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Policy-based or technological interventions are more likely to be effective if aligned with farmers' objectives, constraints, and decision-making processes. The objective of this study was to explore trade-offs and synergies of farming systems in response to innovative rice cultivation activities by understanding current farming systems, main drivers impacting farm management and farmers' perspectives on rice intensification. Understanding these interrelations is key in rice production areas, where smallholder farmers largely depend on growing rice to subsist. A rapid system analysis was conducted interviewing 20 farmers in 4 villages along the Senegal River Valley (SRV) to obtain a general view on farm functioning and farmers' perspectives on farming systems. A detailed system analysis with four farmers was subsequently conducted to provide an insight into the underlying processes regulating farm management. A multi-objective optimization model was used to quantitatively evaluate and explore farm performances based on four selected indicators representing: rice production, household agricultural profit, household labour and farm nutrient balance. The results of this study showed that government programmes and farmers' Unions were strongly influencing farmers' decision-making in agricultural production. Farmers also reported that although rice was still essential for their livelihoods, there were transitions towards less rice production in the wet season with short duration rice varieties and more vegetable production. Both farmers' interviews and the modelling results suggested that farmers would be unlikely to increase or even maintain the area of rice double cropping, which has been strongly promoted by the Senegalese government. Instead, farmers would rather keep investing in vegetable production. This modelling study shows the consequences of policy-based and technological interventions for farming systems and may inform both policy makers and farmers in situations where objectives are strongly divergent. Hence, modelling outcomes may be used to inspire discussion and innovation in order to align the government priority of ensuring national food security and farmers' objectives and constraints in the SRV. [Display omitted] • Farmers in Senegal River Valley outlined their objectives and cropping practices. • Farmers sought to combine rice cultivation with high-value vegetable cropping. • Vegetable crops were more profitable than rice, but also more labour demanding. • Trade-offs existed between profit vs. reduction of labour burden and pollution. • Farmers' choices were influenced by external drivers of policies and services. [ABSTRACT FROM AUTHOR]

Little is known about the impact of long-term intensive irrigated rice cropping on secondary macro and micronutrients in soils and crops. Therefore, the present study analysed the effect of intensive irrigated rice cropping on nutrient concentrations in soils and rice (grain and straw at harvest) in two long-term experiments that were established in 1991 for intensive rice-based irrigated systems in the Senegal River valley at Ndiaye and Fanaye, Senegal. The experiments included six different fertilizer treatments and rice was grown for two seasons per year. The samples were collected in the 2016/17 dry season (26 years or 52nd continuous rice cropping season after the establishment). Average grain yields from 1991 to 2016/17 for the different fertilizer treatments indicate that yield was limited by N and P at both sites. At Ndiaye, 120 kg N ha−1 seemed sufficient to reach highest achievable yields, whereas 180 kg N ha−1 was necessary at Fanaye. Soil organic carbon and total soil N did increase considerably over the full length of the experiment at both sites and in all treatments even though all crop residues were removed every season. The estimated increase in total topsoil N (across all fertilizer treatments) per season was 10.8 and 11.4 kg N ha−1 at Ndiaye and Fanaye, respectively. Fertilizer treatments differed in their N, P and K rate but significant effects on total soil concentrations were only detected for P. Using the Mehlich3 soil test, we analysed treatment effects on available P, K, Ca, Mg, S, Mn, Zn and Fe. Critical Mehlich3 values from the literature indicated likely P limitation at both sites and in all but one treatment (high PK treatment), a starting but minor K limitation at Fanaye, a strong S limitation at Fanaye, and a minor Zn limitation at Fanaye and Ndiaye. These indications were mostly confirmed by the grain and straw analysis but with the exception of the P limitation, the actual effect of these possible nutrient limitations on production would need to be tested with targeted field experiments. We conclude that continuous rice cultivation in the Sahel for 26 years can be sustained and even increases soil organic carbon and total soil nitrogen. However, in addition to the common N and P deficiencies, likely deficiencies of K, S and Zn are appearing and may begin to limit rice yields in intensive systems in Africa. The Mehlich3 test seems an efficient tool to identify such deficiencies in irrigated rice soils. • 26 years of continuous rice cultivation increased SOC and total soil N significantly • System N losses are therefore over-estimated when based on crop uptake only • Fertilizer application effects on total soil concentrations were only detected for P • The Mehlich3 method indicated possible upcoming limitations from K, S and Zn [ABSTRACT FROM AUTHOR]

