Influence of weather conditions, irrigation and plant age on yield and alpha-acids content of Czech hop (Humulus lupulus L.) cultivars

This study quantifies the effects of weather conditions, irrigation, and plant age on yield and alpha-acids content of Czech hop cultivars Saaz, Sládek, Premiant and Agnus in a 25-year long period, i.e., from 1993 to 2018. The yields of Czech hop cultivars were increasing for the first three years of plant age until they stabilized and then started to decline slightly for 15 to 20 years until they reached the optimal time for replanting. The highest alpha-acids content in hop cones was achieved in the first year of cultivation, followed by a logarithmic decline in the upcoming years. Rainfall was the most significant factor that positively influenced the yield of Saaz hops with correlations of r = 0.59 and 0.61 (P < 0.01) for total seasonal rainfall (April-August), 0.65 (P < 0.001) and 0.60 (P < 0.01) for daily rainfall above 3 mm, 0.37 (P < 0.05) and 0.58 (P < 0.01) for rainfall in May and 0.50 (P < 0.01) and 0.32 (P < 0.05) in July in the Saaz region and the Stekník farm, respectively. The yield of cultivars Sládek, Premiant and Agnus was not statistically influenced by the amount of precipitation, but there was a positive effect of irrigation level on yield increase with correlations 0.58 (P < 0.01), 0.55 and 0.49 (P < 0.05), respectively. High air temperatures during summer were the most significant factor that negatively influenced the alpha-acids content with the correlations ranging from -0.56 to -0.83. However, cv. Agnus showed a stable weather-independent alpha-acids content.