf - OAR@ICRISAT

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Table 1. Percentage of cultivated area sown to major crops, as sole crop or in a crop mixture, in three agroclimatic zones of<br />

Burkina Faso, I C R I S A T survey results, 1981.<br />

Zone<br />

Sahel<br />

Sudan<br />

savanna<br />

Northern Guinea<br />

savanna<br />

Crop<br />

Sole<br />

Mixture<br />

Sole<br />

Mixture<br />

Sole<br />

Mixture<br />

Millet<br />

White sorghum<br />

Red sorghum<br />

Maize<br />

Groundnut<br />

Earthpea<br />

Cowpea<br />

Cotton<br />

Other<br />

92<br />

4<br />

-<br />

1<br />

1<br />

-<br />

0<br />

-<br />

1<br />

0<br />

-<br />

-<br />

1<br />

1<br />

-<br />

42<br />

-<br />

1<br />

27<br />

53<br />

4<br />

2<br />

9<br />

2<br />

0<br />

1<br />

2<br />

-1<br />

-<br />

1<br />

-<br />

-<br />

-<br />

60<br />

0<br />

0<br />

13<br />

31<br />

15<br />

4<br />

4<br />

-<br />

0<br />

30<br />

2<br />

0<br />

2<br />

2<br />

12<br />

5<br />

2<br />

20<br />

1<br />

0<br />

1. - = Less than 0.5%.<br />

and 15% in the northern Guinea savanna zones.<br />

Millet is replaced principally by sorghum, which<br />

rises from about 5% in the Sahel to 60% in the Sudan<br />

savanna (the transition zone between millet and<br />

sorghum), and to 45% in the northern Guinean<br />

savanna, where sorghum is a competitive crop with<br />

cotton on similar soil types.<br />

Approximately 60% of the millet area is sown as<br />

an intercrop, most frequently with cowpea as the<br />

secondary component. Cowpea density generally<br />

varies from 1000-5000 plants ha -1 , and millet from<br />

10 000-30 000 plants ha -1 . The intercropping frequency<br />

increases in more arid zones, but with a<br />

decline in the densities of both components. Intercropping<br />

is more important among limited-resource<br />

farmers who are not equipped with animal traction<br />

equipment (as in approximately 85% of the farm<br />

units in Burkina Faso).<br />

Research conducted by the ICRISAT Agronomy<br />

Program in Burkina Faso, has found that although a<br />

cowpea intercrop generally has little effect on millet<br />

grain yields, increased millet density can severely<br />

reduce cowpea grain yields (Stoop 1984a). Whether<br />

there are important differences among millet cultivars<br />

competing with cowpea has not been examined,<br />

but such research on sorghum cultivars has found<br />

highly significant differences among cultivars (Stoop<br />

1984a). If similar differences exist for millet, then<br />

compatibility with a cowpea intercrop would be an<br />

important selection criteria in millet improvement<br />

programs, especially those targeted at limited-resource<br />

farmers in the Sahel and Sudan savanna.<br />

Land Use Patterns<br />

The highly diverse cropping patterns of W A S A T<br />

farmers reflect not only their objective of producing<br />

a varied diet, but also their strategy to exploit soil<br />

microvariability and to reduce risk. Farmers lack the<br />

means to modify land quality by intensive use of<br />

purchased inputs, deep plowing, or irrigation. However,<br />

they match land types to crop requirements to<br />

maximize aggregate productivity and to lower the<br />

risk of year-to-year production variability. Millet is<br />

important in satisfying both these objectives.<br />

Soil microvariability is principally related to distance<br />

from habitation points and toposequence<br />

position. Studies in Burkina Faso (Prudencio 1983)<br />

and elsewhere in West Africa (Norman et al. 1981)<br />

have found that, because of high transport costs,<br />

manure and other organic wastes are concentrated<br />

around habitation points, and their use declines<br />

rapidly with distance from dwellings. Farmers exploit<br />

this fertility gradient by planting crops which they<br />

consider to be the most responsive to enhanced soil<br />

fertility within an intensively cultivated inner management<br />

ring, while planting less responsive crops<br />

on fields at greater distances. Maize and red sorghum<br />

are the crops most frequently concentrated within<br />

the inner management ring, while millet is most<br />

commonly sown on those distant fields which are<br />

least frequently manured (Prudencio 1983).<br />

Exceptions to these general land-use patterns are<br />

imposed by soil quality differences linked to toposequence<br />

position. Fields located on upper slopes tend<br />

235

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