Rice Scheme Research Articles

Host choice and multiple blood feeding behaviour of malaria vectors and other anophelines in Mwea rice scheme, Kenya

BackgroundStudies were conducted between April 2004 and February 2006 to determine the blood-feeding pattern of Anopheles mosquitoes in Mwea Kenya.MethodsSamples were collected indoors by pyrethrum spay catch and outdoors by Centers for Disease Control light traps and processed for blood meal analysis by an Enzyme-linked Immunosorbent Assay.ResultsA total of 3,333 blood-fed Anopheles mosquitoes representing four Anopheles species were collected and 2,796 of the samples were assayed, with Anopheles arabiensis comprising 76.2% (n = 2,542) followed in decreasing order by Anopheles coustani 8.9% (n = 297), Anopheles pharoensis 8.2% (n = 272) and Anopheles funestus 6.7% (n = 222). All mosquito species had a high preference for bovine (range 56.3–71.4%) over human (range 1.1–23.9%) or goat (0.1–2.2%) blood meals. Some individuals from all the four species were found to contain mixed blood meals. The bovine blood index (BBI) for An. arabiensis was significantly higher for populations collected indoors (71.8%), than populations collected outdoors (41.3%), but the human blood index (HBI) did not differ significantly between the two populations. In contrast, BBI for indoor collected An. funestus (51.4%) was significantly lower than for outdoor collected populations (78.0%) and the HBI was significantly higher indoors (28.7%) than outdoors (2.4%). Anthropophily of An. funestus was lowest within the rice scheme, moderate in unplanned rice agro-ecosystem, and highest within the non-irrigated agro-ecosystem. Anthropophily of An. arabiensis was significantly higher in the non-irrigated agro-ecosystem than in the other agro-ecosystems.ConclusionThese findings suggest that rice cultivation has an effect on host choice by Anopheles mosquitoes. The study further indicate that zooprophylaxis may be a potential strategy for malaria control, but there is need to assess how domestic animals may influence arboviruses epidemiology before adapting the strategy.

Blood-feeding patterns of Culex quinquefasciatus and other culicines and implications for disease transmission in Mwea rice scheme, Kenya

Studies were conducted in Mwea Rice Scheme, Kenya during the period April 2005 and January 2007 to determine the host-feeding pattern of culicine mosquitoes. Mosquitoes were collected indoors and outdoors and tested for human, bovine, goat, and donkey blood meals by an Enzyme-Linked Immunosorbent Assay. A total of 1,714 blood-engorged samples comprising Culex quinquefasciatus Say (96.1%), Culex annulioris Theobald (1.8%), Culex poicilipes Theobald (0.9%), Aedes cuminsi Theobald (1.0%), Aedes taylori Edwards (0.1%), and Mansonia africana Theobald (0.1%) were tested. Except for A. taylori, in which the single blood meal tested was of bovine origin, the other species fed mostly on both bovine (range 73.3-100%) and goats (range 50-100%). Donkeys were also common hosts for all species (range 19.4-23.5%) except A. taylori and M. africana. C. quinquefasciatus was the only species containing human blood meals (0.04), and indoor collected populations of this species had significantly higher frequency of human blood meals (9.8%) compared with outdoor-collected populations (3.0%). Mixed blood feeding was dominant among culicine species comprising 50.0%, 73.3%, 73.5%, 80.6%, and 94.1% of the samples for M. africana, C. poicilipes, C. quinquefasciatus, C. annulioris, and A. cuminsi, respectively. Ten mixed blood meal combinations including a mixture of all the four hosts were observed in C. quinquefasciatus, compared to one blood meal combination for M. Africana, and two combinations for C. poicilipes, C. annulioris, and A. cuminsi. Mixed bovine and goat blood meal was the most common combination among the five culicine species followed by a mixture of donkey, bovine, and goat blood meals. We conclude that culicine species in Mwea are least likely to be vectors of lymphatic filariasis due to their high "preference" for livestock over human hosts, but they present an increased risk for arbovirus transmission particularly Rift Valley Fever virus, in which domestic animals serve as amplification hosts.

