from the soil where little or no external inputs are applied. The depletion in essential plant nutrients of the Rice (Oryza sativa L.) demand in West Africa is unmet because of predominantly sandy Alfisols and Ultisols of the region insufficient production. Legume fixed N [biological N fixation (BNF)] may sustainably increase rice productivity in low-input systems. How-is seen as a major threat to the sustainability of smallever, P deficiency limits BNF on the acid soils encountered in the holder production systems (Smaling and Braun, 1996). region, despite the prevalence of phosphate rock (PR). Pot and fieldDiagnostic on-farm experiments in Cô te d'Ivoire showed experiments were conducted in Cô te d'Ivoire in 1996-1998 to study negative nutrient balances under intensified land use, the impact of combined legume and PR on rice performance. Triple

SUMMARYThe new techniques proposed for agriculture in the Amazon region include rotational fallow systems enriched with leguminous trees and the replacement of biomass burning by mulching. Decomposition and nutrient release from mulch were studied using fine-mesh litterbags with five different leguminous species and the natural fallow vegetation as control. Samples from each treatment were analyzed for total C, N, P, K, Ca, Mg, lignin, cellulose content and soluble polyphenol at different sampling times over the course of one year. The decomposition rate constant varied with species and time. Weight loss from the decomposed litter bag material after 96 days was 30.1 % for Acacia angustissima, 32.7 % for Sclerolobium paniculatum, 33.9 % for Iinga edulis and the Fallow vegetation, 45.2 % for Acacia mangium and 63.6 % for Clitoria racemosa. Immobilization of N and P was observed in all studied treatments. Nitrogen mineralization was negatively correlated with phenol, C-to-N ratio, lignin + phenol/N ratio, and phenol/phosphorus ratios and with N content in the litterbag material. After 362 days of field incubation, an average (of all treatments), 3.3 % K, 32.2 % Ca and 22.4 % Mg remained in the mulch. Results confirm that low quality and high amount of organic C as mulch application are limiting for the quantity of energy available for microorganisms and increase the nutrient immobilization for biomass decomposition, which results in competition for nutrients with the crop plants. As novas técnicas propostas para a agricultura na Amazônia incluem sistema de rotação de capoeira enriquecido com árvores leguminosas e transformando a queima da biomassa em cobertura morta sobre o solo. A decomposição e a liberação de nutrientes da cobertura morta foram estudadas usando sacos de liteira com malha fina que continham cinco tratamentos com diferentes espécies de leguminosas em comparação a um tratamentocontrole com vegetação natural. As amostras para cada tratamento foram analisadas para conteúdos de C total, N, P, K, Ca, Mg, lignina, celulose e polifenóis solúveis em diferentes tempos de amostragem durante um ano. A razão constante de decomposição variou com a espécie e com o tempo. A perda de massa nos sacos de decomposição foi de 30,1 % para Acacia angustissima, de 32,7 % para Sclerolobium paniculatum, de 33,9 % para Inga edulis e para a vegetação secundária, de 45,2 % para Acacia mangium e de 63,6 % para Clitoria racemosa. Foi observada imobilização de N e P em todos os tratamentos, sendo a mineralização do N negativamente correlacionada com o fenol, razão C/N, razão (lignina + fenol)/N, razão fenol/P e o conteúdo de N nos sacos de liteira. Depois de 362 dias de incubação no campo, 3,3 % de K, 32,2 % de Ca e 22,4 % de Mg permaneceram no material em decomposição. Os resultados evidenciaram que a baixa qualidade mineral e a alta quantidade de carbono orgânico e aplicado como cobertura morta podem limitar a quantidade de energia disponível para os microrganismos resultando em uma competição por nutrientes com as plantas agr...

Experiments were conducted during 1996-1998 in screen house and in the field in the humid forest zone of Côte d'Ivoire, to evaluate the effects of phosphorus (P) from phosphate rock (PR) on the performance of the root nodulating legume Crotalaria micans grown for 8 weeks. The experimental soils were acid Ultisols with <4 mg/kg extractable Bray-1 P. Tilemsi PR from Mali and triple superphosphate (TSP) were applied at 60 kg P ha −1 (screen house) and 90 kg P ha −1 (field) to the legume. Legume N-fixed (BNF) was estimated by the 15 N-isotope dilution and δ 15 N natural abundance methods, using Cassia obtusifolia L. as a non-fixing legume reference plant. Without P supply, and under the field conditions, C. micans produced less than 1 tonne of biomass and accumulated 29 kg N/ha. The application of PR-P enhanced legume N by about fourfold over the unfertilised control. There was no significant difference between the effects of TSP and PR. Phosphorus application mainly affected the total amount of N accumulated rather than the percentage derived from the atmosphere (%N dfa) per se. Furthermore, the cumulative effects of PR-P on the performance of C. micans greatly improved with time in the screen house. This study confirms that Tilemsi PR is an agronomically effective source of P for short-duration legume green manure (GM) even in the first year of its application to acid P-deficient soils in the West African humid zone.

The study investigates the effect on rice yields of rock phosphate (PR) combined with a pre-rice green manure (GM) (Aeschynomeme afraspera) as compared with its application directly to the rice crop grown in rotation in Côte d'Ivoire. Ten days after incorporation of the legume residues into flooded potted soil, the anaerobic decomposition of relatively large amounts of applied organic matter, resulted in intense gas emissions from the pots and formation of copper-coloured film in the water surface. A few days later, rice seedlings started to die, presumably due to the release of toxic compounds formed during the GM decomposition. Grain yield increase averaged over GM was 1.6- (PR) and two-fold (triple superphosphate, TSP) above the no-P control treatments. Similarly, mean grain yield over fertilizer P sources was significantly greater following GM than following bare fallow. The relative agronomic effectiveness (RAE) was 78% in the absence of GM. Applying TSP to the legume resulted in 62% more rice dry biomass as compared to P applied alone to rice. Combined PR+GM resulted in a 46% increase over PR alone. Incorporation of unfertilized GM improved rice N nutrition by 62 mg N/pot but was not significantly different from that of the control (no-P and no-GM) treatment. The increase in rice P uptake in response to PR application in the presence of GM and in the absence of GM were 32.3 and 15.5 mg P/pot, respectively. Applying PR with GM contributed to increasing 1.2-fold the amounts of extractable Bray-1 P in soil at rice maturity, as compared to PR applied alone.