MORE ADVANCED CONSERVATION FARMING FOR STEEPER SLOPESContour Vegetative Strips Vetiver Grass in Zambia and Malawi
Cultivation on steep slopes is common in the Zambezi and Luangwa valleys and in Eastern Province along the Malawi border. Where slopes are in excess of 3%, Vetiver strips planted on the contour are the most effective way of controlling erosion. Vetiver zizanioides is a widely adaptable, fast growing deep rooted perennial that is unpalatable to livestock. Vetiver forms a living barrier which arrests soil movement. After heavy rain soil builds up against the hedge of Vetiver grass gradually creating a natural terrace effect. Under the MAFF SCAFE Project, Vetiver nurseries have been established in Monze, Mumbwa, Kafue, Lusaka East, GART and at many other sites. In Malawi where ridge cultivation is predominant, farmers follow 3 steps to convert to flat CT/CF. (1) ridges are realigned if they are not on the contour; (2) Vetiver hedges are then planted behind each 10th to 20th ridge depending on the slope; (3) once the hedges are established farmers abandon ridging.
The 'A' Frame for Pegging Contours
The easiest way to peg contours is using an A Frame. The A Frame consists of two 3 m poles (cut exactly the same length and tied together with one pole tied across them exactly 1 m from the bottom to form an A shaped frame. A string with a stone tied at its end is hung from the top. Measure across the horizontal pole and mark the exact centre with a notch. When the string hangs over the notch, each leg of the A frame marks the same level on the ground. Farmers in Malawi have successfully used the A Frame to peg out contours in the field to mark out lines for planting Vetiver. As a rule of thumb, 3-7% slopes (moderately steep), will require a Vetiver hedge every 20 metres and 8-12% slopes (steep), every 15 metres.
Pegging out 1 hectare will take 2 adults 1-2 days work. Using the A Frame farmers can learn to mark out contours themselves. Notice the pegs.
Marking out in the Field
To do the job the following will be required:- 2 Adults, the A Frame, a flat stone for hammering in the pegs and about 250 pegs per hectare. Starting at the top of the field, level up the A frame and hammer a peg into the soil beside each foot of the A Frame. Holding one leg of the A frame firmly in its original spot, swing the other leg down the slope and back upwards until the string hangs over the notch. Hammer in a peg. Now swing the other leg down the slope and repeat the process to peg the first contour.
In Malawi where people have begun to recognise the value of Vetiver, progress has been made by contracting farmers or groups with access to water from dambos or rivers to propagate Vetiver and make tillers available to their neighbours. Large centralised nurseries do not work because of the high cost of transportation. A 0.1 ha nursery should receive 30 kgs of Compound D broadcast before planting. The tillers of Vetiver (4-5) called slips, are planted at 45 x 45 cm spacing.
Harvesting Vetiver Tillers
After 12 months a well maintained and watered nursery will produce 25- 40 tillers from the original 4 tillers planted at each station. To harvest, cut the leaves back to 15 cms and dig out the centre of the clump of tillers with their roots leaving 4-5 slips from the side undisturbed. These will provide the harvest for the following year. Trim the roots of the harvested tillers back to 10 cms.
Planting in the Field
Split the clumps into bunchs of 4-5 tillers each (these are called slips) and plant at 15 cm spacing along the pegged contour. A well maintained nursery of 0. 1 ha, will provide 10 kms of Vetiver hedges.
Planting Leguminous Trees
There are many tree species which have a number of beneficial uses for farmers and rural communities. In the Sections below we discuss the establishment and benefits of a small selection of these.
Vetiver hedges can be strengthened by planting leguminous trees including Senna spectabilis, Leucaena leucocephala, and Glificidia sepium. Senna Spectabilis is the best tree to grow where livestock are common as it is not palatable to them. It also provides the most fuel wood. These species can be direct planted at the onset of the rains. Plant 4-5 seeds at 40 cm spacing in a row 50 cms above the Vetiver hedge. Senna because of it size should be planted 1 metre apart. The trees can be pruned at the beginning of the second season if they are higher than 1 metre. Prune with an upward slanting cut at 40 cms from the ground. The prunings can be fed to livestock, (Gliricidia prunings should be wilted first), or used for green manure or fuelwood. During the growing season prune the trees whenever the shading becomes a risk and distribute the prunings along the crop rows to help reduce weeds and increase available nutrients.