杭州湾南岸滨海围垦区耕层土壤有机碳的变异特征及影响因素分析

Variability of soil organic carbon in plough layers and its impact factors in a coastal reclamation area on south coast of Hangzhou Bay

研究农田土壤耕层有机碳库的变异特征及影响因素,有助于理解耕层土壤碳库变化,并采取合理的种植管理方式来减少土壤碳排放,减缓全球变暖。本文通过对杭州湾南岸滨海围垦区农田土壤有机碳含量及其空间变异的研究,揭示在不同围垦年限、土壤类型演变及典型种植模式条件下,滨海围垦区土壤耕层有机碳库的变异规律。2007—2009年,共调查采集了浙江省慈溪和余姚2市北部滨海围垦区域内耕层（0-20cm）代表土样2 353个。利用随机森林（Random forest）方法和GIS空间插值算法,分别计算各因子之间的重要性和土壤有机碳空间变异。围垦区内耕层土壤有机碳平均值9.78g/kg,变化范围在1.04-38.22g/kg之间,属中等强度变异。在不同种植模式或土壤类型下,土壤有机碳含量差异均有统计学意义（P〈0.05）.其中,种植模式＂稻-稻＂及土壤类型为在水稻土条件下的土壤有机碳含量较高,其平均含量分别达到了18.13g/kg和21.42g/kg;而在＂菜-菜＂＂果园＂种植模式与在滨海盐土、潮土条件下耕层土壤有机碳较为接近（介于8.30-9.48g/kg之间）。在不同围垦年限下,有机碳平均含量在7.14-10.96g/kg之间;除1724—1918年外,在其他围垦年限下耕层土壤有机碳差异均无统计学意义（P〉0.05）;而在相同围垦年限条件下,不同土壤类型之间有机碳差异有统计学意义（P〈0.05）,不同种植模式的＂稻-稻＂与＂菜-菜＂,＂稻-稻＂与＂果园＂之间有机碳差异均有统计学意义（P〈0.05）。种植模式对土壤有机碳的变异具有较高解释能力（22.87%）,其次是土壤类型（8.68%）和围垦年限（4.12%）,并且土壤类型与围垦年限之间存在高度关联性（r=0.64,P〈0.001）。研究区内耕层土壤有机碳含量在空间变异上呈现中北部较低,西北和东南部较高的特征,并与种植模式的分布差异基本一致,种植模式对耕层土壤有机碳的变异影响最大,其次是土壤类型变化,而围垦年限的影响较小。

Summary Soil organic carbon（SOC）has been identified as a key element in the global carbon balance.The studies on spatial distribution and variation of SOC are very helpful for soil monitoring and soil mapping.There are few reports on spatial variability of SOC concentration under different crops in plough layers in coastal reclamation areas.This study isintended to determine spatial distribution of SOC storage and its impact factors in the coastal reclamation area on south coast of Hangzhou Bay.A total of 2 353 soil profiles in plough layer were collected from 2007 to 2009in coastal reclamation area of Hangzhou Bay.SOC concentrations of soil samples were determined according to the dichromate oxidation method with a factor of0.58.Geo-statistical methods were used for interpolation and spatial grids of crop fields,and random forest method was employed to estimate explanation capability and eliminate inter-correlations among impact factors.The average contents of SOC in plough layer is 9.78g/kg,varied from 1.04g/kg to 38.22g/kg,indicating a moderate degree of variability（variable coefficient=65.24%）.For three different cropping patterns,including Vegetables,Rice-Rice and Orchards,the soil points were 1 858,327 and 168,respectively.Specifically,Rice-Rice has the highest SOC content（18.13g/kg）,followed by Vegetables（8.44g/kg）and Orchards（8.30g/kg）.Under different soil types,significant differences were observed among paddy soil,coastal saline and fluvio-aquic soil（P〈0.05）,SOC content in coastal saline soil was close to those in fluvio-aquic soil,and the highest SOC concentration was observed under paddy soil（21.42g/kg）.Besides,for different reclaimed ages,SOC content ranged from 7.14g/kg to 10.96g/kg.Except the reclaimed age of 1724—1918,no significant difference was found among other reclaimed ages（P〉0.05）.Additionally,under each reclaimed age,the significant differences were observed between Rice-Rice and Orchards（P〈0.05）,Vegetables and Rice-Rice（P〈0.05）,and significant differences were also detected among different soil types（P〈0.05）.Moreover,there were highly significant inter-correlations between soil types and reclaimed ages（r=0.64,P〈0.001）,and the highest individual explanation capability of cropping patterns on SOC variability was 22.84% after eliminating the inter-correlations,followed by soil types（8.68%）and reclaimed ages（4.12%）in this region.Finally,geo-statistical interpolation analysis revealed that high SOC concentration was mainly located at southeast and northwest of study area,whereas low SOC content was observed in central north.This high and low distribution of SOC concentration in this study region is consistent with the cropping patterns of Rice-Rice and Vegetables,respectively.In conclusion,a spatial distribution of SOC concentration was achieved in the study region,and SOC content is much higher in the rice planted region and/or paddy soil than those of vegetables,orchards,coastal saline soil and fluvio-aquic soil.The cropping pattern is a more important factor on variation of SOC content than soil type and reclaimed ages in this coastal region,and this could be helpful to adopt appropriate cropping strategies to improve the soil carbon storage in the coastal reclaimed region.