Field investigation was carried out in the experimental station,Institute of Wheat and Potato in Heilongjiang,124°50′E,48°2′N.The experiment soil belongs to the classification of chernozem.The located site is of a typically heavy frigid climate,an annual mean temperature of 1 3℃,ranging from -42 0 to 38 0℃,an annual mean precipitation of 508 2mm,with 52 6% falling in July and August,and an mean annual evaporation of 1189 7mm.The sample of soil was taken from long-term fields rotating with wheat and soybean.The field productivity is of middle level(9 t/hm 2.grain yield in spring wheat). Five zigzagging plots were allocated to different slopes and sunny fields (10hm 2 scope).The plot size is 10m by 10m,6 sub-plots from each plot were chosen to take soil samples one very month from April to September 1993.The soil depths were divided into three layers,0～5,5～10,10～15cm.The macro-faunas were hand-sorted by digging out 100×100cm 2 soil.The soil samples with 100cm 3 and 25cm 3 were taken by circle knives respectively for separating the middle and micro-faunas by methods of Tullgren and Baermann before they were brought back to the lab in nags.Then followed counted and classified faunas.Soil baceria,fungus and actinomycete from the same soil samples were determined with dilution-plate method, separately. At the same time,the soil enzyme activities and physicochemical properties of the same samples were determined.A cellulase activity was detected with the anthrone colorimetric method,urease activity with the diffusion plate,invertase activity with reducing sugar determination method,catalase activity with oxidation-reduction titration technique and dehydrogenase with common method.The soil activer organic matter was determined by H 2SO 4 dilution method,the pH-value was determined with electrical potential method,the soil available P was determined with 0.5mol/L NaHCO 3 extraction and Mo-Sb resistance colorimetry method,the determination of soil moisture,soil temperature and hydrolysable N with the conventional methods. Total soil faunas within the layer of 0～15cm exhibited two high peaks during the investigating periods.Acarina,just as the total soil faunas,were abundant in June and August;Collembola,Nematode and scarce group exhibited a single peak in June,July and August,respectively.
Among three layers,the distributions of soil faunas were different.In 0～5cm layer soil faunas decreased from April to July,and then increased from July to September.In 5～10cm layer,two lower peaks of soil faunas were shown in May and August.In 10～15cm layer,the number of soil faunas fluctuated with a maximum of 6886/m 2 in August. Judging from the seasonal change of the dominant group,Acarina in influenced greatly on the changes of total soil faunas.The 0～5cm layer showed one clear lower peak in Acarina,while two lower peaks appeared in May and August in both 5～10cm and 10～15cm layers.The distributions of Collembola in the upper layer showed less changes,ranging from 1600 to 2000/m 2 and two significantly high peaks of Collembola in soil of 5～10cm layer in June and August and of 10～15cm layer in June and September.As to Nematode,there was one higher peak from the upper layer to the deeper one in May and June,in August,and in July respectively.The scarce group showed one high peak in August.Three types of microorganisms exhibited single peak,with bacteria and actinomycete in July and fungus in June. The study showed changes of eleven factors including soil enzymatic activities and physicochemical properties during the growing season of wheat.The performances of three hydrolytic enzymes were remarkably different.There was one high peaks of cellulase in July,two high peaks in urease in May and August,two lower peaks of invertase in July and August.All these suggested that the catabolism capability of the soil is stronger in July and August.The activities of two kinds of oxidoreductase exhibited different behavior.The peaks of cata