The paper reviews and highlights some of the major conservation tillage practices in southern and eastern Africa. Various constraints are cited contributing to low adoption. Most tillage operations in the region are done manually due to poor mechanisation and lack of draft power and therefore labour is a serious constraint with most farmers being subsistent. As a result weed control which accounts for more than 60 % of labour input in wholly manual production systems is often a major factor contributing to low yields in general and a deterrent to the use of conservation tillage systems. Other important adoption factors include access to credit, management capabilities, land tenure systems the availability to farmers of technical information and the transfer strategies.

Some of the promising technologies in each respective country are tabled and a more elaborate description of the Zimbabwean experiences is given. In this regard conservation technologies are now being promoted as a range of options to suit farmers of a diverse resource endowment and the use of the participatory technology development and extension approach is seen as the best tool to forge the way forward.

1. Introduction

Conservation Tillage is generally defined as any tillage sequence the object of which is to minimise or reduce the loss of soil and water; operationally a tillage or tillage and planting combination which leaves at least 30 % or more mulch or crop residue cover on the surface (SSSA, 1987). In Zimbabwe in particular and the region in general, this term has been loosely used to refer to any tillage system whose objective is to conserve or reduce soil, water and nutrient loss or which reduces draught power input requirements for crop production. It is in this context that the term is used in this paper.

The value of conservation tillage practices in sustaining or increasing crop productivity through conservation of soil, water, nutrients and/ or draught power is well recognised in the region (Elwell, 1993; Oldrieve, 1989; Oldrieve, 1993; Russel, 1996; Vogel et al., 1994). However the use and adoption of conservation tillage systems in the eastern and southern African region is still very low compared to other continents such as South America, North America and Europe due to various constraints.

This paper reviews progress and experiences in the development of conservation tillage systems in the region and identifies some of the major inhibiting factors.

The southern and eastern African Region includes countries such as South Africa, Zimbabwe, Namibia, Botswana, Lesotho, Swaziland, Mozambique Malawi, Zambia, Kenya, Uganda and Tanzania and this paper focuses on experiences from some of these countries.

Most of these countries are tropical with climates described as sub-humid to semi-arid (Barrow, 1987). Rainfall patterns are mostly uni-modal (Southern Africa) with rainy seasons starting from Oct/Nov to March/ April and bi-modal (Kenya, Uganda). Rainfall in the region is often erratic and undependable and seasons are generally characterised by frequent droughts. In general the continent of Africa suffers the most droughts compared to any other continent in the world (table 1). Whilst the total mean annual seasonal rainfall may be adequate for most crops its distribution has been clearly demonstrated to be more important (Willcocks and Twomlow, 1990).

Soils are quite diverse in nature ranging from the dense luvisols of Botswana with high bulk densities to the self loosening vertisols found in south-eastern Zimbabwe, Malawi, Tanzania and Zambia (Willcocks and Twomlow, 1991). Predominant cropping problems include high salinity and sodicity, surface sealing particularly in Namibia, low organic carbon levels, high erodibility, acidity or low pH for example in Zimbabwe (Nyamangara and Mpofu, 1996) and generally low inherent fertility (Thompson and Purves, 1978). Due to the nature of the soils and steep slopes, the soils have a moderate to high risk of erosion (Sant’Anna, 1993; Whitlow, 1988). Land degradation through soil erosion and other forms of land mismanagement is rampant and further threatens the agricultural productivity of most of these countries.

The majority of the populations in these countries are rural based and depend on subsistence and dry-land agriculture for their living (for example Malawi 90 %, Botswana 76 %, Kenya 85 %, Zimbabwe 70-80 %).

Table1: Proportion of land whose agricultural productivity is limited by drought.

Source: (Barrow, 1987)

The above facts namely frequent droughts, poor soils, high erosion risk and high dependence on subsistence farming make it imperative for countries in this region to adopt soil and water management as well as cultural practices that can buffer and mitigate the effects of droughts. One such approach identified to alleviate these problems is the use of conservation tillage systems. Whilst the potential of conservation tillage systems in sustaining agricultural productivity has been realised in most of these countries adoption by farmers of this region has generally been very limited by various constraining factors.

2. Constraints to Adoption of Conservation Tillage

2.1. Low Degree of Mechanisation

Most field operations particularly by small-holder farmers are performed manually thereby limiting the area cultivated per person (Figure 1). In comparison with other developing countries Sub-Saharan Africa ranks the lowest compared to China and India in terms of access to draught power sources such as oxen and tractors (Figure 1 c, d, e). It also ranks lowest in terms of irrigation development and fertiliser use (Figure1 f). The fact that most operations are performed by hand limits the extent to which farmers can adopt certain conservation tillage practices as draught power or mechanisation is almost always a requirement.

