EFFECTS OF SELECTED FACTORS ON THE NUMBER OF TUBERS OF SINGLE CLUSTERIN POTATOES

Tuber number under the hill together with average weight of one tuber pertain to so called yield components in potatoes. Product of these va lues together with plant number per area unit make tuber yield. Plenty of recent authors still return to observation of effects of various f actors on tuber number (Haverkort et al., 1990; Ellisseche et al., 198 9; Coelho, Pinto, 1993). The aim of the present study was to achieve c omplex effect of agrotechnical factors on tuber number under one hill. Authors oriented to effects of nitrogen fertilization, various spacin g of planting, planting depth and seed tuber size. Except of this, eff ects of variety and year were studied. Results of two methods of potat o growing were compared. The first of them was conventional method wit h optimum doses of essential nutrients and integrated plant control ag ainst injurious agents. The second one was the method of growing witho ut mineral fertilizers and pesticides. Precise field trials were carri ed out in 1991 to 1993 at Potato Research Institute, Havlickuv Bred. C limatic conditions are given in Tab. I. Results of analyses of soil sa mples before trial foundation from the depth of up to 200 mm are given in Tab. II. Varieties used: Krasa - very early ware variety, Koruna - very early ware variety, Javor - middle-late industrial variety. Tria l variants: nitrogen fertilization: N-1 - 0, N-2 - 40, N-3 - 80, N-4 - 120, N-5 - 160 kg N/ha; planting depth: H-1 (tuber planting on the le vel of soil surface), H-2 (tuber planting 50 mm under soil surface), H -3 (tuber planting 100 mm under soil surface); spacing of planting: S- 1 (planting to the spacing 750 x 150 mm), S-2 (planting to the spacing 750 x 210 mm), S-3 (planting to the spacing 750 x 290 mm), S-4 (plant ing to the spacing 750 x 400 mm); size of seed tubers: V-1 (size of se ed tubers from 30 to 40 mm), V-2 (size of seed tubers from 40 to 50 mm ); growing technology: T-1 (growing without chemical preparations), T- 2 (conventional growing). From results, that are given in Tabs III to VII, highly significant effects of year and observed varieties on tube r number under one hill, were evident. Tuber number was significantly the highest in 1991, in the year where the rainfall was below normal a nd the temperatures were slightly above normal. Effect of rainfall in the season after planting to season of tuber setting and dynamic tuber growth, i.e. in June and July, was decisive. Variety effect was unamb iguously highly significant factor in all trials and years in the orde r Javor (the mean of all trials 16.87 pieces), Krasa (12.23 pieces) an d Koruna (11.47 pieces). Nitrogen fertilization (Tab. III) did not sho w significant effect on the number of tubers under the hill. According to suggested tendencies, it is possible to conclude certain, however very low, directly proportional relations between nitrogen dose and tu ber number under the hill. Planting depth (Tab. IV) also did not show statistically significant effect on tuber number under the hill. Spaci ng of planting (Tab. V) influenced observed index highly significantly . With increasing distance (from 150 to 400 mm), tuber number under th e hill increased directly proportionately (from 11.03 to 15.47 pieces) . The limits of statistical significance divided the results into two groups. On the one hand, there were values from S-1 variant (750 x 150 mm) and S-2 variant (750 x 210 mm). There was not significant differe nce between them, and the number of tubers found under the hill was 11 .03 and 11.67, resp. On the other hand, there were values with highly significant difference on S-3 variant (750 x 290 mm) and S-4 variant ( 750 x 400 mm) with 14.08 and 15.47 tubers. Seed tuber size (Tab. VI) o n average of years and varieties had highly significant effect on resu lting tuber number under the hill. Larger size of seed tubers (40 to 5 0 mm) resulted in higher tuber number under the hill (14.8 pieces) tha n small seed tubers (30 to 40 mm), where the tuber number was lower (1 2.4 pieces). Highly significant difference presents growth by 19.4% fo r larger seed tubers. Technological method of growing (Tab, VII) repre sented by conventional technology (industrial fertilizers, integrated plant control using pesticides) and alternative technology without che mical preparations, did not significantly affect on average tuber numb er under the hill. However, the variation was 7.3% (0.9 pieces) to ben efit of conventional technology.