稻田—田埂过渡区土壤水分运动与保持特征

为揭示田埂对稻田水分渗漏的影响,以江汉平原典型稻田—田埂过渡区为研究对象,采用室内土壤理化性质分析、水力学参数测定和田间染色示踪等方法量化了过渡区各位点(田内、田埂和灌溉沟)土壤剖面导水与持水性能差异,并揭示了该区域的水流特征。结果表明:(1)不同位点的土壤饱和导水率(Ks)均随土层深度的增加而减小,上层(-20—35cm)高于中、下层(35—65cm),剖面导水性能表现为田埂灌溉沟田内,田埂平均Ks分别是灌溉沟和田内的1.6倍和16.0倍;(2)同一吸力值下不同位点土壤含水量差异较大,田内含水量最高,灌溉沟其次,田埂最低,在持水性能上表现为田内灌溉沟田埂;(3)田埂土壤受动物活动和根系生长影响剧烈,导致其大孔隙(当量孔径0.3mm)含量整体上高于田内,在染色特征上表现为田埂中、下层土壤染色面积显著高于田内。由于稻田-田埂过渡区不同位点土壤的导水和持水能力差异显著,稻田水分不仅可以在田内发生垂直渗漏,还可以通过田埂区域垂直入渗和跨田埂侧流两种方式快速流失,进而加速了稻田水分的散失。

Characteristics of Soil Water Transport and Holding Capacity in Paddy Inner Field-Bund Transition Zones

The objectives of this study were to quantify the characteristics of water transport and conservation in different locations (the inner field,paddy bund,and irrigation canal) in the paddy inner field-bund transition zones,and to identify the dominant pathways for water flow in these zones.Two typical transition zones in a more than 100-year paddy fields were investigated by soil sample analysis and dye tracing field experiment in the Jianghan Plain,Hubei Province.Saturated hydraulic conductivity (Ks) decreased with increasing soil depth for each site,and was characterized by higher standard deviation in the upper soil layers.The highest Ks was observed in the paddy bunds,followed by the irrigation canal,and the lowest in the inner field,indicating that the water preferred to flow through the paddy bunds.In addition,significant differences in soil water retention curves (SWRC) were observed,the highest soil water-holding capacity was identified in the inner field,followed by the irrigation canal,and the lowest in the paddy bunds.The macroporosity calculated based on the SWRCs revealed that there were more macropores in the bunds than in the inner field,which resulted in more preferential flow paths.Corresponding to the macropore distributions,the larger stained area ratio (SAR) of the lower soil layers was also observed in the paddy bunds than in the inner field.Different soil Ks and water capacity between the inner field and paddy bund could be mainly attributed to the enhanced macroporosity in the bunds,which was mainly resulted from soil animal activation and root penetration.Except for the vertical water infiltration in the inner field,two other water flow paths in the paddy inner filed-bunds transition zone were identified:(i) water flowed laterally into the the paddy bund and percolated vertically into the deep soil layers quickly through the macropores;(ii) water flowed laterally into the irrigation canal firstly,then percolated vertically into the deep soil layers.In conclusion,water losses from the paddy bunds should be considered seriously in the water and solute transport researches in the paddy field in the Jianghan Plain.