Abstract:

【Objective】 The different indexes were compared to evaluate the reliability of nitrogen (N) supply capacity of soil in Hanzhong basin, so as to provide references for local soil N management.【Method】Soil samples were collected from 12 farmlands in Hanzhong basin and the surrounding hilly areas. The cumulative N uptake of potted ryegrass was used as a reference. Soil physical and chemical properties parameters were used as the indexes of soil N supply capacity, which included soil N mineralization amount based on three chemical methods (mineral N method, KCl condensation and reflux acid potassium permanganate method) and two biological methods (aerobic incubation and waterlogged incubation). 【Result】Soil type was an important factor that affected the N supply capacity of soil. Total N or organic matter could reflect the potential N supply capacity. However, soil texture, pH, available phosphorus (Ava.P), cation exchange capacity (CEC), calcium carbonate and particle composition (sand, silt and clay) could not reflect the N supply capacity. The correlation coefficient between aboveground N uptake of ryegrass and N value by mineral N method was 0.963 (P<0.01). However, since the initial mineral N could not reflect the amount of organic N mineralization, the mineral N method could only reflect the current N supply capacity, so it was not suitable as an evaluation index of soil N supply capacity. The correlation coefficient between aboveground N uptake of ryegrass and total mineral N measured by KCl reflux condensation method was 0.912 (P<0.01), while the correlation coefficient between aboveground N uptake of ryegrass and the amount of mineralizable N measured by KCl condensate reflux method was -0.766 (P<0.01). Because the leaching process of soil mineralizable N by KCl refluxing method led to the volatilization of ammonium N, which might result in the inconsistency in reflecting the potential N supply capacity and the total N supply capacity, so KCl refluxing method was not an ideal indicator to reflect the soil N supply capacity of Hanzhong basin. The correlation coefficients of total mineral N and mineralizable N with aboveground N uptake of ryegrass were 0.847 and 0.833 (P<0.01), respectively, which could reflect both the potential N supply capacity and the total N supply capacity, and it was the best chemical method. Under the condition of aerobic incubation, total mineral N and mineralizable N were not correlated with aboveground N uptake of ryegrass. While under the condition of waterlogged incubation, the correlation coefficients of total mineral N and mineralizable N with aboveground N uptake of ryegrass were 0.921 and 0.890 (P<0.01), respectively, indicating that the waterlogged incubation method could reflect the potential N supply capacity and total N supply capacity of paddy and wheat rotation soil in Hanzhong basin, and it was a good biological incubation method. The correlation coefficients of N₀ and initial mineral N + N₀ with aboveground N uptake of ryegrass in the first four stages were 0.834 and 0.845(P<0.01), respectively. The correlation coefficients with N uptake of the whole ryegrasses were 0.840 and 0.851(P<0.01), respectively. Both N₀ and initial mineral N + N₀ could reflect the potential N supply capacity. But N₀ could only reflect the potential N supply capacity, while initial mineral N + N₀ could reflect the potential N supply capacity and total N supply capacity. Therefore, initial mineral N + N₀ was an ideal index.【Conclusion】For the evaluation of N supply capacity of rice-wheat rotation soil in Hanzhong basin, the acid potassium permanganate method was the best chemical method, and the waterlogged incubation method was a good biological incubation method. The initial mineral N + N₀ was an ideal indicator to reflect the N supply capacity of soil in Hanzhong basin.

Key words: rice and wheat rotation, potential N supply capacity, total N supply capacity, aboveground N uptake of ryegrass, Chemical determination methods, Biological culture methods, Hanzhong Basin