Abstract: An investigation study was conducted to analyze available silicon contents(SiO2)of 747 soil samples in nine counties (cities, districts) of Ningbo city, Zhejiang province and to determine the effects of land utilization, soil types, topography and soil chemical properties on available silicon contents in the soils. The results indicated that available silicon content in the cultivated soils averaged 68 mg·kg-1 and the soil samples with rich (≥130 mg·kg-1), medium (100-130 mg·kg-1), deficient (50-100 mg·kg-1), and very deficient levels (<50 mg·kg-1) accounted for 15.8%, 5.5%, 19.8% and 589% of total soil samples, respectively. The average silicon contents in upland soils (95 mg ·kg-1) were higher than that in paddy soils (61 mg·kg-1) and the soils with deficient silicon accounted for 58.8% and 83.5% of their total soil samples, respectively. Available silicon contents in different soil types decreased in the order: coastal saline soil (133 mg·kg-1)> fluvioaquic soil (110 mg·kg-1)> paddy soil (61 mg·kg-1). Among paddy soils tested, the highest available silicon content (88 mg·kg-1) was obtained from percogenic paddy soil, and the lowest available silicon content(49 mg·kg-1) was obtained from submergic paddy soil. Available silicon contents in different landscape types decreased in the order: coastal plain> waternet plain> valley plain> hills and mountains. Available silicon contents in the soils were significantly correlated with pH and organic matter contents in the soils(P<0.01), and were not significantly correlated with available phosphorus and potassium contents in the soils. Aiming at the present situation of serious deficient silicon in Ningbo city, the corresponding recommendations of application of silicon fertilizer were put forward．

Key words: available silicon of cultivated land, influential factors, siliceous fertilizer, Ningbo