Modeling water flow in a plastic mulched ridge cultivation system on hillslopes affected by South Korean summer monsoon
Highlights
► Plastic mulching induces horizontal water movement from furrows to ridges. ► Interflow occurs in coarse textured and ploughed topsoil during monsoon events. ► Plastic mulching reduces drainage water up to 16%. ► Plastic mulching increases surface runoff up to 70%. ► We recommend to apply perforated and biodegradable plastic mulch.
Introduction
Agricultural management practices, soil properties and field topography lead to a high variability in soil water movement, solute transport and leaching of nutrients and agrochemicals. In South Korea, ridge tillage with impermeable black plastic mulch covering the ridges is the most common practice for dryland crops such as radish (Raphanus sativus), cabbage (Brassica rapa susp. Pekinensis (lour.), Hanelt, Brassica aleracea convar. Capitata var. alba), beans (Glycine max (L.) Merr.) and potatoes (Solanum tuberosum L.), which are predominately grown on slopes. Intense fertilization together with heavy rainfalls during summer monsoon season poses a high risk of groundwater pollution in the Haean catchment. Additionally, the discharge of phosphorus associated with sediments from agricultural areas causes eutrophication and deterioration of water quality in downstream reservoirs in South Korea (Kim et al., 2001). This is of major significance because the river system of Haean contributes to the Soyang Lake, which is a major source of freshwater for the metropolitan area of Seoul.
The effect of flat row-interrow cultivation on soil water dynamics was investigated for soybean and corn crops in previous studies (Timlin et al., 2001, van Wesenbeeck and Kachanoski, 1988, Paltineanu and Starr, 2000). The findings showed increased soil moisture in row positions due to interception and stemflow. The same effect was also found for potato crops cultivated in ridges (Saffigna et al., 1976), but with the addition of concurrently higher water contents in furrows because of surface runoff from ridges and leaf drip from the outer foliage. Soil and plant biological effects of the plastic mulch were studied by Gürsoy et al. (2011) and Laszlo and Gyuricza (2004), who found favorable physical soil conditions and improved growth and yield of maize and corn crops. Previous research on plastic mulched ridge cultivation focused mainly on rain water harvesting in combination with irrigation techniques in semiarid and arid regions, in which the plastic covered ridges induce runoff to the planted furrow area, leading to an increased crop yield and water availability (Wang et al., 2008, Li and Gong, 2002, Li et al., 2008, Tian et al., 2003, Mahajan et al., 2007). In contrast, dryland crops in South Korea are planted in the plastic covered ridges to suppress weed growth and to support early plant emergence due to increased soil temperature in the ridges.
Only a few modeling studies about ridge cultivation systems exist. Solute transport of pesticides in an irrigated potato ridge cultivation system was investigated by Leistra and Boesten (2010). They demonstrated that the risk of pesticide leaching in furrow soil can be substantially higher than in corresponding level field soil. Abbasi et al. (2004) simulated water flow in a long furrow system with furrow irrigation using Hydrus 2/3D to estimate inversely soil hydraulic properties and transport parameters. Dusek et al. (2010) used the S1D and S2D models to simulate water flow and solute transport in a drip irrigated plastic mulched pineapple cultivation.
Since there are no modeling studies about plastic mulched ridge cultivation in mountainous areas affected by extreme rain events, the aim of this study was to evaluate the effect of plastic mulched ridge cultivation on soil water dynamics under a summer monsoonal climate. Therefore, we used a monitoring network of tensiometers and FDR sensors in two potato fields in the mountainous Haean basin in South Korea to observe soil water dynamics in ridge and furrow positions. The field data sets of standard tensiometers were used to estimate soil hydraulic parameters using an inverse modeling approach based on Levenberg–Marquardt nonlinear minimization algorithm. Subsequently we used the optimized parameters of the water flow model to run scenarios regarding ridge tillage without plastic mulch and flat conventional tillage. The comparison of plastic mulched ridge tillage (RTpm), ridge tillage without plastic coverage (RT) and a flat conventional tillage (CT) allows a better understanding of soil water dynamics and water movement influenced by the plastic mulch.
Section snippets
Study area
The agriculturally used Haean catchment is located in Gangwon Province in the North-eastern part of South Korea (Fig. 1). While rice paddies are dominating in the flat parts of the basin, dryland farming is practiced in the hillsloped areas of the catchment. The annual precipitation sum in Haean basin is about 1577 mm (11-years average) with 50–60% of the annual rainfall occurring during summer from June to August. The Korean peninsula is characterized by two rainfall peaks, one in July and one
Model evaluation and parameter optimization
The comparison between observed and simulated pressure heads (Fig. 5) showed a good agreement at field site 1, whereas the agreement at field site 2 was less satisfactory. While wetting events in particular were simulated reasonably well, the low pressure heads during drying cycles at the beginning of the observation period were underestimated, especially at field site 2. The evaluation coefficients for both field sites are given in Table 2.
The optimization of the water retention parameters (
Discussion
The modeling study showed that the simulation for field site 1 predicted the measured pressure heads reasonably well, whereas pressure head measurements at field site 2 were not well represented by the model simulation.
As the Hydrus 2/3D code does not calculate surface runoff directly, it was necessary to multiply the precipitation data by a factor of 2 for indirectly simulating runoff from plastic mulched ridges to the permeable furrows. This simplified method does not reflect the real field
Conclusion
In this study, a combination of field measurements and process-based model simulations was used to evaluate the effect of plastic mulched ridge cultivation in comparison to ridge cultivation without plastic coverage and conventional flat tillage management on soil water dynamics. It was demonstrated that plastic mulching induces typical soil moisture patterns mainly in the topsoil during dry periods compared to the other tillage systems, whereas the impact of tillage management on soil water
Acknowledgments
This study was carried out as part of the International Research Training Group TERRECO (GRK 1565/1) funded by the Deutsche Forschungsgemeinschaft (DFG) at the University of Bayreuth, Germany and the Korean Research Foundation (KRF) at Kangwon National University, Chuncheon, S. Korea. The author would like to thank especially Andreas Kolb for his technical support during field measurements.
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