Feeding the world in 2050 requires us to find ways to boost yields of the main local crops. Among those crops, cowpea is one of the grain legumes that is playing an important role in the livelihood of millions of people in West Africa, especially in Benin. Unfortunately, cowpea on-farm yields are very low. In order to understand the main factors explaining cowpea yield gaps, we collected and analyzed detailed survey data from 298 cowpea fields in Benin during the 2017, 2018 and 2019′s rainy seasons, respectively. Composite soil samples were collected from cowpea fields and analyzed in the laboratory. Data on farm field management practices and field conditions were recorded through interviews with 606 farmers. Average cowpea grain yields were low and seldom surpassed 700 kg ha−1 on farmer’s fields. Significant differences were observed between cowpea grain yields from northern to southern Benin (p < 0.05), and the lowest yields were observed in northern Benin. These low yields are related to crop management practices, soil nutrient contents, and the interaction of both. According to the model of regression tree from northern to southern Benin, the use of mineral fertilizer, insecticide sprays to control pests, and the improvement of phosphorus, nitrogen, potassium (P, N, K) and cation sum content in the topsoil would increase cowpea grain yields. Insect pests, diseases, and soil fertility decline are the largest constraints limiting grain yield in Benin. Future research should focus on formulating site-specific fertilizer recommendations for effective cowpea cultivation in Benin, as well as the control of insect pests and diseases.

Inorganic fertilizers are alternative ways of providing the necessary nutrients to rice crop and increase its productivity. In order to identify the factors determining inorganic fertilizer technology adoption and rainfed rice yield, a survey was carried out among 763 farmers in 11 municipalities in four agriculture development centers (ADC) of Benin. Composite soil samples were collected from 227 farmer fields and analyzed at the laboratory. Rainfed rice yields were determined in these different fields. Data collected was analyzed with R version 3.5.1 software. Results show that inorganic fertilizer technology adoption depends significantly on age, educational status, household size, contribution of rice to household income and organic fertilizer use (0.004 < p < 0.034). However, using intensity of inorganic fertilizer is significantly influenced by the age of the farmer, the quality of the training of the farmer on soil fertility management, filed areas under rice crop, contribution of rice to household income, years of farming experience, inorganic fertilizers availability and organic fertilizer use (0.0001 < p < 0.023). Inorganic fertilizer use intensity ranges from 12.6 to 248.9 kg•ha −1 with a mean of 74.68 kg•ha −1. The quantities of inorganic fertilizer applied differ more importantly from one farmer to another and range from 4.58% to 90.5% with a mean of 27.15% of the level recommended by research. However, nitrogen, phosphorous, potassium, organic carbon, pH water, and exchanging capacity cation determine the rainfed rice yield. The policies that aim at promoting inorganic fertilizer among rainfed rice farmers must take into account these factors.

The fertilizer used in Benin by rainfed rice farmers, doesn’t meet the required expectation because of lack of many essential agronomic information to formulate the appropriate nutrient compositions. Despite all the advances in improvement of rice production, its yields in traditional cropping systems are very low and the only inputs of Nitrogen, Phosphorous and Potassium do not effectively increase rice yields. The purpose of this study was to assess nutritional status of rainfed rice crops in Benin. The study covered the rainfed rice production areas of Benin Center where 72 leaves samples were taken on 3600 plants from the farmer fields. The concentrations of nitrogen, phosphorus, potassium, calcium, magnesium, iron and zinc were determined in leaves samples. The preliminary DRIS (Diagnosis and Recommendation Integrated System) norms for the rainfed rice growing in the Benin center were selected for various nutrient ratios obtained from the high yield population of the rainfed rice crop. The yields of the two subpopulations were significantly different (p < .0001). The nutrient requirement for the rainfed rice production was ranked as N> Fe> Zn>K>Mg>P>Ca. The DRIS-derived sufficiency ranges for N, P, K, Ca and Mg from the nutrient indexing survey of the rainfed rice plants grown in Benin center were 1.91-3.66, 0.30-0.64, 2.00-3.89, 0.37-1.05 and 0.18-0.38g kg-1 respectively. The limits for Fe and Zn were 89.27-206.3 and 8.21-24.91 mg kg-1 respectively. On the basis of sufficiency ranges, 4.22, 57.75, 66.20, 56.34, 45.07, 46.50 and 29.57% of samples were low in N, P, K, Ca, Mg, Fe and Zn respectively. The DRIS norms put emphasis on nutrient balance and help to differentiate between healthy and unhealthy rice plants from the nutrition status. However, it needed further researches to determine the amount of the fertilizers to supply in order to maintain nutrient balance.

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