Beyond symmetry: asymmetric input shocks, the mechanization paradox, and dynamic pathways to grain yield stability in China (1983–2023)

The dynamic response of China's grain yield to agricultural input shocks and whether these responses differ between short- and long-run horizons remains inadequately understood. This study employs a Dynamic ARDL simulation framework on national data from 1983 to 2023 to dissect the short- and long-run effects of irrigated area, cultivated land, fertilizer use, and agricultural mechanization on grain yield. Long-run elasticities reveal that irrigated area, cultivated land, and fertilizer exert positive and significant effects on grain yield, whereas mechanization exhibits a negative coefficient. Short-run dynamics indicate that only irrigation and cultivated land confer immediate benefits; mechanization and fertilizer effects materialize over multiple years, with a stable and rapid error-correction mechanism confirming swift adjustment toward equilibrium. Dynamic simulations further reveal three robust patterns: positive irrigation and land shocks generate sustained yield gains; mechanization shocks initially suppress yield before a delayed recovery; and fertilizer shocks are fundamentally asymmetric—positive shocks stabilize yields at higher levels, whereas negative shocks paradoxically produce short-run spikes followed by substantial long-run losses. Policy should prioritize gradual fertilizer reduction, irrigation expansion in water-scarce regions, and a fundamental shift in mechanization subsidies from horsepower to yield efficiency.