Nitrogen use efficiency trends for sustainable crop productivity in Lake Victoria basin: smallholder farmers’ perspectives on nitrogen cycling

Abstract

Nitrogen Use Efficiency (NUE) is one of the established metrics for benchmarking management of Nitrogen (N) in various systems. Numerous approaches to calculate NUE exist, making it difficult to compare the performances of systems depending on the methodology used. This study adopted the conceptualized framework by European Union Nitrogen Expert Panel (EUNEP) to calculate NUE values for cereal crops to determine future trends for the first time in the Lake Victoria region. Data were collected through in-person interviews among maize and rice smallholder farmers within the Lake Victoria region. A total of 295 observations were recorded. Collected data on yield and N fertilizer were used to make projections on the changes of NUE based on scientific and policy recommendations for Sub-Saharan Africa for 2020 (base year), 2025, 2030, and 2050. Significant differences in maize grain yield for both fertilized and unfertilized farms were observed with very low yields of 2.4 t ha-1 (fertilized) and 1.4 tha-1 (unfertilized). The graphical representation of NUE of both maize and rice showed that most farmers were in the zone of soil N mining. Projected results showed that most maize farmers within Lake Victoria region will continue to experience NUE values >90%, low N inputs <50 kg N ha-1) and less than 5 t ha-1 maize crop yield over the years. For rice farmers, Nyando and Nzoia catchments had surpassed the set target of both yield (6 t ha-1) and N input (50 kg N ha-1). However, NUE values remain higher than the optimal ranges of 50-90% (127.14% -267.57%), indicating risks of depleting soil N status. The unbalanced N fertilization also showed a trend below the linear neutrality option and the average N output for good N management for both crops. Therefore, farmers need to explore various crop management options that could increase N use efficiencies. This should be coupled with policies that promote farmers to access more N input and advocate for optimal management of N and improved quality of the cereals

Nitrogen budgets and nitrogen use efficiency as agricultural performance indicators in Lake Victoria basin

“…In Nyando, all the cases showed an extreme deficit for NUE in both fields with and without the application of mineral N fertilizers. This could be due to different soil properties in the regions characterized and defined by Ntinyari et al (2022a). Vertisol in Nyando, Fluvisols in Sondu, humic gleysols in Nzoia, and Ferralsols in Yala.…”

“…Data used in this study were obtained from participatory interviews using open-ended semi-structured questionnaires in an open data kit (ODK) as described by Ntinyari et al (2022b). A total number of 447 observations comprising of 154 farms, 135 rice fields and 158 maize fields were compiled from four catchments of the Lake Victoria basin, namely: Nyando, Sondu, Yala, and Nzoia.…”

“…Poor N management practices contribute to un-optimal NUE due to poor synchrony between applied N and the crop demand (Sharma and Bali, 2017). According to Ntinyari et al (2022a), NUE can be used as a reasonable indicator to show the target threshold with good management and close simulation of farmer practices for improved N performance. Presentation of NUE as a percentage or mass fraction of N input, output, surplus, and possible changes in the N stocks in the soil system would provide a specific indicator for improved N management (EUNEP, 2015).…”

“…There are concerted efforts by the African governments and development partners to promote the increased use of fertilizers to close the yield gaps of most essential crops like maize and rice (AGRA, 2019). Consequently, fertilizer use has increased from 8 kg nutrient/ha in 2006 to slightly above 20 kg nutrient/ha in 2019 (AFDB, 2020;Ntinyari et al, 2022a). There is an overdue need to understand the sources, fate, and efficiency of N use in densely populated African agricultural regions to support future planning and investments.…”

Focus on reactive nitrogen and the UN sustainable development goals

“…Management conditions of irrigated rice, identifying the right varieties and cropping season while maintaining modest N addition, proved essential for avoiding environmental damage at high production levels at two sites in Kenya (Gweyi-Onyango et al 2021). The trends and scenarios of NUE in smallholder farms were determined for the Lake Victoria region, also in East Africa (Ntinyari et al 2022). Results indicate the need to improve yields and avoid soil mining rather than increasing NUE.…”