| Phyisical and chemical properties of paddy fields are clearly different from Northern to Southern China because of regional distribution of soils. Compared to sourthern paddy fields, total applied N amount is lower and N efficiency is higher in cold area. Soil N supply ability is closely related to nitrogen application and N efficiency. N mineralization ability is closely related to the soil N supply of paddy fields. At present, there is still a lack of suitable measurement indicators to evaluate soil N supply ability in cold paddy soil. This experiment compared in situ method with anaeroboic incubation method to disclose the N mineralization character and N supply index of cold paddy soil. The results were as follows:Improved in situ method could be used as evaluate index of soil for nitrogen ability. The soil mineralized N content had no difference between two sanmples incubated with anaeroboic method at40℃for28days, however, the mineralized N determined in situ method had significant difference. By improving the traditional in situ method, using the phase in situ method suggest that soil N supply curve were in conformity with rice N uptake curve. Soil N supply had good relationship with rice N uptake, the correlation coefficient were0.846and0.948, which reached the significant level of1%. The soil mineralized N with inmproved in situ method could explain soil N supply ability for70%to90%.Accoding to anaeroboic incubated Northern and Southern paddy soil with high and medium fertility, we found that soil N mineralization potential(N0) of northern soil was higher than southern soil with corresponding fertility under25℃. The content of accumulative soil mineralized N and soil N mineralization potential(No) of northern soil were lower than southern soil with corresponding fertility under40℃. Ratios of the hydrolysamino acid N and amino acid N to total N were higher in southern paddy soil than the northern soil with corresponding fertility. Accumulative soil mineralized N and the mineralization potential and soil pH reached5%significant level. Compared to southern paddy soil, the rate of N mineralization in northern soil was slower and faster in the early and late stage,respectively. This N mineralization character for northern paddy soil matched to rice N uptake, which was one of the reasons for high N use efficiency in cold area.Field experiments showed that N uptake of rice of two sites accounted for22%to24%of the total N uptake of rice before panicle initiation stage. Panicle initiaion stage to heading stage,the N uptake during different stages of rice accounted for45%to62%of the total N accumulation except FFP treatment of A Cheng. Heading stage to mature stage, N uptake of rice of two sites accounted for17%to30%of the total N uptake of rice.Therefore, N uptake peak of rice was from panicle initiation stage to heading stage. Panicle initiation stage to heading stage, the content of soil supply N of different treatments accounted for51%to63%of N uptake of rice, therefore, applied N fertilizer was the key to the rice at this period. Compared the effect of N applied in different periods through the contrast test in the field, which, showed the N applied in panicle initiation stage ensure sufficient supply of N at the critical stage, which increased dry matter accumulation and N accumulation by11%-12%and0.3%-4%. Therefore, compared to FFP treatment, OPT increased NUE2.53and18.78percentage points, increased AE by3.14kg·kg-1and13.30kg·kg-1, and increased PE by6.57kg·kg-1and21.15kg·kg-1in Wu Chang and A Cheng. Through controlling the total N fertilizer, optimized nutrient management could increase the yield and N efficiency of rice. |
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