USE OF CLUSTER ANALYSIS IN THE DETERMINATION OF THE INFLUENCE OF AGROTECHNICAL DATES AND PHENOLOGICAL PHASES ON FIELD CUCUMBER (Cucumis sativus L.) YIELDS IN POLAND

The aim of the work was to separate, by means of cluster analysis, sets of agrotechnical dates and phenological phases that are conducive to big and low yields of field cucumber of pickling cultivars and the evaluation of solar and thermal conditions accompanying these sets. On the basis of cluster analysis three, significantly different, groups of observations in relation to the course of growth and development, determining different volumes of cucumber yields in Poland, were isolated. Cluster 2 included observations which were characterised by high yields (amounting to 37.7 t.ha(-1) for the total yield and 20.1 t.ha(-1) for the marketable yield), and cluster 3 by low yields (respectively 27.6 and 15.6 t.ha(-1)). The following calendar of agrotechnical dates and phenological phases was conducive to high yield of cucumber (cluster 2): sowing on 14(th) May, the end of emergence 27(th) May, the beginning of flowering 29(th) June, the beginning of fruit setting 4(th) July, the beginning of harvesting 13(th) July, the end of harvesting 24(th) August. The delay, in relation to the dates in cluster 2 (high yield), of the sowing date by 6 days, emergence by 16 days, flowering and fruit setting by 18 days, the beginning of harvesting by 19 days, and the end of harvesting by 22 days may contribute to a decrease in cucumber yields even by about 27% and 22%, respectively for the total yield and the marketable yield. Higher than average values of both sunshine duration and air temperature, which during the vegetation season amounted respectively to 7.9h and 17.5 degrees C, were conducive to earlier agrotechnical and phenological dates, and, in consequence, high cucumber yields (cluster 2).