Table 2 highlights the distribution of sources of power for primary land preparation for some SADC countries. In terms of development of mechanised power sources South Africa (70%), Zimbabwe (55 %) and Botswana (40 %) are the most developed in this regard due largely to the extent of commercialisation of agriculture in these countries.

Table 2: Sources of power for primary land preparation in 5 SADC countries

Source : Ellis-Jones, 1997

Thus the development of mechanical power has been associated with scales of production associated with the colonial history of the respective countries. The use of draft animals is confined to the small-holder farming sector with Botswana (40 %) and Zimbabwe (30%) ranking the highest Mwinjilo (1992) states that virtually all cultivation is done by hand-hoes in Malawi with only 4.9 % of the farmers owning draft animals.

The adoption of conservation tillage systems is related to the resource ownership of the farmers particularly draught power. In Zimbabwe for instance it is estimated that 5-10 % of the commercial farms are under conservation tillage whilst the use of conservation tillage in the small-holder farming sector is estimated to be below 1%. Furthermore socio-economic surveys in the small-holder farming sector in a high potential region of Zimbabwe revealed that farmers participating in the development of a conservation tillage technique, no-till tied ridging, were better resourced and owned more draft power than their non-participating counterparts (Nyagumbo,1992).

2.2 Implements

The availability of implements in most countries in the region has also contributed appreciably to the relatively low adoption of conservation tillage systems. This is because farmers lack the means to acquire these implements or the institutional set-up has not enabled farmers to access these implements. In most of the countries in the region the most commonly available implement is the plough which in Zambia, Botswana, Malawi and Tanzania is imported from Zimbabwe. Over 80 % of the farmers in Zimbabwe own single furrow mouldboard ploughs while ridgers are owned by 2-5 % (Nyagumbo, 1992; Ellis -Jones 1997). The ripper tine was also found to be owned by less than 5 % of farmers in a high potential region in Zimbabwe ( Nyagumbo,1992). The ridgers and ripper tines are key implements for the type of conservation tillage systems promoted in Zimbabwe.

Thus most of the small-holder farmers in the region suffer from the problem of lack of appropriate implements coupled with limited access to draught power.

2.3 Access to Credit

A limited access to credit for these farmers to acquire relevant inputs has also curtailed the potential of conservation tillage systems. The communal tenure systems inherited from the colonial past, which are prevalent across, preclude farmers from securing loans as they have no collateral security which is a prerequisite accessing credit from financial institutions.

2.4 Weed Control

The control of weeds under conservation tillage systems also poses a major threat to the use of conservation tillage systems in the region. Ellis-Jones and Mudhara (1997) found in Zimbabwe, that the system used by farmers depends on resources that they have available to them and established that households with 3 adult equivalents, working 6 hours a day have sufficient labour for 1.1 ha where operations were fully manual with no access to draught power; 4.0 ha where the mouldboard plough was used as the basic implement but with some draught power limitation and 7.4 ha a range of animal drawn implements were available and access to draft power was unlimited.

Riches et al., 1997 working at Makoholi Experiment Station also found that the weeding effort which accounted for more than 60 % of the labour used for maize production in semi-arid Zimbabwe, was greatly eased while grain yields and return to weeding labour significantly improved where animal drawn implements such as cultivators and ploughs were used to control weeds. The efficiency of weed control was also found to greatly improve where farmers used re-ridging with the plough as a weed control measure under no-till tied ridging in the sub-humid north of Zimbabwe (Nyagumbo, 1993). Complimentary work by Shumba et al. (1992) showed that the use of the ripper tine for primary land preparation allowed for timely planting but resulted in earlier and heavier weed infestations. Thus unless effective weed control can be achieved the benefits of timely planting accrued using the ripper tine are lost.

The relatively higher adoption of conservation tillage in the large scale commercial farming sectors of Zimbabwe, Zambia and South Africa could therefore be attributed to the availability of suitable machinery and the use of herbicides which have tended to be unaffordable to small-holder farmers in Zimbabwe.

2.5 Farmer Management Capabilities

The management levels associated with conservation tillage systems is a lot higher and this has tended to contribute towards low adoption. Small-holder farmers own less than 5 ha of land in most countries in the region and because of this they do not want to risk crop failure by using technologies they are unfamiliar with considering their labour and resource limitations.

In general the above are the major factors contributing to low adoption of conservation tillage in the region. However developments on conservation tillage together with other soil and water conservation techniques in some of the countries in the region are outlined in the next section.
 
