秸秆深还对土壤团聚体中胡敏素结构特征的影响

秸秆还田主要是覆盖和表层浅施,存在着影响种子发芽生长、土壤升温慢和病虫害增加等问题。秸秆深还(corn stover deep incorporation,CSDI)是指将玉米秸秆施入土壤亚表层(20~40 cm),不仅能解决秸秆焚烧的问题,还能达到保碳、蓄水、培肥、稳产的目的,使秸秆还田得到改善。虽对秸秆深还后胡敏素(Hu)的结构性质有一些研究,但是对秸秆深还后土壤团聚体中Hu的变化还未见报道。探究秸秆深还对土壤腐殖质的影响,可以为如何提高土地肥力、如何利用秸秆深还创建合理耕层提供理论依据。本试验采集于吉林农业大学试验站玉米连作耕地试验田,采用湿筛法将其分为2 mm、2~0.25 mm、0.25~0.053 mm和0.053 mm 4个粒级并提取Hu,通过元素组成、红外光谱和差热分析研究秸秆深还对团聚体中Hu结构特征的影响。结果表明:用此方法制备的黑土Hu的平均含碳量为721 g kg-1;H/C的平均值为0.776;Hu的缩合度高于相应的HA;秸秆深还促使土壤表层和亚表层团聚体中Hu的氧化度降低,脂族链烃减少,活性结构增多,稳定性降低,Hu的结构趋于简单化、年轻化。

Effect of Corn Stover Deep Incorporation on Composition of Humin in Soil Aggregates

How to handle surplus crop straw has become an important topic that calls for urgent solution in the agricultural regions of China. Straw incorporation into the field is one of the main methods of straw utilization. The method of straw incorporation used to either overcast the straw on the surface of the field like mulching or incorporate the straw into the shallow topsoil layer,which would obviously bring about some problems,like hindering seed germination and seedling growth,impeding rise of soil temperature,and favoring incidence of plant diseases and insect pests,while its effect on accumulation of soil organic matter is so limited that it would not help solve the problems,like thinning of the plough layer and depleting of organic matter in the subsoil layer. Corn stover deep incorporation(CSDI)extends the extent of soil building from topsoil,as it was previously,down to subsoil,which would not only help solve problems,like thinning of the plow layer,shortage of organic manure,declining water holding capacity,but also reduce environmental pollution from burning of straw,while achieving the ends of sequestrating carbon,conserving soil water, building up soil fertility and raising crop yield. Although some reports are available on change in structure of Hu after CSDI,few have been published on Hu in soil aggregates. Soil samples were collected from an experimental corn field under long-term mono-cropping in the Jilin Agricultural University Experiment Station. The experiment field of black soil was divided into two plots,one cultivated under CSDI and the other without CSDI(CK). In the plot under CSDI,ditches were dug along the furrow in-between two rows of corn plants in November 2011,with a section like a bottom-up isosceles trapezoid,60 cm wide in the upper opening,40 cm wide in the bottom and 40cm in depth. In the process of digging,the soils of the toplayer(0~20 cm)and the sublayer(20~40 cm)were dug out layer by layer and placed separately on either side of the ditch. Once a ditch was dug into shape,corn stover,cut into 3~5 cm in length were applied into the deep ditch evenly at a rate of 12 000 kg hm-2,together with N fertilizer(urea 450 kg hm-2),and then the removed soil was placed back into the ditch,the sublayer soil first and then the toplayer soil forming a big ridge,which was let subside naturally. After the practice of CSDI finished,the two plots were cultivated with corn in the same pattern. The findings of the study may provide some theoretical basis for how to improve soil fertility and build up a proper plow layer with CSDI. Results show that the Hu in the plot of CSDI is higher in carbon content,varying in the range of 542~839 g kg-1 and averaging 721 g kg-1,with H/C in the range of 0.662~0.958,and being 0.776 in average,and higher than HA in carbon content and condensation degree. CSDI was found to increase carbon and nitrogen contents,and reduce Hu oxidation and aliphatic hydrocarbon degrees. The effects are more significant in the sublayer soil than in the toplayer soil. Besides,CSDI increases active structure of the Hu, but lowers its stability,To sum up,CSDI increases carbon and nitrogen contents in Hu,while making it simpler and younger in structure.