2.4. Chemical analysis
The residues of weeds were collected after the experiment,
and the mass was measured after being oven dried at
70 -C for 72 h. Total nitrogen in soil and weeds was
analysed by micro-Kjeldahl method (Dewis and Freitas,
1984). Total phosphorus in soil and weeds was analysed by
means of absorption spectrophotometry after decomposition
with potassium peroxodisulphate (Central Kagaku Corporation,
2001).