  (a) Distribution of Farm power sources in Sub-Saharan Africa

(b) Comparison of extent and utilisation of power in Sub-Saharan Africa and Asia

( c ) Cultivated area per worker

(d) Cultivated area (ha) per draught oxen

(e) Cultivated area (ha) per tractor

(f) Fertiliser use and extend of irrigation

Source : Adapted from (FAO., 1987) and Ellis-Jones, 1997).
Figure 1. Distribution of farm power sources in Sub-Saharan Africa and the extent and utilisation of hand, animal draught and tractors in Sub-Saharan Africa and Asia.
 

3. Some Regional Experiences with Conservation

Zambia

Zambia suffers from widespread land degradation mainly through soil erosion. Currently practised soil conservation measures include contour ridges, grass strips, crop rotations and ploughing across the main slopes. However as suggested by Mukanda (1993) the lack of effective law enforcement laws after independence led to a complete collapse and a abandonment of conservation measures particularly by small-holder farmers. The traditional CHITEMENE system of shifting cultivation is also thought to have contributed to accelerated rates of soil erosion due to shorter fallow periods and longer cropping cycles caused by increased population pressures (Mukanda, 1993). Some research work on tied ridging has been undertaken at Lusitu Research station with some encouraging results.

The use of conservation tillage systems in Zambia has mainly been spearheaded in the last 3 years by efforts of the Zambia National Farmers Union (ZNFU) Conservation Farming Unit in the southern province of Mazabuka as reported by Aagaard and Gibson, (1996). These efforts were initiated following recurrent droughts in 1992/3 and 1994/5 which caused crop failures, devastated cattle herds and led to hunger and famine in the worst hit areas of the Zambezi valley. Small holder farmers abandoned their farms in search of casual work on commercial farms while commercial farmers endured escalating recurrent costs and low profitability. Links with Hinton Estates in Zimbabwe culminated with ten commercial farmers establishing 20 - 70 ha under conservation tillage with encouraging results. Since December 1995 the Conservation Farming unit was established to promote conservation tillage in both large and small scale farming sectors. Some work on the promotion of various animal drawn rippers which have been extensively tested with farmers through extension brochures (Stevens, 1998) is in progress through a programme known as Smallholder Agricultural Mechanisation Promotions (SAMeP).

Botswana

In Botswana some tillage research has been undertaken since the 1970s. However up to the present the most common form of tillage practice is mouldboard ploughing carried out on the day of planting. More recent research on different tillage methods (Persaud et al.,1990) recommends two methods namely double ploughing i.e. spring ploughing followed by another ploughing at planting and spring ploughing followed by tine cultivations at planting. Some work was also carried out on strip tillage on sandy loam soils and shallow tillage or herbicides on vertisols as reported by Willcocks and Twomlow (1991).

Malawi

In Malawi the ridging constructed by hand-hoes is the most common practice used by about 95 % of the small holder farmers (Mwinjilo,1992). Zero tillage or no-till are not used at all due to cost of herbicides and lack of draught and labour resources (Kumwenda, 1990). Some effort is being made to reduce labour requirements for construction of ridges by the use permanent ridges as compared to annual ones. Other forms of conservation practices include maize-legume inter-crops and rotations.

Tanzania

In the southern highlands of Tanzania 95 % of the farm sizes are less than 5 ha and land preparation is mostly manual (Ley, 1990). Antapa and Mwakosya (1994) report of serious land degradation problems in large scale commercial wheat farms in northern Tanzania (approx 28 000 ha).

Soil & water conservation technologies now being implemented to combat this problem include:

• Contour grass strips

• absorption channel terraces (2-3 m wide; 0% grade for maximum water retention

• Graded channel terraces (0.3-0.4 % grade for safe water disposal

• Broad based terraces (~ 10 m ; cultivated and allow machinery passage)

In addition to these structures conservation tillage systems are in use with implements capable of retaining 70 % crop residues on the surface after a tillage operation. Weed control is achieved with the use of herbicides such as round-up. Problems cited include lack of appropriate machinery, experience and grazing of stover by livestock.

Traditional techniques locally developed in the southern highlands of Tanzania and suitable for use on steep slopes include the Matengo pit or Ngoros ( a series of pits 2.4 m long x 2.1 m wide x 0.14 -0.30 m deep) and the Matuta ridge systems (vegetation slashed and aligned across the hillsides and buried with soil thrown down-slope (Temu and Bisanda, 1996; Twomlow, 1998). These techniques have shown immense benefits in terms of soil and moisture conservation for crops as well as fertility improvements.

Kenya

The traditional conservation technique is the fanya juu. In a recent study on traditional techniques mobile trash lines at 15 and 7.5 m spacings significantly out-yielded ( maize & cow pea ) and reduced soil loss and run—off levels compared to the control (Okuba et al., 1998). The use of these trash lines in combination with static structure such as fanya juus and stone bunds is recommended.

