不同土地利用方式下我国北方土壤有机、无机碳库的变化趋势及原因分析

【目的】土壤碳酸盐含量的变化对干旱半干旱地区大气中CO2的吸附固定有重要影响。探究不同土地利用方式下土壤无机碳(SIC)含量沿土壤剖面的变化特征及其影响因素,理解其在土壤中的循环转化,有助于准确预测土壤碳储量对全球环境变化的响应和碳减排的效果。【方法】搜集、提取1990—2018年我国已发表的涉及撂荒地、灌木地、草地、林地和农田5种土地利用方式下0—100 cm不同土壤剖面深度土壤有机碳(SOC)和SIC含量的相关数据,分析不同利用方式下SOC和SIC的相互关系。【结果】SOC含量随土壤深度增加而降低,而SIC含量随土壤深度变化的特征在5种土地利用方式下有明显差别。在0—60 cm土层,农田和草地具有较高的SOC含量,灌木地具有较高的SIC含量,撂荒地中各土壤剖面层次的SOC和SIC含量均显著低于其他利用方式(P <0.05)。在60—100 cm土层,撂荒地和灌木地SOC和SIC含量均明显低于其他3种土地利用方式。在0—20 cm土层,SOC/SIC值在农田土壤中(0.80±0.05)最高,而在撂荒地(0.40±0.02)和灌木地(0.50±0.03)最低。在20—60 cm土层,草地和农田土壤的SOC/SIC值在剖面各层显著高于撂荒地和灌木地(P <0.05)。在60—100 cm土层,草地土壤中SOC/SIC值显著高于其他4种土地利用方式(P <0.05)。在撂荒地、灌木地、林地(除了60—80 cm土层)和农田土壤中,SOC和SIC含量在各个剖面层次上均呈现显著正相关关系,而草地土壤中SOC和SIC含量则在各个土壤剖面呈现出显著负相关关系。根据估算,0—100 cm土层SIC储量能够占到整个土壤碳库(SOC+SIC)的60%~80%。草地0—100 cm的SOC储量最高,为C (56.65±4.00)kg/m^2,是其他土地利用方式的1.6~3.7倍,撂荒地的SIC储量最低,为C (51.05±5.11) kg/m^2,是其他4种土地利用方式的51.1%~57.5%。【结论】在我国北方干旱半干旱地区,农田、草地、灌木和林地土壤中秸秆、根茬、植株残渣等有机碳源的输入刺激了微生物的分解作用,促进了土壤有机碳向无机碳的转移过程,有利于大气CO2的截存。而撂荒地地面植被较少、生物化学风化作用弱,且易受环境扰动,不利于对大气CO2的吸附固定。此外,灌溉、耕作、施肥等人为因素驱使土壤中碳酸盐向深层土壤运移,导致农田土壤无机碳库在土壤深层积累,对CO2截存作用更大。而灌木地则通过根系水分输送驱动土壤深层碳酸盐向表层运移,导致深层土壤无机碳库减少,降低CO2固定潜力。

Long-Term Effect of Industrial Waste Water Irrigation on Soil Chemical Properties

A laboratory experiment was conducted in Soil Science Division of BRRI during 2011 aimed to determine the vertical distribution of soil chemical properties under long-term industrial waste water irrigated rice field. Waste water irrigated rice field seemed to create some differences in soil pH profile. The pHW and pHKCl in all soil depth was higher with waste water irrigated rice field. The surface charge of both the soils was considerably negative. Waste water irrigated rice field developed more negative charges in soils. Irrigation with waste water increased Electrical Conductivity （EC） in rice soils profile. The organic carbon content （%） started to decrease sharply with the increase in soil depth. Organic carbon content was higher with waste water irrigated rice soils Total nitrogen （%） was high with underground water irrigated rice soils in surface but at deeper, total N was similar in both soils. Olsen P （mg/kg） was higher with underground water irrigated soil at 0-5 cm depth but at 5-100 cm soils profile, it was higher with waste water irrigated rice soils. Micronutrients （Zn, Fe, Cu and Mn） and heavy metals （Pb, Cd, Ni and Cr） in soils were increased significantly through irrigation with waste water in rice-rice cropping pattern.