Dynamics of chlorophyll content (SPAD-values) and nitrogen content of winter wheat genotypes

The objective of the present research was: - dynamics of chlorophyll content (SPAD-values) and nitrogen content in different growth stages of winter wheat, - effect of insertion of leaves on plant and points of measurements on lamina leaf on dynamics of SPAD-value, - reaction of winter wheat genotypes on two levels of nitrogen nutrition on SPAD-values and nitrogen content in leaves, - relations among SPAD-values and nitrogen content in grain and straw in different growth stages of winter wheat. Pot experiment with five winter wheat genotypes (Ilona, PS-19/94, SK-679-18, SK-656-2 and SO-1441) and two variants of nitrogen nutrition (No - non-fertilized control, N40 - 40 mg N/kg of soil) was established in three replications in November 1998. Eight vernalized winter wheat seeds were planted into pots and cultivated in control conditions of growth chamber, day light 16 hours (16 day/8 night), irradiance 350 micro mol/square m/s, at temperature 23/16 degree C (day/night). SPAD-meter readings were taken in five growth stages (GS 15 - five leaves unfolded, GS 32 - the 2nd node detectable, GS 55 - half of inflorescence emerged, GS 68 - anthesis complete, GS 75 - medium milk), nitrogen content was determined in four growth stages (GS 32, 55, 68, 75). Chlorophyll content (SPAD-values) in the first two terms was measured on two leaves of each plant (L1 and L2) and from two points (P1 and P3) of each leaf. In the next three terms, measurements were on three leaves from the top plant (L1- L2 - L3) and from three points of leaf (P1- P2 - P3). Nitrogen sufficiency index (NSI) was calculated for varieties as percentage rate of SPAD-values on non-fertilized variant No to SPAD-values on fertilized variant N40. In each term of SPAD-meter readings (besides the first term) one plant from pot was taken for determination of nitrogen content. In the second term (7.1.1999) nitrogen content was determined in whole plant, in the next three terms independently in leaves (on which SPAD-meter readings were taken) and independently in upper and lower half of stem (including leaves). In maturity from each pot average sample was prepared for nitrogen determination in grain and straw. Nitrogen content was determined by Dumas method on an analyser CNS-2000. SPAD-values from the first to the fourth term increased from 45.90 to 57.27, while nitrogen content on the contrary decreased from 4.515% to 2.504%, during the same period. In the first growth stages the second leaf had the highest SPAD-values, in the other growth stages the first leaf from the top. Differences in SPAD-values between the first and the third leaf were increased with growth stage and insufficient nitrogen nutrition. On the first leaf SPAD-value decreased from the tip to basal part of lamina. Maximum SPAD-value was changed with leaf position and with term of evaluation via middle part to basal part of leaf in consequence to maximum SPAD-value was at the end of experiment (in growth stage medium milk) on the third leaf and on the base. Genotype response on insufficient N-fertilization was different in consequence to nitrogen sufficiency index (NSI) varied among genotypes (93.9 to 100.6%; 92.5 to 97.1%; 97.8 to 103.5%; 91.4 to 99.2%). In the same term critical values of NSI of some genotypes lower than 95% was in absolute value higher than at other genotypes at sufficient N-fertilization. From the results followed, that critical SPAD-value for decision to apply additional N is necessary to state for the concrete genotype and the growth stage and utilise differences in SPAD-value between the first leaf and the third one. Among leaf chlorophyll content in individual growth stages and grain nitrogen content and straw one in harvest correlations were from medium to high. The highest correlations were between SPAD-values on the third leaf and grain nitrogen content and straw one. This fact is necessary to take into consideration at selection on higher grain nitrogen content. Similar correlation conditioned by genotypes and N-fertilization were between leaf nitrogen content respectively in stem in different growth stages and grain nitrogen content and in straw