The Zimbabwean Experience

In Zimbabwe considerable efforts has been made towards the development of conservation tillage systems. The agricultural sector is divided into two main sectors that is the large scale commercial sector and the small-holder farming sector. Small-holder farms (freehold tenure) occupy about 42 % of all land in Zimbabwe with over 90 % of them lying in the semi-arid and low potential Natural regions III, IV and V (CSO, 1987). Most of the prime agricultural land (Natural Regions I & II) is occupied by commercial farms. The average arable land size in communal areas is 3 ha (Elliot, 1989; Ellis-Jones, 1997; Lacher and Dikito, 1991; Nyagumbo, 1992; Shumba, 1984), hence the demand for more arable land . Labour during peak seasonal periods is also a serious constraint as there are on average only 2-3 permanent persons per household (Elliot 1989, Nyagumbo 1992). Due to these and other constraints highlighted earlier the use of conservation tillage techniques is estimated to be below 1 % in the small-holder sector and between 5 -10 % in the large scale commercial sector.

The history of conservation in Zimbabwe dates back to the colonial period during which a strong law enforcement machinery was in place to enforce the construction of contour ridges (channel terraces). No arable land could be opened up without these structures in place. Various other laws prohibiting stream bank cultivation, the use of vleis, sledges etc. were also effected. The enforcement of these laws relaxed after independence (1980) particularly the maintenance of contour ridges which were resented by farmers due to their high labour demand and colonial connotations. As result sheet and rill erosion is now rampant in most small-holder farming areas today with estimates of soil loss over 50 t/ha /annum (Elwell and Stocking, 1988). Studies by Whitlow (1988) have characterised most small-holder farming areas as severe to very severely eroded. Land degradation in the small-holder farming areas poses a major threat to crop productivity. The mouldboard ploughing system, promoted by Alvord since the 1930s now further worsened by shallow ploughing due lack of adequate draught power is major contributor to sheet erosion losses. On the commercial scale escalating costs of diesel fuel and other production costs have called for increased attention to conservation tillage systems. This realisation has led to development of conservation tillage systems to combat this problem by various institutions since the 1980s.

Some of the key institutions carrying out this research work include:

• Chiredzi Research Station (Semi-arid regions, development of water harvesting techniques for small-holder farmers)
• Kadoma Cotton Research Institute (commodity based research on tillage techniques for cotton for small farmers)
• Institute of Agricultural Engineering (Conservation Tillage Programme)

(research and development of sustainable conservation tillage systems for and with farmers in the sub-humid and semi-arid regions)

• Hinton Estate
• Art Farm (Research on conservation tillage systems for commercial farmers)

From these institutions some promising conservation tillage techniques have been evaluated (Oldreive 1989; Oldreive 1993; Mashavira, 1997; Vogel 1993; Vogel et al. 1994; Nyagumbo 1993; Nyamudeza and Nyakatawa 1995). These include the following:

• no-till tied ridging
• mulch ripping
• no till strip cropping
• clean ripping
• hand-hoeing or zero till
• tied furrows (for semi-arid regions)
• open plough furrow planting followed by mid season tied ridging

 These are used in combination with mechanical structures such as

• Graded contour ridges
• Dead level contour ridges with cross-ties (mainly for semi-arid regions)
• Infiltration pits dug at intervals along contour ridge channels
• fanya juus (for water retention in semi-arid regions)
• Vetiver strips
• Broad based contour ridges ( mainly used on commercial farms).

Soil loss measurements on-station (slope 4.5 %, test crop: maize) by the Conservation Tillage Programme (CONTILL) at Domboshawa Training Centre and at Makoholi Experiment Station gave the results presented in Figure 2. The soils on these stations are generally shallow sands with less than 10 % clay and organic carbon levels below 1%. The results generally show effectiveness of the tested conservation tillage techniques against sheet erosion particularly no-till tied ridging and mulch ripping. On both stations a dramatic increase in soil loss levels was observed under the conventional tillage system after 4 cropping season probably indicating declining soil organic carbon below some threshold value below which soil erodibility abruptly increases. Since the season 1993/4 (fifth cropping season) conventional tillage system has consistently given the lowest maize yields at Domboshawa compared to other tillage systems (Figure 2 c) but with a somewhat erratic performance at Makoholi (Figure 2d). From these and other results mulch ripping and tied ridging are considered as the most sustainable tillage techniques. The reader is referred to reports by Cuma and Hagmann(1995); Munyati (1997); Vogel (1993); and Vogel et al. (1994) for detailed descriptions of some of the work on these sites.

