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作 者 ：许文强*,陈曦,罗格平,张清,张豫芳,唐飞2

期 刊 ：生态学报 2010年 30卷 14期 页码：3707~3716

关键词：土壤有机碳；管理模式；人工绿洲；作物轮作；CENTURY模型；

Keywords:soil organic carbon, land management, anthropogenic oasis, crop rotation, CENTURY model,

摘 要 ：近半个世纪前，中国西北干旱区人类大规模的水土开发活动使得流域下部的荒漠覆被土地转变成了人工绿洲，强烈的人类耕作活动使得人工绿洲土壤有机碳库发生了显著变化。以干旱区典型的三工河流域下部的人工绿洲为例，基于CENTURY模型，研究人工绿洲开发前后及农业管理模式变化对表层土壤有机碳库（0-20cm）的影响。CENTURY模型模拟结果表明：（1）研究区荒漠灌木林地开垦为人工绿洲后，在最初的2a土壤总有机碳（TOC）快速增加，随后呈逐渐下降的趋势；（2）研究区人工绿洲在被开发后50a的连续耕作下，平均土壤TOC呈先增后减再增的“N”型变化趋势，但最终土壤TOC超过了原始自然状态下的TOC，而且2008年土壤TOC比原始荒漠状态增加7.74%，说明研究区表层土壤有机碳总体呈“碳汇”趋势。尤其在研究区实施了免耕、秸秆粉碎还田、科学测土配方施肥等保护性耕作措施后，土壤固碳效应明显，这完全不同于热带森林、中国北部温带半干旱草原及非洲Savanna半干旱稀树草原开垦为耕地后土壤有机碳大量损失的结论。

Abstract:Large-scale reclamation in arid land over North-western China during the past 50 years has converted the natural desert landscape into anthropogenic oasis, particularly in the lower part of watersheds. Drastic human activities may have caused the change in soil organic carbon (SOC) in anthropogenic oasis. Fubei farm, a typical anthropogenic oasis at the lower part of Sangong river watershed reclaimed 50 years ago, is selected as the representative area to assess the dynamics of SOC before and after the land reclamation and to analyse the effect of different management practices on soil carbon pools. Based on field investigation, history of crop rotations, and past farm practices in Fubei farm, land management practices were divided into five categories, corresponding five periods, 0-1958, 1959-1984, 1985-1992, 1993-1998 and 1999-2008. This study employs the CENTURY model to investigate the effects of land reclamation and management practices in oasis agriculture on the dynamic of SOC at different periods. CENTURY model (Version 4.0) was run based on a monthly time step, and simulated three conceptual SOC pools, namely active, slow, and passive pools, represented fast, medium, and slow rates of turnover of carbon in the soil profile, respectively. The model successfully simulated the soil total organic carbon (TOC) dynamics of the top layer soil (0-20 cm) in the different periods in the study area. The model was run for 1950a to reach steady state which assumes the land was a natural desert shrub with low-intensity grazing. In the equilibrium state, the proportions of active, slow, and passive organic carbon pools in soil TOC were 3.78%, 61.41%, and 34.81%, respectively, indicating that soil TOC in the study area was dominated by the slow and passive carbon pools. Model simulation showed that soil TOC increased rapidly in the first 2 years of oasis agriculture when the natural desert shrubland with its weak nutrient recycling was replaced by annual crops with better nutrient recycling. Over the 50 years′ cultivation (1959-2008), the mean change in soil TOC exhibited complex ways. TOC increased rapidly in the first 2 years (1959-1960) after shrubland reclamation, and declined slowly during the period 1961-1984 and then decreased rapidly from 1985 to 1992. Between 1993 and 1998, it remained relatively stable, and climbed rapidly again during 1999-2008. The trend in soil TOC showed “N” shape, i.e., increase, decrease, then increase. Soil TOC is greater (7.74%) in 2008 than in 1958 under the natural desert shrub. The improvements of land management practices such as ploughing being replaced with no tillage, straw being crushed before returning it to soil, and reasonable application of fertilizers, played a key role in the change in soil TOC. Especially, soil carbon sequestration was obviously increased since protective management practices were implemented in 1993. The results were different from the conclusions that loss of soil organic carbon would happen due to reclamation and continuous farming in tropical forests, semi-arid grasslands of northern China and Nigerian semiarid Savannah.

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