Modeling Water Regime of Arable Chernozems under Bare Fallow and under Corn for Two Growing Seasons with Contrasting Precipitation

Resumo

Water regime of arable chernozems was simulated for two plots at the Voronezh experimental station. The first plot is under continuous corn monoculture since 1966. The second plot is under permanent bare fallow since the same time. The free HYDRUS-1D software was used. Evaporation from bare soil surface and evapotranspiration from the plot under corn were estimated using the FAO56 method. Simulations were performed for the 2013 and 2014 growing seasons with contrasting precipitation. Precipitation sum in May–September 2013 was 427 mm, and it was only 195 mm in May–September 2014, whereas the long-term average precipitation sum from May 1 to September 30 is equal to 284 mm. The monthly precipitation in July 2014 was only 2 mm. During both growing seasons, the simulated water regimes at the two plots were different. In the 70–140 cm layer, the soil water content was no less than 0.25 cm³/cm³ under bare fallow and it decreased to 0.17 cm³/cm³ under corn. The driest layers were formed under corn at the depths from 70 to 120 cm. At the plot under bare fallow, the cumulative evaporation from the soil surface from May 1 to September 30 in 2014 was higher than the precipitation sum for the same period. At the plot under corn, the cumulative evaporation was less than the precipitation sum, and the lower soil water content at this plot is explained by root water uptake with the cumulative value of 23 cm for the period from May 1 to September 30.