Figure 2 (next page): Effects of 4 conservation tillage systems on cumulative seasonal soil loss (t/ha) and maize grain yields (t/ha) at Domboshawa Contill site (sub-humid north ) and at Makoholi Experiment Station (semi-arid south). Treatments: CT(Conventional Tillage mouldboard ploughing); CR (clean ripping or ripping without residues); TR (no-till tied ridging) ; MR (Mulch ripping or ripping into residues); HH ( hand hoeing) .

(a) Cumulative Soil loss (t/ha) at Domboshawa for 9 seasons

(b) Cumulative soil loss (t/ha) at Makoholi for 9 seasons

(c) Comparison of maize grain yields at Domboshawa for 10 seasons


(d) Comparison maize grain yields at Makoholi for 9 seasons.

Table 3: Seed Cotton yield (kg/ha) responses to five tillage systems over five season at ITAFA farm, Kadoma, Zimbabwe.  Source: Mashavira et al.,1997) 

Complimentary work by the Cotton Research Institute with tractor drawn implements has also shown ridges outperforming other tillage systems in terms of seed cotton yields (table 3) but weed densities prior to the first weeding exceed those of the conventional ploughing system (Mashavira et al., 1997). On-station work on tied furrows at Chiredzi Research Station also showed superiority of these in terms of moisture conservation (Nyamudeza and Nyakatawa, 1995).

Whilst the performance of some of these techniques as measured on research stations their performance on-farm has tended to be erratic and site specific varying depending on season characteristics, soils, farmer management capabilities etc. Table 4 shows typical yields from the sub-humid north obtained from farmer managed adaptive trials. Across -site ANOVA on the 1992/3 yield results (Nyagumbo, 1993) showed a significant treatment X Farmer interaction leading to the conclusion that the performance of the tied ridging system was strongly dependent on farmer circumstances i.e. (management, rainfall, soil type and resources ). Similar results from work in Masvingo (Chuma and Hagmann, 1993), led to the conclusion that there was no scope for giving blanket recommendations to farmers on no till tied ridging.

Transfer Strategies

Years of on-farm research work with small-holder farmers have yielded no appreciable adoption of these technologies by farmers due to the factors highlighted earlier. However from the conclusions arrived at in the latter paragraph, transfer strategies particularly the traditional top-down approach extensively used by the local extension service AGRITEX, was identified as one of the key factors hampering adoption. Cook book solutions were being resented by farmers with only certain aspects of recommended technologies being taken up by farmers. This realisation led to the development of various farmer participatory technology development and extension strategies as the best approaches for technology transfer through farmer experimentation (Hagmann et al., 1996a; Hagmann et al., 1996b; Nyagumbo, 1997).

A farmer participatory research and extension approach known as Kuturaya (lets try) was initiated and developed in Masvingo in Chivi district Hagmann et al., 1996a). This approach involved the development of a research and extension approach which recognises farmer’s views and aspirations. Farmers are taken as partners and equals in research and takes farmers indigenous technical knowledge as the basis for innovation development. Farmers are exposed to various technological options which they can experiment on and implement according their own resource endowments and preferences. Annual evaluations are carried out together with farmers where farmers play a leading role. Due to the success of this approach farmers have embarked on various innovations which they try to test on their own.

The use of this approach, ratified by a technical workshop in Masvingo in 1995 (Twomlow et al., 1995), has resulted in the identification and recognition of farmer innovations, for example the widespread use of infiltration pit originates from a farmer in Zvishavane (Maseko, 1995). Most local institutions including NGOs have now adopted the participatory approach as a tool for implementation in various small-holder projects.

Current initiatives

Another constraint and recommendation identified during the Masvingo (1995) workshop (Twomlow et al., 1995) was the unavailability of technical information on the promising technologies and the need to develop reference material for extensionists, technocrats and farmers. The development of these materials is being facilitated by the Integrated Rural Development Programme (IRDEP) in Masvingo (material for technocrats and extensionists) and (DFID) the United Kingdom Department for International Development (material for farmers) together with other local and international stakeholders. Final draft copies of this material are due to be ready by September 1998.

Other complementary current new initiatives include:

• The Indigenous Soil & Water Conservation Project (Phase 2) dubbed (ISWC2) co-ordinated by the Institute of Environmental Studies, University of Zimbabwe is aimed at further strengthening and developing indigenous local farmer knowledge and innovations through joint experimentation with farmers. This project comes as a result of another phase (ISWC1) in which current and indigenous soil & water conservation practices in Africa were identified and documented as reported by (Reij et al., 1996).
• Farmer participatory development of sustainable soil &water management techniques in the small-holder farming sector of Zimbabwe. This project is a joint effort by the Department of Agricultural technical and Extension Services (AGRITEX) and the Department of Research and Specialist Services (DR&SS) and is to be funded by the Agricultural Services Management Programme (ASMP). Project aims at focusing on conservation technologies from a catchment perspective and intends to engage in participatory experimentation with soil and water management technologies for both uplands and vleis.
• Care International working on a catchment perspective for the rehabilitation of small dam catchments.

