Groundwater Recharge Through Winter Flooding of Rice Areas

Abstract

Starting from October 2017, the hydrological balance of a 36 hectares' rice area located in Lomellina (PV), where the practice of winter flooding has been adopted since 2004, has been under investigation. Flow meters were installed on the irrigation and drainage channels, piezometers were positioned inside and outside the study area, and a soil survey was performed. A conceptual hydrological model simulating the water balance at the paddy field scale was developed and calibrated. Main results show that: (a) irrigation efficiency of the pilot area during the first summer season is well in line with those found for other paddy areas in the region; (b) higher percolation rates are observed in wintertime compared to summer season; (c) despite the higher percolation, groundwater level reached in winter season is slightly lower than in summer, and the groundwater depletion after the end of the flooding period is faster compared to that observed after the summer flooding; (d) to maintain higher groundwater levels at the beginning of the cropping season, which would increase irrigation efficiency, winter flooding should be maintained longer over time and involve larger paddy areas.

On the effects of winter flooding on the hydrological balance of rice areas in northern Italy

“…1.1, = 0.6 (Mayer et al, 2019). Rice growth stages (ini, dev, mid, end;Allen et al 1998) were registered by the farmer in the farm diary (site E) or obtained through the processing of ESA-Sentinel2 data (site Z; Facchi et al, 2020). When fields were flooded, the maximum value between rice Kc and water Kc (1.05) was considered in Eq.…”

“…The most plausible hypothesis to explain it is a change in the soil hydraulic conductivity (in particular of the low conductive soil layer, LCL, as defined in Facchi et al, 2018), probably due to the effect of a winter flooding practice conducted over a long period of time (since 2004) on the soil permeability. Preliminary results of a hydrological modelling exercise, carried out by applying a soil water balance approach based on a Darcy-type model (Facchi et al, 2018), are presented in Facchi et al (2020) for the site Z. Anyway, the reason of this change in hydraulic conductivity is unknown, but it could be due mainly to bio-clogging phenomena (increase in bacterial biomass, as well as in extracellular polymeric substances -EPS -and gases produced by bacteria at high temperatures; Seki et al, 1996).…”