荒漠开垦后的绿洲化演进中土壤碳积累过程及固碳潜力计量研究

In the past several decades, arid region of northwest China had been undergone extensive land use change with conversion of native desert to irrigated farmland. Soil carbon dynamics after cultivation of desert soil and subsequently agricultural use can indicate evolution extent of soil quality and oasis function. The newly cultivated farmlands are the most important areas for soil carbon sequestration in arid desert oasis agroecosystem. In this project, we select the farmlands cultivated during the recent 60 years in Hexi corridor region as research object. We use long-term field fertilization experiment established in 2005, long–term monitoring fields in the Chinese Ecosystem Research Network Station established in 2004, and the fixed fields of 0-60 year cultivation chronosequence to make data accumulation analysis and further sampling analysis. Based on the determination of soil properties including soil particle size distribution, soil aggregates and aggregate-associated C, total inorganic and organic C, N, labile organic C fractions such as microbial biomass C, hot-water extractable C, 13C-NMR in soils under different long-term fertilization treatments and in the different cultivated fields, the project is to determine soil organic and inorganic C accumulation processes，C sequestration effects and C retention capacity, and to identify soil C sequestration rate under different fertilization patterns, as well as to resolve major C stabilization mechanisms in the oasis evolution process following conversion of desert to irrigated farmlands. Also, the project is to build soil carbon retention capacity model for desert oasis fields and analysis soil carbon saturation deficit and time scale that reach carbon stable and equilibrium level in the farmlands of different cultivation periods from the views of soil carbon sequestration physicochemical potential and biological potential.The results can provide scientific basis for assessment of C sequestration potential and for soil management regulation and control of enhancing soil organic matter level in desert-oasis farmlands in arid northwest China.

近几十年来西北干旱区经历了大规模的自然荒漠向灌溉农田的土地利用转变。荒漠开垦后的绿洲化演进中土壤碳过程研究是揭示人为土壤形成及演变规律的重要方面。新垦农田也是干旱区绿洲农田土壤碳增汇的潜力所在。本项目选择河西走廊中段近60年来的新垦农田，通过长期肥料定位试验、生态系统研究网络站长期监测样地的数据积累挖掘与进一步研究、以及对近60年来不同开垦时间序列的绿洲农田土壤耕层及剖面样的测定，分析土壤粒级组成、土壤团聚体形成及其稳定性、无机碳、有机碳及活性组分、化学组成等特征；解析荒漠开垦为灌溉农田后的土壤碳汇效应和碳积累过程、以及不同农业管理措施下的C稳定机理；确定不同开垦时期荒漠农田土壤C饱和亏及达到C稳定水平的时间尺度；定量分析近60年来新垦荒漠绿洲农田土壤固碳的生物潜力和物理化学潜力。为干旱区荒漠绿洲农田土壤C增汇潜力提供评价依据，也为干旱区新开垦绿洲农田土壤有机质提升的土壤管理提供依据。

根据项目研究计划，开展了荒漠开垦时间序列(0-60年)土壤碳积累过程和固碳速率研究、长期不同施肥处理的土壤养分特征及碳积累过程研究、新垦绿洲农田不同农业管理模式下土壤有机碳及其组分研究。取得了如下研究结果：干旱区荒漠土壤开垦为灌溉农田后，耕层土壤砂粒含量随开垦利用年限的增加而逐渐降低，但显著的变化发生在开垦16年后的农田；在沙地开垦后的最初20年，耕层土壤有机碳）及全氮含量呈线性增加，20年后增加趋势减缓。沙地开垦46年后0-60cm土层SOC年平均固存量为0.75kg•hm-2•a-1。肥料长期定位试验结果表明：连续不同施肥处理10年后，SOC含量提高了1.68-2.84倍，土壤全氮、全磷、碱解氮及有效磷均有一定程度的提高，但单施化肥及有机肥与氮磷化肥配施有效钾含量下降。SOC的积累速率单施化肥、有机无机配施和单施有机肥处理分别为0.27、0.59和0.87g kg-1a-1。增施有机肥、适量减少化肥投入、氮磷钾化肥的平衡施用是绿洲沙地农田土壤肥力持续提升的施肥管理对策。不同覆盖和耕作处理4年后，SOC和全氮含量较试验前分别增加5.4%-34.0%和9.3%-34.9%，少耕秸秆覆盖处理较常规耕作地膜覆盖（CK）SOC含量高27.2%，但在秸秆覆盖和地膜覆盖下减少耕作对SOC的短期影响均不显著。种植10年的苜蓿地和5年苜蓿5年玉米地较连续种植10年的玉米地，SOC分别高72.7%和27.7%，全氮含量分别高54.3%和17.1%。颗粒有机碳是指示SOC动态对短期农业管理措施响应的理想指标。荒漠沙地转变为灌溉农田后有巨大的碳固存潜力；土壤黏粉粒增加对SOC及养分的积累和保持起重要作用。通过增施有机肥、秸秆覆盖还田、种植多年生苜蓿或苜蓿插入轮作体系是快速提升SOC水平、培肥地力的有效措施。发表论文6篇，培养研究生1名。