EFFECTS OF LONG-TERM CONSERVATION TILLAGE ON SOIL NITROGEN CONTENT AND ORGANIC NITROGEN COMPONENTS IN A CHINESE MOLLISOL.

The effect of different long-term (2001-2016) tillage practices on soil nitrogen forms in different soil layers were studied to provide a scientific basis for evaluating soil fertility and establishing rational fertilization measures. Soil contents of total nitrogen (TN), particulate organic nitrogen (PON), microbial biomass nitrogen (MBN), water soluble organic nitrogen (WSON), NO3-N content, NH4-N content ammonium nitrogen and organic acid nitrogen component contents were measured under notillage (NT) and mould plow (MP) treatments based on a long-term (16 year) conservation tillage experiment in Northeast China. The results showed that no-tillage increased soil total nitrogen, active nitrogen, inorganic nitrogen and organic nitrogen content, which varied with soil depth. Compared with MP, NT significantly (p < 0.05) increased total nitrogen and active nitrogen content in the surface soil (0- 30 cm); TN, PON, MBN and WSON increased significantly (p < 0.05) by 28.32%, 23.07%, 15.13% and 25.21% in 0-5 cm and by 10.17%, 19.4%, 15.97%, and 31.33% in 5-10 cm, respectively. For soil inorganic nitrogen, the content of ammonium nitrate at 0-5 cm and at 5-10 cm under NT was significantly (p < 0.05) higher than that of MP by 28.1% and 32.13%, respectively, and the content of ammonium nitrogen in soil at 0-5 cm was significantly (p < 0.05) higher, by 12.86%, than that of MP. No-tillage significantly increased the content of total hydrolysable nitrogen, hydrolysable ammonia nitrogen, hydrolysable amino acid nitrogen and hydrolysable unidentified nitrogen in the 0-10 cm soil layer, but no significant effect was found on the content of hydrolysable amino sugar nitrogen. Soil nitrogen content was closely related to tillage practices. These results suggest that no-tillage was beneficial in augmenting soil nitrogen supply capacity by increasing soil total nitrogen, active nitrogen, inorganic nitrogen and organic nitrogen content. [ABSTRACT FROM AUTHOR]