Composting is a common method for managing organic waste and creating nutrient-rich soil amendments. Recently, biochar, a carbon-rich material from biomass pyrolysis, has been noted for potentially improving composting. This study examines the impact of adding biochar to compost made from cow manure and kitchen waste through a controlled lab experiment. The treatments were labeled as CMX (cow manure), KWX (kitchen waste), and CMKWX (both) with X being the percentage of CM, KW, and CMKW minus that of biochar in the mixture. Key parameters such as temperature (T), pH, and electric conductivity (EC) were tracked during the composting processes, and the final composts were analyzed for total nitrogen (N), available nitrogen (AN), total phosphorus (TP), available phosphorus (AP), total potassium (TK), organic carbon (OC), calcium (Ca²⁺), magnesium (Mg²⁺), and organic matter (OM). The results showed that adding less than 10% biochar influenced composting positively. Specifically, 5% biochar amendment led to higher thermophilic temperatures (45–57 °C) and stable pH levels (6.3–8.7) compared to controls. However, biochar did not significantly enhance EC, which peaked at 1.78 dS/m in both the control and 5% biochar treatments. Nutrient analysis revealed that biochar increased Ca²⁺ (13.62 meq/g) and Mg²⁺ (5.73 meq/g) retention in CM composts (CM85 and CM100). The highest OM content was 16.84% in CM90, while the lowest was 3.81% in CM95. Higher OM negatively affected TN, with CM treatments having more OM and KW treatments having more TN. TP and TK were higher in control treatments without biochar. This study highlights the benefits of integrating biochar with organic waste for enhancing compost nutrient profiles and soil fertility. It was observed that the more diverse the compost feedstock, i.e., CMKW, the higher the nutrient content for treatments containing less than 10% biochar.

Biochar (B) has low nutrient content and is recalcitrant to biodegradation. Supplementing B with a fast-releasing nutrient source may improve soil fertility and physical conditions and increase crop productivity. A three-season field study was conducted on sandy loam and sandy clay loam textured soils to investigate the effect of B mixed with livestock manure (LM) on soil properties (pH, organic carbon (OC), cation exchange capacity (CEC), total Nitrogen (TN), available Phosphorus (Avail P)), and French bean yield (Phaseolus vulgaris L.) in Rwanda. The study used a factorial randomized block design with four replications. Treatments comprised three levels of B (0, 1, and 3 t/ha) and three levels of LM (0, 1, and 3 t/ha). Biochar was used from S. sesban, G. sepium, A. angustissima, Eucalyptus, and Grevillea sp., prepared using a drum kiln, while LM was prepared using the pit method. The Analysis of Variance (ANOVA), Tukey (HSD) function at p < 0.05, and linear mixed-effects model were performed in R software version 4.3.3 (R Core Team, 2024). The analysis showed that the treated plots significantly increased French bean yield compared to the control plots, with the highest value found in plots treated with 3 t/ha. The combined plots showed an increased yield compared to sole Biochar or manure. The seasonal increase has been observed, with percentage increases recorded as follows: 16%, 33.56%, 173.06% in sole B plots; 40.28%, 14.43%, and 11.76% in sole LM plots and 125%, 156%, and 209.8% in B + LM plots for season 1, 2, and 3, respectively. Furthermore, the results indicated that the application of B alone or combined with LM significantly enhanced soil pH, OC, TN, avail P, and CEC with the pH ranging from 6.77 to 5.43 for B alone, 6.7–5.35 for LM alone, 8.53–6.06 for B-LM plots, and 4.34–3.78 for control plots. Applying Biochar, either alone or in combination with LM, at a low rate demonstrated positive effects on French bean yield and soil nutrients in smallholder farmers. This study encourages using natural materials such as B and LM to improve soil fertility and increase vegetable production while reducing chemical fertilizers that can cause pollution and damage the environment.

Biochar (B) in combination with organic manure could improve the biochar efficacity in improving soil functions related to hydrophysical properties. Short-term field experiments were conducted with three levels of B and livestock manure (LM) (0, 1, and 3 tons/hectare (t/ha)) to assess its effect on physical properties of soils such as bulk density (BD), soil porosity (SP) and aggregate stability (AS), along with soil hydro properties, including field capacity, permanent wilting point (PWP), Plant available water (PAW), and hydraulic conductivity (Ksat). Each treatment was replicated four times in a factorial randomised block design (RBD) using French beans as a test crop in sandy soils and sandy clay loam-textured soils in Rwanda. The data were analysed using analysis of variance (ANOVA) together with the Duncan test at P < 0.05 using R Studio. The findings demonstrated that the co-application of B and LM at varying application rates significantly (P < 0.05) reduced soil bulk density (BD), with the lowest BD observed at the highest application rate (3t/ha). Additionally, the results indicated that the combined application of B and LM at lower rates significantly affected soil water retention characteristics, including permanent wilting point (PWP), field capacity (FC), and saturated hydraulic conductivity (Ksat). The improvements in these properties became more pronounced with increasing B rates when mixed with LM. These results contribute to a better understanding of soil water dynamics following B and LM applications and suggest a promising approach to mitigating water loss, especially in sandy soils.

Agroforestry is widely promoted as an ecosystem-based adaptation strategy to enhance climate resilience, restore degraded landscapes, and support smallholder livelihoods. However, empirical evidence on how project-supported agroforestry interventions influence tree species composition, stocking density, and biomass accumulation remains limited. This study assessed tree and shrub diversity, stocking density, and aboveground biomass across different agroforestry practices in Kayonza District, Eastern Rwanda, comparing project intervention sites supported by the LDCF II Ecosystem-based Adaptation approach project with no intervention areas. Using systematic band transects covering 26 sampling units, all woody species were inventoried and measured for diameter and height, and aboveground biomass was estimated using an allometric equation. A total of 39 species were recorded in no-intervention areas and 36 species in intervention areas, with both systems dominated by a small number of widely preferred species, including Eucalyptus spp., Grevillea robusta, Mangifera indica, Persea americana, Euphorbia tirucalli, and Senna spp. Tree and shrub density was four times higher in intervention areas (172 stems ha-1) than in non-intervention areas (43 stems ha-1), while diameter class distributions were dominated by small trees (<10cm DBH) in both zones. Despite smaller average tree sizes, intervention areas exhibited substantially higher aboveground biomass (15.33 t ha-1) compared to no-intervention areas (4.51 t ha-1), largely due to higher stocking density and wider adoption of biomass-efficient practices. Scattered trees on farm consistently ranked highest in biomass contribution across both zones. These findings demonstrate that targeted agroforestry interventions can rapidly enhance landscape-level biomass and carbon sequestration potential, even at early stages of tree establishment. To sustain and maximize these benefits, future interventions should prioritize agroforestry practice diversification, adaptive management, greater integration of native species and long-term monitoring to balance productivity, biodiversity, and income.