How Do Agricultural Infrastructure Investments Shape the Mechanism Through Which China’s Farmland Titling Policy Influences Grain Production Capacity?

China’s farmland titling program aims to strengthen tenure security and promote agricultural productivity. This study examines whether land titling affects grain production capacity at the prefecture level using panel data from 30 cities over 2011–2021. We employ a staggered Difference-in-Differences (DID) design that exploits variation in the timing of titling milestones across cities. The results show no statistically significant average treatment effect on grain output, grain yield, or per capita grain production. However, the effect on grain yield exhibits substantial conditional heterogeneity: titling reduces yield in cities with weak agricultural infrastructure but increases yield in cities with high irrigation and mechanization intensity. Mechanism analysis indicates that land transfer intensity, irrigation, and mechanization correlate positively with grain yield, consistent with the hypothesis that titling requires complementary infrastructure to translate into productivity gains. These findings suggest that land tenure reforms alone do not guarantee food security improvements; coordinated investments in agricultural infrastructure remain essential.