Research On Dynamics Of Soil Organic Carbon,Total Nitrogen And Available Phosphorus Contents In Tai-Lake Paddy Soils Of China Based On 1:50 000 Soil Database

Soil organic carbon?SOC?,nitrogen?N?,phosphorus?P?contents could indicate soil productivity condition of the paddy soils and play a crucial role in plant growth.Tai-Lake region as the main grain-producing area in China,farmers have been accustomed to applying a large number of fertilizers to obtain high crop yields in recent years.Ecological environment problems caused by irrational fertilization and field management measures were increasing seriously such as soil erosion and cyanobacteria outbreak.Therefore,it was a vital role that studying the dynamics changes of SOC,Soil total nitrogen content?STN?and soil available phosphorus?AVP?contents in the paddy soils in Tai-Lake region to improve the productivity of the ecosystem and the stability of the ecological environment.In this study,an area of 2.32 M·hm² of paddy soils,or 37 counties?or cities?of in the Tai-Lake Region,was delineated as study zone.Systematically analyze the variations and master factors of SOC,STN and AVP contents in the whole region,differences of soil subgroups,sub-regions and regional in the past 20 years.The results would provided a reference for the reasonable formulation of agricultural management policies in the Tai-Lake region and rice fields in southern China.The main conclusions were as follows:?1?Analysing the dynamic changes of SOC contents in the paddy soils in Tai-Lake region results show that,SOC content in paddy soils of Tai-Lake region was 15.11 g·kg^-11 in 1982,and rose to 18.29 g·kg^-11 in2000,most of the paddy soils in the Tai-Lake region turned out the“carbon sink”effect.The order of increase of SOC contents in different of soil subgroups of the paddy soils showed:Bleached>Hydromorphic>Degleyed>Percogenic>Submegenic,and the highest SOC change(5.02g·kg^-1)was associated with bleached paddy soils.The order of increase of SOC contents in different of soil sub-regions of the paddy soils showed:Low moutain and hilly>Polder>Tai-Lake plain>Alluvial,and the SOC change increased significantly in the low mountain and hilly region and alluvial region(4.43 g·kg^-11 and 3.72 g·kg^-1,respectively),While the Tai-Lake plain region and polder region increased slowly(2.68 g·kg^-11 and2.40 g·kg^-1,respectively).As for administrative area,?except Wu County,Qingpu County and Songjiang County?the SOC contents of other counties?or cities?showed a"carbon sink"effect,and the SOC change of Chuansha county,Yuhang county,Chongming county,Anji county,Dantu county,Jiangyin county and Jintan county were almost above 5.00 g·kg^-1.?2?Analysing the dynamic changes of STN contents in the paddy soils in Tai-Lake region results show that,the STN contents was 1.58g·kg^-11 and 1.79 g·kg^-1,respectively,which increased by 0.21 g·kg^-1,and the enrichment area was 1.58 M·hm²,displaying a significant enrichment trend in 1982 and 2000.As for soil subgroups,and the STN change of Bleached,Hydromorphic,Degleyed,Submegenic were almost above 0.20g·kg^-1,while the gleyed paddy soil was the only soil subgroups of decline.The dynamics of STN also varied with soil sub-regions,the STN change increased significantly in the low mountain and hilly region and alluvial region(0.44 g·kg^-11 and 0.26 g·kg^-1,respectively),While the Tai-Lake plain region and polder region increased slowly(0.18 g·kg^-11 and 0.04g·kg^-1,respectively).Moreover,the dynamics of STN varied,too,with administrative zone,the mean STN of Anji,Changxing,Chuansha,Minhang,Yuhang and Chongming increased by more than 40%;while that of Wu,Qingpu,Jiashan and Danyang decreased somewhat.?4?Analysing the dynamic changes of AVP contents in the paddy soils in Tai-Lake region results show that,the AVP contents in the surface paddy soil of Tai-Lake region was 9.80 mg·kg^-11 and 12.91 mg·kg^-11 in1982 and 2000,respectively,which increased by 3.11 mg·kg^-1,presented a enrichment condition.From the spatial distribution of AVP,phosphorus enrichment was mainly distributed in the western,southern and southeastern regions of the Tai-Lake region,with an enrichment area of1.87 M·hm²,accounting for 80.44%of the whole paddy soil area in the region.As for soil subgroups,except the gleyed paddy soils,the AVP contents of paddy soils in Tai-Lake region increased to an unused degree,and the most significant increase was found in the bleached paddy soils,which increased by 4.83 mg·kg^-1,while the other soil subgroups from1.81-4.16 mg·kg^-1.The dynamics of AVP also varied with soil sub-regions,the AVP change increased significantly in the low mountain(6.65mg·kg^-1),While polder region increased slowly(1.96 mg·kg^-1).Moreover,the dynamics of AVP varied,too,with administrative zone,except for the decrease of AVP content in Taicang County,Baoshan County,Wu County,Songjiang County,Jiashan County,Minhou District and Jiangyin County,the increase of available phosphorus in other counties?or cities?between0.83-7.72 mg·kg^-1.?4?Analysing the affected factors on dynamic changes of SOC,STN and AVP content in the paddy soils in Tai-Lake region results show that,the soil organic matter?SOM?could interpret the variation of SOC and STN contents in the whole region,differences of soil subgroups,sub-regions and regional form 6.6%-77.3%and 8.9%-71.9%,which was higher than the effect of clay,pH and bulk density on SOC and STN contents.pH explains the variation of AVP content from 2.6%-17.3%,which was higher than the effect of SOM,clay and bulk density.The temperature of climate factors showed significant negative correlation with the variation of SOC,STN and AVP in paddy soils in the whole region at p<0.001 level;While the precipitation showed significant positively correlation at p<0.001 level.