CHARACTERISTICS OF VEGETABLE SOILS AND CONSTANT UTILIZATION IN SEMI-WRID REGION

The characteristics of vegetable soils was lnvestigated through surveylng 200 different growth year vegetable soil samples and typical representative soil profiles in Tianjin area. It was found that old vegetable soil has good soil structure, thick arable level and maturation level, good proportion of three phases. It was observed through scanning electro microscope that microaggregate of soil is round, the surface is coarse, the bonds among them are loose, and has more pores compared to the new cultivated vegetable soils whose microaggregate has a tighter bonds among them, less pores,smoother surface and has no interrelated channels each other. The nutrient accumulation in soil arable level is obvious, the characteristic of accumulation is readily availible Ptotal NOMtotal Preadily availible N, and soil total potassium difference is not obvious. The distribution of nutrients in soil profiles showed the characteristic of deep level accumulation of nutrients, the order of accumulation ls approximately same with the arable level. The analytical results of soll total elements and clay minerals showed that ignition loss and Cao content of total soil body is twice or three times higher than.that of control treatment; the content of MgO, MnO, Al2O3, Fe2O3, P2O5 is 20%-60% higher and the cohtent of SiO2. Na2O is 2O%~4O% lower than that of control;the content of TiO2. K2O has almost no change. The total vegetable soil body mainly comprises of water-mica along with some quartz. mont morillolite and a little kaolonite.The mineral composition of the total soil body has .no change compared to the control treatment. Bacterias and fungi in soils are 2~3 times higher and actinomycetaceae is one time higher than control; soil enzyme activity is high, the activity of enzyme in 4 soils is 2-5 times higher than that of control. The changing trends of microflora in vegetable soils of different development ages showed that old vegetable soil has a trend that amount of bacteria, actinomycetaceae is more and amount of fungi is less. The diagnostic results of eleven nutrients abundance/ deficiency by using method of soil nutrients systematic approach indicated that in old vegetable soils, the order of limiting factors is NKPMn, the relative yield in no fertilizer plot reached over 70%, in new vegetabie solls, the order of limiting factors is PNKZnFeMnS, the relative yield in no fertilizer plot reached only over 20%. There is a great difference in vegetable yield and productivity due to the different soil fertility. It's an urgent need to improve fertility of new cultivated vegetable fields for high yielding, good qualities, and high efficiency of vegetable production.