An objective of composting is to convert animal wastes into products which are easy to handle and safe to health. Another objective is to convert the animal wastes into organic fertilisers which are safe for plant and soil (Harada et al., 1993). Harada (1992) suggested that the amount of manure and compost applied to the cropped land should be within a certain limit. Mineral fertilisers are recommended to use together with animal manure. Chong (1995) added that if mineral fertiliser should be replaced entirely by organic fertilisers, the application rate of organic fertilisers is much higher than normal rate. According to Gallardo-Lara and Nogales (1987), when high doses of compost (town refuse compost) were used, an inhibitory effect on seed germination may appear.
The large amounts of animal manure and/or compost tend to be applied in some cropped lands. However, heavy application of compost may cause environmental pollution. Not all of the nitrogen released from compost is taken up by crops, and the unutilised nitrogen is transformed into nitrate by nitrification. The nitrate leached down into the subsoil and groundwater, because soil has a poor ability retain nitrate (Smith and Peterson, 1982). Also an overloading of the soil by phosphorus can be a result of compost application.
The purposed of the experiment is to study the process of nitrogen mineralisation from two different sources of compost in comparison to mineral nitrogen.