Is newer better? The effect of varietal age on real-world maize yield in Kenya

Replacing old maize varieties with new ones is central to agricultural policy across Sub-Saharan Africa, widely promoted as a pathway to boosting productivity and strengthening food security. Yet the extent to which varietal turnover translates into higher yields on farmer-managed plots remains uncertain. We provide new evidence from Kenya, quantifying the yield effects of maize varietal age. We use a three-visit, multi-season panel survey of 4160 smallholder households across Kenya to estimate the effect of varietal age on maize yield, employing entropy balancing and weighted regression models to address endogeneity. Our results establish a strong negative relationship between varietal age and yield. New varieties yield 147 kg/ha more than old in the long rains and 91 kg/ha more in the short rains. More granular age categorization shows that switching to varieties released within the past five years delivers the highest gains – 360 kg/ha in the long rains and 269 kg/ha in the short rains – over varieties that have been in the market more than 20 years . These findings suggest that slow varietal turnover lowers yields and crop production. We show that while farmers generally perceive new varieties favorably in terms of yield potential, early maturity and grain quality, their concerns that new varieties require more labor may delay adoption. Providing farmers with clear, locally-relevant performance data and opportunities for on-farm experimentation may help shift perceptions and drive wider and faster adoption.