With rapid population increase, labour scarcity, and soil nutrient depletion, agricultural lands must be used sustainably to meet the ever-increasing demands for food and livelihood. Perennial rice varieties show promise in meeting the conflicting needs for reducing input use while increasing agricultural production. But, little is known about their agronomic and economic performances and the suitable cropping system in West Africa. The objective of this study was to evaluate the effects of the cropping system and perennial rice variety on grain yield, labour productivity, and profitability in irrigated lowlands in West Africa. Experiments were conducted over two years at two sites: Mbe in Côte d′Ivoire and Ndiaye in Senegal located in the sub-humid and Sahelian climatic zones, respectively. The treatments consisted of three cropping systems [one transplanting and two ratoons per year (rice–ratoon–ratoon), one transplanting and all other ratoons (rice–ratoon continuous), and transplanting twice a year (rice–rice)], and six varieties (five perennial rice varieties: PR101, PR107, PR23, PR24, and PR25 and a local check variety, which was WITA9 and Sahel108 in Mbe and Ndiaye, respectively. There were significant effects of the cropping system and variety, and their interaction on grain yield, labour productivity, and profitability at both sites. In the rice–ratoon–ratoon system, the cumulative grain yield over two years of PR23 and PR25 at Mbe (28.8 t/ha) and PR107 at Ndiaye (22.1 t/ha) was similar to that of the local check in the rice–rice system. The average cumulative grain yield across varieties over two years was the lowest in rice–ratoon continuous system at both sites. Grain yield declined with an increased number of ratoon cropping seasons in the rice–ratoon continuous system. Crop duration and the percentage of regrowth rates (ratio of the number of panicles of the ratoon crop to the number of panicles of the main crop in percentage) were the main drivers of grain yield in the ratoon cropping seasons. At Mbe, the highest labour productivity (39.6 – 39.9 kg/day) and profit (5814 – 5844 USD/ha) were achieved with PR23 and PR25 in the rice–ratoon–ratoon system, while at Ndiaye, the highest labour productivity (24.3 kg/day) and profit (2689 USD/ha) were achieved with PR107 in the rice–ratoon–ratoon system, as they had lower labour input and production costs than those in the rice–rice system with the local check. Grain yield could not be sustained in two years of the continuous ratoon cropping system with perennial rice. The rice–ratoon–ratoon system with PR23 and PR25 at Mbe and PR107 at Ndiaye offers alternative options to the conventional rice–rice system for increasing labour productivity and profitability but may require more water due to the longer crop duration. Realizing the full potential of perennial rice requires the identification of the causes of rapid yield decline and the development of agronomic practices for enhancing grain yield under ratoon cropping systems in West Africa. • Performances of perennial rice varieties were evaluated in double rice and ratoon cropping systems in West Africa. • Rice yield declined with an increasing number of ratoon cropping seasons. • Low rice yield in the ratoon cropping seasons was attributed to short crop duration and poor regrowth rate. • Labour input and production costs were lower in ratoon systems than in double rice cropping. • Varieties and cropping systems with higher labour productivity and profit were identified. [ABSTRACT FROM AUTHOR]

Rice double cropping in irrigated systems is essential for increasing rice production and ensuring food security in West Africa. Rice breeding programs must develop genotypes that are expected to perform well either across wet and dry seasons or for a specific season. This study aimed to investigate the consistency of genotypic performance across two seasons and identify high-yielding genotypes and their characteristics. 50 diverse genotypes were grown under irrigated conditions in wet and dry seasons at three sites in West Africa (M'bé in Côte d'Ivoire, and Fanaye and Ndiaye in Senegal) for three years (2018–2020). Mean grain yield across all genotypes was higher in dry season in Fanaye (593 vs. 495 g/m2) and Ndiaye (737 vs. 415 g/m2) than in wet season, but the same for the two seasons in M'bé (512 vs. 507 g/m2). The consistency of genotypic performance across wet and dry seasons was the highest in M'bé (r = 0.88, P < 0.01), followed by Fanaye (r = 0.71, P < 0.01), and lowest in Ndiaye (r = 0.49, P < 0.01). Thus, correlations for yields between two seasons becomes poorer as difference in yield level between two seasons becomes larger. Two (NSIC Rc240 and Giza 178) and one (MG 2::IRGC 79837-1) genotypes from other regions were identified for high yield in both seasons in Côte d'Ivoire and Senegal, respectively. High-yielding genotypes were characterized by large aboveground biomass and high harvest index in both seasons in all three sites. Grain yield was positively correlated with days to heading and number of grains per panicle in both seasons in M'bé and Fanaye. In Ndiaye, none of the yield components was consistently related to grain yield across two seasons. It is possible for rice breeding programs to develop and identify genotypes that are expected to perform well in two seasons. High-yielding genotypes identified in this study can be used as donors for improving rice productivity in West Africa. Field experiments were conducted in three sites in two countries only, and further effort is needed to evaluate consistency of genotypic performance across diverse agro-ecological zones in West Africa. • Yield consistency of 50 rice genotypes grown across wet and dry seasons was investigated. • Correlation coefficients for yield between wet and dry season ranged from 0.49 to 0.88. • Correlations between two seasons decreased as difference in yield level between the seasons increased. • Several genotypes out-yielded local checks in both seasons in Côte d'Ivoire (2) and Senegal (1). These results indicate that there is no need for separate breeding programs for wet and dry seasons. [ABSTRACT FROM AUTHOR]

