Effects of the period of wetland reclamation on the character of soil profiles, C and N contents in Sanjiang plain

صينى. 系统探讨三江平原湿地开垦后不同种植年限对土壤剖面性质及碳、氮含量变化等的影响规律，分析其相互关系，为该地区现有种植方式下耕地质量建设提供参考依据。采用野外实地调查方法，系统调查了三江平原宝清县北部、抚远县东南部两个垦区中不同农业利用年限土壤剖面层次、容重、植被组成等的变化，并采集表层和亚表层土壤样品，测定相应的碳、氮含量，分析其含量变化与种植年限的相互关系。随着种植年限的延长，土体中相应层次的形成和分化愈明显，腐殖质层厚度愈变薄，二者间呈显著负相关；土壤容重则随种植年限延长而增加，且二者间呈直线相关；表层和亚表层土壤有机碳的含量均随种植年限的增加而减少，二者间的相互关系可用二次多项式（Y = b0 + b1x + b2x2）形式表示；表层土壤全氮含量的变化与种植年限间亦呈显著负相关，且亦可用二次多项式形式来表示；土壤C/N比值亦随种植年限而变化，但与其所处的环境条件具有一定关系，且近年来其比值有下降的趋势。此外，还讨论了湿地农业利用后土壤有机碳储量的变化、立地条件对湿地性质的影响及湿地保护等相关问题。在当前三江平原耕地种植方式下，随着种植年限的延长，土壤耕层变薄、有机质及氮素含量下降的趋势较为明显，必须通过增加有机肥施用量、强化耕地养分管理、改进耕作方式等措施，防止这种趋势的继续，保证区域农业持续、稳定发展。

إنجليزي. This paper is aimed to explore the effects of the period of wetland reclamation on the property of soil profiles and changes of C and N content in Sanjiang plain, and to analyze their relationships systemically so as to provide foundations for land quality construction under local tillage way nowadays in this region. Through investigation in the field, the changes of soil profiles layer, soil bulk density, and vegetation of wetlands with different period of tillage were conducted in northern Baoqing County and southeast Fuyuan County of Sanjiang plain. Surface and subsurface soil samples were collected, and C and N contents were detected and their changes with tillage years were analyzed. Humus layer gradually became thinner while the soil layers became more apparent with the period of tillage lengthened, and there was a significantly negative relationship between them, and soil bulk density increased with the period of tillage prolonged just with a liner correlation. Whereas, the amount of organic carbon of surface and subsurface soil was reduced with the period of tillage lengthened, which could be described with the quadratic polynomial Y = b0 + b1x + b2x2. A significant negative relationship was also found between total nitrogen change in surface soil and the period of tillage, which could also be described with a quadratic polynomial. The C/N values of soils varied with the period of tillage changed, but they were affected by environmental conditions and had a degrading trend in recent years. Besides, the changes of organic carbon storage after wetland reclamation, and impact of growth environmental condition on wetland property, and wetland protection were all discussed in this study. There was an obvious degrading trend for organic matter and nitrogen content as well as thinner arable layer with tillage years prolonged. Therefore, it is necessary to increase applied amount of organic fertilizer and strengthen land nutrient management and improve cultivating type etc. in order to prohibit this condition and ensure sustainable and stable development of agriculture in this region.