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PART C - CASE STUDIES

4.1 Tied Ridging -- Domboshawa, Zimbabwe

Introduction

Zimbabwe has experienced low and erratic rainfall for the decade prior to 1995. To offset agricultural losses related to low rainfalls and variations in rainfall related to these vagaries of nature, researchers investigated tillage methods that conserve soil moisture. The major objective in moisture conservation tillage methods is to conserve moisture in the soil in order to increase germination and yields. Runoff is greatly reduced and infiltration rates are increased. Moisture conservation tillage technologies include tied-ridging, mulching, contour ploughing and minimum tillage, described in Part B, Chapter 1, "Agriculture".

This case study looks at ridging and tied-ridging in Domboshawa, an area about 30 km north of Harare, the capital city of Zimbabwe. It is located in the Highveld of Zimbabwe at an altitude of about 1200 m above sea level. The average annual rainfall ranges from 800 mm to 1 000 mm per annum. The rainfall is seasonal with approximately 90% falling in the months of October to March.

Technical Description

Ridging and tied-ridging as carried out in Zimbabwe is widely documented (FAO, 1966). Most of the equipment used for ridging and tied-ridging was locally manufactured, and designed to be animal-drawn. A typical, ox-drawn disc ridger, developed by the Department of Agricultural and Technical Extension Services (AGRITEX) in conjunction with GTZ, is illustrated in Figure 42. The high wing ridger body is used for making the ridges, and is an accessory to the mouldboard plough. When making ridges, the ridger body is attached to the plough instead of the mould board. The ridger produces ridges which are 250 mm high.

The high wing ridger is of French design but is manufactured locally. The ridger has two adjustable discs angled to form a wide `V' shape. Although the unit looks heavy, the draft requirement is actually less than that required for the conventional mouldboard ploughs. Depending on the ridge requirements, the disc sizes and shapes can be varied.

Ridges made using this technology can be tied using hand hoes. In Zimbabwe, simple ox-drawn tie-makers have been produced locally. As illustrated, these can be made from old mouldboard plough shares or discs fitted on to metal or wooden uprights. In order to avoid having too many operations, ties can be coupled to the ox-drawn disc ridger (Figure 43). They can also be fitted onto cultivators (Figure 44). Ties are made by scraping the tie-maker along the furrows between the ridges until enough soil has been collected. The collected soil should be about 1/2 to 2/3 the height of the ridges.

Figure 42. Ox-drawn disc ridger with tie-maker attached.
Source: Makoholi Research Station

Extent of Use

Nevertheless, there has been some measure of resistance to changes in the traditional methods of cultivation. This resistance was compounded by shortages of labour and draft power. Shortages of labour resulted from male migration to urban areas in search of employment, while the shortage of draft power resulted from reduced animal stocks due to the drought. All of these obstacles have not yet been overcome, and, although the method is acceptable to the farmers, it is not widely practised. Only 1% of the farmers in the area use the method (Elwell, 1993)

Operation and Maintenance

Ridgers and tie-makers do not require any special skills to operate or maintain. There are few components that need replacement, and, hence, the technology is very suitable for communal operations. Disc--ridgers and ridger bodies wear out with time, but replacement is not a problem since the equipment is locally manufactured.

Level of Involvement

The government, local communities and non-governmental organizations were all involved in the project. The government provided the personnel for the research and extension while GTZ provided some of the funding.

Figure 43. Ox-drawn disc-plough tie-maker. Source: Institute of Agricultural Engineering, Harare, Zimbabwe Figure 44. Light Cultivator with tie-maker mounted. Source: Institute of Agricultural Engineering, Harare, Zimbabwe

Costs

The major cost is the purchase of the ridgers and the tie-makers. Where the farmers already have mouldboard ploughs or cultivators, the cost will be low because the ridger body and the tie-maker can be fitted easily. A new ox-drawn ridger costs $300 and a new mouldboard plough costs $30. If the farmers do not have their own implements, the cost of hiring the equipment to have one hectare ploughed and tie-ridged will be $250. Effectiveness of the Technology As shown in the following table, the results of the field trials showed that there was a reduction in runoff from fields with tied-ridges compared to those with conventional tillage.

Advantages

The advantages of tied-ridges include reduced erosion and conservation of soil moisture. The equipment used is simple and easy to use, and capable of being locally manufactured and maintained. The field trials clearly showed improved crop yields.

Disadvantages

Tied-ridgers require new or additional equipment, and substantial time and effort required to prepare the lands each year. This increases farmers' costs. In areas with highly variable rainfall, ridges can fail due to overtopping. When this occurs, greater soil losses may result.

Further Development of the Technology

The technology has great potential for use in arid and semi arid regions. However, in order for the technology to be accepted and adopted, much effort has to be put in the research and extension services. The government has to be strongly involved in the exercise. The technology is easy to adopt if the farmers are mechanized and they have enough draft power. Availability of draft power is essential because substantial time and effort is required for the land preparations. For countries wishing to adopt this technology, it is very important to make sure that an effective extension service, adequately financed, is in place.

Sources of Information

Contacts

D. Dube, ARDA, Post Office Box CY 1420, Causeway, Harare, Zimbabwe.

Institute of Agricultural Engineering, Post Office Box BW 330, Borrowdale, Harare, Zimbabwe, tel. 263-4-860119 or 263-4-860055.

I. Nagambie, Conservation Specialist, Institute of Agricultural Engineering, Post Office Box BW 330, Borrowdale, Harare, Zimbabwe, tel. 263-4-860119 or 263-4-860055.

G. Nehanda, Chief Planning Officer, Head of Station, Institute of Agricultural Engineering, Post Office Box BW 330, Borrowdale, Harare, Zimbabwe, tel. 263-4-860119 or 263-4-860055.

A. Senzanje, Department of Soil Science and Agricultural Engineering, University of Zimbabwe, Post Office Box MP 167, Mount Pleasant, Harare, Zimbabwe.

Bibliography

Elwell, H.A. 1993. "Development and Adoption of Conservation Tillage Practices in Zimbabwe." FAO Soils Bulletin 69, Soil Needs in Africa Needs and Challenges. FAO, Rome.

FAO (Food and Agriculture Organization of the United Nations) 1966. Equipment of Tied Ridge Cultivation from Power and Machinery. Informal Working Bulletin No. 28, Rome.

Vogel, H. 1992. Conservation Tillage for Sustainable Crop Production Systems. Project Research Report 5, Institute of Agricultural Engineering (IAE), Harare.

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