Nitrogen concentration (Nc) in leaves, in each stage of sugar beet development, is the major factor stimulating the accumulation of dry matter in leaves, which in turn affects the dry matter concentration in storage roots and, consequently, determines sugar beet yields. This thesis was verified based on the data obtained from a static field experiment conducted in 2001-2003, with eight fertilizing variants: without nitrogen (absolute control, PK), without one of the main nutrients (KN, PN), with a reduced amount of phosphorus and potassium (N + 25% PK, N + 50% PK) and the recommended amount of all basic nutrients (NPK, NP*K, P* – P in the form of PAPR). Nitrogen concentrations in leaves and storage roots of sugar beet tended to decline during the growing season, but the former tendency adhered to a linear-plateau model while the latter corresponded to an exponential one. This discrepancy, revealed in the second part of the season, can be considered as an indicator of a high yield of storage roots, especially in years favorable for sugar beet vegetation. The growth analysis allowed us to determine the time and the maximum rate of canopy and storage root growth during the season. Irrespective of the fertilizing variant, both organs of sugar beet reached the maximum rate of growth from 92 to 113 day after sowing (DAS). Plants grown under conditions of ample water and nutrient supply (2001) reached a three-fold higher rate of leaf growth than in dry years (2002, 2003). The storage root showed much smaller differences in the absolute rate of growth. However, the effect of fertilizing variants was stronger, especially from 92 DAS onwards. Trends of the relative growth rate for each of the two tested plant organs were very similar. The highest growth rate for both organs occurred in early stages of sugar beet development and then progressively declined. Nevertheless, only this growth parameter responded significantly during the season to the variability of Nc in both sugar beet organs. The relationships showed that sugar beet plants could compensate the dry matter growth rate during early stages of sugar beet development, especially in years favorable for sugar beet growth. The impact of nitrogen concentrations in leaves on the relative storage root growth dynamics was curvilinear in 2001 but linear in the other years, i.e., the ones when droughts were frequent. At the same time, the relationship between Nc and storage root fraction was always linear. This type of a relationship clearly demonstrates the natural conservatism of the storage root to its variable nitrogen concentration during the growing season.

17.3.2012