| Soil fertility and minimum tillage equipment trials in the North Central, Namibia by C. Rigourd, T. Sappe and P. Talavera Northern Namibia
Rural Development Project, Abstract The paper highlights investigations conducted to identify soil types and their fertility status in the North Central Division of Namibia. The survey was necessary to describe the soil status before introducing minimum tillage and soil conservation tillage practices in the area. Several animal drawn implements were tested on the farmers' fields. These included cultivators from Senegal, Zimbabwe and Zambia. Pleriminary results of the survey have been reported and discussed. 1. Introduction The Northern Namibia Rural Development Project (NNRDP) started its activities in 1994. The project adopted an Action Oriented Research approach, working with farmers as equal partners in pilot communities of the North Central Division (NCD). Project staff and farmers identified weeding as a major constraint in the area. Consequently, in 1994/95 and 1995/96, tests on three animal drawn cultivators, the Senegalese cultivator, French cultivator and BS 41 were conducted. By 1996, the use of the cultivator for weeding had become an extension message. During the 1996/97 and 1997/98 seasons, tests on minimum tillage and dry sowing with animal traction in the North Central were initiated. It was realized that the selection of appropriate equipment and the definition of comprehensive extension messages would be incomplete without a fair knowledge of the soil types in the area. In 1996 a soil survey was therefore initiated and carried out in 1997 and 1998. 1.1 Objectives The main objectives of the survey were:
2. Materials and methods The following activities were carried out:
3.1 General problems related to fertility During the survey, some common features which were observed included:
3.2 Identification of soil types
Other soils Termite hills ("oshiwanda"), old termite hills ("oshitunu") and riverine type of soils ("omulonga") have been described by farmers but have not been investigate properly. 3.3 Farmers’ conclusion At the field level soils are extremely heterogeneous. Basically, all the types described previously can be found within the same field. Therefore, a transect representing the location of the soil types has been established. Consequences have been as follows:
3.4 Technician’s conclusion In the NCD soils vary from sandy to sandy loam. On average, the sand content is 87%, the clay content is 9.5% and the silt is 3.5%. In the NCD, soils have a rather poor water holding capacity and soils are poor in nutrients. 4. Discussion 4.1 Farmers’ management of fertility Cattle and goat manure are well known by farmers to improve the fertility of their field. Donkey manure is hardly use in the NCD. Manure is always applied in big quantities, when available, spread all over the field, under the form of a "dry kraal powder" (and not "fresh manure"). It is usually used pure, only few farmers mixing it with straw or grass. Manure is usually applied in November/ December, to allow the crops to take benefit from it. However, to apply manure is labour intensive and manure is not always available in adequate quantities, especially if cattle are sent to cattle posts and do not stay around the homestead, in kraals. 4.2 Ridges and soil preparation Reasons for erecting ridges, in the NCD, are to eliminate the excess of water in water logging soils. Crops are cultivated on top of the ridges. The ridges evacuate the excess of water toward an Oshana or a water reserve area. It has to be noticed that excess water in the furrow can constitute a reserve of soil moisture. In sandy soils (eastern areas) farmers sometimes cultivate their crops in the furrow left by the plough and water may settle in it. Fertilisers are hardly used by farmers because they are expensive (poor cost/benefit ratio) and not always balanced. In the NCD, fertilisers should have phosphorus predominant. Some well-balanced fertilisers could be useful to upgrade the phosphorus and magnesium content of the soft and deep sandy soils. 4.4 Other management practices In the NCD, farmers do not practice fallow and do use crop rotation. It is the traditional to use the hand hoe for land preparation. However, it is time consuming and this technique does not allow farmers to prepare their whole field on time. Furthermore, farmers can erect ridges using the hand hoe, but it is time consuming and labour intensive. 4.5 Utilizing animal drawn implements Such implements allow farmers to prepare the field on time, to erect ridges easily and to control the plough depth. However, in water-logged or hard dry soils, continuous ploughing at the same depth must be avoided, as it will enhance the formation of the hard pan. Animals must be ready, trained and healthy at this time of land preparation yet this is usually the time of great fodder shortage. 