Sustainable Agriculture may be defined as the successful Management of Resources for Agriculture to satisfy changing human needs while maintaining or enhancing the quality of the environment and conserving natural Resources (CGIAR. 1989). Therefore a farming or production system will only be sustainable if it can 

• Maintain or enhance environmental quality;
• Satisfy societies demand for food and;
• Assign the economic and social well being of producers.

Soil erosion 

Most of the Soil type in Namibia are dominated by sandy soil type. Wind erosion is the major constraint in North Central region of the country due to the total decrease of trees in the area and larger field been cultivated. In North Eastern Region of country soil erosion is at the moment not the big problem but it need Greater attention before it become a greater issue. 

Grey loose sands (occasionally broken by various shades of brown) dominate in the east of Ohangwena and Oshikoto extending into Kavango with minimum interruption. In this zone presence of Termitaria appears to indicate the most favourable sites for Cultivation. Except for the river terrace system and Ephemeral River Basin where alluvial soils are found the Kavango is largely a Featureless monotonous and plain with zones of visible sandy Dunes, Aeolian sands are the dominant soils in Kavango. 

Therefore the highly erodible structureless soils being cultivated in Namibia make conservation tillage a primary concern for the sustainability of the production system. 

Measure to combat soil erosion 

In 1980 commercial farmers had switch over from conventional ploughing to conservation tillage system. Most farmers in the commercial farms had sold their disc implement and had buy light tine implements. Soil erosion had become major constraint to the farming communities in the commercial sector. 

Conversation tillage had greatly save on input cost, save time water run off prevention. The stable mulch is left on soil surface to prevent moisture looses. The evaporation rate decrease which result in lower temperatures less erosion is taken place because of stable mulching. 

Farmers had drive away their livestock from field so that stover can remain on the soil surface to protect soil from erosion and water run off. In so doing water holding capacity has also been increased. On the other hand communal or smallholder farmers in certain areas of Namibia had also realize the importance of conserving soil. 

Farmers normally intercrop maize or pearl millet beans or cowpea and the stover is left on the field to prevent soil erosion. Some farmers plough across the slopes to prevent water run off. Farmers also plough some fallows to conserve water by making ridges. Soil condition improvement is a key reason for both traditional and improved fallow agricultural system. 

The soil condition improvement can be measured indirectly by the crop yield and the improved conditions that support the crop yield. The soil conditions for improvement is many, and can be physical, chemical or biological monitoring these properties at one time or over a period of time provide the basic information for making relationships and associations. Indigenous knowledge on soil conversation practices are also encourage to combat soil erosion and declining soil fertility. 
  

Successful Dissemination of Conservation Tillage 

Namibia is the driest country in Southern Africa and wind erosion is more become evident in certain Regions of the country. Namibian government had realize that most fertile soil has been lost due to soil erosion or by water run off. Government is trying to make awareness companies to the farming communities to conserve soil. Agroforestry a practice aimed at maximising the use of land for forestry and agricultural purposes, is an old practise, which has come to light in recent years with a new conceptual framework and technologies. 

In Namibia there is a very strong case for dry land agroforestry systems which is basically aimed at the deliberate management and introduction of high value trees on farm land; be it be cultivated farm or pastures or bits of uncultivated land between settlements. 

The dry wood land of Namibia do contain some trees such as schinzophyton rauteneii (mangeti nut) and other species which produce nuts and oils which are domestically used for food and have the potential for other industrial uses. Therefore there is need to introduce agroforestry approach in farming to conserve soil for productive use. 

Good examples are the use of trees to conserve soil fertility and also to improve crop production by acting as windbreaks, shade crops ant through Nitrogen fixation. The commercial as well as small holders farmers are now becoming concern about the declining soil fertility. Government and various stakeholders are now looking ways and means to disseminate conservation tillage practises in the country. 
 

Conclusion 

Soil erosion and declining soil fertility is a greater concern in Namibia farming communities. Action plans and sound policies need to be put in place to address this global phenomenon. We had to switch over from conventional ploughing practises to lighter conservation tillage system. Agroforestry approach need to encourage with focuses on conservation or minimum tillage. Intercropping and using of tine implements and discourages heavy mechanised cultivation which compact soil and encourage water run off. Future activities regarding tillage should therefore greatly consider inclusion of sound environmental friendly tillage system. 

^{Ministry of Agriculture Water and Rural Development; Division of Research and Training; P.O. Box1405; Rundu; Namibia.}