Characteristics of Preferential Flow in the Intermediate Zone between Paddy Field and Ridge
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Supported by the National Natural Science Foundation of China (No. 41601215) and Central China Normal University Fund (Nos. CCNU16A05015 and CCNU17TS0001)

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    Abstract:

    【Objective】Studies available in the literature have shown that the ridges around the paddy fields are likely to lead to low water use efficiency and pollution of shallow groundwater. Preferential flow is a physical process of water and solutes moving along certain pathways, like pores and fissures in the soil, while bypassing the part of soil matrix and is ubiquitous in the paddy field under continuous flooding. Therefore, to study the status of preferential flow in paddy soil and its influencing factors may help quantify characteristics of water leakage in paddy fields and improve water and fertilizer utilization efficiency, and hence reduce the risk of pollution of shallow groundwater by agricultural chemicals in paddy regions. In order to elucidate effects of the ridges on soil water leakage in the intermediate zone between fields and ridges, comparison was made of different monitoring points in the field, transition zone and ridges for differences in characteristics of preferential flow.【Method】Field bright blue dye tracer experiments were conducted of the soils in the two typical intermediate zones (i.e., the intermediate between field and ridge and the intermediate between ridge and ditch ) of > 100 years old paddy field in the Jianghan Plain, Hubei Province.【Result】Results show that stained soil area ratio (SAR) fluctuated downwards with depth of the soil profile and a peak was observed in the 0~20 cm soil layer, accounting for 53.85%~88.55% of the total SAR of the soil profile; that the field was the highest in SAR in this soil layer, and followed by the transition zone, and the ridge; that although SAR was quite low in soil below 20 cm in depth at all the monitoring sites, the ridge was still 3.15 times as high as the field in mean SAR; that staining of the soil appeared quite consistent horizontally and vertically, that with increasing soil depth, the area of staining at horizontal levels gradually decreased from a plane to a dot. The ridge, impact in soil texture, was higher than the field in staining path number (SPN) that in the 0~29 cm soil layer. staining path width (SPW) varied in the range 10~80 mm and beyond, while in the soil layers down below, only a few paths <10 mm were observed; that the water flow in the field was mainly of the type of heterogeneous finger flow – highly-interacted macropore flow, while in the transition zone and ridge, it was mainly of the type of mixing macropore flow- highly-interacted macropore flow, for the SPW therein varied in the range of 10~80 mm and below. When water flowed from the field into the transition zone, it lost through seepage vertically and laterally, the two typical pathways, (i) via earthworm pores, root pores and fissures, which were more plentiful in the ridge, facilitating vertical and horizontal seepage of the water, while the plough pan in the field made it hard for the water to leach downwards, thus forcing the water to flow into the ridge and then percolate rapidly into deep soil layers; and (ii) further into ditches through the intermediate between ridge and ditch, of which the two were relatively different in elevation, so the water infiltrating into the ridge continued flowing vertically through the ridge and eventually into the ditch, besides percolating downwards.【Conclusion】Affected by the distribution of macropores in the field, transition zone and ridge, only a small amount of water in the field infiltrated through the plough pan and a large one lost through seeping laterally into the ridge and then percolating quickly and vertically into deep soil layers through macropores, thus leading to low water use efficiency and nitrogen pollution of water bodies. It is, therefore, essential to pay high attention to the influence of water flow in the ridges on leakage of soil moisture and solutes from paddy fields.

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LI Shenglong, YI Jun, LIU Muxing, ZHANG Jun, YANG Yan, ZHANG Hailin. Characteristics of Preferential Flow in the Intermediate Zone between Paddy Field and Ridge[J]. Acta Pedologica Sinica,2018,55(5):1131-1142.

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History
  • Received:November 09,2017
  • Revised:February 13,2018
  • Adopted:March 01,2018
  • Online: April 24,2018
  • Published: