The microcalorimetric method was applied to analyze the influences of successive reforestations with Eucalyptus granddis × E. uophylla, Pinus massoniana, and continuous sugarcane production on the soil microbial activities. 500 g of each refined representative sample was collected in rainy and dry seasons from four 100 m2 homogeneously and perfectly defined acrisol quadrats in subtropical China. Two of them were Eucalyptus plantations with 10 (E10) and 20 (E20) year–old stands. The other two were 10–year–old pine tree plantation (P10) and sugarcane land (SL10) correspondingly contiguous to E10 and E20 and used as references for E10 and E20, respectively. Blocks of E10/P10 were 1500 m away from that of E20/SL10. Microcalorimetric experiments were carried out using 1.2 g soil samples and 0.6 ml of solution containing 5.0 mg of glucose and 5.0 mg of ammonium sulphate at 28°C. The effects of land management practice on soil quality were examined by measuring their physicochemical and biological properties. The results showed that: 1) zymogeneous bacteria were the dominated microbes in the land of continuous sugarcane production, but autochthonous floras were the ones for forest; 2) when compared with its control (SL10), land of eucalyptus (E20) had lower soil packing degree and inhibitory effect on microbial activities, but higher seasonal fluctuation in microbe constitution and activities under the same circumstance; 3) compared with its control P10, the land of eucalyptus E10 had alike soil packing degree and higher seasonal fluctuation degree of microbial activities, but lower inhabiting degree of soil microbial metabolism.
Key words: Microcalorimetry, microbial activity, eucalyptus, pine tree, sugarcane.