内蒙农牧交错带地区土地利用方式和施肥对土壤碳库的影响

内蒙武川是我国典型的内蒙农牧交错带地区,土地利用方式转变和施肥是影响该地区农业生产和土壤碳储量的重要人类活动。选取内蒙武川地区,针对不同土地利用方式(耕地、退耕还林/还草)和施肥措施(化肥、有机肥)的长期定位试验土壤,分析土壤有机碳(SOC)、土壤无机碳(SIC)和全氮(TN)含量和储量,结合13C和15N稳定同位素方法,研究土地利用方式和施肥措施对于该地区土壤碳氮转化的影响规律。研究表明,退耕还灌/还草后,SOC储量较耕地均有显著提高(提高幅度0.60~0.98 Mg hm-2 a-1),SIC储量也增加或保持相同水平(柠条地除外)。相比不施肥处理,施用有机肥能显著增加SOC(1.08~1.19 Mg hm-2 a-1),施化肥处理则会降低SIC(0.06~0.16 Mg hm-2 a-1),且主要影响次生碳酸盐。施肥SIC中原生碳酸盐比例(0~23%)低于自然土壤(3%~29%)。施肥措施对于土壤碳氮的转化强度远大于土地利用方式的改变。对于内蒙等干旱半干旱地区土壤,土地利用和施肥措施对于土壤有机和无机碳的影响应该在区域固碳管理中给予全面考虑。

Impact of Land Use and Fertilization Measures on soil C Stock in Farming-grazing Interlacing Zone of Inner Mongolia, China

Objective]Land use and fertilization are the two important types of human activities that can influence agricultural production and soil carbon(C)stock,especially in farming-grazing interlacing zone,like Wuchuan County,Inner Mongolia of China. [Method]In this study soil samples were collected from a longterm field experiment on land-use and fertilization located in Wuchuan County for analysis of soil organic carbon(SOC),soil inorganic carbon(SIC),total nitrogen(TN),δ13CSOC,δ13CSIC and δ15N to investigate impacts of land-use(land planted with Horqin peashrub(Caragana korshinskii),land planted with ryegrass and deserted land)and fertilization(chemical fertilizer, organic manure and no fertilization)on C and nitrogen(N)transformations and C stock in the soil.[Result]Results show that SOC stock in the land under Horqin peashrub(Caragana korshinskii) or ryegrass was 0.60~0.98 Mg hm -2 a -1 higher than that in the crop land,and similarly,SIC was slightly higher than or on the same level,except in the land under Horqin peashrub. Compared with the deserted land,the lands under “grain for green”(planted with Horqin peashrub or ryegrass) were lower in content of primary carbonate and almost unchanged in soil TN level. Compared with CK (no fertilization),application of organic manure significantly increased SOC stock(1.08~1.19 Mg hm-2 a-1),while application of chemical fertilizer decreased SIC stock,mainly of secondary carbonate, at the rate of 0.06~0.16 Mg hm-2 a-1. Compared with application of chemical fertilizer alone,application of organic manure and application of organic manure in combination with chemical fertilizer increased SOC and SIC stock at the rate of 0.6 and 0.1 Mg hm-2 a-1,respectively. Changes in land-use did not have much impact on δ13C of SOC and SIC,but the crop land was significantly higher than the deserted land or the lands under “grain for green” in soil δ15N,due to application of chemical fertilizer. Application of organic manure significantly decreased δ13C value of SOC,but application of chemical fertilizer had a reverse effect, which was further enhanced by soil acidification caused by chemical fertilization. The discrepancies between fertilization treatments in SIC loss maybe attributed to leaching of SIC into deeper soil layers,which indicates that it is necessary to do in-depth study on SOC and SIC in deeper soil layers. [Conclusion]The impact of fertilization on soil C and N transformation is much higher than that of changes in land-use in this farming-grazing interlacing zone. As regards the soil in the arid and semi-arid Inner Mongolia,the effects of land use and fertilization on SOC and SIC should be taken into full consideration in the management of regional C sequestration.