模拟氮沉降对内蒙古典型草地土壤pH和电导率的影响

Effects of Simulated Nitrogen Deposition on Soil pH and Electric Conductivity in a Typical Grassland of Inner Mongolia

陆地生态系统氮沉降增加可导致土壤酸化,从而可能造成土壤生态系统结构和功能的退化。依托内蒙古典型草地设置的模拟氮沉降试验,研究了连续6年9个氮添梯度(0、1、2、3、5、10、15、20、50 g m^(-2)a^(-1)),2个氮添加频次(一年两次或一月一次)及2种管理方式(封育或刈割)等4种模式对土壤p H和电导率的影响。结果表明,4种模式下氮添加量3 g m^(-2)a^(-1)以下4个处理间的土壤p H无显著差异,在氮添加量为20 g m^(-2)a^(-1)(与我国粮食作物年施氮量接近)时,土壤p H分别比对照平均降低了1.1~1.9个单位;封育一年两次添加氮素在添加量5 g m^(-2)a^(-1)以上时土壤p H显著下降,而封育每月一次添加氮素在添加量20 g m^(-2)a^(-1)以上时,土壤p H才出现显著下降的现象。4种模式下土壤p H与土壤阳离子交换量及土壤交换性钙呈极显著正相关,说明高量氮添加促进了土壤中盐基离子的耗竭。高量氮添加(50 g m^(-2)a^(-1))显著增加了土壤EC值;除封育每月一次添加氮素处理外,氮添加10 g m^(-2)a^(-1)以下各处理间的土壤电导率(EC)无显著差异;土壤EC值与土壤硝态氮含量呈极显著正相关。研究结果将为我国北方半干旱草地土壤酸化的量化表征及氮素管理提供数据支撑。

Increase in nitrogen（N） deposition in terrestrial ecosystems may lead to soil acidification, and degrade the structure and fuction of soil ecosystems. Based on a six-year simulated N deposition experiment conducted in a typical grassland in Inner Mongolia Autonomous Region of northern China, the effects of N additions on soil p H and elctric conductivity（EC） were examined. There were nine N addition rates（0, 1, 2, 3, 5, 10, 15, 20 and 50 g m-2a-1）, two frequencies of N addition（twice or 12 times annually）, and two management modes（grass harvesting or not）, and the treatments were classified as four modes. Results showed that there was no significant difference among the four treatments with N addition below 3 g m-2a-1, while it decreased by 1.1- 1.9 units, respectively, as N addition rate being 20 g m-2a-1（which was equivalent to the normal annual N application rate in farmlands of China）. Soil p H was significantly decreased in treatments at N addition rate larger than 5 g m-2a-1in the mode with twice N additions and without harvesting of grasses, while it significantly decreased only at the addition rates larger than 20 g m-2a-1in mode with 12 times N additions. Soil p H was positively and significantly correlated with cation exchange capacity（CEC） and exchangeable calcium, indicating that heavy addition of N may stimulate the depletion of base cations in soil. Heavy addition of N（50 g m-2a-1） significantly increased soil EC values, while no significant difference of EC values was observed among treatments with N additions below 10 g m-2a-1, except in the mode with 12 times N additions and without harvesting of grasses. Soil EC was significantly and positively correlated with NO3--N concentrations. These results would provide data supports for the quantification of soil acidification and N management in the semi-arid grasslands of northern China.