Abstract: To clarify the change of organic nitrogen fractions with continuous fertilization, a sitespecific plot experiment was used to study the effects of continuous application of biocharbased fertilizer and biochar on the fractions of organic nitrogen in brown soil. Five treatments were employed, including the control without fertilization (CK); low application level of biochar; high application level of biochar; nitrogen, phosphorus and potassium combined fertilization; and biocharbased fertilizer. Soil samples were collected in 0-20 and 20-40 cm soil layers after the harvest of peanut in 2014. An organic N fractionation method by Brenmer was used to determine soil organic nitrogen fractions. The results showed that after 4 consecutive years of fertilization treatments, total soil nitrogen increased for all the treatments. The total soil nitrogen of biocharbased fertilizer treatment was significantly higher than that in the original soil and CK group, with increases of 69.8% and 4.8% respectively. The contents of soil organic nitrogen fractions in different fertilization treatments were in the order of ammonium N > amino acid N > nonhydrolysable N > hydrolysable unidentified N > amino sugar N. The input of biocharbased fertilizer significantly increased the contents of ammonium N and amino acid N in acid hydrolysable organic nitrogen of soil. Compared with the original soil, the input of biochar-based fertilizer increased the contents of ammonium N and amino acid N by 65.9% and 128.0% respectively. As the application rate of biochar increased, ammonium N content showed an increasing trend, but such increment in the biochar treatments was far lower than that in the biocharbased fertilizer treatment. The applications of biochar, NPK fertilizers and biocharbased fertilizer increased the content of hydrolysable unidentified N, and the total content of non-hydrolysable organic nitrogen, but the differences among the treatments were not significant. Overall, continuous application of biochar-based fertilizer or biochar significantly increased the contents of ammonium N and amino acid N from acid hydrolysable organic nitrogen in soil, promoted the activation of nitrogen, and benefited the uptake and transport of nitrogen of low-and middleyield peanut field.

Key words: triclosan, metabolites, ecological risk., toxic effect