Contribution of agrisilviculture system in improving soil quality in gishwati – mukura landscape,case of satinsyi river watershed in western midhighland of Rwanda

Abstract

Adoption of agroforestry system is believed to improve soil quality in Rwanda as the quality have been degraded for a long time due to natural and man-made activities. The undertaken study was to assess the contribution of agrisilviculture on soil quality in case of of main river satinsyi watershed in western midhighland of Rwanda. Stratified soil sampling method has been used to collect samples along a toposequence on four subwatersheds (Nyamakanda, Satinstyi, Rustiro and Rucanzongera) and a total of 27 composite samples analyzed in the laboratory. The soils in the study area were deep (>90cm) and well drained (Sandy loam). The upper, middle and lower slopes bulk densities were low ranging from 0.88 to 1.29 g/cm3; 0.89 to 1.19 g/cm30.88 to 1.132 g/cm3 in the lower slope. The sand content rated as very high and ranged from 68 to 82 % in the upper land; from 72 to 84% in the middle land and from 72 to 66 % in lower land, respectively. The clay and silt content was low compared to sand ranging from 8 to 14 % for clay and 6 to 24% silt. The porosity was high ranging 51.36 % in the upper land; 52.55 to 63.54 % in the middle and from 50.47 to 57.35 % in the lower land slope. The soils reaction along all subwatersheds rivers was strongly acid ranging from 4.5-5.1 in the upper slope; 4.38-4.9 in the middle slope and 4.35-4.97 in the lower slope. The organic content in the upper middle slopes were rated as medium ranging from 1.38 to 2.47%, corresponding to 2.38 and 4.26% and 1.33 to 2.47% corresponding to 2,29 and 4.26 % OM respectively. The study sites showed a relatively high amount of available phosphorus ranging between 9.78 and 19.69 in the upper slope; 12.16 and 23.21ppm in the middle slope and 12.58 and 25.31 in the lower slope. Rucanzongera subwatershed seems to have high amount of available phosphorus than the rest. Also, available P is increasing downward the slope the upper, middle and lower slopes showed medium to high levels of nitrate ranging from 19.15 to 38.34 ;16.97 to 32.75 and 18.24 to 30.28 respectively. Generally, the distribution of the soil properties along the topo sequencein 3sub watersheds (Nyamakanda, Satinsyi and Rustiro sub catchments) had indicated that most of the soil properties increased or decreased along a topo sequence whereas Rucanzongera sub watershed doesn’t show any trends of increasing or decreasing which show the good contribution of agroforestry on soil quality.