Generally efforts on soil and water conservation in Zimbabwe are now not only focused on the use of conservation tillage alone but rather in combination with some of the mechanical barriers highlighted earlier.

4. Conclusions

The natural climatic and physical environment in southern and eastern Africa characterised by frequent droughts, poor soils and high soil erosion losses, calls for the use of appropriate soil and water conservation strategies including conservation tillage systems that optimise and sustain crop production and at the same time mitigate the negative effects of frequent droughts.

Adoption of conservation tillage systems in Southern and Eastern Africa is still very low due to several constraining factors including lack of adequate draught and implements, low mechanisation levels, limited access to credit and insecure land tenure systems (small-holder farmers), weed control problems and generally lack of technical information and in appropriate technology transfer strategies.

In Zimbabwe various technologies have been developed by researchers but more still needs to be done in terms of utilisation of these technologies. Participatory technology development and extension with farmers is probably the only way forward.

There is also need to address the effectiveness of support services such as implement manufacture, credit and market infrastructure as well as accessibility to draught power sources.

5. Acknowledgements

Acknowledgements go to Mr T.T. Mashavira, Cotton Research Institute and Dr Steve Twomlow, Silsoe Research Institute for editing the technical content of this paper. Special thanks also goes to Mr Nehanda, Soil & Water Conservation Branch, AGRITEX for his valuable comments.

6. References

Aagaard, and Gibson, D., 1996: "ZNFU Conservation Farming Unit Mission to Zimbabwe: Recommendations for the establishment of a Zimbabwe Conservation Farming Unit," Rep. No. Draft report. World Bank, Harare.

Antapa, P. L., and Mwakosya, G. M., 1994:. Land degradation experiences from the Hanang Wheat Farms, Hanang, northern Tanzania. In "Proceedings of the 5th annual Scientific conference: SADC Land & water Management Research Programme" (C. Lungu, ed.), pp. 198-220. October 1998, SACCAR, Harare,Zimbabwe.

Barrow, C., ed., 1987: "Factors affecting tropical agricultural development,", pp.. 1-3-55. Longman Scientific & Technical, Longman Group UK Limited, Date ,Essex.

Chuma, E., and Hagmann, J., 1995: Summary of results from on-station and on-farm testing and development of conservation tillage systems in semi-arid Masvingo. In "Soil & Water Conservation for small-holder farmers in Zimbabwe: tansfers between research and extension." (S. J. Twomlow, J. Ellis-Jones, J. Hagmann and H. Loos, eds.), pp. 41-60. 3-7 April 1995, Belmont Press, Masvingo,, Masvingo, Zimbabwe.

CSO, 1987: " Statistical Yearbook of Zimbabwe 1987,". Central Statistical Office, Harare, Zimbabwe.

Elliot, K., 1989: Draught power shortage in the small scale farming sectors of Zimbabwe: Background, workshop objectives and strategy formulation. In "Proc of a workshop on animal draught and tractor power use in the small scale farming sector of Zimbabwe: Strategy Formulation to reduce draught power shortage". 25-28 th September 1989, AGRITEX/IAE, Harare, Zimbabwe.

Ellis-Jones, J., 1997: A farming systems approach to increasing the productivity of draught animals. In "Improving the Productivity of Draught Animals in Sub-Saharan Africa" (J. Ellis-Jones, A. Pearson, D. O'Neill and L. Ndlovu, eds.). 25-27 February 1997, UZ, AGRITEX, DR&SS, CVTM , SRI., Institute of Agricultural Engineering, Hatcliffe, Harare, Zimbabwe.

Ellis-Jones, J., and Mudhara, M., 1997: Conservation tillage for resource poor farmers: the critical importance of farm power. In "Proceedings of 14th ISTRO Conference: Agro-ecological and economical aspects of soil tillage". 27 July - 1 August 1997, Pulaway, Poland.

Elwell, H. A., 1993: Development and adoption of conservation tillage practices in Zimbabwe. In "FAO Soils Bulletin", Vol. 69, pp. Chapter 10; 129-164. Food and Agriculture Organisation of the United Nations, Rome.

Elwell, H. A., and Stocking, M., 1988: Loss of soil nutrients by sheet erosion is a major hidden farming cost. Zimbabwe Science News 22, 7/8, ., 1988.

FAO., 1987: Africa Agriculture: The next 25 years. . Food and Agriculture Organisation, Rome.

Hagmann, J., Chuma, E., and Murwira, K., 1996a. Kuturaya (let's try): Reviving farmers knowledge and Confidence through Experimentation. In "Farmer's research in Practice" (ILEIA, ed.).

