Soil Water Dynamics of Shallow Water Table Soils Cultivated with Potato Crop.

Agricultural areas with shallow water table (WT) are commonly subirrigated relying on upward soil water flux to supply the crop evapotranspiration (ETc). The objectives of this study were to estimate the capillary water movement in shallow WT under seepage, tile drainage, subsurface drip (SDI) and sprinkler irrigation, and use the upward soil water flux to identify WT levels providing specific soil moisture content in the soil root zone considering potato ETc. Potato crop was grown under each irrigation system during the spring of 2015 and 2016. Hydraulic soil conditions were measured at 15, 30 and 45 cm of depth and van Genuchten parameters determined to calculate the soil water flux using Darcy’s law. Seepage irrigation area was classified as loamy sand soil, while tile drainage, SDI and sprinkler irrigation were in a sandy soil texture. Average soil organic matter at the loamy sand soil was 26.1 g.kg^-1, while sandy soils averaged 6.1 g.kg^-1. Soil texture and soil organic matter affected soil water holding capacity, field capacity was higher in the loamy sand soil (0.25 cm³.cm^-3) than in sandy soils (0.16 cm³.cm^-3). WT level directly affected soil water flux, and WT levels providing adequate upward soil water flux to potato root zone were 69 cm for the loamy sand soil, which was under seepage irrigation, and 42 and 45 cm for sandy soils under tile drainage and SDI, respectively. The sprinkler irrigation had a minimal WT contribution to ETc, with average of 27% in 2015 and 25% in 2016. WT elevation to precipitation ratio was higher in the loamy sand soil (34.4) than sandy soils (25.6); however, the capacity of soil water drainage after rainfall events depended on irrigation systems, in which tile drainage allowed fastest water drainage. Soil hydraulic characteristics play important role on subirrigation systems management, in which sandy soils and low soil organic matter require higher WT levels than loamy sand.