Rice In West Africa Research Articles

Combined Effects of Legumes with Rock Phosphorus on Rice in West Africa

Rice (Oryza sativa L.) demand in West Africa is unmet because of insufficient production. Legume fixed N [biological N fixation (BNF)] may sustainably increase rice productivity in low‐input systems. However, P deficiency limits BNF on the acid soils encountered in the region, despite the prevalence of phosphate rock (PR). Pot and field experiments were conducted in Côte d'Ivoire in 1996–1998 to study the impact of combined legume and PR on rice performance. Triple superphosphate and PR were applied at rates of 60 (pot) and at 90 (field) kg P ha−1 to rice and the legume Aeschynomene afraspera grown for 8 wk and then incorporated before rice transplanting. Legume fixed N was determined by 15N isotope dilution. Under field conditions, addition of PR doubled the biomass of A. afraspera. Irrespective of P source, P application increased the amount of BNF‐N (three‐ to eightfold) to 36 mg N plant−l in pots and to 84 kg N ha−1 in the field. Nitrogen derived from the air was correlated with legume P uptake (r = 0.97∗∗∗, where ∗∗∗ = significant at the 0.001 level) and nodulation (r = 0.91∗∗, where ∗∗ = significant at the 0.01 level). The synergy of PR and BNF on N and P cycling improved P nutrition and total biomass of subsequent lowland rice under pot conditions. Combining legume green manure (GM) with PR enhanced soil extractable Bray‐1 P and may thus play an important role in improving the availability of PR. Under field conditions, due to asynchrony in GM nutrient release and demand, the impact of the combined GM–PR treatment on rice yield was minimal.

A framework to improve fertilizer recommendations for irrigated rice in West Africa

A framework to optimize soil fertility management in irrigated rice, based on soil and climate variability, fertilizer and paddy prices and farmers' objectives is presented. The framework uses three models in succession. The dynamic ecophysiological ORYZAS model simulates potential rice yields under irrigation, based on weather conditions, cultivar choice and sowing date. This yield potential is used in the static FERRIZ model, together with site specific information on recovery efficiency of applied N, P and K, indigenous soil N, P and K supply, and maximum N, P and K accumulation and dilution in rice dry matter. Resulting outputs are required fertilizer doses to obtain different target yields depending on yield potential and soil nutrient supply. The framework allows sensitivity analysis and agro-economic evaluation of different fertilizer options. In a last step, the dynamic decision tool RIDEV is used to simulate optimal timing of different management actions such as fertilizer application, weeding, and harvest. Resulting integrated crop management recommendations ensure high resource use efficiency adapted to local socio-economic and bio-physical conditions. Provided necessary input data are available, this framework can be applied to field, perimeter or regional scale. The framework was applied to the Office du Niger in Mali, using field data of 58 farmers. In the wet season, fertilizer doses adjusted to three soil fertility classes outperformed current uniform recommendations only slightly, except on soils with very low K supply (10 cases). Only on these soils was application of K profitable. Profit-optimizing fertilizer doses had high costs and low value/cost ratios. Target yields close to potential yield increased farmers' risk. Adjusting fertilizer doses to the lower yield potential in the dry season reduced costs and risk without reducing profit, resulting in better value/cost ratios. New simple recommendations for both wet and dry seasons were formulated.

Black Rice: The African Origins of Rice Cultivation in the Americas

Black Rice: The African Origins of Rice Cultivation in the Americas

The African antecedents of Uncle Ben in U.S. rice history

This article examines the cultural antecedents of rice cultivation in South Carolina, arguing that its establishment in the colony represents the transfer of an African knowledge system via slavery to the Americas. Slaves from West Africa's rice region provided the critical knowledge that transformed lowland environments for the cereal's cultivation, which would lead Carolina rice to global economic prominence. The ecological, ethnic and gendered basis of this knowledge system are examined historically in West Africa's rice region, where a separate species of rice was domesticated more than two thousand years ago. An overview of African land use, methods of cultivation, and processing reveal the lineaments of African rice culture in South Carolina. The familiar motif of Uncle Ben on packages of converted rice represents an enduring social memory of that legacy.

