STUDY ON DECOMPOSITION OF PLANT RESIDUES IN SOILS OF GUANGZHOU AND WUXI
Lin Xinxiong, Wen Qixiao Xu Ning (Institute of Soil Science, Academia Sinica, Nanjing)
Experiments on decomposition of residues of plants including various cereal crops, leguminous and aquatic green manure crops under field conditions were carried out on microplots of paddy soils and upland soils in Guangzhou (southern subtropics) and Wuxi (northern subtropics) respectively. The fraction of originally added plant C retained in soil after the decomposition for 1 or 2 years was, as what has been previously found in the study at southern Jiangsu, correlated positively with the lignin content of plant residue regardless of different environments in which it decomposed, but it was related neither to its nitrogen content nor to its water-soluble substances content. For a given plant residue, the decomposition pattern in Guangzhou was very similar to that in Wuxi. Moreover, the decomposition rate of plant residue in Guangzhou was as fast as that in Wuxi, although the mean annual temperature and precipitation in Guangzhou were 6.4℃ and 550mm higher than those in Wuxi respectively. Evidence obtained indicates that this is due to the lower pH value of soils in Guangzhou. It was found that in case of the same soil used for the decomposition experiments both in Guangzhou and Wuxi, its decomposition rate in Guangzhou was significantly faster than that in Wuxi. It was suggested that because of the effect of soil properties, the decomposition rate of organic materials in the southern subtropics would not faster than that in the northern subtropics. Soil erosion might be an important factor causing the drastic decrease of organic matter content of soils in tropics and southern subtropics after the soils being cultivated.