Photometric express diagnostics of nitrogen nutrition of plants

The purpose of the study is to establish the degree of correspondence of the SPAD502 N-tester indicators to the true content of chlorophyll and nitrogen in crop plants. The study was conducted in 2020-2021 on the land use territory of the Zarya poultry farm OJSC, which belongs to the agro-ecological zone of the Krasnoyarsk forest-steppe. Monitoring plants for chlorophyll content was carried out in industrial crops of spring wheat Novosibirskaya 29 and Novosibirskaya 31, as well as in crops of various varieties of rapeseed, soybeans, oil flax and wheat at the GSU site, located on leached chernozem with a humus content of 6.8-7.3 %; pHsol. - 6.9; P2O5 - 175 mg/kg; K2O - 210 mg/kg (according to Chirikov). Field determination of chlorophyll concentration was carried out using a portable device N-tester SPAD-502. The flag leaf of plants was studied. All work was carried out in sunny, windless weather at a temperature of 21-23 °C. Leaves tested with a portable device were further analyzed in the laboratory for chlorophyll and total nitrogen content. Chlorophyll contents were determined spectrophotometrically using an Agilent Technologies Cary 60 UV-Vis instrument at wavelengths of 470, 649, 665 and 720 nm. Pigments were extracted from plant tissue using a solvent (96 % ethanol). The determination of total nitrogen was carried out colorimetrically using the wet ashing method and the reaction of indophenol green formation. It was found that the content of chlorophyll a varied in the range of 1.22-8.26 mg per 1 g of dry plant biomass, the content of chlorophyll b - in the range of 1.19-9.16, the content of total chlorophyll - in the range of 2.68-17, 42, total nitrogen content - 0.28-0.31 %. The SPAD value varied from 2.9 to 44.7 units. A close correlation was revealed (r = 0.703-0.868) between the instrument readings and the content of chlorophyll and nitrogen in plants. The research results show the possibility of using the photometric method as a tool for rapid diagnosis of nitrogen nutrition of plants. The use of this device can replace more labor-intensive and expensive methods of chemical diagnostics.