Abstract: Soil nitrogen leaching not only causes soil nitrogen loss, but also has great contribution to the water body eutrophication. By the method of laboratory simulation test, this paper studied the effects of applying biochar on the leachate volume, pH, electrical conductivity (EC), and ammonium nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃^--N) concentrations in a batch of yellow soil columns under simulated raining condition. The biochar was made from eucalyptus chips, and its application rates were 1%, 2%, 4%, and 10% of soil mass. Comparing with the control, applying 10%, 4%, 2%, and 1% biochar decreased the leachate volume by 14%, 0.03%, 0.02%, and 0.01%, respectively. With the increasing amount of applied biochar, the leachate pH and EC increased. Under the application of 10%, 4%, and 2% biochar, the leachate NH₄⁺-N and NO₃^--N concentrations increased by 235%, 28.1% and 31.6%, and 4.2%, 14.5% and 25.6%, respectively,while under the application of 1% biochar, the leachate NH₄⁺-N and NO₃^--N concentrations decreased by 15.8% and 19.2%, respectively. This study showed that the effects of applying eucalyptus chips on the nitrogen leaching of yellow soil depended on the applied amount of the biochar. The addition of 1% biochar reduced the nitrogen leaching, while excessive biochar increased the nitrogen leaching. Whether the species of biochar materials may affect soil nitrogen leaching would be an issue to be investigated in the future.

Key words: Land vegetative cover index, Image classification, Accuracy evaluation, RS detection, Landscape ecology