Potential use of contour Calliandra calothyrus hedges with napier grass (Pennisctun Purpureum) for soil-erosion control in a high potential area of Embu, Kenya
Angima, Samson Danford
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The potential contour Calliandra calothrsus hedges in combination with Napier grass (Pennisetum Purpurem) hedges, in controlling runoff and soils loss, from a cropped field were studied during two cropping seasons in Nitisol soil under semi-humid conditions at the National Agroforestry Research Project-Embu, Eastern Province, Kenya. The experiment had eight runoff plots measuring 5 x 30m, on a 18% slope, and was conducted in a randomized complete block design with two replicates and four treatments as follows: 1) Control: only maize; 2) Grass Hedge: Pennisetum purpureum; 3) Tree hedge: Callliandra calothyrsus: 4) Combination hedge: Pennisetum punnisetum purpureum + Callindra calothyrsus. Maize and beans intercrop were planted during the first season (Short rains), and maize monocrop in the second season (long rains) soils and water runoff losses after each major rainfall event and the changes in crops cover as well as total dry matter from the two fodder types used were measured. Topographic surveys of the experimental plots were carried out at the end of each cropping season. Rainfall intensity and changes in infiltration rates and bulk density along the hedges were also determined. Soil losses from the plots with hedges were lower than the control, though not significant. Over the two seasons, the average cumulative soil losses from plots with tree hedge and combination hedge were 71%, and 53% lower than that of the control plot, while grass hedge plots were higher than the control by 14%. On the other hand, water runoff losses from tree hedge, combination hedge and grass hedge plots were 50%, 70% and 96%, respectively, lower than that of the control plots, although not significant (p=0.9). In both the short rains and long rains seasons, there were no significant differences between the treatments in both runoff and soil loss. Likewise, Least Significant Difference carried out on the treatment means for runoff and soil loss showed no significant difference among treatments. It concluded that the effect of the hedges at this stage, had not become significant in reducing both runoff and soil loss. Soil bulk density did not change while infiltration rates at the end of the experiment along the hedges were slightly higher than in the beginning of the experiment. Percentage average decrease in slope followed this order: combination hedge > tree hedge > grass hedge with 1.83%, 1.77% and 1.74% respectively, while the control plot had a 0.67% increase in slope angle. Total dry matter in the two lines of hedge produced 12 t/ha/yr of Napier for the grass hedge and nearly 8 t/ha/yr of Napier from the single line of Napier in the combination hedge. The fodder harvested from the tree hedge averaged 2 t/ha/yr and 0.8 t/ha/yr of stems, while the combination hedge produced 0.7 t/ha/yr of fodder from the tree hedge and 0.3 t/ha/yr of stems. This indicates some extra benefits for use of hedges for soil conservation, compared to mechanical earth structures.