The stability of hop yields is significantly dependent on the occurrence and time distribution of natural rainfall in major hop-growing regions of the Czech Republic. To eliminate consequences of droughts on the hop yard production, additional irrigations are established and provided. In the Czech Republic there are more than 2,000 hectares of hop yards within the reach of irrigation systems. Irrigations are used as a stabilizing factor, rating costs and the work done in hop cultivation. The need and the efficiency of irrigation water is derived from the target function of irrigations, which is the stability of hop yields to the level corresponding to the production potential of hop yard-irrigated. The additional character of irrigations in climatic conditions of hop-growing regions of the Czech Republic requires a regional, operative, short-time balance, of irrigation regime of crops. The occurrence of natural rainfall, determining the need and the efficiency of irrigation, is of stochastic character with significant differentiation in space and time. The technical solution of irrigation is passing from all-area irrigation by spraying to progressive, located irrigation methods - trickle irrigation, microsprinkling. The efficiency of hop irrigation by trickle irrigation was evaluated in experiments. The piping with irrigators (in-line system) was placed on the ceiling of the hop yard, above each row of hop shrubs. The irrigation has a direct influence on one the third of the total area of hop yard. The results of field trial conducted in the top yard of the Hop Institute, Ltd., at Zatec in 1992 confirmed a high production and economic efficiency of trickle irrigation. In conditions of a year with deficit of rainfall (Tab. I) the need of five effective irrigation doses (Tab. II) was settled by the method of prognosis of the need of effective irrigation doses (Slavik , 1980, 1990). By supplying 520 m3/ha of irrigation water the yield of dry hop amounting to 13.1 t/ha was obtained on irrigated area. The effect of irrigations is 3.56 t/ha. The difference in yields is statistically significant. Production efficiency of 1 m3 of supplied water represents 68 kg of dry hop, thus providing an increase in receipts on irrigated hop yard by 41,437 Kc/ha. Investment costs of building the trickle irrigation amount to 76,520 Kc/ha, which costs the provider at the time of service life of the system 10 years by the sum 7,652 Kc/ha yearly. Actual operational costs amounted to 650 Kc/ha in 1992, that is total 8,282 Kc/ha. Economic contribution of effectively operated trickle irrigation represents 33,155 Kc/ha. The hop quality was not significantly affected by irrigation (Tab. V). The results of experimental studies confirm the meaning of effective building and exploitation of irrigation systems for hop growers in conditions of hop-growing regions of the Czech Republic. The suitability and expediency of the method used for the management of irrigation regime of hop was verified. The method determines an amount of water to be supplied in the subsequent operational period (week, decade) to cover the moisture need of hop at the given stage of development. Irrigation dose can be supplied in two to five terms in such a way to support the air-conditioning function of irrigation through trickle irrigation, distributing the water close to the spare of shrub. A method applied for the management of irrigation regime of hop and technical solution of irrigation permit an operative correction of irrigation in relation to the actual occurrence of precipitation during the operational period. Precipitation reduces, and even eliminates the demand for irrigation in real time. Thus, water, energy, and live labour are saved markedly at the full use of production yielding capacity of a hop yard.