Drainage problems in the rice schemes of the Office du Niger (Mali) in relation to water management

This paper quantifies the impact of water management on the incidence of drainage problems. It is based on an empirical study in the rice schemes of the Office du Niger. The rice schemes face perpetual drainage problems at harvest, which incur increased production costs as well as production and/or quality loss. The rice schemes discharge water into natural depressions and their filling-up poses an ultimate bottleneck to the disposal of drainage water. Results demonstrate that the principal causes of drainage problems are the saturation of the drainage system with excess irrigation water and the insufficient maintenance of the collector drains. Once the collector drain is no longer saturated, maintenance of the tertiary drains becomes important, while the disparity in harvest dates between adjacent fields always aggravates the drainage problem. Since the benefits of individual efforts often accrue to neighbors or are dissipated throughout the entire drainage system, water management practices related to drainage should be tackled at the collective level using Water User Associations as a platform.

A grid-based infrastructure for ecological forecasting of rice land Anopheles arabiensis aquatic larval habitats

BackgroundFor remote identification of mosquito habitats the first step is often to construct a discrete tessellation of the region. In applications where complex geometries do not need to be represented such as urban habitats, regular orthogonal grids are constructed in GIS and overlaid on satellite images. However, rice land vector mosquito aquatic habitats are rarely uniform in space or character. An orthogonal grid overlaid on satellite data of rice-land areas may fail to capture physical or man-made structures, i.e paddies, canals, berms at these habitats. Unlike an orthogonal grid, digitizing each habitat converts a polygon into a grid cell, which may conform to rice-land habitat boundaries. This research illustrates the application of a random sampling methodology, comparing an orthogonal and a digitized grid for assessment of rice land habitats.MethodsA land cover map was generated in Erdas Imagine V8.7® using QuickBird data acquired July 2005, for three villages within the Mwea Rice Scheme, Kenya. An orthogonal grid was overlaid on the images. In the digitized dataset, each habitat was traced in Arc Info 9.1®. All habitats in each study site were stratified based on levels of rice stageResultsThe orthogonal grid did not identify any habitat while the digitized grid identified every habitat by strata and study site. An analysis of variance test indicated the relative abundance of An. arabiensis at the three study sites to be significantly higher during the post-transplanting stage of the rice cycle.ConclusionRegions of higher Anopheles abundance, based on digitized grid cell information probably reflect underlying differences in abundance of mosquito habitats in a rice land environment, which is where limited control resources could be concentrated to reduce vector abundance.

Mosquito species diversity and abundance in relation to land use in a riceland agroecosystem in Mwea, Kenya

We conducted an entomological survey to determine the mosquito species diversity and abundance in relation to land use in the Mwea rice scheme, Kenya. Adult mosquitoes were collected by indoor spraying of houses and outdoors by CDC light traps in three villages representing planned (Mbuinjeru) and unplanned (Kiamachiri) rice agroecosystems and a non-irrigated agroecosystem (Murinduko). During the 12-month sampling period, a total of 98,708 mosquitoes belonging to five genera and 25 species were collected. The five most common species collected during this study were Anopheles arabiensis Patton (52.5%), Culex quinquefasciatus Say (36.7%), Anopheles pharoensis Theobald (5.2%), Anopheles coustani Laveran (1.4%), and Anopheles funestus Giles (1.3%). Anopheles arabiensis, Cx quinquefasciatus, and An. pharoensis were more abundant in rice agroecosystems than in the non-irrigated agroecosystem, and in planned than in the unplanned rice agroecosystems. In contrast, An. funestus was more abundant in the non-irrigated agroecosystem. The mosquito species diversity (H) and evenness (E(H)) in the non-irrigated agroecosystem (Shannon diversity Index, H = 1.507, EH = 0.503) was significantly higher than in the rice agroecosystems (H) = 0.968, E(H) = 0.313, unplanned; and H= 1.040, E(H) = 0.367 planned). Results of lag cross correlation analysis revealed a strong relationship between rainfall and the abundance of An. arabiensis, and C. quinquefasciatus in the non-irrigated agroecosystem but not in the rice agroecosystems. It is inferred from the data that different levels of habitat perturbations with regard to rice cultivation have different effects on mosquito diversity and abundance. This provides an understanding of how mosquito diversity is impacted by different habitat management and rice cropping strategies.

