耕地撂荒对土壤结构及有机碳的影响

Effect of the abandonment of cultivated land on soil structure and organic carbon

目前我国耕地撂荒现象严重,为了探究耕地撂荒前后土壤质量的变化,选用耕地和撂荒地的表层(0~15 cm)和表下层(15~30 cm)土壤为研究对象,利用湿筛法和土壤有机碳分组法,从土壤的团聚体稳定性和有机碳特性2方面来研究土壤质量的变化。结果表明:1)在表层土壤中,撂荒地土壤中>0.25 mm水稳性大团聚体含量(WAS)显著高于耕地土壤(P<0.05),而在表下层土壤中团聚体稳定性差异较小;2)土壤有机碳(SOC)的含量与团聚体稳定性呈正相关关系,变化规律一致;3)SOC的分组研究发现,SOC主要储存于大团聚体中(>60%),且主要以不溶性胡敏素(HMr)的形式储存(>60%);4)撂荒地土壤中稳定性较高的胡敏素(HM)的比例(67%和69%)较低,而稳定性较差的大团聚体中SOC的比例(76%和65%)较高。由此可知,撂荒地土壤中SOC的含量虽高,但稳定性较差,为避免撂荒地再次利用时土壤有机碳的减少和土壤结构的恶化,在后续研究中需确定撂荒地土壤有机碳恢复至稳定状态的时间。

[Background]The abandonment of cultivated land is a common phenomenon in China.Understanding the changes of soil quality after the cultivated land abandoned is very important for land resource protection and the reuse of abandoned cultivated land.Herein,the soil in arable land and abandoned cultivated land(for 6 years)under topsoil(0-15 cm)and subsoil(15-30 cm)were selected to explore the changes of soil quality after the cultivated land abandoned.[Methods]The varieties of soil quality were studied from the soil aggregate stability and soil organic carbon(SOC)characteristics.The stability of soil aggregate was determined by wet sieving.The characteristics of SOC was determined through chemical-physical composition of soil organic carbon which obtained by humic fractionation and aggregate fractionation.[Results]1)The content of>0.25 mm water stable aggregate(WAS)in abandoned cultivated land topsoil was significantly higher than that in arable land topsoil,however,no significant difference was observed for subsoil in abandoned and arable land(P>0.05).2)This was the result of that abandonment of cultivated land facilitated the increase of SOC content in the topsoil and had no influence in subsoil.The stability of aggregate was positively correlated with fractionation of SOC.3)By grouping aggregate of SOC we found that SOC was dominantly stored in macro-aggregate(>0.25 mm),and by humic fractionation of SOC we found that HMr(insoluble humin residues)was the dominant components of SOC.4)The result of SOC fractionation indicated that the SOC had a lower humification and a weak chemical protection for soils in the abandoned cultivated land.In addition,the proportion of SOC in macro-aggregate was higher for soils in the abandoned cultivated land than that in the forest land,indicating that the physical protection of aggregate to SOC was weaker for soils in abandoned cultivated land.[Conculsions]Abandonment of cultivated land would increase soil aggregate stability and organic carbon content.Soils in the abandoned cultivated land had a higher content of organic carbon,but possessed a weak chemical and physical protection to soil organic carbon.It could be speculated that cultivation on the abandoned cultivated land at present time,could generate the destruction of macroaggregates and released a large amount of soil organic carbon which would be mineralized and decomposed by microorganism,and degrading soil structure.Therefore,it is essential to determine the optimal time for the restoration of soil structure and soil organic carbon on abandoned cultivated land for better recultivation in future.