旱地农田不同耕作系统的能量/碳平衡

摘要：加强农田土壤保持耕作管理，科学认识和调控农田耕作系统能流碳流，提高农业生态系统固碳减排能力，对于减缓农业对全球温室效应的贡献具有重要意义。本研究以北方半湿润偏旱区山西寿阳旱作春玉米土壤保持耕作试验研究为基础，利用田间定位观测数据、辅助能投入参数，土壤呼吸田间原位测定，以及农业生态系统能量/碳平衡分析及碳循环过程模拟方法，综合分析和比较不同耕作（CT传统、RT少耕和NT免耕）系统能量/碳平衡及能-碳关联影响。与CT比较，采用RT和NT措施下工业能耗CO2-C损失降低约4%—12%（相当11—35 kg CO2-C?hm-2?a-1）。在RT和NT系统下耗能系数可降低约6%—10%，能量生产效率可提高约7%—12%。2006—2007年由田间原位测定土壤呼吸CO2-C释放通量估算，在玉米休闲期（尤其是秋耕处理后），NT条件下土壤呼吸速率一般为最低（NT NT（2005380）>CT（1987375）。不同耕作下的玉米籽粒产量与生育期土壤呼吸通量趋势基本吻合，如2006-2007年玉米产量（kg?hm-2?a-1）平均为，RT（5614268）>NT（5533564）>CT（5487278）。玉米籽粒产量与生育期土壤呼吸通量之间呈密切相关（R2=0.88）。本研究结果得出，RT和NT对农田耕作系统的影响呈碳汇效应，且一般为NT >RT；而CT处理表现为碳源。RT和NT通过增加土壤碳投入是维持和提高土壤有机碳的有效途径。

Coupled energy and carbon balance analysis under dryland tillage systems

Abstract Scientific regulation of both energy and carbon flows in farm tillage system with soil conservation tillage practices is of great significance for saving energy input in farmland, mitigating greenhouse gases to the atmosphere, and increasing carbon sequestration potential in soils. Based on the field experimental studies on conservation tillage in dryland maize cropping systems, located in Shouyang Dryland Farming Station in Shanxi province of China, through field observations, embodied energy input parameters, soil respiration measurements, carbon dynamic processes simulations, and energy /carbon balance estimations in dryland agro-ecosystems, the aim of the study was to integrally analyze and compare the impacts of different tillage systems (including conventional tillage (CT), reduced-tillage (RT), and no-till (NT) practice) on coupled energy /carbon balance. Compared with treatment CT, conservation tillage (RT and NT) could increase carbon input (about 1.6 tC?hm-2) with increasing stover return and root stubble biomass in the soils, but reduce carbon losses by stover burning /or removal (about 1.6 tC?hm-2) and by soil erosion (about 1.2-1.6 tC?hm-2). The energy inputs (MJ?hm-2) were ranked as CT(13829) >RT(13289) >NT(12434), which were equivalent to carbon emissions (kgC?hm-2), respectively, as follows, CT(283) >RT(272) >NT(248). The embodied energy consumption could reduce by about 4-12% (equivalent to 11-35 kg CO2-C?hm-2?a-1) with NT and RT practices, as compared to the CT practice. The coefficiency of energy consumption could decrease by about 6-10% and the coefficiency of energy production increase by 7-12% under conservation tillage systems, as compared to the CT practice. The estimations from field tests and soil organic carbon balance equation with modeling approaches showed that with changes in tillage methods from conventional to conservation practices, the rates of soil organic carbon sequestration (kg C?hm-2?a-1) would tend to increase from -104 with treatment CT to 144-149 with treatments NT and RT. The field measurements during periods 2006-2007 showed that the soil respiration rates with NT were generally lowest (-13%) during the fellow periods (the means (kg CO2-C?hm-2?a-1) were ranked as NT (54030) NT (2005380) >CT (1987375). The changes in maize grain yields showed the same trend with soil respiration associated with tillage practices, for instance, the mean maize grain yields (kg?hm-2?a-1) also were ranked as RT (56141298) >NT (5533631) >CT (54871320), showing a positively close relationship between maize grain yields and soil respiration during growing stage (R2=0.88). Although different methods were used to estimate CO2-C emissions by soil respiration processes, the analysis showed the same trends in carbon sink /source under tillage systems, such as a increasing trend in carbon sink with conservation tillage practices (generally RT >NT) compared to carbon source with CT, indicating that stover incorporation combined with conservation tillage practices through increasing carbon input is the effective way for maintenance and enhancement of soil organic carbon.