Potential of Acacia angustissima, Leucaena pallida and Mimosa scabrella in agroforestry systems on a Rwandan Ferralsol

Agroforestry using coppicing legume trees and shrubs is a way to improve livestock fodder quality and soil fertility in the tropics. However, tree establishment and appropriate management are challenging, hampering their integration into agriculture and livestock systems. This thesis evaluates the biomass production by Acacia angustissima, Leucaena pallida and Mimosa scabrella legume tree species grown on a Ferralsol in Southern Rwanda, determines their effects on fodder quality and assesses the fertiliser quality of the resulting manure and its effect on a maize crop yield and the fertility status of a Rwandan Ferralsol. In field studies, biomass production and nutritive value of the three agroforestry species when subjected to 0.3 and 1.0 m cutting height were determined and the effects of micro-dosing manure, fertiliser and lime on soil properties and maize yield were examined. Higher biomass production was generally found at lower cutting height. Acacia angustissima had the highest biomass production, whereas M. scabrella was sensitive to repeated harvests. Crude protein (CP) was not affected by cutting height, but neutral detergent fibre (NDF), acid detergent fibre (ADF) and total polyphenols were higher at grater (1.0 m) cutting height. The highest CP was found in A. angustissima and the highest NDF and ADF in M. scabrella. Mixing legume leaves with Chloris gayana grass improved feed CP content, dietary mineral content and digestibility. Adding A. angustissima into C. gayana grass based feed increased the total nitrogen, organic carbon and base cation content in the manure produced. Manure application increased soil pH, soil nutrient content, soil organic carbon, soil cation exchange capacity and water-holding capacity at maize planting stations. Maize agronomic parameters and yield increased with manure micro-dosing method. Thus A. angustissima and L. pallida appear to be robust species for use in agroforestry systems with similar biophysical conditions and cutting methods to those tested in this thesis, and can be recommended to improve low-quality forage. Manure micro-dosing is a promising practice for soil fertility replenishment in crop production by smallholder farmers with limited income and access to manure

Distribution and dynamic changes of Huanglongbing pathogen in its insect vector Diaphorina citri

The Asian citrus psyllid (ACP) Diaphorina citri Kuwayama is the leading vector of Candidatus Liberibacter asiaticus (CLas), the causative agent of citrus Huanglongbing (HLB) disease. The distribution and dynamics of CLas within ACP are critical to understanding how the transmission, spread and infection of CLas occurs within its host vector in nature. In this study, the distribution and titer changes of CLas in various tissues of ACP 5th instar nymphs and adults were examined by fluorescence in situ hybridization (FISH) and real-time quantitative PCR (qPCR) techniques. Results demonstrated that 100% of ACP 5th instar nymphs and adults were infected with CLas following feeding on infected plants, and that CLas had widespread distribution in most of the tissues of ACP. The titers of CLas within the midgut, salivary glands and hemolymph tissues were the highest in both 5th instar nymphs and adults. When compared with adults, the titers of CLas in these three tissues of 5th instar nymphs were significantly higher, while in the mycetome, ovary and testes they were significantly lower than those of adults. FISH visualization further confirmed these findings. Dynamic analysis of CLas demonstrated that it was present across all the developmental ages of ACP adults. There was a discernible upward trend in the presence of CLas with advancing age in most tissues of ACP adults, including the midgut, hemolymph, salivary glands, foot, head, cuticula and muscle. Our findings have significant implications for the comprehensive understanding of the transmission, dissemination and infestation of CLas, which is of much importance for developing novel strategies to halt the spread of CLas, and therefore contribute to the efficient prevention and control of HLB

Effect of grass-diet and grass-legume-diet manure applied to planting holes on smallholder maize production in Rwanda

Animal manure provides plant nutrients and also affects soil nutrient availability, pH buffering and soil physical properties through its contribution to soil organic matter pools. However, the quality and quantity of manure are often low on smallholder farms in sub-Saharan Africa and the initial effect of manuring on crop yield may be small or even negative. In a two-factorial experiment over four seasons in southern Rwanda, the fertiliser value to a maize crop of manures produced by cattle fed a basal diet of only Chloris gayana grass or a mixed C. gayanaAcacia angustissima diet was compared with that of NPK 17-17-17 and no fertiliser. The potential liming effect of the manures was also evaluated through inclusion (or not) of travertine as the second factor. All amendments were applied only to maize planting holes. The crop failed in season 1 due to drought, but manure application (5 t ha-1) approximately doubled maize yield compared with the unfertilised control during seasons 2-4, while NPK (70 kg N ha-1) increased yield by 3- to 4-fold, with corresponding improvements in crop performance indicators. The mixed diet increased manure quality and maize yield compared with the grass diet in season 4. Liming showed a consistent tendency to improve crop performance indicators and yield, but significant differences were only identified in some cases, possibly because the pH increase was small. The results suggest that in regions where manure availability is limiting, application of reduced rates only to planting holes may be an efficient technology. Enhanced animal feed can result in higher quality manure, and ultimately increase crop yield, if nutrient losses during manure handling and storage can be limited

