Effect Of Gliricidia Sepium And Senna Spectabilis Prunings On Soil Nutrients, Macrofauna, And Maize Yield In Bugesera District, Rwanda

Abstract

The continuous cultivation of land in most of sub-Saharan Africa (SSA) countries has led to a decline in soil fertility as a result of both low organic resource and sub-optimal fertilizer application. A study was conducted at Karama Research station (RAB) and Kintambwe village located in Bugesera District, Rwanda for one season (September 2017 to March 2018) to evaluate the potential influence of two locally available organic residues namely, Gliricidia sepium (Gliricidia) and Senna spectabilis (Cassia) prunings on soil nutrient, soil fauna diversity and maize yields. Organic resource comprised of Gliricidia sepium and Senna spectabilis. The treatment were G. sepium alone (5 t ha-1)=T1; S. spectabilis alone (5 t ha-1)=T2; G. sepium + S. spectabilis (5 t ha -1)=T3; G. sepium (3.75 t ha -1 + 50 kg ha -1 DAP)=T4; S. spectabilis (3.75 t ha -1 + 50 kg ha -1 DAP )=T5; G. sepium + S. spectabilis (3.75 t ha-1 + 50 kg ha -1 DAP)=T6; G. sepium (2.5 t ha -1 + 100 kg ha -1 DAP )=T7; S. spectabilis (2.5 t ha -1 + 100 kg ha -1 DAP)=T8; G. sepium + S. spectabilis (2.5 t ha -1 + 100 kg ha -1 DAP)=T9; inorganic fertilizer alone (200 Kg ha-1 DAP)=T10; Control=T11. The treatments arranged in randomized complete block design (RCBD) replicated four times. Data obtained were subjected to analysis of variance (ANOVA) using GENSTAT whereas differences were evaluated using Fisher’s least significant difference (LSD) at 5% level of significance. Statistical significance of the relationship between soil chemical properties and macrofauna abundance and richness were also conducted using GENESTAT. The decomposition and mineralization rates of nitrogen, phosphorus, potassium, calcium, magnesium for pruning Gliricidia sepium and Senna spectabilis prunings were measured using litter bags for 16 weeks. Rate of weight loss was highest between the 6th and 8th week, where Gliricidia sepium and Senna spectabilis lost 97% and 88% of the weight, respectively. By the end of the 16th week, Senna spectabilis and Gliricidia sepium had lost nearly 100% of the biomass. Nitrogen and phosphorus release was relatively faster in the first xiii two and four weeks for Gliricidia and Senna, respectively. Adding prunings of Gliricidia sepium and Senna spectabilis and their combination significantly (P<0.001) increased soil C, N, and P across all treatment compared to the control. Inorganic fertilizer alone (200Kg ha-1 DAP) doubled maize yields compared to the control and the prunings +inorganic fertilizers increased maize yield significantly compared to where they were applied alone. However, Gliricidia + inorganic fertilizers and /or without fertilizers increased maize yield significantly, while Senna + inorganic fertilizers and /or without did not increase yields. The combination of the two prunings, however, showed a higher yield when combined with inorganic fertilizers compared to where they were applied alone. These yield results were consistent with the faster release of N and P from the mineral fertilizers compared to the organic prunings. Addition of prunings from both sources of organic matter applied at different rates positively influenced the macrofauna diversity and abundance. Among the treatments, 5t ha-1 of prunings increased macrofauna diversity and abundance compared to the control and fertilizer treatment (200 Kg ha-1 DAP) and or where they were applied in three quarter supplemented with inorganic fertilizer (3.75t ha-1 + 50Kg t ha-1) and half dose supplemented with inorganic fertilizers (2.5 t ha-1 + 100 Kg DAP ha-1) respectively. Only earthworms and millipedes positively correlated with Mg and Na, respectively. All other macrofauna groups weakly correlated with total N and extractable P. Earthworms, grasshoppers and cockroaches positively correlated with soil pH, K, Mg while flies and moths negatively correlated with the soil pH. Results of this study demonstrated the potential of the use of Gliricidia sepium and Senna spectabilis prunings in maintaining soil fertility and health and therefore increasing maize productivity.