Sammanfattning av doktoranduppgiften
Acacia angustissima, Mimosa scabrella and Leucaena pallida in agroforestry systems on Rwandan Ferralsols: tree growth, digestibility, manure fertilizer value and soil fertility improvement
Ferralsols are the most dominant agricultural soils in Rwanda. They are known to be chemically poor and highly weathered soils. Despite limited farm size in Rwanda, farmers incorporate trees and shrubs within the farms by choosing appropriate niches for planting multipurpose tree species. Agroforestry shrubs have been established on farms with a combined production purpose such as fuelwood production, soil erosion control, stakes for climbing beans, green manure and fodder for livestock.
The general aim of this research is to contribute to scientific information by evaluating the potential of Acacia angustissima, Mimosa scabrella and Leucaena pallida as fodder trees in the sub humid tropical climate and on Ferralsols of the southern region of Rwanda. Specifically the research determines the effect of cutting height on biomass production, nutritional value and digestibility, evaluates the trees´ usefulness as livestock feeds, and the effect of manure derived from animals fed with A. angustissima species on crop production and soil fertility compared with manure from animals fed only grass.
The research consists of four parts:
1) Effect of cutting height on tree biomass production and survival:
A field experiment has been conducted at Tonga research station/UR/CAVM in a Randomized Block Design with six replicates where two cutting management at 30 and 100 cm were applied. Tree management effects are being evaluated.
2) Effect of cutting height of A. angustissima, M. scabrella and L. pallida on nutrient concentrations, digestibility and potential use as feed for livestock:
Chemical analysis of nutrient content has been done with the aim of assessing the effect of cutting height on the nutrient concentrations, and the digestibility has been assessed by gas production techniques. The effect of admixture with legumes into a basal Chloris gayana (grass) diet has been assessed.
3) Effect of A. angustissima supplementation on manure quality as shown through effects on maize growth and yield:
A field trial has been conducted to assess the effect on manure quality of supplementing the basal diet with legume fodder. Manure from cattle fed with Chloris gayana supplemented or not supplemented with A. angustissima has been collected, composted and applied to soil. Its effect on maize production is being assessed. Interactions with liming and sole effects of liming are also assessed.
4) Effect of A. angustissima supplementation on the effect of soil fertility indicators:
Soil chemical and physical parameters important for crop production are being determined in the field trial in 3).