保护性耕作对稻田土壤有机质的影响

研究使用常规犁耕-休闲(DTF),常规犁耕-小麦(DTW),保护耕作-休闲(CTF),保护耕作-小麦(CTW)4个处理,评价连续实验10a后保护性耕作对稻作区SOM的影响。结果表明:垄作、免耕和小麦种植的结合是稻作区一种较好的保护性耕作实践。它不仅显著增加SOM在土壤表层的聚集,而且它也通过改变SOM的组成和结构显著影响土壤胡敏酸的光谱和热解特性。相比其他处理,垄作免耕(稻麦)在0～10cm土层拥有最多的SOM含量,但随着土层厚度的增加,这一含量下降的也较为迅速。垄作免耕(稻麦)土壤胡敏酸在波长665nm处的光密度为0.122,465nm处为0.705,而常规平作(中稻)在这两个波长处却分别为0.062和0.321。垄作免耕土壤胡敏酸DTA曲线在360～365℃处放热峰的焓变值比常规平作低,1000～1050cm-1吸收峰常规平作也比垄作免耕强。垄作免耕土壤腐殖质的氧化稳定系数增高,表明长期垄作免耕土壤腐殖酸的缩合度增高,芳构化程度增强。通过保护性耕作和作物实践可以管理稻田土壤,维持充分的SOM积累,缓解土壤有机碳的丢失。

Effects of conservation tillage on soil organic matter in paddy rice cultivation

In this study, the effect of conservation tillage on soil organic matter (SOM) in paddy rice cultivation after 10 yr was investigated. Four treatments, disk till-fallow (DTF), disk till-wheat (DTW), conservation till-fallow (CTF) and conservation till-wheat (CTW) were used. The results indicated that the combinative application of no tillage, ridge culture and wheat cultivation was a sound conservation practice in paddy rice cultivation. It not only significantly increased the concentration of SOM in the topsoil, but also further affected humic acids (HA) optical and pyrolysis characteristics through changing the composition and structure of SOM. At 0-10 cm, the greatest SOM content was in CTW, but declined sharply with depth, while in DTF, DTW and CTF was not as high at the surface as in CTW, but the SOM content did not decline as fast as in CTW. The oxidation stabilization of SOM was generally greater in no tillage and ridge culture than that of disk till. The HA optical density in CTW at wavelength 665 nm and 465 nm was 0.122 and 0.705, while in DTF was 0.062 and 0.321, respectively. E4/E6 ratios in CTW were higher than that of in the other treatments. The enthalpy capacity of exothermal peak (360-365 ℃) for HA DTA curve in no tillage and ridge culture was lower than that of in disk till, while the HA absorption peaks in 1000-1050 cm-1 presented the reverse trend. The oxidation stabilization coefficient of HA in no tillage and ridge culture was higher than those in disk till, indicating that polycondensation degree and aromatization of HA were stronger. Those findings suggest that it may be possible to manipulate paddy soils through conservational tillage and crop practices and thereby maintain adequate SOM concentrations, mitigate soil organic carbon loss from soil to atmosphere.