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Grain Legumes and Green Manures for Soil Fertility in ... - cimmyt

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Table 3. Effect of <strong>for</strong>age legumes on soil organic carbon content (%)<br />

at Wedza <strong>and</strong> Buhera<br />

Treatments <strong>Soil</strong> organic carbon content (%)<br />

Natural Region II Natural Region IH<br />

Natural Region IV<br />

Maize 0.47 0.38 0.24 <br />

Maize/Cowpea 0.50 0.36 0.38 <br />

Maize/velvet bean 0.52 0.28 0.40 <br />

Maize/Lablab 0.41 0.37 0.25 <br />

Cowpea 0.43 0.28 0.67 <br />

Velvet bean 0.39 0.30 0.29 <br />

Lablab 0.56 0.31 0.42 <br />

Ley 0.48 0.51 0.28 <br />

Mean 0.47 0.35 0.35<br />

LSD (P < 0.05) n.s n.s ns<br />

n.s. - no significant differences among treatments.<br />

yield benefits. Monocropp<strong>in</strong>g of maize promotes<br />

unsusta<strong>in</strong>able crop yields as revealed by lower<br />

maize yields. Ley gave significant residual N benefits<br />

especially <strong>in</strong> lower ra<strong>in</strong>fall zones. Sole cropp<strong>in</strong>g<br />

<strong>and</strong> <strong>in</strong>tercropp<strong>in</strong>g had similar effects on soil organic<br />

C build up. Residual soil P differed significantly between<br />

treatments <strong>in</strong> the higher ra<strong>in</strong>fall region <strong>and</strong><br />

seemed to depend on the dem<strong>and</strong> of the crop comb<strong>in</strong>ations<br />

previously grown.<br />

Acknowledgements<br />

The authors are very grateful to the Biotechnology<br />

Trust of Zimbabwe (BTZ) <strong>for</strong> fund<strong>in</strong>g the research<br />

work upon which this paper is based on. There is<br />

also need to mention the co-operation of SPRL technical<br />

<strong>and</strong> field staff <strong>for</strong> the fieldwork a!1d soil analysis.<br />

We also acknowledge the ef<strong>for</strong>ts of extension<br />

officers <strong>and</strong> farmers <strong>in</strong> the participat<strong>in</strong>g wards.<br />

References<br />

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Table 4. Effect of <strong>for</strong>age legumes on available soil P205 content at<br />

Wedza <strong>and</strong> Buhera sites<br />

Treatments<br />

Available soil Pcontent (ppm)<br />

Natural Region II Natural Region III Natural Region IV<br />

Maize 7.13 9.14 8.30 <br />

Maize/cowpea 23.9 19.6 10.9 <br />

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Lablab 8.51 13.6 8.94 <br />

Ley 9.16 , 16.0 14.0 <br />

Mean 11.9 14.3 10.0 <br />

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168<br />

<strong>Gra<strong>in</strong></strong> legumes <strong>and</strong> <strong>Green</strong> <strong>Manures</strong> <strong>for</strong> <strong>Soil</strong> <strong>Fertility</strong> <strong>in</strong> Southern Africe

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