| Red soil is one of the most important land resources in south China and is the production base of tropical and subtropical economic fruit.It plays an extremely significant role in the sustainable development of agriculture,economy and society.As a result of tropical and subtropical monsoon climate and the uneven rainfall space-time distribution,the region has long been suffered strong soil erosion.What's worse,the high-intensity development and utilization make this problem more serious.Soil erosion redistributes soil particles and associated organic C.Organic carbon is an important indicator for soil fertility and crop growth.In order to under the process of soil erosion redistributing soil organic carbon?SOC?,we selected two slopes located at Sunjia watershed,Yingtan,Jiangxi province and sampled soil down 100 cm depth at top,middle and foot slope positions,and determined 137 Cs,SOC,sesquioxides,and water stable aggregates and so on.Our main results were summarized as follows:?1?The SOC content followed in the order: middle slope < top slope < foot slope.SOC decreased with soil depth,which was fastest at middle slope and the slowest at foot slope.The effect of the slope position on sesquioxides was negligible except the free iron?Fed?.The free,amorphous,complex iron and aluminum generally presented an increase trend with increasing soil depth but it was on the contrary for the complexing iron.The complexing iron presented a similar pattern with the SOC along soil profile so they were perhaps interacted.The slope position had a little effect on aggregate stability?MWD?but the soil depth played a critical role in it.At 0-40 cm depth,aggregate stability decreased with increasing soil depth,whereas at 40-100 cm depth,it increased with increasing soil depth,indicating soil organic matter?SOM?may be the main binding agent of soil aggregates at top 40 cm depth and sesquioxides the main binding agent of soil aggregates at below 40 cm depth.?2?Based on 137 Cs,the two investigated soil slopes presented a similar soil erosion pattern.At slope one,soil erosion module showed 64 t·km-2·a-1 at top slope,3635 t·km-2·a-1 at middle slope,and-2134 t·km-2·a-1 at foot slope.At slope two,soil erosion module showed 11 t·km-2·a-1 at top slope,3598 t·km-2·a-1 at middle slope,and-2400 t·km-2·a-1 at foot slope.The middle slope was experienced the most serious erosion along arable slope,while the foot slope received sediments.The linear relationship between 137 Cs and SOC?R2?0.66,P < 0.001?indicates soil erosion played an important role in the distribution of SOC.?3?Soil erosion changes spatial distribution and composition of soil organic carbon.Based on the method of Six et al.,soil organic carbon could be divided into unprotected organic carbon,physically protected organic carbon and chemically protected organic carbon.The three kinds of organic carbon content follow the same trend as total soil organic carbon content in different soil depths.However,the content of the three kinds of organic carbon shows significant difference and presents a trend as follows: chemically protected organic carbon > unprotected organic carbon > physically protected organic carbon.The results in our study indicate that soil erosion of arable slop land in red soil region is quite serious.The erosion rate of middle slope has reached moderate erosion class according to the Ministry of Water Resources(2500-5000 t·km-2·a-1).The erosion lead to a massive loss of organic carbon in the middle slope,while in the foot slope,more organic carbon accumulates.Therefore,doing research on soil erosion and the resulting soil organic carbon distribution is quite important to global change assessment and sustainable development of agro-ecological environment. |
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