控制条件下水肥耦合对黄泥田还田秸秆腐解及土壤碳转化的影响

【目的】研究秸秆还田后不同水温和肥剂管理措施下土壤碳素转化特征。【方法】以华中双季稻区低产水稻土黄泥田为供试材料,模拟早稻和晚稻秸秆还田的田间环境,在实验室控制条件下,开展了两种温度环境中(15℃、35℃)不同水分(40%和100%最大田间持水量,即40%WHC、100%WHC)、配施氮肥类型(尿素、猪粪即U、M)、以及促腐菌剂添加对秸秆腐解效果及其过程中土壤碳素转化影响的研究。对水稻秸秆腐解过程中土壤CO2释放量、以及土壤可溶性有机碳(DOC)和总有机碳(TOC)含量在105天培养周期内变化特征进行动态监测分析。【结果】两种温度环境中整个培养周期内,各处理的CO2释放速率和释放总量通常表现为100%WHC-M100%WHC-U40%WHC-M40%WHC-U,即猪粪优于尿素的规律,而不论配施何种氮肥都存在100%WHC40%WHC(P0.01)的现象,同时40%WHC条件下辅施菌剂可显著提升CO2释放量;与此相反,两种温度环境下DOC含量都表现为40%WHC-M40%WHC-U100%WHC-M100%WHC-U(后两者差异小),即40%WHC条件下DOC含量显著高于100%WHC(P0.05),且配施猪粪处理优于配施尿素处理,但这两种氮肥处理间差异随培养时间延长而减小;以CO2-C释放量计算0 7 d、0 28 d、0 105 d内物料分解率,结果表明,35℃时100%WHC-U的处理中物料分解最快,15℃时40%WHC-M的处理中物料分解最慢。与之对应,105 d内TOC含量和净增量则在35℃时100%WHC-U的处理中最小(P0.01),而在15℃时40%WHC-M的处理中最大(P0.01);TOC的净增量和净损失量在相同温度条件下,尤其试验前期不同水分(P0.01)、氮素(P0.05)间均存在显著差异,且促腐菌剂添加普遍减小TOC含量;培养周期内所有处理的CO2释放速率与DOC含量间存在显著相关(P0.05)。【结论】水分状况对碳素的转化存在极大影响,其次是氮肥类型,且氮肥的影响作用随秸秆还田时间的延长而减弱;高湿条件更利于促进秸秆腐解,但导致土壤DOC含量较低,TOC的固持量也较少,而配施猪粪则可促进土壤DOC含量的提升及TOC的固持;促腐菌剂添加可促进秸秆腐解,但由于40%WHC条件下显著激发了CO2的释放而不利于土壤固碳。因此在华中低产黄泥田双季轮作稻区,早稻还田时由于气温高周期短,建议保持100%WHC、辅施适量尿素、并配合添加秸秆腐解菌剂,侧重秸秆快腐;而晚稻还田时气温低周期长,建议保持40%WHC并辅施缓效猪粪,侧重土壤固碳。     

含关节间隙的Delta机器人弹性动力学与振动特性分析

针对经济实用型并联机器人关节间隙对动平台位置精度与系统振动特性影响的问题,以Delta机器人为研究对象,利用数理统计原理对含关节间隙的Delta机器人支链进行了运动学分析,结合Lankarani-Nikravesh碰撞接触力模型与具有动态修正系数的Coulomb摩擦模型对关节间隙广义碰撞力进行了研究。利用空间有限元理论与拉格朗日方程,充分考虑主、从动臂的空间动力特性与运动协调关系,建立了Delta机器人弹性动力学模型,在定义杆件虚长度的基础上,将关节间隙产生的广义碰撞力结合到弹性动力学模型中,建立了含关节间隙的Delta机器人弹性动力学模型。借助FARO激光跟踪仪对间隙弹性动力学模型进行了验证分析,利用脉冲锤击法与Workbench软件仿真对Delta机器人的振动特性进行了研究分析。试验结果表明,考虑关节间隙时动平台中心点的运动轨迹较不考虑关节间隙时更靠近试验运行结果,验证了间隙弹性动力学模型的合理性与正确性,并且,系统前两阶非零固有频率的理论值与试验值的相对误差分别为3.544%和12.026%,两者相当接近。另外,由仿真结果可以发现3组从动臂是Delta机器人整机系统中最薄弱的环节。该研究可为经济实用型并联机器人的位置误差补偿与系统减振优化提供参考。     