Hagmann, J., Murwira, K., and Chuma, E., 1996b: Learning together: Development and Extension of Soil & Water Conservation in Zimbabwe. Quarterly J. of International Agriculture 35, 2, 142-162., April-June 1996.

Kumwenda, W. F., 1990: Tillage and water management on Small rainfed farms of Malawi. In "Proceedings of the 1st annual Scientific Conference" (M. Kronen, ed.), pp. 251-256. 8-10 October 1990, SADCC Land & Water Management Research Programme, Gaborone, Botswana.

Lacher, C., and Dikito, M. S., 1991: "Socio-economic Survey with specific considerations of gender issues in Gutu District Communal Lands.,". Co-ordinated Agricultural Rural Development, Masvingo, Zimbabwe.

Ley, G. T., 1990: Tillage and water management in southern highlands of Tanzania. In "Proceedings of the 1st Annual Scientific Conference: SADCC Land & Water management Research Programme" (M. Kronen, ed.), pp. 225-232. 8-10 October 1990, Saccar, Gaborone, Botswana.

Maseko, P., 1995: Soil & Water conservation for small-holder farmers in semi-arid Zimbabwe. In "Proceedings of a technical workshop, Soil & Water conservation for smallholder farmers in semi-arid Zimbabwe-transfers between research and extension." (S. J. Twomlow, J. Ellis-Jones, J. Hagmann and H. Loos, eds.). 3-7 April 1995, Belmont Press, Masvingo, Zimbabwe.

Mashavira, T. T., Dhliwayo, H. H., Mazike, P. S., and Twomlow, S. J., 1997: Agronomic consequences of reduced tillage. In "Improving the Productivity of Draught Animals in Sub-Saharan Africa" (J. Ellis-Jones, A. Pearson, D. O'Neill and L. Ndlovu, eds.). 25-27 February 1997, UZ, AGRITEX, DR&SS, CVTM, SRI,, Institute of Agricultural Engineering, Hatcliffe, Harare, Zimbabwe.

Mukanda, N., 1993: The conservation and rehabilitation of the soil resources of Zambia. In "Proceedings. of the 4th.Annual. Scientific. Conference" (M. Kronen, ed.), pp. 396-407. 11-14 October 1993, Sadc Land and Water Management Research Programme, Saccar, P.Bag 00108, Gaborone, Botswana, Windhoek, Namibia.

Munyati, M., 1997: Conservation tillage for sustainable crop production: Results from on-station and on-farm research in Natural Region II ( 1988 - 96). The Zimbabwe Science News 31, 2, 27-33., April/June 1997.

Mwinjilo, M. L., 1992: Animal traction technology in Malawi: potential and constraints. In "Animal Traction Network for Eastern &Southern Africa (ATNESA)" (P. Starkey, E. Mwenya and J. Stares, eds.). 18-23 January 1992, CTA,GTZ, Lusaka, Zambia.

Nyagumbo, I., 1992: The influence of socio-economic factors on potential adoption of no-till tied ridging in four communal areas of Zimbabwe. In " Proceedings of the 3rd annual Scientific Conference" (M. Kronen, ed.), pp. 319-329. 5-7 th October 1992, SADC Land and Water Management Research Programme, Harare, Zimbabwe.

Nyagumbo, I., 1993: Part II: Farmer Participatory Research in Conservation Tillage: Practical Experiences with no-till tied ridging in Communal Areas lying in the Sub-humid north of Zimbabwe. In "Proceedings. of the 4th.Annual. Scientific. Conference" (M. Kronen, ed.), pp. 236-249. 11-14 October 1993, Sadc Land and Water Management Research Programme, Saccar, P.Bag 00108, Gaborone, Botswana, Windhoek, Namibia.

Nyagumbo, I., 1997: Socio-cultural constraints to small-holder farming development projects in Zimbabwe: A review of experiences from farmer participatory research in conservation tillage. The Zimbabwe Science News 31, 2, 42-48., April/June 1997.

Nyamangara, J., and Mpofu, S. E., 1996: Soil pH and lime requirement for high potential communal areas of Zimbabwe. Journal of Applied Science in Southern Africa 2, 2, 77-81., .

Nyamudeza, P., and Nyakatawa, E. Z., 1995: The effect of sowing crops in furrowsof tied ridges on soil water & crop yield in Natural Region V of Zimbabwe. In "Proceedings of a technical workshop, Soil & Water conservation for smallholder farmers in semi-arid Zimbabwe-transfers between research and extension." (S. J. Twomlow, J. Ellis-Jones, J. Hagmann and H. Loos, eds.). 3-7 April 1995, Belmont Press, Masvingo, Zimbabwe.

