Treated pig dung which does not stink has become a popular fertiliser with farmers. Researchers say they cannot keep up with demand for the mixture of sawdust and dung which is composted into odourless fertiliser. 'We are not mass-producing because we are only doing experiments, but farmers are already demanding more than we can provide,' City University biologist Professor Nora Tam Fung-yee said. Farmers can save money on chemical fertilisers, said a spokesman from the Tsui Keng Vegetable Marketing Co-operative Society in the New Territories. 'Chemicals are expensive but this stuff is free.' Last year, the Agriculture and Fisheries Department distributed about 50,000 kilograms to more than 50 farmers at the government farm in Ta Kwu Leng. The new method took advantage of the natural process of composting to maximise nutrient value. Professor Tam said the trick was to regulate moisture and air supply. Fresh pig dung contained a high level of bacteria which consumed nutrients and damaged plants, she said. But as the mixture decomposed, it produced excellent fertilisers containing nitrate, phosphorus and potassium.