Wheat Yield Response to Chemical Nitrogen Fertilizer Application in Africa and China: A Meta-analysis

Sustainable food production and feeding a growing population are among the main challenges in the world nowadays. Studies suggest that improving nitrogen use efficiency (NUE) is among the key strategies for sustainable crop production. However, yield response to chemical nitrogen fertilizer use (N use) and the NUE was not fully investigated both in China and Africa. The purpose of this article was, therefore, to investigate the findings of different nitrogen fertilization rate experiments and thereby identify a potential approach that could be used to improve wheat yield and NUE in Africa and China. In addition, we aimed to evaluate the effects of soil characteristics, such as pH and soil organic matter (SOM) on wheat yield responses to N uses. A meta-analysis was conducted to systematically assess the results of previous studies published in peer-reviewed journal articles. We identified and used 65 studies conducted in different African countries and 154 in different provinces of China. The articles were obtained from Tylor, Google Scholar, and Web of Science databases. The result indicated that the mean yield response to chemical nitrogen fertilizers use (N use) in Africa was far lower than that in China, implying the presence of higher wheat yield gaps in Africa than in China. In addition, the wheat yield responses to N uses showed different patterns in both regions. That is, while it was increasing with N application in Africa, it increased and reached a peak at 200 kg ha−1 in China, indicating the existence of nitrogen accumulation in the provinces of China. The findings also showed significant influences of soil organic matter (SOM), pH, and precipitations on wheat yield responses to N uses. The higher yield gap in Africa can be improved by increasing nitrogen use to the optimum nitrogen fertilizer rate level, which can also increase nitrogen use efficiency and yield response. In Africa, the high yield response to N use was accompanied by N depletion, while in China it was with a high N surplus in the soil. The effects of pH, SOM, and precipitation were generally more pronounced in Africa than in China.