Abstract:

【Objective】 A long-term field experiment located at the south edge of the Loess Plateau in Shaanxi was conducted to study the effects of different fertilizer treatments on the forms of organic nitrogen and the potential nitrogen mineralization (N0) in soils. 【Method】 Soil organic N was fractionated by acid hydrolysis-distillation method (Bremner method), and N mineralization was estimated by using 30-week aerobic incubation method of Stanford and Smith. 【Result】 The results showed that the range of organic nitrogen forms in soil was in the following order, amino acid N＞non-hydrolysable N＞hydrolysable unidentified N＞ammonium N＞amino sugar N. Compared to the un-fertilization (CK) treatment, the addition of chemical fertilizers (NPK treatment) increased the different forms of organic N in soil, but the increasing rate was low. Compared with the CK treatment, the SNPK (NPK plus straw) and MNPK (NPK plus manure) treatments significantly increased the contents of different fractions of organic nitrogen in soil, especially the content of amino acid N, whereas they decreased the proportion of total hydrolysable N accounted for total nitrogen. Application of MNPK significantly increased the potentially mineralizable nitrogen (N0) and the rate of N mineralization. The significantly negative correlation was found between amino acid N and N0 (P＜0.05); and the negative correlationships between hydrolysable unidentified N and non-hydrolysable N and soil N0 were not statistically significant (P＞0.05). 【Conclusion】 Long-term application of NPK with manures or crop straw is an efficient way to enhance the nitrogen supplying capacity of soil, and amino acid N is the major contributor to the soil mineralized nitrogen.

Key words: long-term fixed-site fertilizer experiment')">long-term fixed-site fertilizer experiment, fractions of organic nitrogen, potentially mineralizable nitrogen, tier soil