Phosphorus input-output on an ultisol cropped to upland rice in West Africa

A long-term (1993-98) experiment was conducted in Man, Cote d'Ivoire, West Africa, to study the effect of four proved upland rice cultivars to direct phosphorus (P) in 1993 and to residual P in 1994, 1995, 1996 and 1998, applied at five rates only once in 1993. The soil at the site in the humid forest zone is an Ultisol. The four rice cultivars were WARDA-bred cultivars WAB56-125, WAB56-104 and WAB556-50 and check IDSA6, and the five rates of P fertilizers, applied as triple superphosphate were (0, 45, 90, 135 and 180 kg P/ha). All plots received a uniform application of N (applied as urea at 100 kg/ha) and K (applied as KCl at 100 kg/ha). At harvest, rice grain and straw yields were recorded and total P uptake in rice biomass was computed by analysing the P content of the grain and straw samples. The P input-output value (amount of P applied and amount of P taken up in the grain plus straw in five crops) was negative in the no-P treatment but positive in treatments where P fertilizer was added. The results showed that in five crops, only a small fraction of the applied P fertilizer was removed by the rice crop, which varied from 5.5-9.4%, and this value decreased with the increase in the rate of P applied. In 1998, however, after 5 years of successive cropping, available P in the soil was found to be similar and not affected by the rate of P fertilizer applied in 1993

Nutrient application reduces iron toxicity in lowland rice in West Africa

Iron toxicity is a widespread nutrient disorder that affects rice growing in inland swamps and on irrigated lowland soils throughout the humid forest and savanna zones of West Africa. It has been reported to reduce lowland rice yields in West Africa by 12-100%, depending on the intensity of the toxicity and the tolerance of the rice cultivar (Sahrawat et al 1996). The disorder occurs when large amounts of iron are mobilized in situ or when an inflow of iron occurs from adjacent upper slopes, especially in the inland valley systems of West and Central Africa. In mineral soils, the occurrence of iron toxicity is associated with a range of concentration of ferrous ions in the soil solution. Light-textured soils high in extractable acidity are especially prone to iron toxicity (Moormann and van Breemen 1978). It is also known that a high concentration of iron in solution decreases the absorption of other nutrients, especially phosphorus (P), potassium (K), and zinc (Zn) (Yoshida 1981).

Arthropod populations and rice yields in direct-seeded and transplanted lowland rice in West Africa

Two methods for planting rice in irrigated lowland were evaluated during the wet seasons of 1994 and 1995 to determine their effect on rice arthropod numbers, insect-caused rice plant damage and rice grain yield. The six treatments tested were: hand transplanting of seedlings at spacings of 14 cm × 14 cm, 20 cm x 20 cm, and 30 cm x 30 cm; and direct-seeding of rice at 60 kg seeds ha -1 , 90 kg seeds ha -1 and 120 kg seeds ha -1 . The most abundant arthropods in the study were the diopsid flies, Diopsis longicornis Maquart and D. apicalis Dalman; the green leafhoppers Nephotettix spp.; the white leafhoppers Cofana unimaculata (Signoret) and C. spectra (Distant); spiders; dragonflies and damselflies; and stem borers. There was no overall difference between transplanting and direct-seeding, or between plant densities, in regard to sweep net counts of Cofana spp. and spiders. Diopsis longicornis and D. apicalis adult numbers were highest in the 20 cm × 20 cm transplanted plots in 1994, but no significant differences occurred in 1995. Nephotettix spp. adult numbers were highest in the 120 kg seeds ha -1 direct-seeded plots in 1995 but no significant differences occurred in 1994. The percentage of tillers infested with stem borers was highest in the three transplanted and the 120 kg seed ha -1 direct-seeded treatments in 1994 and the three transplanted treatments in 1995. In 1995, the percentage of whiteheads (empty panicles) caused by stem borer feeding was highest in the direct-seeded treatments, increasing from the low rate of 60 kg seeds ha -1 to the highest rate of 120 kg seeds ha -1 . Grain yields were generally similar in the transplanted and direct-seeded plots. Implications of planting methods and plant density as management practices in rice IPM and labour requirements for rice production are discussed.

