Maize (Zea mays L.) yields and water productivity as affected by cowpea (Vigna unguiculata (L.) Walp.) intercropping over five consecutive growing seasons in a semi-arid environment in Kenya

Research on maize (Zea mays L.)–cowpea (Vigna unguiculata (L.) Walp.) intercropping in sub-Saharan drylands, especially involving continuous measurements of soil water dynamics, remains limited. To address this gap, we conducted a field experiment in southeastern Kenya. The study aimed to assess whether intercropping enhances maize yields, quantify cowpea’s contribution to grain and biomass production, and evaluate its potential to improve water productivity for both maize and the overall cropping system. Using a randomized complete block design, we compared maize sole cropping and maize–cowpea intercropping systems by monitoring yield components, canopy height, leaf chlorophyll content, and soil water dynamics and assessing water productivity over five growing seasons (2019–2021). Observed maize yields averaged 2730 kg ha⁻¹ for sole cropping and 2281 kg ha⁻¹ for intercropping. Intercropping did not significantly compromise maize yields but led to reduced maize canopy height. No systematic increase in maize leaf chlorophyll content was observed in the intercrop. Cowpea provided modest benefits to the intercrop, primarily through vegetative mass rather than grain yield. Yields depended more on the timing of rainfall events than on the total rainfall amount. Intercropping did not significantly increase water productivity. Despite significant seasonal differences in observed yields and crop water use, water productivity remained statistically similar across season, indicating losses through evaporation. Our findings suggest that measures aimed at conserving soil moisture or reducing soil water depletion are likely to enhance the benefits of intercropping.