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

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 SIMD-ualKc for Humulus lupulus L. cv. ‘Nugget’. The model computes the soil water balance using the dualKcapproach, thus partitioning crop evapotranspiration (ETc) into crop transpiration, ground covertranspiration and soil evaporation. Calibration and validation were performed using TDR soil watercontent measurements, which produced small root mean square errors (RMSE) ranging from 0.012 to0.015 cm3cm−3. The initial, mid-season and end-season basal crop coefficients (Kcb) that allow com-puting hop transpiration were respectively 0.16, 0.97 and 0.83. The single Kcfor the same crop growthstages, 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 bal-ance, particularly hop transpiration (THop), ground covered transpiration (Tcover) and soil evaporation (Es).THoprepresented 92% of actual evapotranspiration (ETc act) during the mid-season, and Esaveraged 69% ofETc actduring the initial stage. It was observed that Tcoverwas strongly influenced by soil and ground covermanagement. The impacts of water use and THopon hop yield quantity and quality were assessed. A lin-ear regression between hop cone yield and THophas been found, with a high coefficient of determinationr2= 0.92, while the linear regressions of THopwith alpha and beta-acids had regression coefficients notsignificantly different from zero. These results denote appropriate irrigation management with absenceof stresses that could affect yields or the concentration of bitter acids