Spatially targeting Culex quinquefasciatus aquatic habitats on modified land cover for implementing an Integrated Vector Management (IVM) program in three villages within the Mwea Rice Scheme, Kenya

BackgroundContinuous land cover modification is an important part of spatial epidemiology because it can help identify environmental factors and Culex mosquitoes associated with arbovirus transmission and thus guide control intervention. The aim of this study was to determine whether remotely sensed data could be used to identify rice-related Culex quinquefasciatus breeding habitats in three rice-villages within the Mwea Rice Scheme, Kenya. We examined whether a land use land cover (LULC) classification based on two scenes, IKONOS at 4 m and Landsat Thematic Mapper at 30 m could be used to map different land uses and rice planted at different times (cohorts), and to infer which LULC change were correlated to high density Cx. quinquefasciatus aquatic habitats. We performed a maximum likelihood unsupervised classification in Erdas Imagine V8.7® and generated three land cover classifications, rice field, fallow and built environment. Differentially corrected global positioning systems (DGPS) ground coordinates of Cx. quinquefasciatus aquatic habitats were overlaid onto the LULC maps generated in ArcInfo 9.1®. Grid cells were stratified by levels of irrigation (well-irrigated and poorly-irrigated) and varied according to size of the paddy.ResultsTotal LULC change between 1988–2005 was 42.1 % in Kangichiri, 52.8 % in Kiuria and and 50.6 % Rurumi. The most frequent LULC changes was rice field to fallow and fallow to rice field. The proportion of aquatic habitats positive for Culex larvae in LULC change sites was 77.5% in Kangichiri, 72.9% in Kiuria and 73.7% in Rurumi. Poorly – irrigated grid cells displayed 63.3% of aquatic habitats among all LULC change sites.ConclusionWe demonstrate that optical remote sensing can identify rice cultivation LULC sites associated with high Culex oviposition. We argue that the regions of higher Culex abundance based on oviposition surveillance sites reflect underlying differences in abundance of larval habitats which is where limited control resources could be concentrated to reduce vector larval abundance.

Irrigation performance at tertiary level in the rice schemes of the Office du Niger (Mali): Adequate water delivery through over-supply

The performance of irrigation in rice schemes of the Office du Niger in 1995 is compared with the situation nearly 10 years later (2004). Major physical rehabilitations and economic and institutional reforms carried out from the 1980s onwards succeeded in making a success story of the Office du Niger. This paper analyzes the irrigation performance at tertiary level in the light of the interventions implemented and current water management practices using the performance indicators proposed by Molden and Gates. The interventions succeeded in establishing a good adequacy of water supply (0.96 for 1995 and 0.92 for 2004), thus creating the necessary conditions for boosting rice production. Because of the minimal management strategies of farmers and water bailiffs, efficiency is however low and shows no sign of improving between 1995 (0.51) and today (0.56). Dependability and equity are also poor according to Molden and Gates’ criteria, but given that water supply is generally adequate, these indicators appear less relevant. An alternative calculation procedure is proposed for situations where water is not scarce. Results of the adapted indicators show satisfactory levels of dependability and equity. Measures aimed at increasing efficiency will inevitably be costly, but are redeemed justified. Indeed, even though water is not a limiting factor during the main growing season until today, this is to change soon as the irrigated surface will be strongly expanded. In addition, increased irrigation efficiency might help to solve the recurrent drainage problems that trouble the harvest in the rice schemes of the Office du Niger.

