MULCHING AND ORGANIC-INORGANIC FERTILIZER APPLICATION REDUCE RUNOFF LOSSES OF NITROGEN FROM TOBACCO FIELDS

Nitrogen loss has limited the sustainable development of tobacco agriculture and led to serious non-point pollution in China, especially those areas suffered from excessive rainfalls. A study on the characters of nitrogen loss under different cultural practices was conducted in eastern China. The cultural practices were distinguished by different nitrogen application methods and different cultivated conditions, including CK (no fertilizer with no mulching), IF-NM (inorganic fertilizer with no mulching), IF-M (inorganic fertilizer with mulching), OIF-NM (60% organic+40% inorganic fertilizer with no mulching) and OIF-M (60% organic+40% inorganic fertilizer with mulching). Results showed that the main nitrogen form in the runoff waters was NH3--N. The concentration of NH3--N in runoff waters correlated closely to the time of both basal and additional fertilizer application. Mulching increased runoff volume by 12.5% while decreased the NH3--N concentration, overall reduced the accumulative amount of NH3--N and significantly (p<0.05) decreased the amount of total N in runoff waters. Combined application of organic and inorganic nitrogen fertilizer also reduced the concentration of NH3--N and the amount of NH3--N and total N, but the effectiveness was not as good as that of mulching. Mulching combined with the organic-inorganic fertilizer application (OIF-M) reduced the runoff losses of total N by 50.4%, NH3--N by 52.5%, NH4+-N by 52.9% and the N in other forms by 35.9%, and was proved to be optimal in decreasing the runoff losses of nitrogen among the different treatments. This mainly because that OIFM was more conductive to reserve the NH3--N in plough layer and enhance the nitrogen mineralization, thus increase the crop nitrogen use efficiency. Therefore, we highlight the importance of mulching in reducing the nitrogen loss in runoffs and recommend similar areas to use organic-inorganic compound fertilizer under a mulch-cultivated condition.