Improved water control and crop management effects on lowland rice productivity in West Africa

Much of the rapidly-growing demand for rice in West Africa will be met from production in inland valley swamps which are abundant and relatively robust with regard to cropping intensification. Rice yields in the traditional, predominating non-bunded systems are low (about 1.5 Mg ha−1). Informal development of traditional rainfed lowlands is currently occurring across the region, mainly with low-cost interventions such as the building of field bunds. Relating lowland rice yield to quantitative information on resource base quality and agronomic practices will improve future research priorities and guide site and system-specific targeting of available technical options. Diagnostic on-farm trials were conducted in 62 traditional and 40 improved (bunded) rainfed lowland fields in three agro-ecological zones of Cote d'Ivoire (Guinea savanna, bimodal forest, and monomodal forest zones) to quantify effects of improved water control on productivity. Weed biomass and rice grain yield were determined in farmers' fields and in super-imposed researcher-managed subplots (clean weeding, zero N control treatment, and mineral fertilizer N application). Grain yield variability was attributed to agronomic practices using multiple regression analysis. Bunding significantly increased rice grain yield across sites by about 40% and controlled weeds, with approximately 25% less weed biomass in bunded than in open plots. Mineral fertilizer N application significantly increased rice yields (18% on average across sites) only in bunded fields, where N use efficiency was 12 compared to 4 kg of rice grain per kg of applied N in open fields. Across environments, about 60% of the observed variability in rice grain yields was explained by water control and the timing of agronomic management interventions (weeding, N application). The increased development of lowland rice areas through the construction of field bunds has the potential to significantly increase rice production in West Africa, while also possibly reducing labor requirements for hand weeding and allowing for a more efficient use of mineral N fertilizers. The benefits from construction of bunds are likely to be largest in the relatively well-drained inland valleys of the savanna and bimodal rainfall forest, compared to the high-rainfall monomodal forest zones.

Mechanisms for iron toxicity tolerance in lowland rice

Iron toxicity is a widespread nutrient disorder of lowland rice in West Africa. Soluble iron present in the soil solution under waterlogged conditions is absorbed by roots and accumulates in leaves. It causes poor growth and tillering and severe yield reductions, associated with leaf discoloration. Field experiments were conducted during 1994–1996 at an iron‐toxic lowland site at Korhogo (Ivory Coast) to study the interactions between iron toxicity and the addition of various plant nutrients. Nine nutrient element treatments (combinations of N, P, K and Zn, including no fertilizer) were tested on one iron‐susceptible (Bouake 189) and one iron‐tolerant (CK 4) cultivar. The application of P, K and Zn with N reduced iron toxicity symptoms and increased yield in both cultivars. Strong correlations were observed between grain yield and scored leaf iron toxicity symptoms across seasons and treatments. The iron‐tolerant rice cultivar absorbed less iron or transported less from roots to leaves, indicating the presence of a physiological avoidance mechanism. At any given concentration of iron in the leaves, net photsynthetic rates were lower in the susceptible than in the tolerant cultivar. The iron‐tolerant cultivar owed its superior performance under iron‐toxic conditions partly to avoidance (less iron accumulation in leaves) and tolerance (superior photosynthetic potential in the presence of absorbed iron in the leaves). Data indicated that these mechanisms can be further enhanced through the application of P, K and Zn.

The influence of cyst nematodes (Heterodera sacchari) and drought on water relations and growth of upland rice in Côte d'Ivoire

This study was undertaken to examine the influence of cyst nematodes (Heterodera sacchari) and drought stress, in isolation and combination, on the water status and growth of rice in Cote d'Ivoire. Drought is considered one of the main yield-limiting factors to upland rice in West Africa, while H. sacchari is emerging as a potentially serious pest. A field study conducted during 1997 at the West Africa Rice Development Association (WARDA) showed that under low water availability in sandy soil, damage to a nematode susceptible Oryza sativa (cv IDSA6) is significant. Visual drought score and physiological parameters were significantly affected (P≤0.01) in plots with a mean population density of 39.4 H. sacchari eggs ml-1 soil at 81 days after sowing, compared to plots with a mean density of 1.2 eggs ml-1. Stomatal conductance, leaf water potential and relative water content were lower, leaf chlorophyll content was greater, and near total yield losses were observed in higher nematode density plots. In 1-l pots following 5 days of imposed drought, the H. sacchari-resistant and drought-resistant O. glaberrima (cv CG14) showed a reduction in stomatal conductance of 73% and in leaf water potential by 0.96 MPa (54%). The effect of H. sacchari (473 eggs l-1 soil) inoculated as cysts to soil before sowing was similar but less severe. The combination of both stresses had similar but yet more pronounced effects than the single stresses on stomatal conductance, leaf water potential and leaf dry weight in CG14. IDSA6 responded in a similar manner to CG14, but less acutely to both stresses. Only the combined stresses resulted in a significant (P≤0.05) reduction in osmotic potential and root dry weight compared with the control, for either CG14 or IDSA6. It is suggested that H. sacchari increased the effects of drought and drought-related losses. This may give a false impression of drought susceptibility in field screening for cultivars, and complicate models which predict crop damage caused by nematodes.

