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In view of the current situation of black soil degradation, straw return as an important conservation tillage measure has been extensively promoted. Based on 15N tracing technology, this paper carried out experiments of different straw returning modes, including CK (conventional fertilizing tillage with straw-free returning), straw mulching (i.e., M), straw mixed with topsoil (i.e., T), and straw deep incorporation (i.e., D), to explore the influence of straw returning on the distribution and stability, and the carbon and nitrogen content of water-stable aggregates in black soil, and to analyze the distribution and stability of aggregates on the carbon and nitrogen content of aggregates. The results showed that the macroaggregate content, mean weight diameter (MWD) and geometric mean diameter (GMD) of the returned soil layers were 16.53-84.65%, 16.73-128.73% and 23.47-97.14% higher than those in CK, respectively. The contents of organic carbon, total nitrogen and 15N accumulation of aggregates in the straw-returning soil layer were 6.38-23.55%, 8.65-31.19% and 13.52-150.19% higher than those in CK, respectively. Pearson correlation analysis and redundancy analysis showed that the content of macroaggregates and stability of aggregates were positively correlated with the carbon and nitrogen contents. In conclusion, straw return significantly improved soil structure characteristics and carbon and nitrogen content. The results of this study provided a theoretical basis and technical guidance for farmland soil improvement in black soil areas, and selected an appropriate straw returning mode according to local soil conditions to maximize the effect of straw returning.

Biogas slurry is not suitable for liquid fertilizer due to its high amounts of volatile materials being of complicated composition and peculiar smell. In order to remove volatiles from biogas slurry efficiently, the dynamic headspace and gas chromatography-mass spectrometry were used to clear the composition of volatiles. Nitrogen stripping and superfluous ozone were also used to remove volatiles from biogas slurry. The results showed that there were 21 kinds of volatile compounds in the biogas slurry, including sulfur compounds, organic amines, benzene, halogen generation of hydrocarbons and alkanes, some of which had strong peculiar smell. The volatile compounds in biogas slurry can be removed with the rate of 53.0% by nitrogen stripping and with rate of 81.7% by the oxidization and stripping of the superfluous ozone. On this basis, the removal rate of the volatile compounds reached 99.2% by chloroform and n-hexane extraction, and almost all of odor was eliminated. The contents of some dissolved organic compounds decreased obviously and however main plant nutrients had no significant change in the biogas slurry after being treated.

Urbanization is a crucial criterion of assessing a nation’s or a particular region’s level of modernization. It has been accelerated all over the world in the 21th century. The main purpose of this research is to provide a strategy of spatial pattern of urbanization for rural areas in Jilin Province based on the reality of economic development in Jilin and the imbalance of natural resources distribution. The strategy divides the nine central cities of Jilin Province into three economic circles. The outer economic circle, open circle, includes Yanbian, Baishan, Tonghua and Baicheng, covering the eastern and western parts of Jilin Province. The middle one includes Jilin, Liaoyuan, Siping and Songyuan. The inner one, centring as Changchun, includes Gongzhuling, Yitong, Nong’an, Jiutai and Dehui. It needs to centre as Changchun which has the good foundation of economic development and more economic increase, then by economic effect extending out gradually, other areas develop subsequently. To construct Jilin as a green ecological province, cultivation in the outer circle should be controlled, with the main aim to recover grassland. Large population should be moved to other places by developing labor economy. From economy and ecology, to decrease the load of the land can reduce the loss of the resources and benefit the balance of ecology. Subsequently, the whole province’s economy will be developed sustainably.