Use of humate-sapropelic suspension when growing sunn hemp (Crotalaria junceae L.) in protected soil conditions (greenhouse)

Among the species of the genus Crotalaria L., Crotalaria juncea is the only cover crop cultivated for its fiber. The quality of the latter depends on nutritional conditions, the accumulation of biophilic elements in the biomass and the synthesis of proteinogenic amino acids. Thus, the purpose of the study was a qualitative and quantitative assessment of the green harvest at the stage of active flowering, before the phase of bean formation, when the entire biochemical cycle of the plant is reconfigured, and biochemical indicators are maximum. The plants were grown for 140 days (from April 22 to September 9, 2023) in protected soil conditions. The experimental design consisted of two blocks of 50 plants: in the first (control) plants were grown in a soil mixture without any additives; in the second, the crop was treated three times during the growing season with an organic suspension of humic acids (1000 ppm) obtained from sapropel (Pskov region) – UDGSS, by applying it when watering at the root. The soil substrate in both cases was typical chernozem (Kamennaya Steppe nature reserve, Voronezh region, 51°01ʹ41.6ʹʹN 40°43ʹ39.3ʹʹE) with a 20% addition of volcanic zeolite. Over the course of every 14 days, a systematic record of the dynamics of changes in the morphometric indicators of crop growth (height and dry biomass) was carried out, by removing five cultivars from each block of variants. After 140 days, the remaining five replicates per variant were subjected to biochemical analysis using inductively coupled plasma mass spectrometry (ICP-MS) and high-performance liquid chromatography (HPLC) using 7500 and LC 1200 instruments (Agilent Technologies, USA), according to the manufacturer's method. Treatment with UDGSS increased productivity and shoot height by 51.1% and 11.3%, respectively. The concentration of macroelements in dry biomass was in the following order: Na>K>Ca>S>P>Mg in the control and Na>K>Ca>Mg>P>S in the variant with UDGSS, and the export of microelements – Fe>Mn>Zn> Ba>B>Cu>Mo and Fe>Mn>B>Zn>Ba>Cu>Mo. At the same time, in total, the increase was more manifested in the amount of accumulation of microelements, due to a twofold increase in the concentration of iron ions. Among amino acids, an increase in the concentration of L-Lysine, L-Glycine, L-Glutamine and L-tyrosine was observed. The first three are structural components of biological tissues, which indirectly indicates an increase in the fiber strength of the culture.