4.6 Use of tractors Tractors allow farmers to prepare large fields quickly. However they are not always available when needed or on time. Like with animal traction, on water logged and hard dry soils continuous disking at the same depth must be avoided due to the formation of the hard pans. According to farmers disking can create hard pans in "hard-pan-free" sites and disking does not allow farmers to control tillage depth. 5. Experimenting with weeders From preliminary findings were clear that it was worth trying implements for minimum tillage using animal traction. The implements tested in the NCD were for minimum tillage and dry sowing This implement was tested in 1996/97. The tool was 1 cm thick, 24 cm long and was characterised by a working depth of 8 to 10 cm. This tool was attached to the body of the cultivator. The implement was light and could be pulled by a single donkey. It made small line and on sandy soils, sand fell back into the furrows. The positioning of the chisel tine at the middle of the frame of the cultivator made the implement unstable.It was therefore, decided together with farmers, to test an improved tine with a larger angle bar and an attachment at the rear side of the cultivator. This implement was tested in 1997/98. The angle bar was welded on the chisel tine and was about 5 cm wide. The chisel tine was 24 cm long and it was positioned at the rear side of the body at the beginning of the handle.The prototype was produced by a local welding company (Oshakati Best welding) at a cost of N$ 20.00. A single donkey could still pull the implement. With the improved manipulated chisel tine the furrow was still not deep or wide enough. It didn’t prove suitable for hard soils (water logged or hard dry soils), sandy soils (soft and deep)s or low ground and swamp, loamy soils). It was suitable only for soft soils (good deep and dark soils).The improved chisel tine and improved manipulated chisel tine were not adapted to the NCD conditions, except in very special soil conditions which were good, deep and dark. 5.3 The Zimbabwean curved ripper This unit was adapted from the Senegalese cultivator. This implement had been tested in 1997/98. The Zimbabwean curved ripper was bigger than the improved manipulated chisel tine and made larger furrows. But since it was adapted from the Senegalese cultivator it remained lighter than the Magoye ripper which was held on the traditional plough beam. The Zimbabwean curved ripper was 28 cm in length, 6.5 cm in width and it was attached on the rear side of the body of the Senegalese cultivator. Adapting the Zimbabwean curved ripper on the Senegalese cultivator required a special attachment system. This one was produced by the same local welding company at a cost of N$ 20.00. With wings adapted to it two donkeys were needed to pull the equipment. On performance, depth and width of the lines were correct. On soft and deep sandy soils, wings were compulsory. However, the implement was not tested on farms as farmers were reluctant to try it.The Zimbabwean curved ripper penetrated hard soils which were water logged and hard and easily so. Draft requirements were low on soft soils. The Zimbabwean curved ripper was therefore the most versatile and required minimal draft. This implement which utilized the traditional plough beam was tested in 1996/97 and 1997/98. This implement was 24 cm in length, 9 cm wide and 0.9 cm thick. The unit required two donkeys to pull it. When wings were added at least two donkeys were needed. A pair of oxen was even better. The depth and the width of the furrows was correct and even better than the ones obtained with the Zimbabwean curved ripper. In soft and deep sandy soils, wings were needed to keep the soil from falling back into the furrow. The Magoye ripper penetrated very easily, opened the soil nicely but was heavy to pull in water logged and hard dry soils. The Magoye ripper with wings was very well adapted to soft and deep sandy soils. Occasional problems of the Magoye not fitting on the plough beam were encountered. The mouldboard was also occasionally difficult to remove since farmers did not always have the tools needed to take it off when installing the ripper. Unlike the Zimbabwean curved ripper, the Magoye ripper was applicable in most soil types. The wings on both the Zimbabwe curved ripper and the Magoye Ripper were well suited for deep sandy soils, which tended to flow back into the furrows. The wings were 19 cm wide and 22 cm high. With the wings, at least two donkeys were needed.Soils in the NCD are sandy and very poor in nutrient and organic matter content. They are highly heterogeneous. It is recommendable that conservation tillage, animal drawn implements have wings and be capable of deep and wide furrows. Two implements appeared appropriate for the NCD conditions These are the Zimbabwean curved and the Magoye rippers. It was noted that animal drawn implements allow farmers to prepare larger fields. Animal drawn minimum tillage implements encouraged farmers to plant in lines which was conducive to the use of cultivators for weeding. Two questions remained un-answered :
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