Scheduling the cropping calendar in wet-seeded rice schemes in Malaysia

The Besut Irrigation Scheme, Terengganu, Malaysia is one of the eight gazetted main rice-growing areas in Malaysia. These eight granaries are targeted to produce only 65% of the total rice requirements of the nation. This scheme faces water scarcity especially during the off-season with the present existing cropping schedule. This study discusses the ways and means to overcome the water scarcity problem by setting the calendar for cropping schedules taking into consideration rainfall, river flow available and irrigation water requirements. A water balance approach using 48 years of rainfall and weather data was pursued in this study. The present main season from land preparation to crop harvest lasts from 1st November to 6th April, with land preparation being carried out during the heaviest rains in early November. However, the heavier rains may result in the postponement of seeding. Delays in crop planting during this main season can result in the cancellation of the following off-season crop from May to October. Shifting the land preparation works from November 1 to an earlier date, September 15, would result in a better match of crop water needs with the prevailing rainfall season (normally most of the rainfall occurs between September and December). This proposed schedule (15th September–10th February) also increases the probability that land preparation and subsequent seeding can be done for a second crop in the revised off-season period, 15th March–10th August. The present off-season schedule is from 5th May to 7th October and water scarcity during the vegetative and reproductive phases of the crop growth can be a problem. With the shifting of the off-season to start on March 15, severe water shortage can be avoided. The proposed revised cropping schedules could reduce the irrigation water requirements for the main season and off-season by 30% (equivalent to 60 mm of water) and 19% (equivalent to 37 mm of water), respectively.

Malaria transmission in Southern Madagascar: influence of the environment and hydro-agricultural works in sub-arid and humid regions: Part 1. Entomological investigations

A 4-year entomological study was carried out in Southern Madagascar to identify malaria vectors, evaluate the transmission and compare the influence of irrigation in the sub-arid and adjacent humid regions. Three villages were involved in this entomological survey: Androvasoa (located in the natural sub-arid ecosystem), Pépiniére (sited at the centre of an irrigated rice scheme in the sub-arid region) and Esana (bordered with rice fields in the humid region). Mosquitoes were collected inside and outside dwellings when landing on human beings, with light traps and with knockdown indoor sprays. Anopheles arabiensis, Anopheles merus and Anopheles funestus were found in every village while Anopheles gambiae s.s . was only found in the village bordering the rice-fields (Pépiniére) and Anopheles mascarensis, a mosquito native to Madagascar, was only found in the humid region (Esana). In Pépiniére, the annual entomological inoculation rate (EIR) was low (EIR=0.4 infective bites/man/year (IBM)). In the irrigated scheme of the sub-arid region, malaria transmission was 150 times higher (mean EIR=63 IBM) than in the natural ecosystem and A. funestus was the main vector, responsible for 90% of infective bites. In Esana, the level of malaria transmission was high (EIR=41 IBM) and 2/3 of the infective bites were due to A. mascarensis, despite the presence of A. gambiae s.s . and A. funestus. These results are discussed with reference to the impact of irrigation on malaria in Africa (“the paddies paradox”).

Explaining yield gaps on farmer-identified degraded and non-degraded soils in a Sahelian irrigated rice scheme

Farmers in the Foum Gleita irrigation scheme in southern central Mauritania experienced declining rice yields, and within a decade after its establishment 12% of the scheme's land had been abandoned. Actual rice yields (≤4.0 t ha −1) are low in comparison with potential yield (ca. 8 t ha −1) and with yields elsewhere in the Sahel (4–6 t ha −1). Farmers related the productivity problems to salt efflorescences on the soil surface. Rice yields on the ‘upper and middle slope’ soils were lower (3.4 t ha −1) than the yields on soils further down the slope (> 4.2 t ha −1). Farmers classified the ‘upper and middle slope’ soils as degraded, but following the USDA classification the soils could not be classified saline or sodic. Low yields on the ‘degraded’ soils were related to co-limitation of nitrogen (N) and phosphorus (P), which was due to low soil N supply (ca. 18 kg ha −1), low soil P supply (ca. 8 kg ha −1), occasional low N fertilizer doses (35 kg N ha −1) in combination with low N fertilizer recovery efficiency (0.3 kg kg −1), or non-application of P fertilizer. On the ‘non-degraded’ soils, soil P supply (ca. 16 kg ha −1) was higher and N deficiency prevailed despite a higher soil N supply (ca. 32 kg ha −1) and a higher N fertilizer recovery efficiency (0.4 kg kg −1). Higher contents of carbonate salts in the ‘degraded’ soils increase soil pH (> 7.5) and are, therefore, likely to contribute to low soil P supply and low N fertilizer recovery efficiency.

