Effect of irrigation and organic fertilization on the yield of crisphead lettuce grown under ecological conditions

The aim of the study conducted in the years 2014-2016 was to determine the effects of different irrigation systems and doses of different organic fertilizers on the yield of crisphead lettuce. The experiments were conducted in a certified organic field of the Research Institute of Horticulture in Skierniewice. The study compared micro-sprinkler irrigation, drip irrigation and the control combination (without irrigation). The fertilization combinations involved the use of compost at 30 t/ha, Ekofert L in a dose corresponding to 50 and 100 kg N/ha, Fertilan L in a dose corresponding to 50 and 100 kg N/ha, and the control (no fertilizer). It was found that the use of irrigation in the first and third year of the study did not produce positive results, which was due to sufficient rainfall that fully satisfied the water requirements of lettuce plants. However, with a total rainfall not exceeding 80 mm (in 2015), the use of the irrigation systems had a significant impact on yield. Compared with the control, the irrigation with micro-sprinklers in 2015 increased the yield of lettuce by 35%, and in the case of drip irrigation by 40%. The response of lettuce plants to the applied organic fertilization varied in the individual years of the study; however, of all the tested fertilization treatments, the use of compost at 30 t/ha produced the best yield-enhancing effect. Fertilization with the lucerne-based fertilizers resulted in an increase in yield, in relation to the control combination, in only one year of the study (2015). The results showed that the organic fertilizers Ekofert L and Fertilan L were slow-acting fertilizers because their impact on the yield of lettuce, a plant with a short vegetative period, was relatively small. These fertilizers are more effective in the cultivation of species that have a long period of vegetative growth.