Influence of compost amendment rate and level of compaction on the hydraulic functioning of soils

There has been widespread interest in using compost to improve the hydrologic functions of degraded soils at construction sites for reducing runoff and increasing infiltration. The objective of this study was to determine the effects of compost amendment rate on saturated hydraulic conductivity (K_s) and water retention in order to identify target compost rates for enhancing soil hydrologic functions. Samples were prepared with three soil textures (sandy loam, silt loam, and sandy clay loam), amended with compost at 0%, 10%, 20%, 30%, 40%, and 50%. All soils were tested at a porosity of 0.5 m³/m³, and the sandy loam was further tested at high (0.55 m³/m³) and low (0.4 m³/m³) porosities. The K_s and water retention data were then used to model infiltration with HYDRUS-1D. With increasing compost amendment rate, K_s and water retention of the mixtures generally increased at the medium porosity level, with more compost needed in heavier soils. As porosity decreased in the sandy loam soil, the amount of compost needed to improve K_s rose from 20% to 50%. Water distribution in pore fractions (gravitational, plant-available, and unavailable water) depended on texture, with only the highest compost rates increasing plant-available water in one soil. Results suggest soil texture should be taken into consideration when choosing a compost rate in order to achieve soil improvement goals. Hydrologic benefits may be limited even at a high rate of compost amendment if soil is compacted.     

橡胶坝对河流沉积物氮转化功能基因丰度和营养盐的影响

沉积物氮转化功能微生物是河流脱氮和水体净化的重要生物因素.为探讨橡胶坝对沉积物氮转化功能基因丰度及氮营养盐的影响，本研究以沂河沂水城区蓄水段为研究对象，从橡胶坝前不同距离采集沉积物，利用实时荧光定量PCR（qPCR）方法研究了沉积物的反硝化功能基因（nirS、nirK、nosZ）、厌氧氨氧化功能基因（AMX）和反硝化型甲烷厌氧氧化功能基因（pmoA）的丰度及沉积物营养盐特征.结果表明：橡胶坝促进了沉积物中nirK、nirS、nosZ和pmoA基因的聚集，反硝化功能基因nirK、nirS、nosZ丰度在坝前120 ~330 m范围内较高；橡胶坝促进了沉积物NH4+、NO3-、TN、TP、TOC、有机质（OM）等营养盐的滞留，主要在120 ~360 m区域聚集，多元线性回归模型拟合度较高.相关分析表明，16S rRNA、nirK、nirS、nosZ、pmoA基因丰度与环境因子NH4+、NO3-、TN、OM、TOC、孔隙度呈正相关；PCA分析结果表明，随着沉积物环境因子主成分的增长，氮转化功能基因丰度主成分呈升高趋势.橡胶坝可促进沂河沉积物氮素等营养盐的滞留和氮转化功能微生物的聚集.