Effect Of Long-Term Fertilization On Soil Organic Nitrogen Fractions And The Relationship With Nitrogen Indices

Nitrogen is one of the most important nutrient elements for crops. The nitrogen uptake by crops mainly comes from soil. Organic nitrogen is an important form of soil nitrogen, and it is the source of nitrogen mineralization and supply. It is important to study the effect of fertilization on organic nitrogen components, and to improve efficiency of nitrogen fertilizer. Combined with brown soil long-term fertilization experiment, this paper carried out organic nitrogen components, nitrogen indices research as well as yield and nitrogen efficiency research, to explore the effects of different fertilization and to find simple and stable nitrogen indices. The main results are as followed:The yield ranged from 3424.03-13250.00 kg·hm-2; the trend of different treatments was:NPK, NP>N1>N2>CK. For the five nitrogen levels under different treatments, the highest yield of NP and NPK was at N180, close to international level. The highest yield of N1,N2, CK was at N180, N60, N120, which shows that N2 treatment has been excessive. The effect function shows that NPK treatment has the more intense demand for nitrogen fertilizer in the coordination of phosphorus and potassium. When soil conditions are consistent, with the increasing of nitrogen fertilizer, the efficiency will be decreasing. In different soil conditions, it influenced by the demand of crops for nitrogen.The trend of soil mineral nitrogen content was:mature and fertilizer application> single mature application, single nitrogen fertilizer application>multiple fertilizer> no fertilization treatment; with the depth of soil layer, the content of mineral nitrogen decreased. The total organic nitrogen content ranged from 570.1-961.0 mg·kg-1, M2NPK was the highest. The application of manure can increase the content of organic nitrogen forms. The average ratio of total organic nitrogen in soil total nitrogen of each group was 67.91%,73.03% and 75.75%, respectively. Mature combined with multiple fertilizer acted best. Compared with different indices, the correlation coefficient between NaHCO3-205, NaHCO3-260 and alkali solution nitrogen was higher. And the method was more simple and time-saving. Besides, the extraction source of NaHCO3-205 and NaHCO3-260 was amino acid nitrogen and amino sugar nitrogen. Therefore, NaHCO3-205 and NaHCO3-260 could be considered as evaluation indices of soil nitrogen supplying of this study, the applicability of other types of soils remains to be further verified.Organic nitrogen is important for soil nitrogen supply. This study aimed to provide theoretical basis for the management of soil nitrogen by studying the change of organic nitrogen and the indices of nitrogen supply under long-term fertilization, so as to guide agricultural production to achieve high yield and high efficiency.