Zhu Youyong, a professor at the Yunnan University of Agriculture, said the scientific planting of different crops together was perfectly in accord with the concept and could remarkably reduce the use of pesticides and fertilizers.

Zhu, who also works as head of the key laboratory for agriculture bio-diversity and disease control affiliated to the Chinese Ministry of Education, is researching crop matches in terms of "mutual promotion and mutual restraint".

To better promote this method nationwide, China this year will launch a project to plant different varieties of quality rice in a mixed pattern on some 400,000 hectares across the country.

This method is expected to reduce the pesticide use to less than 60 percent of normal amounts, while increasing the yield by 600 to 900 kilograms per hectare.

An advisor to the project, Zhu gave an explanation of the concept.

"Mutual promotion" means different crops planted together in an appropriate pattern may benefit from the nutrients produced by neighboring species, and also greatly improve the photosynthetic efficiency, Zhu said.

"Mutual restraint" means different crops, which are prey to different pests and diseases, if planted in a well-arranged pattern, will protect each other with natural "shielding belts" preventing the spread of pests and diseases.

For instance, broad beans are a good match for wheat. The two are subject to different diseases and insects, and the former's root tubercle can produce nitrogen that wheat constantly needs.

Mixed cultivation, compared with planting only one species of either broad bean or wheat, can reduce pesticide use by 50 percent.

Meanwhile, corn has been planted with potatoes, peanuts and other crops on more than 50,000 hectares, which has led to a drop of over 50 percent in pesticide per hectare.

The mixed cultivation has not only brought a remarkable increase in economic returns, but also revived about 100 traditional quality grain species, preventing some from becoming extinct.

Over the past five years, China has planted some 380,000 hectares of rice by way of mixed cultivation in Yunnan, Guizhou, Sichuan and other provinces.

Seiji Ouchi, a Japanese expert on plant diseases, praises this method, saying it not only reduces diseases, but also improves output.

A farmer surnamed Li, from Mila County in Yunnan Province, said he sprayed pesticides on the same patch of paddy field only once after planting three different rice species in a mixed pattern, although he had to spray three to four times when growing just one species.

At present, broad beans have been planted with a good variety of crops such as wheat, cole and barley on more than 50,000 hectares.

Chinese farmers have inclined to plant the improved species of rice which has a higher yield than traditional ones, and consequently have overlooked the benefits of mixed cultivation.

The number of rice species that had been planted with other crops in a mixed pattern increased from two in 1997 to 98 in 2002, experts say.

A traditional species named "yellow-shell glutinous rice" has been widely planted in the move to expand mixed cultivation, and the cultivated area in Yunnan has reached 20,000 hectares, according to the experts.

(Xinhua News Agency March 26, 2003)