Rice yield gaps in West Africa

Rice is a staple food for many countries in Africa but the production has never satisfied the demand which largely depends on imports. Therefore, more efforts are needed for raising yield in order to reduce the gap between potential and actual farmers’ yields. To increase yield, improved management options are to be considered. Thus, this thesis has estimated the range of yields and yield gaps at three rice production systems in West Africa across climatic zones, the affecting factors and has explored management options to reduce the gap between potential and actual farmers’ yield. Field surveys were carried out between 2012-2014 in 22 sites located in eleven West African countries covering the main production systems and the main climatic zones. Management practices were recorded through interview, crop status from field observations and yield recorded at harvest. In central Benin, Nitrogen use efficiency was estimated at different field water status using experimental and farmer’s practices’ fields. Finally yield gain was estimated after implementation of GAP in selected farmers’ fields. Boundary function was used to estimate attainable yield. Random forest evaluated the importance of variables explaining yield and yield gap variability. Average yield was 4.1, 2.0, and 1.5 t/ha in irrigated lowland, rainfed lowland, and rainfed upland rice production systems, respectively, with maximum attainable yields of 8.3, 6.5, and 4.0 t/ha. The factors affecting yields were specific to each production system. Yield gaps between potential/water limited yields and actual farmers’ yields ranged from 1.1 to 10.2 t/ha and from 3.5 to 10.3 t/ha in irrigated and rainfed systems, respectively. Farmers’ yield was 27-51% of potential yield at optimum sowing date in irrigated system, and 17-22% of water limited yield at optimum sowing date in rainfed systems. In irrigated system, 34% of the yield gap was attributed to weeds, N fertilizer application rate and crop establishment methods. In rainfed systems, 30% of this gap was explained by rice variety, field hydrology and weed infestation at maturity stage. The implementation of GAPs in farmers’ fields reduced the average yield gaps between 13 and 25% in irrigated system and between 20 and 42% in rainfed lowland system. These results suggest that there is a large scope for increasing rice yield in West Africa. There is a need for site-specific decision support guide including targeted GAPs for an efficient use of the available farmers’ resources

PROBING VIBRATIONAL WAVE PACKETS IN ORGANOPHOSHOROUS MOLECULES USING FEMTOSECOND TIME-RESOLVED MASS SPECTROMETRY

Organic phosphates and phosphonates share a basic structure with organophoshorous chemical warfare agents and cellular components such as DNA. To understand ultrafast nuclear dynamics in isolated organic phosphates and phosphonates, Femtosecond Time Resolved Mass Spectrometry (FTRMS) was employed. FTRMS applies the pump-probe technique with mass spectrometric detection. In our experiment an ionizing $10^{14}$ W cm$^{-2}$, 1500 nm, 18 fs pump and a non-ionizing $10^{13}$ W cm$^{-2}$, 800 nm, 25 fs probe pulse were used. Experiments were performed on four related compounds: dimethyl methylphosphonate (DMMP), diethyl methylphosphonate (DEMP), diisopropyl methylphosphonate (DIMP) and trimethyl phosphate (TMP). The yields of parent molecular ions generated by the pump pulse exhibited ultrafast oscillations with the period depending on the parent molecule. These oscillations indicate the presence of a vibrational wave packet that is excited upon ionization. In DMMP, a well resolved peak of 45 fs ($732\pm28$ cm$^{-1}$) was observed with a weak feature at 610-650 cm$^{-1}$, while DIMP exhibits bimodal oscillation with frequencies of $554\pm28$ and 670-720 cm$^{-1}$. Oscillations for DEMP were barely visible due to rapid decay. The high- and low- frequency oscillations in DMMP and DIMP were assigned to coherent excitation of O-P-O bend and P-C stretching respectively based on DFT calculations. Bimodal oscillations at 770 and 880 cm$^{-1}$ in TMP were also observed and are tentatively assigned to the symmetric and asymmetric P-O stretching modes. These results suggest that this group of compounds exhibits similar coherent vibrational excitation upon ionization. These results may have applications to development of new organophosphorous chemical warfare agent detection and destruction techniques based on the coherent control and may point to reaction pathways in organophosphorous compounds of biological relevance