Actual and potential salt-related soil degradation in an irrigated rice scheme in the Sahelian zone of Mauritania

Salt-related soil degradation due to irrigation activities is considered a major threat to the sustainability of rice cropping under semi-arid conditions in West Africa. Rice productivity problems related to soil salinity, alkalinity and topographic position were observed in an irrigated rice scheme in southern central Mauritania. Detailed study of soils in a toposequence revealed that highest topsoil salinity and alkalinity were found at the shallow soils (<1.2 m) of the middle and upper slopes. Here, soils have formed in situ from the schist parent rock, which releases carbonate rich salts upon weathering. Within these soils large differences in salinity and alkalinity level occur at short distances, indicating minimal groundwater flow and a strong variation in the geochemical composition of the vertically positioned bedrock. Further downslope, soils have a (partly) colluvio–alluvial origin. Here, sedimentation during annual floods increased soil depth (>2.5 m) and salinity levels remained low due to leaching. Foum Gleita’s irrigation water used is amongst the most alkaline in the Sahel. However, no clear indications of secondary salinization or alkalinization due to irrigation activities were observed. A comparison of historical data revealed no significant changes of topsoil salinity and pH over the last 30 years. The PHREEQC 2.0 model was used to study actual and potential development of soil salinity and alkalinity problems, by simulating excessive concentration of the irrigation water through evaporation. The evolution into a strongly sodic-alkaline solution due to precipitation of Mg-calcite and -silicate minerals did not fit with current composition of ground and surface water, which showed geochemical control of alkalinity at high concentrations. Incorporation of cation exchange processes, using a small (1.0 mmol c per 100 g dry soil) but calcium saturated CEC, resulted in a better fit with field data. Results indicate that the soil’s buffer capacity to counteract alkalinization processes is large. However, the soil water and salt balance needs to be quantified in order to determine development rate and equilibrium levels of soil salinity and alkalinity for different soil type × water management combinations. This study does neither reject the hypothesis that salt-related soil degradation jeopardizes the sustainability of rice cropping in the Sahel, nor does it provide evidence for its verification. However, our results are in line with other studies in west Africa, in that current salt-related production problems are inherited, rather than being induced by irrigated rice cropping.

Land use and extension services at Wovwe Rice Scheme, Malawi

Over the last one-and-half decades Malawi has experienced frequent food shortages due to droughts, the effects of the influx of refugees from neighbouring Mozambique, and official policies that emphasised export-oriented cash crop production. To enhance the country's food security, and to give increased opportunities to small farmers, there has been a shift to small-scale irrigation schemes in selected areas of the country. Evidence from a rice scheme in the northern part of the country suggests that small-scale irrigated operations are characterised by high turnover rates, seasonal variations in patronage, under-utilisation of the key facilities provided, and incessant political tensions. They create fissures in the social structures and in the traditional farming systems. This article thus concludes that small-scale irrigated schemes cannot be regarded simplistically as a panacea to food security and increased agricultural production at the local community levels. The argument that the small operations result in the fast delivery of services may also be exaggerated. In fact, they are quite bureaucratic, and associated with the state's patronising attitude and control of resources.

Efficiency and profitability of an IPM package against insects, blast, and nematodes in irrigated rice

