Mechanization is accompanied by changes in the quantity and type of labour required for an activity. Agricultural mechanization is often touted by policy makers as reducing the drudgery associated with agricultural work and as increasing the productivity of the farming system, especially in contexts where traditional technologies appear to be stagnant. For good or for ill, mechanization is expected to replace labour in agriculture. This can either create unemployment, in a pessimistic scenario, or release labour for more productive work outside of the agriculture sector. However, little rigorous analysis has examined the impacts of agricultural mechanization on labour use in agriculture. This is partly due to the challenge of measuring these impacts in a well-identified setting. It can be difficult to attribute changes in production systems and household welfare to the use of mechanized technology, rather than to more general changes in agricultural conditions and associated infrastructures. This paper considers these claims and provides evidence of a more complex set of impacts. By reducing labour use in some activities and at certain points in the growing season, agricultural mechanization can actually increase demand for labour in other activities and at other seasons. In northern Ghana, tractor use allows for shortening the length of time required for land preparation, making it possible for farmers to grow maize in locations where the crop would otherwise be marginal at best. Because maize cultivation is relatively labour-using, compared to other agricultural activities, mechanization of land preparation leads to an increase in the overall demand for agricultural labour. In this context in Ghana, small- and medium-scale farmers access mechanized plowing technology via a service market, rather than through individual ownership of machines. This paper bases its causal identification on a government scheme that generated plausibly exogenous positive shocks to the supply of machinery services at the district level. Bearing in mind the methodological difficulties and limitations of the approach, evidence is presented of the short-term impact on a range of variables relating to the farming system and household welfare. Findings indicate that for these marginal users of agricultural machinery, mechanized plowing does not significantly reduce the labour used for land preparation, and in fact increases labour use for other operations. The area cultivated increases, with proportionate increases in maize cultivation and an increased proportion of land controlled by women. I propose that these results are consistent with tractor plowing alleviating a time constraint for farmers, which enables cultivation of more timesensitive crops and increases the expected returns to subsequent production activities.