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Soil tillage in Africa:
needs and challenges

FAO SOILS BULLETIN 69

Soil Resources, Management and Conservation Service
Land and Water Development Division, FAO
Food and Agriculture Organization of the United Nations

Editing, design, graphics and desktop publishing:
Editorial Group,
FAO Information Division

The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.

M-51
ISBN 92-5-103442-7

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying or otherwise, without the prior permission of the copyright owner. Applications for such permission, with a statement of the purpose and extent of the reproduction, should be addressed to the Director, Information Division, Food and Agriculture Organization of the United Nations, Viale delle Terme di Caracalla, 00100 Rome, Italy.

©FAO 1993

ACKNOWLEDGEMENTS

The Food and Agriculture Organization of the United Nations is greatly indebted to the Director-General of the International Institute for Tropical Agriculture (IITA), Dr. Lucas Brader, for hosting the FAO Tillage Training Course, some of the papers of which are presented in this publication.

Sincere gratitude is expressed to Dr. J. Gulley, Dr. B.T. Kang and Mr. D. Couper of IITA who assisted with various lectures and conducted field demonstrations. Special thanks go to Prof. J. Morin, Prof. P. Aina, Prof. Agboola, Dr. O. Opara-Nadi and Dr. Elwell for their contributions. Much of the general information in Zimbabwe was obtained from Moyo et al. (1991). Grateful thanks are due to G.J. Oliver and J. Hagmann for contributing photographs and to the support of GTZ in preparing this document. The assistance of Mr. J.M. Hodgson in editing the manuscript is gratefully acknowledged.

Preface

Chapter 1 Rainfall runoff management techniques for erosion control and soil moisture conservation

Chapter 2 Potential for sustainable agroforestry and alley farming in tropical Africa

Chapter 3 Runoff control by basin tillage techniques

INFILTRATION IMPROVEMENT

CONCLUSIONS

Chapter 4 Rainfall analyses for tillage management decisions

Chapter 5 Soil crusting and sealing

Chapter 6 Major soils for food production in Africa

MAJOR SOILS GROUPS AND THEIR CONSTRAINTS ON FOOD PRODUCTION

CONCLUSIONS

Chapter 7 The challenge of tillage development in African agriculture

Chapter 8 Conservation tillage for increased crop production

Chapter 9 Soil crusting and sealing in West Africa and possible approaches to improved management

Chapter 10 Development and adoption of conservation tillage practices in Zimbabwe

APPENDIX 1 PRELIMINARY RECOMMENDATIONS FROM IAE/GTZ CONTILL PROJECT ON FIELD APPLICATIONS OF CONSERVATION TILLAGE SYSTEMS

References

List of figures

1.	Influence of cover crops in infiltration rate
2.	Agroforestry pathways for shifting cultivation intensification
3.	Average runoff percentage from field plot experiments in northern Cameroon, May-September 1989
4.	Rain end runoff analysis, Mokyo 28 July 1988. Rain and infiltration intensity
5.	Daily rainfall and runoff for the Northern Cameroon Region (1988) as calculated for the highest storms and for given storage and infiltration
6.	Rainstorm chart for Ruhama Station (Israel), 19.12.1985
7.	Rainstorm analysis, Ruhama, 19.12.1985
8.	Rainstorm analysis, Moyko Station, 11.08.1988
9.	Infiltration rate of two soils at various prewetting conditions
10.	Soil moisture profiles before and after a simulated rainstorm
11.	Infiltration rates in a Luvisol as measured by rainfall simulator
12.	Rain and runoff analysis, Gudula, 28.08.1990
13.	Highest I₃₀ intensities 1958-1986 Yavne Station (Nov., Dec. and January)
14.	Highest I₃₀ intensities 1958-1986 Yavne Station (Feb., March and April
15.	Maximum daily runoff depth for given infiltration rates and surface storage Partial series for January, Yavne Station (1958-1986)
16.	Effect of electrolyte concentration on the infiltration rate of a loess soil at two ESP levels
17.	Infiltration rate as a function of cumulative rain depth for loess soil exposed to drops of two sizes (d = 2.5 and 3.4 mm) falling from various heights (h = 0.4, 1.0, 2.0, 6.0 m)
18.	Infiltration rate as a function of accumulated momentum for loess soil exposed to drops of two sizes (d = 2.5 and 3.4 mm) falling from various heights (h = 0.4, 1.0, 2.0, 6.0 m)
19.	Final infiltrationr ates (FIR) as a function of drop impact momentum per unit mass for loess soil exposed to drops of two sizes (d = 2.5 and 3.4 mm) falling from various heights
20.	Possible arrangements of plate-shaped clay particles
21.	Diagrammatic sketch of the structure of kaolinite
22.	Diagrammatic sketch of the structure of smectite
23.	Flocculation values as a function of the sodium adsorption ratio
24.	Range of soil texture in which hardsetting is likely to be encountered in relation to clay mineralogy
25.	Distribution of soil in tropical Africa
26.	Final infiltration rates of stable, dispersive and smectitic soils
27.	Runoff from field plot experiments in northern Cameroon, May-September 1989)
28.	Effect of type of cultivation on infiltrationr ates in a Vertisol (seedbed prepared for wheat)
29.	Infiltration rates in loess and Vertisol soils as a function of accumulated rainfall (aggregate size 0-8 mm)
30.	Rain and runoff analysis for different amounts of surface storage
31.	Major soila ssociations
32.	Effects of mechanized tillage operations on maize grain yield after 12 consecutive crops of maize
33.	Cassava yields in different tillage systems
34.	Ambivalent relationships between time-sequence crust forming and water erosion
35.	Types of soil crusts in a sorghum field
36.	Cumulative rainfall versus rainfall depth as measured under rainfall simulation in northern Niger

