Material and method Directory UMM :Data Elmu:jurnal:E:European Journal of Agronomy:Vol12.Issue1.Jan2000:

70 M. Pospisˇil et al. European Journal of Agronomy 12 2000 69–78 parison with areas under other field crops. This is split-plot method in five replications. Cultivar OS-Nada, its mother 2n=18 and father 4n= the main reason why there are very few profes- sional or scientific studies from this area. 36 lines, were used as test crops. The ratio of mother and father components at sowing was Researchers from North America Campbell, 1968, the UK and Denmark Scott, 1968; 6:0:2. Basic fertilization for seed sugar beet was carried out with 50 kgha of N, 150 kgha of Longden and Scott, 1973; Longden, 1974 con- ducted research with twice as many plants P 2 O 5 , and 300 kg ha of K 2 O. Sugar beet was sown at the end of August at a between-row 300 000 plantsha at harvest as commonly recommended in other production regions. spacing of 50 cm and within-row spacings of 11.4, 8.6, 7.1, and 5.7 cm. In spring, a density correction Trogisch 1985 maintains that a plant density of 150 000–250 000 plantsha at harvest is desirable was made according to the test treatments. Leaf area per plant and the LAI were deter- for seed sugar beet grown under European condi- tions. Under the conditions prevailing in mined in characteristic pheno-stages of seed sugar beet at the start of vegetation in spring, in the Vojvodina FR Yugoslavia, the highest yield and best seed quality of sugar beet were obtained with stage of inflorescence stalk appearance and in full flowering using the punch method Campbell and plant densities of 130 000 to 150 000 plantsha after wintering Stefanovic´, 1987. Based on the trial Viets, 1967. In the said stages, measurements were made on ten plants from each treatment and results achieved in eastern Slavonija Croatia, Kristek and Matic´ 1984 concluded that good involved the number of leaves, the leaf weight per plant and their dry matter. Leaves with blades yields might be obtained with 65 000–80 000 plantsha at harvest. According to the authors, longer than 2 cm were counted. All observations and measurements in the trial were carried out on nitrogen rates applied with topdressing to direct- drilled seed sugar beet vary, depending on the soil, mother plants. Seed sugar beet was harvested at the end of July. Seed yield and quality were from 150 to 250 kgha Longden and Johnson, 1977; Zarisˇnajak and Sˇijan, 1991; Rastija, 1993. determined after the harvest. The data obtained were processed by up-to-date statistical methods The objective of this research is to determine the effect of plant density and nitrogen application analysis of variance, correlation applying com- puter programs Microsoft Excel 5.0 and Mstat. upon the formation and size of leaf area, LAI, yield and quality of sugar beet seed. Investigations Analyses of weather conditions during three growing seasons showed considerable variation in should also reveal how much the yield and quality of sugar beet seed depend on the LAI. precipitation distribution from year to year Fig. 1. Particularly unfavourable precipitation distribution was recorded in 1991–92. Water balance after Thornhwaite’s method indicates a

2. Material and method

balance between potential and actual evapotrans- piration all the way to June, when water deficiency Investigations were carried out through field trials set up on the experimental field of the Faculty appeared in soil. Water deficiency in June and July was unfavourable because seed sugar beet has the of Agriculture, Zagreb, during 1991–92, 1993–94 and 1994–95. The trial comprised four plant densi- biggest needs for water in those months. Very favourable conditions for the growth and develop- ties of seed sugar beet Beta vulgaris var. altissima D. C., after crop wintering 40 000, 80 000, ment of seed sugar beet prevailed throughout 1993–1994. Precipitation distribution in 1994–1995 120 000, and 160 000 plantsha and three nitrogen rates 60, 120, and 180 kgha applied in two was slightly less favourable for seed sugar beet. There was less precipitation, accompanied by topdressings. The first topdressing with half of the foreseen N fertilizer quantity was done at the slightly higher temperatures, in April, at the time when inflorescence shoots were formed, which beginning of the spring growing period and the second immediately prior to the shooting of inflo- accelerated the development of seed sugar beet. Rainfall was sufficient throughout the growing rescence stalks. Trials were set up according to the 71 M. P ospis ˇil et al. European Journal of Agronomy 12 2000 69 – 78 Fig. 1. Relevant components of balance of rainwater in soil trial field Zagreb–Maksimir. 72 M. Pospisˇil et al. European Journal of Agronomy 12 2000 69–78 Table 1 Chemical properties of the plough layer, soil depth 0–30 cm, Zagreb–Maksimir Year pH Humus Total N AL-method mg100 g soil H 2 O 1M KCl P 2 O 5 K 2 O 1991–92 7.7 7.2 2.2 0.14 35.7 17.5 1993–94 7.2 6.6 2.1 0.13 20.3 18.6 1994–95 5.3 4.7 2.1 0.12 10.1 12.6 period, from May to July. Lower temperatures in plants develop a relatively higher leaf weight if springs are colder. Leaf area is mainly formed in May and June, along with sufficient humidity in this period, disturbed the balance between vegeta- the stage of intensive growth, which lasts from stem appearance to the beginning of flowering, the tive and generative growth, which was negatively reflected in seed quality. Water deficiency in soil proceeding of the stage being strongly influenced by weather conditions, notably precipitation and was recorded in July, i.e. at the time of seed formation and maturing. temperature. In 1991–1992 and 1993–1994, most of the leaf area, about 23, was formed in the Soil of the experimental field Zagreb–Maksimir is anthropogenized eutric brown, on slightly luvic period from the beginning of May to mid June. In 1994–1995, the weather conditions throughout loam Vidacˇek et al., 1994. Chemical soil proper- ties are shown in Table 1. April and May favoured intensive development, and sugar beet seeds grew in June and July. Thus, the major part of leaf area was formed in the second part of spring vegetation during June.

3. Results and discussion