Intra-seasonal rainfall patterns and extremes drive maize productivity and nitrogen use in sub-humid Zimbabwe

Background and purpose: Increasing intra-seasonal rainfall variability poses a major challenge to the sustainable intensification of rainfed maize systems in sub-Saharan Africa. This study investigates how intra-seasonal rainfall patterns and extreme dry and wet events affect maize productivity and nitrogen (N) use, particularly under crop residue mulching—a practice widely promoted to improve soil water and N availability. Methods: A maize field experiment with manipulated rainfall conditions was conducted over two cropping seasons (2022–23 and 2023–24) in sub-humid Zimbabwe. The factorial design combined three rainfall treatments (ambient, 30 % reduced rainfall, and heavy rainfall with two additional artificial events of 100 mm day−1 each), with or without mulch (0 vs. 6 t DM ha−1) and N fertilization (0 vs. 80 kg N ha−1). Measured variables included aboveground biomass, plant N accumulation, grain yield, yield components, and harvest indices. The relative influence of rainfall variability and management practices was assessed. Results: The two seasons showed contrasting rainfall: 2022–23 was near-normal, while 2023–24 (an El Niño year) was drier, with uneven rainfall distribution. Intra-seasonal rainfall patterns and extremes explained 78 % of maize yield variability. Poor rainfall distribution significantly decreased maize productivity and N use, despite adequate total seasonal rainfall. Rainfall reduction decreased yield by 22 % in 2022–23 but increased it by 20 % in 2023–24. Heavy rainfall, especially with N fertilization, doubled grain yield in 2023–24. Mulching provided no buffering effect and reduced maize biomass and N uptake by about one-third in 2023–24. Conclusions: Intra-seasonal rainfall patterns and extremes were the dominant factors affecting maize productivity and N use, far outweighing the effects of mulch and N fertilization. These findings highlight the need for cropping strategies that better account for intra-seasonal rainfall variability to improve the resilience and sustainability of rainfed maize systems in sub-Saharan Africa.