List of tables

1.	Effects of methods of deforestation and post-clearing management on erosion and runoff
2.	Residue mulch effect on runoff and soil erosion
3.	Effects of tillage system on soil loss and runoff in Ghana
4.	Soil loss and runoff from plots and watersheds under different management systems
5.	Common agroforestry systems in the tropics
6.	Potential woody species for alley farming in lowland humid and sub-humid tropics
7.	Biomass and nutrient yields of woody species from five prunings of hedgerows, Ibadan, southwestern Nigeria
8.	Effect of six years of alley farming on properties of surface soil, runoff, soil loss and maize yield on a Luvisol with 7% slope
9.	Nitrogen yield from hedgerow prunings during one maize crop. N uptake by the alley farmed maize and estimated N gain from hedgerows to the system
10.	Grain yields of main season maize in maize-cowpea rotation grown on a sandy Apomu soil in alley farming with Leucaena at Ibadan, Nigeria, from 1979-1988
11.	Kinetic energy and number of drops for rainfall of various intensities
12.	Some physical, mineralogical and chemical properties of the dominant soils of northern Cameroon
13.	Physical, chemical and mineralogical properties of 19 soils from South Africa
14.	Effect of tillage system on profile water content to a depth of 1 m at 2 weeks after planting
15.	Effect of tillage on crop yields in the West African semi-arid tropics
16.	Effect of cropping sequence and residue management on cowpea reproductive physiology and grain yield in the Sudan Savannah of Burkina Faso
17.	Effect of different tillage treatments on sorghum grain yield, runoff and soil loss, Luvisol (ICRISAT Centre 1983-1987)
18.	Effects of tillage systems on soil loss and runoff in Ghana (1976)
19.	Soil loss for three tillage systems on a Luvisol, Chagnaramas, Venezuela
20.	Effect of tillage on maximum soil temperature at 5 cm depth under different crops two weeks after planting (1 May 1973)
21.	Effect of tillage on soil moisture retention at 0-10 cm depth under different crops two weeks after planting
22.	Net gain in soil water during fallow with clean and stubble mulch tillage at seven Central Plains locations (USA)
23.	Effect of tillage practices on water use, maize yield and water-use efficiency (early season)
24.	Effects of mechanized tillage methods on soil chemical properties 6 years after imposing the tillage treatments
25.	Effects of tillage methods on crop yield on an acid soil in Liberia
26.	Tillage effects on water storage, sorghum grain yields and water-use efficiency in an irrigated winter wheat-fallow-dryland-grain sorghum cropping system, Bushland, Texas (USA)
27.	Effect of tillage methods on average soil water storage during fallow after irrigated winter wheat and on subsequent rainfed grain sorghum yields, total water use and water-use efficiency at Bushland, Texas, USA
28.	Effect of no-till and conventional till on the yield of maize, soybean, sorghum and groundnut
29.	Effect of nitrogen and tillage on sorghum flag leaf area
30.	Influence of surface conditions on hydrologic parameters on a dry soil in northern Burkina Faso (organic matter: clay 0.3%; clay: 7%; silt: 4%; sand: 89%)
31.	Tentative correlation between susceptibility to soil crusting and certain soil groupings in West Africa
32.	General distribution of soil crusting and related aspects in West Africa
33.	Typical annual losses of soil, rainfall and nutrients for maize lands
34.	Soil losses on well-drained granitic sand on a 6% slope
35.	Mean organic carbon and water-stable aggregate levels as influenced by tillage treatment
36.	Mean organic carbon, water-stable aggregate and yield levels as influenced by minimym tillage treatment
37.	Mean organic carbon, water-stable aggregate and yield levels of zero and conventional tillage on paired trials (all residues returned)