Status quo of chemical weed control in rice in sub-Saharan Africa

If future rice production is to contribute to food security for the increasing population of sub-Saharan Africa (SSA), effective strategies are needed to control weeds, the crop’s fiercest competitors for resources. To gain better insights into farmers’ access to, and use of, herbicides as part of weed control strategies, surveys were conducted in key rice production locations across SSA. Farm surveys were held among 1965 farmers across 20 countries to collect data on rice yields, farmer’s weed management practices, herbicide use, frequencies of interventions and information sources regarding herbicides. Markets were surveyed across 17 countries to collect data on herbicide availability, brand names and local prices (converted to US$ha−1). Herbicides are used by 34$17 ha−1). They are also the most popular herbicides among farmers. For advice on herbicide application methods, farmers primarily rely on their peers, and only a few receive advice from extension services (<23%) or inform themselves by reading the product label (<16%). Herbicide application timings are therefore often (38%) sub-optimal. Herbicide technologies can contribute to reduced production losses in rice in SSA. However, through negative effects on crop, environment and human health, incorrect herbicide use may unintentionally counteract efforts to increase food security. Moving away from this status quo will require strict implementation and monitoring of national pesticide regulations and investment in research and development to innovate and diversify the currently followed weed management strategies, agricultural service provision and communications with farmers

Propagation by grafting of

Introduction. Sclerocarya birrea (A. Rich.) Hochst. is a common species in the dry zones of Africa. Although appreciated by the populations for its fruit, the subspecies birrea, present in Western Africa, remains not domesticated and under-utilized; the subspecies caffra, originating in Southern Africa, was recently domesticated there where it occupies a considerable economic role. Within the framework of a domestication programme led in Senegal, tests studied the development of the grafting applied to S. birrea subsp. birrea. Materials and methods. Scions taken from female mature trees were grafted on young rootstock plants at five periods during the year and according to three grafting techniques (tongue grafting, top grafting and side plate grafting). Results and discussion. The most favorable period for the grafting is at the end of the rain season; no significant difference was observed between the three types of grafting technique tested. Conclusions. The propagation technique highlighted could be developed for the ex situ conservation of the genetic diversity of Sclerocarya birrea subsp. birrea and also for the selection of varieties interesting for the criteria considered (yield and fruit quality, and rusticity). In time, S. birrea subsp. birrea could constitute in Western Africa a fruit tree crop for diversification

Variability and determinants of yields in rice production systems of West Africa

Rice (Oryza spp.) is the major staple food for most countries in West Africa, but local production does not meet demand. Rice is grown mainly by smallholder farmers, and yields are generally low with high temporal and spatial variability. Low yields have been attributed to unfavorable climate conditions, poor soil quality, and sub-optimum agricultural practices. The objectives of this study were to assess variation in yields of three major rice production systems (irrigated lowland, rainfed lowland, and upland) across three climatic zones (semi-arid, sub-humid, and humid), and identify factors affecting that variation. We analyzed data on yield, climate, soil, and agricultural practices for 1305 farmers’ fields at 22 sites in 11 West African countries between 2012 and 2014. A boundary function approach was used to determine attainable yields. Random forest algorithm was used to identify factors responsible for yield variation. Average rice yield was 4.1, 2.0, and 1.5 t ha−1 in irrigated lowland, rainfed lowland, and rainfed upland systems, respectively, with maximum attainable yields of 8.3, 6.5, and 4.0 t ha−1. Yield difference between attainable and average yield tended to be higher in irrigated and rainfed lowland systems. In those two systems, yields were highest in the semi-arid zone, while no difference in yields among climatic zones was apparent for upland rice. High rice yields were associated with high solar radiation, high maximum temperature, intermediate air humidity, multiple split nitrogen (N) fertilizer applications, high frequency of weeding operations, the use of certified seeds, and well-leveled fields in the irrigated lowland system. Minimum temperature, solar radiation, rainfall, construction of field bunds, varietal choice, and the frequency of weeding operations were determinants of rice yield variation in the rainfed lowland system. Varietal choice, bird control, and frequency of weeding operations affected rice yields in the upland system. Improving access to inputs, improving input use efficiencies, and site-specific management strategies are recommended as priority interventions to boost rice yields at regional scale independent of production system and climatic zone