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INTRO by C. Johnsen<br />Some advice from INTSORMIL scientists involves practices that American farmers have used for many years. But this advice may be new information to farmers in developing countries. In this short article, Jenna Gibson explains the advantages of one such practice for subsistence, smallholder farmers like those with whom INTSORMIL scientists work. <br />Crop Rotation<br />By Jenna Gibson<br />For farmers in Africa, every dollar counts. Every harvest can make or break a family’s livelihood for the year. <br />One problem that can cause poor harvests is soil depletion, which results when plants suck up nutrients in the soil, leaving fewer nutrients for the next year’s crop. Farmers can ease soil depletion by leaving their fields empty – or fallow – for a season, to give the soil time to rest and replenish nutrients. But for farmers in African countries where INTSORMIL scientists work, skipping a year of planting and losing that year’s profit is not an option. Some INTSORMIL scientists are helping African farmers use a time-tested process called crop rotation as a way to give the soil a break without leaving a field barren for a whole season. Crop rotation involves planting one crop for one season and a complementary crop the next season. <br />Plants need certain nutrients, such as nitrogen, to grow. Over time, the soil is like an hourglass, with the nitrogen nutrients slowly leaking out of the soil into plants. Planting a different crop, one that creates nitrogen, turns the hourglass over, putting more nutrients back into the soil. For example, cow peas create extra nitrogen in the soil, while sorghum sucks up nitrogen-based nutrients to grow. Planting cow peas one year will add nitrogen to the soil to sustain the next year’s crop of sorghum.<br />One INTSORMIL researcher is using crop rotation to help increase yields and therefore increase profits for farmers in Uganda. In his project, Charlie Wortmann, an associate professor of agronomy and horticulture at the University of Nebraska-Lincoln, compared results from different crop-rotation plans. He and his partners found that planting sorghum after planting cow peas resulted in a 60 to 70 percent increase in sorghum yield over planting sorghum two seasons in a row. <br />Farmers who want to plant only sorghum would have to buy nitrogen fertilizer to put enough nitrogen back in the soil to keep the second year’s harvest healthy, Wortmann said. Crop rotation can therefore cut the cost for farmers to prepare their field, making their end profit even higher.<br />“We got quite good yield responses because of crop rotation with lower investment and more profit,” he said.<br />Not only does crop rotation help solve soil-depletion, it also limits the effects of a pest that hurts sorghum in Africa – a weed called striga. Just clearing out the striga and replanting the same crop is like doing a cursory cleaning job – the hard-to-reach spots behind the refrigerator will still be filthy. But planting a new crop is like full-on spring cleaning, clearing out all the furniture and making sure even the hidden pests are gone. In Wortmann’s research, he used cow peas to clean out striga. Cow pea plants are resistant to the weed, so rotating them with sorghum decreases the effects of striga, Wortmann said.<br />Farmers can also plant both sorghum and cowpeas in separate areas of their field and rotate the plants each year. This technique is called intercropping, which helps farmers get the most out of their fields each year, offering them more than one harvest each year. When combined with intercropping, crop rotation can increase farmers’ profits even more, and can help lower the risk of losing profit in case of a natural disaster, such as drought.<br />The risk-management aspect of crop rotation is a big sticking point for David Mengel, a professor of soil fertility and nutrient management at Kansas State University who trains INTSORMIL-sponsored students. In many countries where fertile soil is rare, where water is scarce or where natural disasters pose threats to crops, crop rotation can help ensure a decent yield each year, he said.<br />INTSORMIL scientists say crop rotation, along with intercropping and other INTSORMIL-recommended techniques, can dramatically decrease farmers’ investments in their fields while increasing their profit from the sorghum yields. <br />