Seasonal Abundance of Rice-Feeding Insects and Spiders in Continuously Cropped Lowland Rice in West Africa

A ‘rice garden’ with monthly plantings of rice was established in an irrigated lowland area in April 1993 and continued for 3 years. Populations of the most common insects, the stalk-eyed flies, Diopsis spp., and the green leafhoppers, Nephotettix spp., and spiders and stemborer damage varied distinctly in relation to month of transplanting. Arthropod populations also exhibited distinct patterns in relation to crop growth stage. Grain yields varied with month of transplanting but there was no distinct trend from one year to the next. This study indicated that continuous cropping of the same fields over a 3-year period did not result in a build-up of insect pests or a decline in grain yield.

Rice yield and productivity gaps in irrigated systems of the forest zone of Côte d'Ivoire

Much of the rapidly growing demand for rice in West Africa will be met from increased production in irrigated lowlands, which cover about 12% of the regional rice-growing area. A large potential for expansion of irrigated areas exists particularly in the inland valleys of the humid forest zone. Current production is characterized by large variability in productivity, management practices and production constraints. Quantifying the variability in rice yield and identifying the determining factors are prerequisites to the development of site-specific recommendations and to improved targeting of technologies. Diagnostic on-farm trials were conducted on 64 irrigated lowland fields in the humid forest zone of southern Côte d'Ivoire, in 1995–1996. This was a part of the regional gradient study of irrigated systems from the desert margin to the humid forest zone. Cropping calendars, field operations and input use were monitored. Weed biomass, rice N uptake, and grain yield were determined in farmers' fields as well as in super-imposed, researcher-managed subplots (clean weeding, no N control, and mineral fertilizer N application). Rice yield potential was simulated by using the Oryza-S crop growth model. Yield losses were attributed to management factors based on performance of rice in researcher-managed subplots (management-related yield gap) and by multiple regression with management options. Grain yields varied between 0.2 and 7.3 Mg ha −1 with mean yields of 3.2 in partially and 4.2 Mg ha −1 in fully irrigated systems, 44% and 57% of the potential yield of 7.3 Mg ha −1, respectively. Age of seedlings at transplanting, timeliness of operations and application of P fertilizer were correlated to yield and explained 60% of the observed variability. Grain yield was correlated with N uptake ( r 2 = 0.93 ***) but not with N application rate. Split application of mineral fertilizer N was associated with a 0.48 Mg ha −1 yield increase ( p = 0.002), regardless of the quantity applied. Additional weeding increased yield only in systems with imperfect irrigation. Weed biomass was reduced with improved water control and it increased with age of seedlings at transplanting, and was higher in direct-seeded than in transplanted rice. Echinochloa spp. were the most common weeds in fully irrigated systems and Panicum laxum was more common in the imperfectly irrigated fields. While improved water management was associated with substantial rice yield increases (1.16 Mg ha −1), the timeliness of transplanting, weeding and N fertilization appears to be the key to increased rice yields in the forest zone of West Africa.

Plant phosphorus and rice yield in an Ultisol of the humid forest zone in West Africa

Little attention has been devoted to calibrating plant tissue tests for phosphorus (P) in the field for upland rice in West Africa, although information is needed for improving crop production through efficient P nutrition. A field experiment was conducted under rainfed conditions in the 1994 season to establish the relationships between plant P content and grain yield of upland rice grown on an Ultisol, having a range in extractable P, in the humid forest zone of Ivory Coast. The critical limit of P content in the whole rice plant tops at the tillering stage, at 90% relative grain yield, was found to be 2 g kg‐1 P for the four upland rice cultivars tested. Total P uptake in the biomass was significantly correlated with rice grain (r=0.81, n=20) and straw (r=0.79) yields of the cultivars.

