Assessing and modelling water use and the partition of evapotranspiration of irrigated hop (Humulus Lupulus), and relations of transpiration with hops yield and alpha-acids

• SIMDualKc simulated hop and ground cover transpiration and soil evaporation.
• Basal crop coefficients for hop were derived from model calibration and validation.
• Soil evaporation was high at initial stages and when active ground cover was controlled.
• Crop transpiration was very high during hop mid- and late-season.
• Hop cones yield increased with transpiration but alpha- and beta-acids did not significantly change.

This study was conducted during three seasons (2012–2014) in an experimental hop yard at Mabegondo, Galicia, NW Spain. The research aimed at calibrating and validating the soil water balance model SIMDualKc for Humulus lupulus L. cv. ‘Nugget’. The model computes the soil water balance using the dual Kc approach, thus partitioning crop evapotranspiration (ETc) into crop transpiration, ground cover transpiration and soil evaporation. Calibration and validation were performed using TDR soil water content measurements, which produced small root mean square errors (RMSE) ranging from 0.012 to 0.015 cm3 cm−3. The initial, mid-season and end-season basal crop coefficients (Kcb) that allow computing hop transpiration were respectively 0.16, 0.97 and 0.83. The single Kc for the same crop growth stages, which refers to transpiration and soil evaporation together, were respectively 0.69, 1.02 and 0.85. SIMDualKc provided to estimate water use by the hop yard and the components of the soil water balance, particularly hop transpiration (THop), ground covered transpiration (Tcover) and soil evaporation (Es). THop represented 92% of actual evapotranspiration (ETc act) during the mid-season, and Es averaged 69% of ETc act during the initial stage. It was observed that Tcover was strongly influenced by soil and ground cover management. The impacts of water use and THop on hop yield quantity and quality were assessed. A linear regression between hop cone yield and THop has been found, with a high coefficient of determination r2 = 0.92, while the linear regressions of THop with alpha and beta-acids had regression coefficients not significantly different from zero. These results denote appropriate irrigation management with absence of stresses that could affect yields or the concentration of bitter acids.