Okoba, B., Twomlow, S. J., and Mugo, C., 1998: evaluation of indigenous soil and water conservation technologies for run-off and soil loss control in semi-arid Mbeere District, Kenya. In "Proceeding of a DFID Land Management Workshop "Modern Methods from Traditional Soil & Water Conservation Technologies"" (S. Briggs, J. Ellis-Jones and S. J. Twomlow, eds.). 13-15 January 1998, White Horse Inn, Kabale, Uganda.

Oldrieve, B., 1989: Conservation Tillage in Action. In "Conservation Tillage: A handbook for Commercial Farmers in Zimbabwe" (M. Vowles, ed.). Commercial Grain Producers Association.

Oldrieve, B., 1993: "Conservation Farming for communal , small scale, resettlement and co-operative farmers of Zimbabwe: A farm Management Handbook.," Prestige Business Services (Pvt) Ltd.

Persaud, N., Monageng, K., McPherson, A., Molapong, K., Tilahun, B., and Williams, L., 1990: Conservation tillage and Fertilizer Practices for dryland Cereal Production in Eastern Botswana. In "Proceedings of the 1st annual Scientific Conference" (M. Kronen, ed.), pp. 215-224. 8-10 October 1990, SADCC Land & Water Management Research Programme, Gaborone, Botswana.

Reij, C., Scoones, I., and Toulmin, C., eds., 1996: "Sustaining the Soil: Indeginous Soil & Water Conservation in Africa.," 1/Ed. Earthscan Publications Ltd., London, UK.

Riches, C. R., Twomlow, S. J., and Dhliwayo, H., 1997: Low-input weed management and conservation tillage in semi-arid Zimbabwe. Experimental Agriculture 33, 173-187., .

Russel, 1996: The value of crop residue as ground cover. In "Farmer's Weekly". July1996.

Sant'Anna, R., 1993: Major soils for food production in Africa. In "Soil Tillage in Africa: needs and challenges" (M. a. C. S. Soil Resources, Land and Water Division, FAO, ed.), Vol. 69, Rome.

Shumba, E. M., 1984: Animals and the cropping system in the Communal Areas of Zimbabwe. Zimbabwe Science News 18, 7/8, ., 1984.

Shumba, E. M., Waddington, S. R., and Rukuni, M., 1992: Use of tine tillage with attrazine weed control to permit earlier planting of maize by small-holder farmers in Zimbabwe. Experimental Agriculture 28, 443-452., .

SSSA, 1987: "Glosary of Soil Science Terms,", Madison, WI.

Stevens, P. A., 1998: "Ripping with draft animals: IMAG-DLO extension brochure,". Smallholder Agricultural Mechanisation Promotions, Lusaka, Zambia.

Temu, A. E. M., and Bisanda, S., 1996: Pit cultivation in the Matengo Highlands of Tanzania. In "Sustaining the soil: indigenous soil & water conservation in Africa." (C. Reij, ed.), pp. 145-155. Earthscan Publications Ltd, London, UK.

Thompson, J. G., and Purves, W. D., 1978: A guide to the soils of Rhodesia. Rhodesia Agricultural Journal, Technical Handbook No.3,, ., .

Twomlow, S. J., 1998: Personal Communication , Silsoe Research Institute, UK.

Twomlow, S. J., Ellis-Jones, J., Hagmann, J., and Loos, H., eds, 1995: In "Proceedings of a technical workshop, Soil & Water conservation for smallholder farmers in semi-arid Zimbabwe-transfers between research and extension." , 3-7 April 1995, Belmont Press, Masvingo, Zimbabwe.

Vogel, H., 1993: " An evaluation of five tillage systems for smallholder agriculture in Zimbabwe.," Rep. No. Contill Research Report No.5. Institute of Agric. Engineering., Harare.

Vogel, H., Nyagumbo, I., and Olsen, K., 1994: Effects of tied ridging and mulch ripping on water conservation in maize production on sandveld soils. Der Tropenlandwirt "Journal of Agriculture in the tropics and Subtropics" 3-4, April 1994, 33-44., April 1994.

Whitlow, R., 1988: Potential versus actual erosion in Zimbabwe. Applied Geography 8, 2, 87-100., .

Willcocks, T. J., and Twomlow, S. J., 1990: An evaluation of sustainable cultural practices for rainfed sorghum production on vertisols in East Sudan. In "AgEng 90", pp. 12. , Berlin.

Willcocks, T. J., and Twomlow , S. J., 1991: Tillage methods and soil and water conservation in Southern Africa. In "12th International Conference of ISTRO". 8-12th July 1991, ISTRO, IITA, Ibadan , Nigeria.