Biomass and nitrogen accumulation by green manure legumes as affected by phosphate rock in submerged soils

Lowlands in West Africa are increasingly absorbing the growing pressure on land for food crop production. However, the current intensification of lowland cropping systems result in the mining of soil nutrient reserves, particularly of nitrogen (N) and phosphorus (P). While N can be supplied via biological N fixation (BNF) by legumes, P deficiency frequently limits both food crop growth as well as legume BNF, especially on acidic soils in the humid forest and savanna regions. Fortunately, large deposits of phosphate rocks (PR) exist in many African countries; and moreover, the PR efficacy can be enhanced when applied to submerged acidic soils. Thus the use of PR may not only supply the limiting P to soil and food crops, but also stimulate BNF-N by legumes including legumes used for green manuring in production systems. A screen house experiment was conducted to evaluate the effect of PR-P on the performance of N-fixing legume Aeschynomene afraspera L. during three successive 15 cropping cycles under submerged conditions. BNF was estimated by the N-isotope dilution technique, using rice (Oryza sativa L.) as a non-fixing plant. The experimental soil was Ultisol low in available P. -1 Unprocessed PR from Mali was applied at 60 kg P ha . Initial application of PR significantly increased legume above ground biomass and BNF over the unfertilized control by 1.4- and 3-fold respectively. This PR-induced growth stimulation further increased during the subsequent cropping period with a -1 -1 maximum biomass of 6.4 tons ha and 80 kg of BNF-derived N ha above the unamended control. The application of P significantly increased the percent N derived from the atmosphere (% Ndfa). However, compared to the first two cropping cycles, the efficacy of applied PR-P declined during the third cropping cycle, probably as a result of rise in soil pH following soil reduction. The results suggest that PR can be a useful P source for food crops in rotation with legumes

Rock phosphate-P enhances biomass and nitrogen accumulation by legumes in upland crop production systems in humid West Africa

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 15N-isotope dilution and δ15N 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 zon

Response of interspecific and sativa upland rices to Mali phosphate rock and soluble phosphate fertilizer

In West Africa, two-thirds of upland rice is grown on acidic phosphorus (P)- deficient soils. Phosphorus is one of the most limiting-nutrients affecting crop productivity. A three-year field experiment was conducted on a Ferralsol in Coˆ te d’Ivoire to study the response of four interspecific rice cultivars and a sativa (control cultivar) to Tilemsi phosphate rock (PR) and soluble triple superphosphate (TSP) fertilizer. PR was applied at 0, 150, 300, and 450 kg ha71 P once in the first year and residual effects were measured in the following years. TSP (0, 50, 100 and 150 kg ha71 P) was applied yearly. More significant yield increasing (38%) was observed in the second year. Annual application of 50 kg P ha71 as TSP or a one-time application of 150 kg P ha71 as PR was the optimum rate for the production of all cultivars. Higher rates of P from TSP (100 and 150 kg P ha71) gave 2–3 times greater residual P in soil than the optimum rate, inducing no further response of rice. Two interspecific cultivars were identified as the most acid- and low P-tolerant cultivars for improving rice production in West Africa humid forest zone

Rice yields enhanced through integrated management of cover crops and phosphate rock in phosphorus-deficient ultisols in West Africa

The relatively low solubility and availability of phosphorus (P) from indigenous phosphate rock could be enhanced by legumes in the acid soils of humid forest agroecosystems. Crotalaria micans L. was grown in a screenhouse without P or with P from triple superphosphate (TSP) and Malian Tilemsi Rock P. The P response of 20 cover crops was field-evaluated using TSP and Rock P. In both experiments, the fertilized cover crops were followed by upland rice without mineral N or P application. Mean rice grain yield and agronomic residual P-use efficiency were similar for both P sources. In the field, 1-year fallow treatment of Canavalia ensiformis (velvet bean) supplied with Mali Rock P gave the highest rice grain yield of 3.1 Mg ha-1, more than 180% that of 2-year continuous unfertilized rice (cv. 'WAB 56-50'). Among continuous rice plots, 'NERICA 2' (interspecific rice) supplied with Rock P produced the highest yield (2.0 Mg ha-1), suggesting that 'NERICA 2' might have greater potential to solubilize rock P. Results indicate that when combined with an appropriate legume, indigenous rock-P can release sufficient P to meet the P requirement of the legume and a following upland rice crop in rotation

Why NERICA is a successful innovation for African farmers

This paper responds to ‘Funding international agricultural research and the need to be noticed: a case study of NERICA rice’ by Stuart Orr, James Sumberg, Olaf Erenstein and Andreas Oswald, published in this issue of Outlook on Agriculture. In summary, the article by Orr et al, based on an internal WARDA document written in November 2003 and augmented with results from Internet searches, is outdated and does not seem to be fair, objective or useful. We invite the authors to visit WARDA or any of its partners in Sub-Saharan Africa for evidence of the impact of NERICA varieties or the other improved varieties and technologies that have been developed and disseminated by WARDA in recent years

Multivariate Analysis of Diversityof Landrace Rice Germplasm

Multivariate analysis is based on a statistical principle involving observation and analysis of more than one statistical variable at a time. The variability of 434 accessions of rice (Oryza sativa L.) germplasm from Côte d'Ivoire was evaluated for 10 agro-morphological traits in upland conditions at M'bé, Côte d'Ivoire (7°5′ N, 5°1′ W) in 2002 using augmented experimental design and analyzed with multivariate methods. The unweighted pair group method of the average linkage (UPGMA) cluster analysis, canonical discriminant analysis, and principal component analysis (PCA) were used to analyze the data obtained. This enabled the assessment of the extent and pattern of variation of the germplasm and identification of the major traits contributing to the diversity. Seven cluster groups were obtained from the 10 agro-botanical traits using the UPGMA. Canonical discriminant analysis showed the contribution of each trait to the classification of the rice accessions into different cluster groups. The first three principal components explained about 72.24% of the total variation among the 10 characters. The results of canonical discriminant analysis and PCA suggested that traits such as plant height, number of days to heading and maturity, tillering ability, and grain size (weight, length, width, and shape) were the principal discriminatory characteristics. It was concluded that variation exists in the germplasm, which provides opportunities for this collection to be useful for genetic improvement

Multivariate analysis of diversity of landrace rice germplasm

Abstract Multivariate analysis involves observation and analysis of more than one statistical variable at a time. The variability of 434 accessions of rice (Oryzasativa L.) germplasm from Côte d&apos;Ivoire was evaluated for 14 agromorphological traits in upland conditions at M&apos;bé, Côte d&apos;Ivoire (7°5´ N; 5°1´ W), using augmented experimental design, and analyzed with multivariate methods. The unweighted variable pair group method of the average linkage cluster analysis (UPGMA), canonical discriminant analysis (CAN) and principal component analysis (PCA) were used to analyze the data obtained. This enabled assessment of the extent and pattern of variation of the germplasm, and identification of the major traits contributing to the diversity. Seven cluster groups were obtained from the 14 agro-botanical traits using UPGMA. CAN showed the contribution of each trait to the classification of the rice accessions into different cluster groups. The first three principal components explained about 58.41% of the total variation among the 14 characters. The results of CAN and PCA suggested that traits such as plant height, leaf length, number of days to heading and maturity, tillering ability, panicle length and grain size (weight, length and width) were the principal discriminatory characteristics. It is concluded that variation exists in the germplasm, which provides opportunities for this collection to be useful for genetic improvement