Supplementing grass-based cattle feeds with legume leaves and its effects on manure quality and value as a soil improver for an Anthropic Ferralsol in Rwanda

Combined use of lime, animal manure and inorganic fertilisers is effective in replenishing the fertility of degraded acid soils. However, many smallholder farmers lack access to sufficient amounts of these inputs to improve the fertility and reduce the aluminium toxicity of Ferralsols. Organic manures are available but often have low nutrient content, which limits their ability to supply nutrients to soils. In a two-factor field experiment over four seasons on an Anthropic Ferralsol in Southern Province, Rwanda, we assessed (i) the effect of cattle manure on soil properties at a reduced rate affordable to smallholder farmers compared with that of NPK fertiliser applied, with and without lime also at a reduced rate, and (ii) the effect of supplementing grass in a basal cattle diet with legume leaves on manure quality and its effect on soil properties. Manure from cattle fed only the grassChloris gayana(grass-only manure) and from cattle fedC. gayanasupplemented withAcacia angustissimaleaves (grass+legume manure) was applied at 5 t dry matter ha(-1)(25% of the recommended rate) at the beginning of each growing season. NPK was applied as split doses supplying a total rate of 70 kg N ha(-1). Lime was applied annually at a rate of 2.0 t CaO ha(-1), which was 25% of the rate required to neutralise total acidity at the site. All amendments were applied only to the soil surrounding the maize plants (planting stations), which is estimated at 25% of the plot area. Maize stover was left on plots after harvest and planting stations were retained over all growing seasons. All treatments altered soil properties at the planting stations. Lime generally increased pH but there was no significant difference between lime plus manure treatments and non-limed manure treatments. Soil organic carbon concentration and cation exchange capacity were higher in manure and NPK treatments than in non-fertilised treatments. The manure treatment increased soil water-holding capacity compared with the NPK and non-fertilised treatments. There was no significant difference in total N, Ca2+, Mg(2+)and K(+)between the NPK and manure treatments. Micro-dosing animal manure can thus replace mineral fertiliser plus lime for soil fertility replenishment in smallholder farming. Grass+legume manure contained higher concentrations of total N, Ca, Mg, K and Na than grass-only manure, but its effect on soil properties did not differ significantly from that of grass-only manure

Effect of cutting height on nutritional characteristics of three agroforestry tree legume species and their feed supplement value on Chloris gayana Kunth

This study investigated the effect of cutting height (30 and 100 cm) on chemical composition and in vitro digestibility in field-grown Acacia angustissima (Mill.) Kuntze. (Prairie acacia), Leucaena pallida Britton & Rose (guaja) and Mimosa scabrella Bentham. (bracatinga) legumes and their value in supplementing a basal diet of Chloris gayana Kunth. (Rhodes grass). Cutting height did not affect major chemical composition. Crude protein (CP) was highest in A. angustissima and lowest in M. scabrella, while neutral detergent fibre (NDF) and acid detergent fibre (ADF) were highest in M. scabrella. Degradation parameters were greater at 100 cm cutting height. L. pallida showed high in vitro organic matter digestibility but A. angustissima had the highest metabolisable energy. Addition of A. angustissima, L. pallida and M. scabrella to the basal diet increased improved the nutritional value and increased the CP content from 8.4 to 19.8% and 18.1 and 16.1%, respectively. Cutting height of A. angustissima, L. pallida and M. scabrella had no effect on their nutritional value. Their other functions and benefits will determine choice of cutting height as management practice when used on farms

Biomass production and nutrient content of three agroforestry tree species growing on an acid Anthropic Ferralsol under recurrent harvesting at different cutting heights

Agroforestry systems may alleviate challenges relating to soil degradation and low livestock production for smallholder farmers. Species-adjusted management regimes will determine how agroforestry fits in farming systems. Long-term productivity of biomass in agroforestry systems managed for fodder production requires tree species that coppice after repeated cutting. This study evaluated the effect of different cutting heights (0.3 and 1.0 m) and repeated harvests (1-5) on biomass production and chemical composition of the leguminous trees Acacia angustissima, Leucaena pallida and Mimosa scabrella in a field study on an Anthropic Ferralsol in Southern Rwanda. Shoot biomass production was highest at 0.3 m cutting height for A. angustissima and L. pallida, but M. scabrella could not survive that cutting height. Shoot biomass was highest for A. angustissima and lowest for M. scabrella, which did not adapt to repeated harvests. Leaf:stem ratio was not affected by cutting height. Cutting height did not affect crude protein (CP), but neutral detergent fibre (NDF), acid detergent fibre (ADF) and total polyphenol (TP) concentrations were higher at 1.0 m cutting height than at 0.3 m. Crude protein was highest in A. angustissima and lowest in M. scabrella, while NDF and ADF were highest in M. scabrella. Although all species provided high feed quality in terms of high CP content at both cutting heights, low cutting height (0.3 m) is recommended for A. angustissima and L. pallida for higher overall quality and biomass production