耕作方式对紫色水稻土轻组有机碳的影响

Abstract

Physical fractionation of soil organic carbon(SOC) has been useful in distinguishing specific carbon pools that are responsive to management and identifying the physical control of organic matter.Density fractionation allows the separation of SOC fractions from different locations in the soil and degree of association with mineral particles.The free light fraction carbon(F-LFC) includes loose organic particles in the soil and particulate organic carbon adhering to the exterior of secondary organomineral complexes,which is chemically very close to litter and has generally a very fast decomposition rate.The occluded light fraction carbon(O-LFC) is the fraction of uncomplexed organic matter that is trapped and physically protected within secondary complexes(intra-aggregate organic carbon).This fraction shows a more advanced degree of decomposition and a slower turnover.The heavy fraction carbon(HFC) is composed mainly of highly decomposed materialand has a very slow decomposition rate.Changes in these different fractions,especially in the low-density fractions,may be more sensitive to management-induced impacts on soil than the total SOC or the complicated heavy fraction organic carbon.However,there are few direct data quantifying these two light fractions and their contributions to total SOC storage as related to changes in tillage practices. The impact of tillage on SOC fractions has been of great interest in recent years.The tillage experiment was located at the farm of Southwest University(30°26′N,106°26′E) in Chongqing since 1990.In this paper four tillage treatments including conventional tillage with rice only system(DP),conventional tillage with rotation of rice and rape system(SH),no-till and ridge culture with rotation of rice and rape system(LM),and ridge culture with rotation of rice and rape system(LF) were selected as research objectives to measure the contents of different soil carbon fractions.Soil sampling at the depths of 0—10,10—20,20—30,30—40,40—50 and 50—60 cm was performed with a soil drill after the rape harvest in the spring of 2009. Results indicated that most carbon(69.6%—92.7%) was held in the HF,carbon dynamics in the whole soil were controlled by the behavior of this fraction.The proportion of F-LF carbon to the total SOC was 5.03%—26.43%.O-LF contained the least amount of organic carbon(1.37%—4.93%) of total SOC.In the four tillage soils the greatest contents of F-LFC,O-LFC and HFC were found in the 0—10cm depth.In the whole soil layer(0—60cm),the order of F-LFC contents was LM(4.36g/kg) DP(2.11g/kg) LF(1.74 g/kg) SH(1.46 g/kg),and the corresponding proportions of F-LFC to total SOC were 17.12,14.00,12.17 and 11.29%,respectively.The order of O-LFC contents was LM(0.82 g/kg) DP(0.51 g/kg) LF(0.36 g/kg) SH(0.34 g/kg),and the corresponding proportions were 3.36,3.45,3.00 and 2.71%,respectively.Compared with the other tillage systems,LM treatment significantly increased the contents and proportions of the two light fraction carbons which suggested LM could improve the soil quality in a purple paddy soil in Southwest China.Additionally,the data analysis showed that F-LFC was the most sensitive pool of organic carbon to detect changes in SOC due to soil tillage.