Abstract:

A 17 years experiment, including conservation tillage such as ridge culture (rice-wheat/rapeseed), wide ridge culture (rice-wheat/rapeseed), and paddy-upland rotation (rice-wheat/rapeseed) and conventional tillage (rice-fallow) (CK), was conducted on purple paddy soil in Sichuan basin to investigate the influence of ridge culture on the changes of soil humus substances (HS) and its optic properties．The results showed that significant differences of HS contents and optic properties were discovered under ridge (wide ridge) tillage. The extracted organic carbon (OC) contents under ridge and wide ridge culture were remarkably higher than that under CK. The percentage of their increase in the layer of 20-40 cm was higher than that at the depth of 0-20 cm. The proportion of OC in humic acids (HA) accounted for 38%-65% and 12%-29% compared with extracted OC and SOC contents, respectively. While that of fulvic acids (FA) was 12%-25% as compared to SOC. The OC contents in HA and FA under ridge and wide ridge culture after 17 years increased and were significant higher than that in CK at the same time. E4/E6 ratios of HA were in the range of the 4.65-5.89 and significant differences between ridge (wide ridge) and other treatments were observed. The ⊿㏒K of HA and FA extracted with NaOH+Na4P2O7 (a) agent were lower than that with NaOH (b) agent. HA extracted with (a) and (b) agent were Rp and B type humic acid, respectively. The RF of FA was lower than that of HA, which indicated that the oxidation and aromatic components of HA in purple paddy soil were enforced comparing with FA.