SynopsisThe development, by collaborative study, of a standardized method for the determination of chlorophyll pigments (mainly pheophytins, which are produced by loss of magnesium from the molecules of respective chlorophylls) in crude vegetable oils is described. The chlorophyll pigments are determined by spectrophotometric measurement at 670 nm.

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.

Photosynthesis and transpiration rates in the interval of 30 min before and 30 min after copper fungicide application show an increase from the level of 5.0 to 7.0 µmol CO 2 /m 2 /s and 0.75 to 1.00 mmol H 2 0/m 2 /s. Long-term measurements show that the increase of photosynthesis rate after copper application is temporal and fades away after 10

Spatial distribution of the root system of hop (Humulus lupulus L.) in the soil profile is a less explored issue. However, it is known that it can play an important role in the development of new tillage technologies, fertilisation and irrigation, including the use of precision farming principles. In the period from 2015 to 2018, the distribution of the hop root system was evaluated on twelve hop plants of five Czech hop cultivars. The age of the plants ranged from 3 to 15 years. The evaluation took place in the Saaz region at regularly cultivated hop gardens. As part of the evaluation, the root systems of hop plants were removed from the soil profile and subsequently spatially reconstructed. With the help of infrared image analysis, the root intensity in the soil profile and the morphology of the root systems were determined. The root depth of the plants ranged from 1 m to 2.25 m. The lateral width of the hop root system ranged from 0.6 m to 1.5 m. As a result of the rows cultivation, the lateral development of the roots in the upper soil layers was limited. The results were confirmed using the infrared image analysis method to specify the distribution of the root system and the root density of hop plants in the soil profile.

This paper evaluates the influence of genotype on the photosynthetic activity of hops in the period critical for generating yield. Results over three years from measuring the photosynthesis rate statistically show an increase in the photosynthetic activity of hop plants in the flowering stage. The average photosynthetic rates from measurements on the second date (BBA 65) in the years 2007, 2008, and 2009 increased by 17.9%, 45.6%, and 49.2%, respectively. Different photosynthesis curve trends during the final stage of ontogenesis of the plants indicate the maturity level of each hop genotype. As regards the genotypes for which photosynthesis did not reduce significantly, it may be assumed that such plants had not reached technical maturity. The results from the three-year study also show that any promising genotype, with respect to the photosynthesis rate and yield, is the result of breeding of new varieties with greater resistance to drought and high temperatures. Very good results in photosynthetic activity were reached by the new varieties exhibiting high yield and a similar chemical composition to Saaz hop and those sharing the same origins to Saaz, showing a higher content of bitter substances. In 2008 and 2009, all three new forms reached yield levels of 2.35 to 3.12 t/ha of dry hops.