Leading Chinese scientists are urging farmers to use controlled-release compound fertilizers to protect the environment.

Their call comes in the wake of major algae-bloom outbreaks believed to be mainly caused by run-off from heavy fertilizer use.

China is home to only seven percent of global farmland, but its fertilizer consumption accounts for more than 35 percent of the world's total, said Feng Yuanqi, a senior expert on chemistry.

Nitrogen, phosphorus and potassium fertilizers are frequently overused and misused, and a large quantity is lost to leaching and evaporation, said Feng.

Only 30-35 percent of nitrogen fertilizers applied to farmland play a role in helping crops grow, and the ratios are 15-20 percent and no more than 65 percent for phosphorus and potassium fertilizers respectively, according to Shi Yuanliang, who has long been engaged in the development of new fertilizers.

Scientists say the effectiveness of phosphorus in conventional compound fertilizers drops to 80 percent after being applied to soil for 35-40 days.

The runoff of nutrients from chemical fertilizers not only increases the cost of farming and wastes resources, it also harms the environment.

Statistics show that as much as 14 million tons of nitrogen fertilizer, valued at 50 billion yuan (US$6.6 billion), are lost to leaching and evaporation every year in China.

Over the past several months, nutrient runoff and pollutants caused blue-green algae to bloom in China's major lakes - Taihu, Chaohu and Dianchi - endangering water supply in nearby cities. In July, a reservoir in Changchun City, in the northeast, was sullied after nutrients amassed.

According to a report issued by the Institute of Soil Science under the Chinese Academy of Sciences, fertilizer runoff accounts for about 59 percent of the pollutants that sullied Taihu Lake, while industrial pollutants only accounted for 10-16 percent.

However, China has to produce enough grain to feed its huge population, and the key to a greater grain output lies in fertilizers, said 82-year-old Feng.

Chinese scientists and agricultural workers have developed fertilizers that are more environment-friendly, including ones that allow nutrients to be released at a slower rate throughout the growth process.

The controlled-release fertilizers have been put to use in grain bases in the northeastern and eastern parts of China.

The fertilizers, which remain effective for 120 days, improved the effectiveness by 30 percent and increased wheat and maize production by 20 percent, said Zhang Yulong, president of the Shenyang Agricultural University, citing a comparative study.

The fertilizers have proven effective on about 2.3 million hectares of cropland, and will be used in other areas of China, Zhang said.