In Burkina Faso, major biotic constraints to rice production in irrigated conditions include insects, diseases, and nematodes. Lepidopterous stem borers (Chilo zacconius, C. diffusilineus, Maliarpha separatella, and Sesamia calamistis) can cause up to 33% yield losses (Dakouo et al 1991). A 1% increase in damage of the African rice gall midge is correlated with a 2% yield loss (Nacro et al 1996). Pot trials showed a yield loss of 30% caused by rice root nematode Hirschmaniella spinicaudata (Thio 1992). Rice blast (caused by Pyricularia oryzae) causes yield losses with an estimated value of more than US$10 million in West Africa (WARDA 1995). Pest control in irrigated rice still largely depends on the use of chemicals without meeting the necessary criteria of efficiency and profitability for small-scale farmers. Therefore, a cost-effective integrated pest management (IPM) package was developed by a multidisciplinary team to minimize reliance on toxic and expensive chemicals. This IPM package combines the use of local natural products made of organic manure (5 t ha-1) against nematodes, rice straw ash (2.5 t ha-1) against blast, dry neem (Azadirachta indica) leaf powder against nematodes, and alcoholic extracts of neem seed powder (200 g into 0.25 L of alcohol and 0.75 L of water) against insects. The efficiency and profitability of the package were evaluated during the 2000 wet season at two irrigated rice schemes, Banzon and Karfiguela, near Bobo-Dioulasso, southwest Burkina. Its efficiency was optimized with the use of a rice gall midge-tolerant variety, BW 348-1. The IPM package (T3) was compared with two other treatments, T1 and T2. The first treatment (T1) was the control with no products against pests. T2 was a reference chemical treatment combining the insecticide Basudin (diazinon) at 1,000 g ai ha-1 in foliar sprays at 20, 40, and 60 d after transplanting (DAT), the nematicide Basamid (dazomet) at 100 kg ha-1 (incorporated into the soil 14 d before transplanting), and the fungicide Kitazin (di-isopropyl-sbenzil-thiophosphate) in a foliar spray at 720 g ai ha-1 at panicle emergence. The experimental design was a completely randomized block with three treatments and four replications, a plot size of 60 m2 (10 6 m), and plant density of 25 25 cm. Insect damage (deadhearts and onion shoots) was assessed at 40, 60, 80, and 100 DAT. Foliar blast was evaluated at 35, 49, and 63 DAT and neck blast incidence at 15 and 30 d after panicle emergence (DAPE). Nematode populations were estimated at the time of Basamid application—before transplanting and at 30, 60, 90, and 120 DAT.

Control of the photodissociation process of CsCl using a feedback-controlled self-learning fs-laser system

The time-resolved photoinduced dissociation process of a diatomic molecule (CsCl) was investigated both theoretically and experimentally. It is shown that by applying a sequence of two different laser pulses the dissociation process may be controlled, according to the Tannor–Rice scheme. Using feedback-controlled optimization algorithms a self-learning system has been realized, which is able to control the product channel without a priori knowledge on the molecular potential surfaces.

Femtosecond pump–probe photoelectron spectroscopy on Na2: a tool to study basic coherent control schemes

Femtosecond pump–probe photoelectron spectroscopy has become a common tool in ultrafast gas-phase science because of its sensitivity both to structural and electronic changes in a molecule upon excitation. Here a summary and extended discussion of our experiments is presented. We focus on the potential of this method to study basic femtosecond coherent control schemes. Multi-photon excitation of the Na2 molecule with femtosecond laser pulses leads to preparation of vibrational wave packets. Mapping of the vibrational wave-packet dynamics by time-resolved photoelectron spectroscopy offers the high spatial and temporal resolution required to investigate a variety of laser-control parameters in great detail. Besides an illustration of the Tannor–Kosloff–Rice scheme we demonstrate electronic transitions at Franck–Condon forbidden internuclear distances due to the intensity of the applied laser pulses. Further we discuss the influence of simple phase-modulated (linearly chirped) laser pulses on a molecular multi-photon process. An enhanced population transfer is derived due to synchronization of the wave-packet motion on an electronic potential to an appropriate chirp of the laser pulses. In addition, the influence of the temporal profile on the population transfer and the role of the pulse duration are studied.

SIGBIRIZ, A Tool For Regional WaterManagement In The Senegal River Delta AndLower Valley

