Spatiotemporal dynamics of cropland N balance reveal rising N surplus and poor crop response in the Lake Victoria Basin (2000–2020)

Abstract Understanding spatiotemporal dynamics of nitrogen (N) balance is essential for improving food security and mitigating environmental risks. Yet long-term, high-resolution assessments remain scarce in the Lake Victoria Basin (LVB), despite rising production demands and worsening water quality. In this study, we estimated four major N inputs (fertilizer, manure, atmospheric deposition, and biological fixation) and crop N outputs from 36 species for the period 2000–2020 to calculate nitrogen use efficiency (NUE) and N surplus. Regression and spatial analyses were further conducted to identify the drivers influencing their spatiotemporal patterns. During the two decades, N inputs increased from 10.01 to 17.49 kg N ha −1 (a 75% rise), while N outputs increased from 7.57 to 10.05 kg N ha −1 (33%), leading to a decline in NUE from 76% to 61% and a doubling of N surplus from 3.85 to 8.38 kg N ha −1 . The rising N surplus was mainly driven by greater fertilizer and manure applications, low crop responsiveness to N, cropping patterns, and climatic factors. This first spatially explicit, long-term N balance dataset for the LVB offers insights into N management and regional environmental degradation, supporting targeted strategies to improve productivity and reduce pollution in line with SDG 2 (Zero Hunger) and SDG 6 (Clean Water and Sanitation).