Research backs mix of crops

Farmers will get better yields without extra fertiliser if they plant mixed varieties of a crop rather than sticking with the currently popular monoculture, according to new research published this week in Nature.

Conventional farming practice dictates that the farmer buys one variety of a food crop and fills his fields with this one variety. Dr Christopher Mundt of Oregon State University and colleagues in China and the Philippines have found however that mixing varieties gives a better result, at least when the crop is rice.

The theory and its net effect have been looked at by researchers over the past few years. It holds that monoculture initially gives good results, but long-term dependence on a single crop eventually encourages insect and disease attack involving organisms which are particularly successful against that one variety.

The counter-argument says that by mixing varieties the farmer reduces this risk. While one rice variety might struggle with a fungal disease, others with better resistance will suffer less and keep overall yields up. If one variety proves irresistible to attacking insects, others might fare better and deliver a crop.

The research team persuaded thousands of rice farmers in Yunnan, China to mix rice varieties grown over two years. The results were unequivocal. There was a 94 per cent decrease in fungal rice blast disease and an 89 per cent greater yield on mixed fields.

A British researcher from Wakelyns Agroforestry, Suffolk, in an accompanying re port warns that mixing varieties might not provide all the answers, "but their performances so far in experimental situations merits their wider uptake in practice".