Effets directs et résiduels d’un tri-compost à base de paille de riz, fumier animal et source azotée altérnative (Tithonia Diversifolia ou urine de lapin) sur la production d’amarante

Abstract

The progressive decline in soil fertility represents a major constraint to sustainable agricultural production in tropical regions, particularly in sub-Saharan Africa. In this context, the use of locally available organic amendments constitutes a viable alternative to mineral fertilizers. This study aimed to evaluate the direct and residual agronomic value of tri-composts based on rice straw and animal manures, enriched either with Tithonia diversifolia (Hemsl) A. Gray biomass or with rabbit urine, on the production of amaranth (Amaranthus spp.). The experiment was conducted under greenhouse conditions at the Faculty of Agronomy and Bioengineering, University of Burundi, using a randomized complete block design with eight treatments and three replications. A single application of 10 g of compost per pot (4 kg of soil) was incorporated before sowing. Amaranth was grown over four successive cropping cycles (eight months) to assess both the direct effect (first harvest) and the residual effect (three subsequent harvests). Measured parameters included shoot biomass, root biomass, total biomass, soil pH, and electrical conductivity (EC). Data were analyzed using analysis of variance (ANOVA) at the 5% significance level. Results showed that all tri-compost treatments significantly improved soil chemical properties and amaranth biomass production compared to the unamended control. Soil pH decreased from 9.06 in the control treatment to values ranging between 8.18 and 8.63 in tri-compost treatments (p < 0.001), indicating a buffering effect of organic amendments. Electrical conductivity was also significantly reduced, from 0.042 μS cm⁻¹ in the control to 0.022–0.030 μS cm⁻¹ in enriched compost treatments (P < 0.001). Across the four harvests, mean total biomass increased from 8.44±3.99 g in the control to 13.95 ± 2.23 g with cattle manure and 13.02 ± 1.63 g with the rabbit-urine-enriched tri-compost (B603A). Tri-composts enriched with Tithonia diversifolia (Hemsl) A. Gray produced total biomasses ranging from 11.02±3.31 g to 12.68±2.56 g. Root biomass differed significantly among treatments (p = 0.0356), with higher values recorded in enriched composts (1.63–1.75 g) compared to the control (0.98 g). The treatment × harvest interaction was significant for total biomass (p = 0.00785), indicating a gradual nutrient release and a strong residual effect of tri-composts during later harvests. In generally, tri-composts enriched with Tithonia diversifolia (Hemsl) A. Gray or rabbit urine significantly enhance soil fertility and amaranth productivity. Rabbit urine showed a rapid direct effect comparable to Tithonia diversifolia (Hemsl) A. Gray, confirming its potential as an effective local nitrogen source for sustainable tropical agriculture.