• Efforts of genetic improvement of rice in sub-Saharan Africa (SSA) are reviewed. • Yield of selected varieties was assessed for 4 so-called breeding target domains. • Improving yield performance of existing upland NERICA varieties is possible. • Lowland interspecifics out-yielded improved O. sativa varieties released in SSA. • Old varieties from Asia are still common in SSA, especially in irrigated lowland. Genetic improvement has been given high priority in rice research for development in sub-Saharan Africa (SSA). This paper provides an overview of historical efforts of genetic improvement in SSA focused on improving rice productivity. It further describes yield gain of new rice varieties evaluated in recent field experiments in four selected breeding target domains, and summarizes adoption studies on rice varieties. Efforts to develop rice varieties adapted to diverse rice production systems in SSA have been made by several research organizations, including national agricultural research institutes, bilateral organizations, and three CGIAR centers. The efforts have resulted in the release of around 570 rice varieties in 10 major rice-producing SSA countries by 2020. Among these varieties, the most well-known are interspecfic upland rice varieties "New Rice for Africa (NERICA)" that were developed from crosses between improved Oryza sativa tropical japonica and Oryza glaberrima varieties. However, recent field assessements demonstrated that upland rice yield can be further improved through introduction of upland indica materials from Asia. In contrast, lowland interspecific rice varieties out-yielded the previously released improved O. sativa varieties in selected SSA countries. Field assessments in Senegal and Madagascar did not demonstrate the yield advantage of the recently-developed varieties including hybrids over best performing ones released before. The adoption level of improved varieties in terms of share of area occupied by improved varieties in 18 SSA countries was 40 % in 2008 with old varieties that were released before 2000 being dominant and 7% of the total rice area occupied by NERICA varieties. Especially in irrigated and rainfed lowland rice systems, the majority of dominant varieties were still those introduced from Asia. Panel data between 2002 and 2019 from the Senegal River Valley also confirmed this, and Sahel 108, which was introduced from Asia and released in Senegal in 1994, accounted for >70 % of the total rice area in both the wet and dry seasons in 2019. The implications of this review for future rice genetic improvement and varietal replacement in SSA are discussed. [ABSTRACT FROM AUTHOR]

We integrated recent research on cardinal temperatures for phenology and early leaf growth, spikelet formation, early morning flowering, transpirational cooling, and heat- and cold-induced sterility into an existing to crop growth model ORYZA2000. We compared for an arid environment observed potential yields with yields simulated with default ORYZA2000, with modified subversions of ORYZA2000 and with ORYZA&#95;S, a model developed for the region of interest in the 1990s. Rice variety 'IR64' was sown monthly 15-times in a row in two locations in Senegal. The Senegal River Valley is located in the Sahel, near the Sahara desert with extreme temperatures during day and night. The existing subroutines underestimated cold stress and overestimated heat stress. Forcing the model to use observed spikelet number and phenology and replacing the existing heat and cold subroutines improved accuracy of yield simulation from EF = -0.32 to EF =0.70 (EF is modelling efficiency). The main causes of improved accuracy were that the new model subversions take into account transpirational cooling (which is high in arid environments) and early morning flowering for heat sterility, and minimum rather than average temperature for cold sterility. Simulations were less accurate when also spikelet number and phenology were simulated. Model efficiency was 0.14 with new heat and cold routines and improved to 0.48 when using new cardinal temperatures for phenology and early leaf growth. The new adapted subversion of ORYZA2000 offers a powerful analytic tool for climate change impact assessment and cropping calendar optimisation in arid regions.