Extractable phosphorus and rice yield in an ultisol of the humid forest zone in West Africa

Little attention has been devoted to calibrating soil tests for phosphorus (P) in the field for upland rice in West Africa. The information is needed to improve fertilizer P recommendations. A field experiment was conducted in the rainy season of 1994 to establish the relationship between extractable P by Bray 1 and grain yield of four upland rice cultivars grown on an Ultisol in the forest zone of Ivory Coast. The critical limit of Bray 1 P in the soil at 90% relative rice grain yield varied from 12.5 to 15.0 mg P/kg of soil for the four cultivars tested. The P critical limit in the soil tended to be lower for the cultivars of rice earlier found to be efficient at converting applied P into grain yield.

Striga on rice in West Africa; crop host range and the potential of host resistance

Striga aspera and Striga hermonthica can cause serious losses in upland rice in the guinea savanna areas of West Africa. In pot experiments, seed from Striga spp., collected from maize and rice crops in northern Ivory Coast, were sown with maize, rice, millet and sorghum. S. aspera collected from rice and maize, grew on maize, sorghum and rice, but not on millet. S. hermonthica from either maze, sorghum or rice showed no specificity and parasitized all four test crops. S. asiatica collected from maize and Andropogon sp. grew on maize and rice, but not on millet. In field experiments, five cultivars of Oryza glaberrima and two cultivars of Oryza saliva, IR47255-B-B-5-4 and IR49255-B-B-5-2, offered partial resistance to S. aspera. These rice cultivars also showed lower levels of parasitization by S. hermonthica. Parasitization of rice by 17 Striga stems m −2, reduced rice grain yield by about 50%. Growth of O. glaberrima appeared to be less affected by Striga parasitization than a susceptible O. saliva cultivar.

Incidence, distribution and severity of bacterial diseases on rice in West Africa

Abstract The incidence, distribution and severity of bacterial diseases of rice was studied in West Africa. Two bacterial diseases‐the bacterial leaf streak caused by Xanthomonas campestris pv. oryzicola and bacterial leaf blight caused by Xanthomonas campestris pv. oryzae‐ were detected. Both bacterial diseases were found to be more prevalent and severe in the Sahelian than in the forest zone of West Africa. They are rarely found in the more humid zone of West Africa. Bacterial leaf blight was found to be more widely distributed in the Sahelian region than the bacterial leaf streak. The incidence of bacterial leaf blight was found to be aggravated by high dosages of nitrogen. Lossese ranging from 2.7% to 41.0% in grain yiefd were inflicted on the rice crop by bacterial leaf blight. Some control measures are recommended.

The spurious success of import substitution: The case of West Africa

Rice in West Africa: Policy and Economics by Scott R. Pearson et al. Stanford University Press, Stanford (California), 1981. xix plus 482 pp. including maps and figures. $38,50.

The ecology, bionomics and control of rice stem-borers in West Africa

The importance of rice in West Africa and the problem posed by pests were highlighted. Stem-borers are regarded as major insect pests of rice and available information on yield losses attributable to insect pests in general and stem-borers in particular, was reviewed. Damage caused by stem-borers usually results in “dead hearts” and “white heads” though other effects including a synergistic interaction between stem-borers and rice blast have been recorded. Survey methods and sampling of rice stem-borers were discussed and brief descriptions on distribution, behaviour and biology of the major rice stem-borers namely, Chilo spp., Maliarpha separatella, Scirpophaga spp., Sesamia spp. and Diopsis spp. were given. Current control tactics under investigation in West Africa include chemical, cultural and biological methods.

Rice in West Africa: Policy and Economics

Rice in West Africa: Policy and Economics

Rice in West Africa: policy and economics by Scott R. Pearson, J. Dirck Stryker, and Charles P. Humphreys et al. Stanford University Press, 1981. Pp. xxi + 482. $38.50.

Rice in West Africa: policy and economics by Scott R. Pearson, J. Dirck Stryker, and Charles P. Humphreys et al. Stanford University Press, 1981. Pp. xxi + 482. $38.50.