耕作历史和种植制度对绿洲农田土壤有机碳及其组分的影响

耕作历史和种植方式是影响黑河绿洲农田土壤总有机碳及其组成的重要因素。研究结果显示,随着耕作时间的延长,土壤总有机碳(TOC)、活性有机碳(AOC)、惰性有机碳(NOC)的含量均呈增加趋势,但AOC、NOC的增幅存在差异,AOC因性质活泼,对农业活动等措施引起的变化较NOC有较快响应,因此,在耕作的初期(0~5 a),AOC的增幅高于NOC,而20 a的耕地NOC增幅大于AOC,之后达到AOC与NOC的增幅接近(>100 a)的动态发展趋势,表明总有机碳含量积累的过程是AOC与NOC增幅逐渐接近、NOC积累增速的过程。>100 a的耕地,因种植方式不同,剖面上TOC、AOC、NOC含量呈现出:油菜地>普通玉米地>制种玉米地>小麦地。分析发现,绿洲区近年来大面积种植制种玉米引起TOC、AOC、NOC发生改变,增加秸秆或牲畜粪便的归还量是提高土壤有机碳的有效途径。

Effects of Cultivation History and Cropping System on Soil Organic Carbon and Its Components in Oasis Soils

Cultivation history and cropping system are the important influencing factors of SOC and its components in the Heihe oasis,the objective of this study is to identify the effects.Soil sampling pits are selected and the space positions are determined by using the GPS instrument.The soil sampling depth of 100 cm are divided into intervals of 0-20,20-40,40-60,60-80 and 80-100 cm.After soil sample preparation,total organic carbon(TOC) is measured by acid dichromate digestion and FeSO4 titration,active organic carbon(AOC) is measured by potassium permanganate oxygenation,nonactive organic carbon(NOC) is calculated as the difference between TOC and AOC.Biomass including root and crop straw is surveyed by using 1 m×1 m squares and the net weight is weighted.Cultivation history is obtained by field research.Results show the contents of TOC,AOC and NOC are increased with the extension of cultivation time,but to different degrees.AOC is faster than NOC in 0-5 years for easy transformation characters to agriculture activity after the low organic matter natural soil was converted to cotton field,then lower than NOC in 5-20 years,finally the extent of AOC is close to DOC in >100 years.This indicates NOC content significantly increased and extent of AOC and NOC is gradually close to the increase of TOC.In soil profile >100 years,the contents of TOC,AOC and NOC with the order from high to low is rape plot,general corn plot,corn plot for seed and wheat plot,respectively.Compared with annual variation of organic matter restitution in wheat and corn plots,corn plot for seed ranges between wheat plot and general corn plot.The analysis indicates planting of corn for seed causes change of TOC,AOC and NOC,and effective approach of enhancing SOC content is to increase organic matter return of straw and livestock dejection.