旱地土壤施用生物炭减少土壤氮损失及提高氮素利用率

Application of biochar in dryland soil decreasing loss of nitrogen and improving nitrogen using rate

该试验采用土柱室内模拟的方法，旱地土壤上分别添加不同比例的生物炭（0、0.5%、2%、4%、6%、8%），通过模拟降雨淋洗，探讨生物炭对旱地土壤氮素动态变化的影响。结果表明：添加生物炭能延缓 NO3-和总氮淋洗速度，生物炭添加质量百分数达2%及以上时，可显著降低总氮和 NH4＋淋洗，其添加质量百分数达4%及以上时，可显著降低NO3-淋洗，而添加少量生物炭对氮的淋洗无影响；NO3-淋洗量占旱地土壤氮素淋洗总量的84%～90%，而NH4＋仅占0.4%～2%；各处理下不同土层间土壤全氮含量均无差异，而不同处理间土壤全氮含量差异显著，当生物炭添加质量百分数达2%及以上时，土壤全氮含量随生物炭添加量的增加而增加，且生物炭添加百分数与土壤全氮之间满足极显著的指数关系（R2=0.9944）。因此，在旱地土壤上施用生物炭量至少达2%以上才能显著减少氮素淋洗和增加土壤全氮含量，达到减少土壤氮素损失和提高氮素利用率，减少由氮素带来的环境污染以及改善土壤肥力的综合目标。

Excessive application of nitrogen fertilizer in agricultural soils is considered as a main cause of ecological problems such as nitrogen leaching, which has become an important limitation to improving nitrogen use efficiency in agricultural production. Because of its physical, chemical, and biological stability, biochar when applied to soils can play a key role in nutrient cycling, potentially affecting nitrogen retention and improving soil fertility. However, experimental results were variable and dependent on the experimental set-up, soil properties, and fertilizer application rates and biochar were set up at the high and low levels, which possess a big blind area. A laboratory experiment was conducted to investigate the effects of biochar additions on dynamic changes of nitrogen under artificial rainfall conditions by adding 0, 0.5%, 2%, 4%, 6%, and 8% biochar （the biochar was prepared by pyrolyzing corn straw at 500-550℃ under oxygen limited condition） into soil columns collected from red dryland of southern China under urea application condition （300 kg/hm2）. The results showed that the＆nbsp;speed of leaching of NO3-and total nitrogen was delayed by biochar applications. Compared with urea application treatment, the total nitrogen and NH4＋ contents in leachate were significantly decreased by 4.02% and 8.93%when ≥2% biochar was applied into soil, and the NO3- contents of leachate was obviously decreased by 3.23%-11.87%when the biochar ratio reached 4%. But there was no significant effect of adding small amount of biochar （such as 0.5%） on N leaching compared with urea application treatment. Leaching losses of NO3- had been found to be highest because the NO3-was mobile, and may not be taken up by plants. NO3-leaching amount accounted for 84%-90%of the total nitrogen leaching amount, while NH4＋leaching only accounted for 0.4%-2%;The total nitrogen content of different soil layers in each treatment was similar regardless of the fertilization and biochar applications. While the total nitrogen contents in soils were markedly different among the treatments. Compared with urea application treatment, the content of soil total nitrogen was significantly increased by 4.62%to 10.62%when biochar addition was≥2%, and the relationship between addition amounts of biochar （x） and the content of soil total nitrogen （y） followed an index equation： y=1.6e0.0845x （R2=0.99, n=24）. The results above suggested that biochar could be used as a potential additive for nutrient retention in order to increase the utilization efficiency of chemical fertilizers. In conclusion, biochar additions could decrease the leaching amount of NH4＋, NO3-and total nitrogen and partly increased the concentration of soil total nitrogen. However, the low biochar addition had no significant effects on reducing nitrogen leaching and increasing soil total nitrogen content. Therefore, the purpose to obviously decrease nitrogen leaching and increase the content of soil total nitrogen could be realized only when biochar addition was above 2% in dryland soil. Nonetheless, the effect of biochar addition on reducing soil nitrogen leaching needs to be further verified before biochar can be applied to agricultural fields on a large scale.