An issue often discussed in relation to agricultural development is the effect on agricultural labour productivity of more intensive land-use. Introducing aspects of seasonality into a stylized Malthusian model, we unify two diverging views by showing that labour productivity may go up or down with agricultural intensification, depending on whether technological progress emerges in relation to cultivation or harvesting activities. Our result rests on evidence reported by Boserup (1965) and others, which suggests that harvest seasons in traditional agriculture are characterized by severe labour shortage.