中国农业能源消耗碳排放变化驱动因素及其贡献研究*——基于Kaya恒等扩展与LMDI指数分解方法

农业低碳化发展方式是农业现代化背景下农业可持续发展的有效实现途径。判断农业碳排放影响因素的驱动力、驱动方向等对有的放矢地制定低成本、高效率低碳农业发展策略与措施意义重大。在前人研究的基础上,为探讨常规因素之外还有哪些其他因素对农业碳排放有所影响,本研究以Kaya恒等式为基础,利用Kaya恒等式的数学性质将中国农业碳排放的影响因素分解为一般技术因素、农业低碳技术因素、农村生活水平因素、间接城镇化因素以及人口规模因素等5个因素,并利用LMDI指数分解方法对这些因素进行了驱动强度与贡献率的分析。研究发现:农村生活水平提高是促成农业碳排放的最主要因素;一般技术因素与农业低碳技术因素都负向地驱动农业碳排放,相比较而言,农业低碳技术变动比一般技术变动的碳排放驱动力更为强劲;总人口变动因素对农业碳排放呈现出正向驱动力,但无论从整个长跨度区间还是细分区间来看,其正向驱动力都不强;由扩展的Kaya恒等式得出的间接城镇化指标与一般城镇化指标之间关于50%的水平在坐标系中对称,经转换与修正发现城镇化水平对农业碳排放表现出温和的正向驱动力。1990—2013年中国总的农业碳排放中一般技术因素贡献为?25.85%,农业低碳技术因素贡献率为?166.55%,农村生活水平因素贡献率为220.65%,城镇化水平贡献率为57.63%,人口规模因素的贡献率则为14.12%。文章建议在发展农业现代化过程中,通过发展通用和低碳农业技术,合理有序推进城镇化进程以及营造低碳发展的社会氛围等方面创造更适宜的环境,以达到农业低碳化发展与可持续发展目标。     

两种禾本科冬绿肥生长规律及腐解特征比较

在山东临沂研究了冬播绿肥黑麦(冬牧70)和大麦的生长发育、养分吸收规律,并通过原位培养法比较了绿肥翻压后腐解及养分释放的差异。结果表明,冬牧70和大麦在返青后均迅速积累干物质,大麦的快速生长期在3月下旬,冬牧70的快速生长期在4月上旬,冬牧70进入快速生长期后的生长速率高于大麦。两种绿肥的养分吸收规律与干物质积累规律一致,冬牧70和大麦的氮、磷、钾吸收量基本一致。两种绿肥在翻压30 d内快速腐解,腐解率和氮素释放率达到了80%以上,大麦的腐解速率高于冬牧70,而矿质营养元素的释放率低于冬牧70,根据腐解和养分释放规律确定两种禾本科绿肥的适宜翻压时间为4月上旬。     

Recovering decomposing plant residues from the particulate soil organic matter fraction: size versus density separation

 A detailed size separation of particulate organic matter (POM) from soils amended with straw from Hordeum vulgare or Vicia sativa revealed that the loss of C during the first 56 days of incubation mainly occurred from particles >2,000 μm, without a concomitant reduction in the size of these large particles. Preliminary studies of POM from non-amended soil had shown that the stable heavy (>1.4 g cm^–3) POM fraction was mainly (>80%) composed of particles <400 μm, whereas the light fraction was dominated by larger particles (>80%). Therefore we decided to compare the POM <1.4 g cm³ with POM >400 μm. There was a very close relationship between POM>400 μm and POM <1.4 g cm^–3 with regard to amounts of C and N, as well as the appearance of these fractions under the microscope. Similarly there was a close relationship between changes in the C content of the POM fractions and the CO₂ respired, and this was also the case when comparing changes in POM-N with net N mineralization. This indicated that the biological activity during decomposition was actually localized in the POM. Due to the lighter workload and lower expenditure for reagents in connection with size separation of POM, we recommend the size separation procedure in connection with studies of residue decomposition in arable systems. Received: 23 May 2000     

非算子型泛函微分方程概周期解的稳定性

利用指数型二分性理论及相关分析技巧，研究了一类具有有限时滞的非算子型的中立型泛函微分方程的概周期解问题，得到了方程存在唯一稳定的概周期解的新结果．     

指数施肥技术研究现状及其在桉树育苗中的应用前景

通过介绍指数施肥的原理、方法与优点以及国内外指数施肥研究进展,简要概括我国桉树育苗发展现状及普遍存在的问题,分析得出指数施肥技术可以解决目前我国桉树育苗存在的许多问题,指数施肥在我国桉树育苗上应用前景广阔。     

Succession and phylogenetic profile of eukaryotic communities in rice straw incorporated into a rice field: Estimation by PCR-DGGE and sequence analyses

Abstract

Succession and the phylogenetic profile of eukaryotic communities associated with rice straw decomposition in a rice field were studied using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis followed by 18S rDNA sequencing. Nylon mesh bags containing leaf sheaths or blades were buried in the plow layer of a rice field under flooded conditions after transplanting (Experiment 1) and under drained conditions during the off-crop season (Experiment 2). In addition, rice straw samples in Experiment 2 were taken out before plowing in spring and re-placed in the rice field under flooded conditions at transplanting. Statistical analyses based on DGGE patterns showed that eukaryotic communities were divided into two groups, namely group A before the placement in soil, after the mid-season drainage in Experiment 1 and under the drained conditions in Experiment 2 and group B before the mid-season drainage in Experiment 1 and under the flooded conditions in Experiment 2. Based on the sequence analysis of DGGE bands, which characterized the eukaryotic communities, succession of the communities was revealed, that is, most of the bands in group A were closely related to fungi, whereas the bands in group B were closely related to protozoa. These results indicated that eukaryotic communities associated with rice straw decomposition in the rice field are mainly affected by soil conditions, such as oxic or reduced conditions, irrespective of rice straw parts (leaf sheaths and blades).