保护性耕作对丘陵区水稻土团聚体稳定性的影响

长期保护性耕作通过增加土壤有机碳而成为稻田土壤结构改良的一项有效措施，而保护性耕作对土壤团聚体稳定机制的影响尚未完全清楚。本文供试土样采自耕作制定位试验水旱轮作、冬水免耕、垄作免耕和厢作免耕耕层（0～ 20 cm）土壤，土样经过糊化作用、湿润作用和再次糊化作用等预处理，用以阐明稻田土壤团聚体的破碎机制。研究结果表明：糊化作用和湿润作用后紫色水稻土团聚体稳定性差异不明显，而保护性耕作显著影响团聚体的稳定性。糊化作用后团聚体水稳性强弱顺序为：垄作免耕＞厢作免耕＞冬水免耕＞水旱轮作，湿润作用后团聚体水稳性强弱顺序为：厢作免耕＞垄作免耕＞冬水免耕＞水旱轮作。糊化作用下团聚体稳定性与有机碳浓度相关性不显著（r＝0.432，p＞0.05），湿润作用下团聚体稳定性与有机碳浓度呈极显著正相关（r＝0.626，p＜0.01）。因此，研究结果说明保护性耕作有利于紫色水稻土大团聚体有机碳含量提高，进而增强团聚体的水稳性。

Effects of conservation tillage on aggregate stability of paddy soil in hilly region

Long-term conservation tillage is an effective agricultural management to improve soil structure in severely destroyed paddy soil by increase of soil organic carbon (SOC). More work is still needed to understand the impacts of conservation tillage on the mechanisms of aggregates stability. Soil samples in 0-20 cm layer were adopted from the long-term tillage experiment: (1) paddy-upland rotation and plain culture (rice- rape) (PU-R-RR), (2)no-tillage and ridge culture (rice-fallow) (NT-R-RF), (3) no-tillage and ridge culture (rice-rape) (NT-R-RR) and (4) no-tillage and plain culture (rice- rape) (NT-P-RR). Different pretreatments, such as slaking in fast wetting, wetting and subsequent slaking, were applied to simulate the breakdown mechanisms of aggregates in paddy soil. The results showed that no significant difference of aggregate stability between slaking and wetting pretreatments was observed, while tillage patterns affected greatly aggregate stability. The aggregate stability under slaking and wetting pretreatment ranked in the order of NT-R-RR > NT-P-RR > NT-R-RF > PU-R-RR and NT-P-RR > NT-R-RR > NT-R-RF > PU-R-RR, respectively. The organic carbon concentrations in aggregates were significantly positive related to the aggregates stability under wetting(r=0.626, p<0.01), while low correlation linear relationships were observed under slaking treatment (r=0.432, p>0.05). The results suggest that long-term conservation tillage favorably led to the increase of SOC concentrations in aggregates and the enhancement of aggregates water stabilization.