Choose the option that best completes the sentence. To maintain soil fertility, the farmer in Kaduna practised ___, growing maize one season and groundnuts the next on the same plot.

Growing different crops on the same land in successive seasons is crop rotation. Mixed cropping means growing different crops on the same land at the same time, which the sentence rules out with 'one season ... the next'. Shifting cultivation involves moving to new land, and irrigation concerns water supply.