The Senegal River Delta and Valley (Northern Senegal) are located in the Sahelian climatic zone, which is characterized by a long dry season and a short rainy season. Due to a high evaporation demand in the rainy season and a low and irregular rainfall (around 300 mm/year), rainfed agriculture is unfeasible. Irrigation was introduced in the region in 1960 and actually 80,000 ha (mainly rice) are under irrigation in the Senegal River Delta and Valley. The irrigation schemes differ greatly in their size, layout and management level. One of the main responsibilities of the Senegalese irrigation authority (SAED) consists in supplying the required irrigation water to the main watercourses and to follow up the agronomic activities. In order to assist SAED in assessing the rice water requirement, the BIRIZ model was developed. The estimates of the daily water requirements for different probabilities of rainfall of the individual rice schemes computed by BIRIZ are based on scheme management level, evapotranspiration demand, soil parameters and crop characteristics. To monitor all agro-economic factors in the region, SAED uses a Geographical Information System (GIS). The linkage of BIRIZ with GIS forms the regional water management model GISBIRIZ. The data flow, graphical user interfaces and different modes of running GISBIRIZ to manage the water resources in the Senegal River Delta and Lower Valley are presented in this paper. This model allows SAED not only to compute the irrigation water requirement of all rice schemes in the area but also to estimate the required discharge for the different watercourses to satisfy the scheme water demands. With this tool SAED can also spot schemes having a negative impact on the environment (high water consumption, high water table recharge,...) and resolve bottlenecks between water demand and supply before the onset of the irrigation season.

Women‘s land rights in Gambian irrigated rice schemes: Constraints and opportunities

This paper discusses the significance of gender-based conflicts for thefailure of Gambian irrigated rice projects. In particular, it illustrateshow resource control of a gendered crop, rice, shifts from females to maleswith the development of pump-irrigated rice projects. Irrigation imposes aradically different labor regime on household producers, demanding thatthey intensify labor for year-round cultivation. Yet, the Gambian farmingsystem evolved for a five month agricultural calendar, in which women wereaccorded specific land and labor rights. The need to restructure familylabor, specifically skilled female labor, to meet the cultivation demandsof pump irrigation is crucial for understanding the pattern of gender-basedconflicts in Gambian rice schemes. The case study illustrates thatirrigation involves more than technology transfer. Appropriate irrigationdemands sensitivity to the social structure of household production systems. The paper concludes by emphasizing the centrality of gender issuesfor improving food security in sub-Saharan Africa.

Water requirements for salt control in rice schemes in the Senegal river delta and valley

The paper estimates the water requirements for salt control in rice schemes located on saline soils in the Senegal river delta. When the fields are not cultivated, salts are transported to the top soil by capillary rise from the very saline and shallow ground water table. During the irrigation season, the large quantity of irrigation water adds additional salt to the fields. If the percolation rate of the soil is small, salts will have to be removed from the schemes by flushing the standing water from the fields when the salinity of the water reaches the threshold value of 1.5 ds m−1. The results indicate that if the schemes are located on the river banks (fonde), flushing at the beginning of the season and the percolation losses throughout the season may be sufficient to keep the salts out of the root zone. On the less permeable soils in the depressions (hollalde), an extra flushing is required to evacuate enough salts from the fields during the irrigation season. In total about 2,300 m3 ha−1 of water may be needed for flushing. If flushing is not practised, the schemes have to be abandoned after a few years of cultivation due to build-up of soil salinity.

Water use in rice schemes in the Senegal river Delta and Valley

The water use of rice schemes was derived from field measurements made during the 1991 and 1992 season at 13 irrigation schemes situated in the delta and valley of the Senegal river. The seasonal water consumption, as well as the water distribution throughout the season and the operation of the pumping stations were evaluated. The water consumption was compared with standards which ranged from 16,650 to 21,100 m3 ha−1 depending on the season and the location of the scheme. Half of the analyzed schemes used more water than required. Analysis of the water distribution throughout the season revealed that in general the supply follows the demand. In small-scale schemes however, the fit between supply and demand is often lacking, resulting in crop stress and yield reduction. Furthermore, the study shows that the capacity of half of the pumping stations are under-used as a result of a long stretched saturation period and/or the irrigation of only a small fraction of the total area of the scheme.

Evaluating an insect pest management system in an irrigated rice environment

AbstractThe efficiency and profitability of an integrated pest management system consisting of a phytosanitary survey and threshold interventions (based on levels of insect damage) was tested at the Vallée du Kou irrigated rice scheme in Burkina Faso, for two consecutive crop seasons in 1987. There was a considerable advantage in cost, number of insecticidal applications and yield of a threshold intervention-based system over arbitrary or routine insecticidal application methods. The proposed method is considered to be environmentally friendly.