Soil Organic Nitrogen Forms And Their Contributions To Mineralizable Nitrogen In Water-stable Aggregates Of Paddy Soil In Black Soil Region

The paddy soil has become one of important paddy soil resource in black soil region of Northeast China. The chemical forms and existing conditions of paddy soil organic nitrogen (SON) directly affect the decomposition and mineralization of SON, and it is an important factor that influence the soil N availability. Scientific evaluation of paddy soil N fertility characteristics of black soil region, for the rational use of black soil and fertilizer is of great significance. So far, the paddy soil organic N forms and the relationships with the mineralized N need a further systematic research in black soil region. The article is focused on paddy soil of the black soil region aspect, using Wet sieving method, Bremner method and long-term waterlogged incubation, study the paddy soil water-stable aggregate composition and the distribution of organic N forms and the characteristics of N mineralization at different organic carbon or nitrogen levels, analyze the relationships between the different size soil aggregate organic N forms and the N mineralization, and discuss the organic N form which makes a important contribution to the N mineralization. The main results are as follows:(1) 2-0.25 mm aggregate composition of soil is the largest and is the advantage particle-size, whitch has obvious fixation ability of carbon with nitrogen. Soil organic carbon (SOC) and total nitrogen (TN) content has a marked impact with 2-0.25 mm aggregate composition (P< 0.01).(2) SON is given priority to acid hydrolysable N (AHN) in soils and theirs different size aggregates. The content and the proportion of TN of organic N forms is hydrolysable unknown N (UN)> hydrolysable amino acid N (AAN)> hydrolysable amminia N (AN)> hydrolysable amino suger N (ASN). Organic N forms mainly occur in 2-0.25 mm aggregate. The effects of hydrolysable organic N forms on aggregates formation are various among in different particle-size aggregates. Respectively, soil hydrolysable amminia N with amino acid N and hydrolysable amminia N with amino suger N have significant contributions to the formation of> 0.25 with 2 mm and< 0.25 mm aggregate.(3) The N mineralization potential (No) is 38.0-175.3 mg kg-1, and mineralization rate constant (k0) is 0.022-0.041 d-1 in paddy soil. The N mineralization potential (No) is main in 2-0.25 mm aggregate (50.9-85.8 mg kg-1), next ordinal for >2 mm and 0.25-0.053 mm aggregate, least in< 0.053 mm aggregate. SOC and TN with pH are significantly and positively relate to N mineralization potential (No) (p< 0.01 or P< 0.05), but TN with pH are negatively to mineralization rate constant (ko) (p< 0.05). Obviously, SOC and TN with pH are important factors that affect SON mineralization, and TN and C/N of different size aggregates are important factors that affect soil aggregetes organic N mineralization.(4) In paddy soil, hydrolysable amminia N with amino acid N and hydrolysable amino suger N with non-hydrolysable N are significantly and positively relate to N mineralization potential (No) (p<0.01). hydrolysable ammonia N is a form that has important contribution to mineralizable N and hence the major source of soil mineralizable N; in different size aggregates of paddy soils, the contributions of hydrolysable organic N forms to mineralizable N are various in different particle-size aggregates, in> 2 mm,2-0.25 mm,0.25-0.053 mm and <0.053 mm aggregate, the contributions of hydrolysable organic N forms to mineralizable N respective are non-hydrolysable N, hydrolysable unknown N, hydrolysable amino acid N with amminia N and hydrolysable amminia N with amino acid N.This article has carried on the comprehensive and system research for organic N forms and N mineralization of water-stable aggregate with different carbon or nitrogen level in paddy soil of black soil region, analyzed the contribution of different particle-size soil aggregate organic N forms to the N mineralization. From micro perspective of aggregate, has discussed the mechanism of supplying N of soil. Researching results have important theoretical and application value to clear N fertility characteristics and reasonable fertilizer of paddy soil of black soil region.