Actual evapotranspiration from partially tile-drained fields as influenced by soil properties, terrain and crop

Physical properties of soils have a significant influence on their water regime and should be considered when selecting suitable agricultural crops for particular sites, taking into account the crop productivity and its water requirements. Mean daily rates of actual evapotranspiration (ETa) were obtained by collation of measured or otherwise estimated 10-min values for the years 2004, 2006 and 2009 for a partially tile-drained agricultural experimental catchment in the Bohemo-Moravian Highland (Czech Republic). ETa was measured using the Bowen ratio (β) and energy balance (BREB) method at four weather stations located on different soil types (Stagnosols, Cambisols) and terrain relief positions (defined with respect to the groundwater recharge and discharge zones) over different crops (cereals, oil rape and permanent grassland). A systematic influence of soil properties on the evapotranspiration rate was more pronounced during the periods of limited transpiration (soil drought, crop maturity), when the average daily ETa was significantly lower and the corresponding β significantly higher over coarser-textured soils (shallow Haplic Cambisols), namely (year-ETa (mm/day)/β): 2004 - 1.75/1.66; 2006 - 2.44/0.93; 2009 - 2.60/0.81), than over finer-textured soils (Stagnic Cambisols and Haplic Stagnosols), namely: 2004 - 2.92/0.97; 2006 - 3.06/0.44; 2009 - 3.42/0.39). When the transpiration was not limited by soil water deficit, it acted as an equalizing factor smoothing down evapotranspiration from heterogeneous soil areas, whereby the effect of the soil physical properties was masked. With regard to soil water regime and evapotranspiration, the tile-drained Stagnic Cambisol lands behaved similarly as non-drained Haplic Cambisols. The effects of land use and of the terrain relief position could not be tracked independently, because the permanent grassland was situated in the wetter and texturally heavier parts of the catchment and the positions of the recharge/discharge zone coincided with the positions of texturally lighter/heavier soils, respectively.