List of plates

1.	Areal basins (diguettes). Cameroon 1989
2.	Scanning electron micrograph of 8-5ìm size fraction of Georgia kaolin
3.	Scanning electron micrograph of A: N-montmorillonite from Wyoming, showing typical expanded, flared texture; B: Ca-montmorillonite from Arizona, showing typical tightly woven flakes
4.	Scanning electron micrograph of illitic shale from Montana, showing relatively large flat-lying illite plates with curled edges
5.	Vertical cracking formed in soils rich in swelling clays
6.	Compact surface horizon of a Planosol, northern Cameroon, near Marua airport
7.	Structural crust, slaking type, developed on a _mound_ in a clay loamy soil in northern Niger under simulated rainfall
8.	Structural crust, two-layered sieving type, developed in a sandy soil in southern Côte d'Ivoire
9.	Structural crust, three-layered sieving type, in Central Burkina Faso
10.	Pavement crust, Yatenga region, Burkina Faso
11.	Erosion crust capping a barren patch in northern Cameroon
12.	Still depositional crust near Niamey, Niger
13.	Overland flow on sandy soils caused by soil crusts in Yatenga Region, Burkina Faso
14.	Poor stand of pearl millet near Niamey, Niger
15.	Soil crusted spots in an oil-palm plantation in southern Côte d'Ivoire
16.	' Sahelization ' of a Sudanian land in Central Burkina Faso
17.	Gravel mulch on a mound cropped with yam and maize, northern Côte d'Ivoire
18.	Beneficial aspects of dibbling: the runoff depositional crust which caps the hope is readily disrupted by pearl mullet seedlings, northern Burkina Faso
19.	Stone contour lines, Ader Doutchi, Central Niger
20.	Contour hedgerow (Andropogon gayanus), Yatenga region, Burkina Faso
21.	Straw mulch on yam mounds in northern Côte d'Ivoire
22.	Mulch of branches to rehabilitate a barren and crusted patch, Yatenga region, Burkina Faso
23.	The same spot as in Plate 22 after one year
24.	Traditional seed-bed preparation with excavations containing manure and debris, near Mopti, Mali
25.	Ridges accumulate water and collapse under high rainfall intensity (120 mm h^-1) produced by a Swanson-type rainfall simulator, southern Niger
26.	Traditional shifting cultivation
27.	Contrast in vegetation between high population density communal land and low density commercial farms
28.	Rill erosion down to the plough panin shallow ploughing
29.	Ox-ploughing with single furrow mouldboard plouch
30.	Disc harrowing to prepare seedbed tilth
31.	Air photo view of contour layouts in communal lands
32.	Up-and-down slope operations destroying contour ridges on a commercial tobacco farm
33.	Conventional tie-ridging on Phyllite soils
34.	No-till tied-ridging on AGRITEX/GTZ Contill Project
35.	Crop ridges on contour without ties
36.	Fine tilth after disc harrowing
37.	Wheel-track planted maize
38.	Rip and disc tillage
39.	Tine-planted maize land
40.	No-till strip-cropping: maize and soybean strips
41.	Direct drilling of soybeans into wheat stover
42.	Winged ripper for deep subsoiling
43.	Ox-drawn light cultivator
44.	Chopping residues prior to planting
45.	Tractor-mounted chisel tines
46.	Cage roller mounted behind coilshank spring tines
47.	Rip on row planter
48.	Disc harrow shaking wheat through residue
49.	Ridging with high wing ridger body
50.	Ox-drawn disc ridger with tie-maker attached
51.	Ox-drawn disc-plough tie-maker
52.	Light cultivator with tie-maker mounted
53.	Ox-drawn ripper tine
54.	Hand-operated blade weeder

TABLE OF CONTENTS