Rural labor out-migration and low comparative returns to grain challenge food security in China. This study examines the association between agricultural machinery services (AMS) and the allocation of sown land between grain and economic crops, and whether farmland rent is linked to a countervailing pattern. Using data from the 2021 China Household Finance Survey (CHFS) for 421 villages and 5496 farming households, supplemented by the 2019 wave for the instrumental-variable analysis and additional diagnostics, we estimate province fixed-effects and instrumental-variable models. Greater AMS coverage is associated with a lower economic-crop share. Grain-specific service intensity is positively associated with relative gross sales revenue from grain and with farmland rent. Higher rent is positively associated with the economic-crop share in villages with active rental markets, but the estimated rent-related indirect association is imprecise: its bootstrap confidence interval includes zero. The data do not provide robust evidence that the rent association diminishes at higher rent levels. The association between AMS coverage and the economic-crop share is more negative in villages with better irrigation. These findings suggest that machinery services are linked to grain-oriented cropping, while the possible land-market feedback requires further investigation.