Biological features of the response of fodder grasses to the use of iodine on agrosod-podzolic soils of various cultivation levels

A geochemical anomaly of iodine deficiency the North-Western region of the Russian Federation negatively affects the yield and quality of marketable products of regional agriculture and feed, the viability and productivity of farm animals, and the health of the population. In this study, for the first time in the conditions of the region, the optimal concentration levels of the KI solution for foliar fertilization and the time period of treatment on the annual and perennial grasses dominating in the structure of the acreage of the Non-Chernozem region were established. Our goal was to study the biological characteristics and evaluate the parameters of responsiveness of forage grasses to changes in the concentration of the KI solution and the period of time of iodine foliar treatments. The research was carried out in 2019-2021 in the Menkovo branch of the Agrophysical Institute (Gatchinsky District, the Leningrad Province). Two micro-field experiments were laid down in the system of a long-term fundamental field agrophysical experiment in the field crop rotation link: potatoes-annual grasses + perennial grasses-perennial grasses of the 1st year of use-perennial grasses of the 2nd year of use. The object of the study was mixed crops. Annual grasses were presented by the oat ( Avena sativa L.) variety Skakun and the garden vetch ( Vicia sativa L.) variety Vera, perennial grasses were presented by the red clover ( Trifolium pratense L.) variety Orpheus and the timothy ( Phleum pratense L.) variety Leningradskaya 204. Both experiments had a two-factor scheme. Factor A is the degree of cultivation of sandy loam agrosod-podzolic soil (medium-cultivated, well-cultivated and highly cultivated). The scheme of the first experiment on factor B included nine variants of the concentration of the KI solution: 0, 0.005, 0.01, 0.02, 0.04, 0.08, 0.16, 0.32, and 0.64 %. Foliar treatments of annual grasses were carried out in the booting stage of oat, perennial grasses were in the tillering stage. In the second experiment, four variants of the time period of foliar treatment with 0.02 % KI solution were studied by factor B: KI-0 - control without treatment; KI-1 - early treatment in the tillering stage of oats, red clover and timothy; KI-2 - late treatment in the booting stage of oat and in the stage of branching of red clover; KI-3 - two-fold treatments in terms corresponding to variants KI-1 and KI-2. The yield of the aboveground biomass of grasses used for the preparation of feed was counted by a continuous weight method from a 1 m2 plot. The placement of plots by repetitions and variants was systematic. The repetition in the first experiment was threefold, in the second - sixfold. A chemical-analytical analysis of selected soil and plant samples was carried out. As a result of short-term field experiments, it was found that the responsiveness of forage grasses to the iodine foliar treatment under a geochemical anomaly of iodine deficiency is determined by a combination of weather-climatic and agrochemical soil conditions with biological characteristics of crops and depends on the period of time of treatment and the concentration of the KI solution. For annual grasses, the treatment was more effective in the booting stage of oat (yield increased by an average of 2.49 t/ha, or 29 %; р ≤ 0.05), whereas for perennial grasses in the tillering stage of red clover and timothy (an increase of 3.39 t/ha, or 18 %; р ≤ 0.05). The optimal CKI for the treatment of annual grasses was 0.16 %, regardless of the degree of cultivation of the soil, and of perennial grasses on soils of medium, good and high cultivation was 0.04, 0.08 and 0.16 %, respectively. The increase (р ≤ 0.05) in productivity reached 3.69-9.38 t/ha, or 67-80 %, for annual grasses and 3.91-8.03 t/ha, or 22-30%, for perennial grasses. The positive effect of iodine increased with the optimization of soil and agrochemical conditions to good and high cultivation by 68 and 128 %. Due to high tolerance to the concentration of the KI solution, toxic effect was detected only at CKI 0.32-0.64 %, when crop losses reached 19 %. Legume types of herbs were more sensitive to the excess of iodine. The reduction of iodine toxicity in the experiments was facilitated by an increase in soil cultivation and a change in the botanical composition of crops with an increase in the proportion of cereals. Perennial grasses accumulated 9 % less iodine than annual ones. In the variants with optimal CKI, the iodine content in the aboveground biomass of annual and perennial grasses increased on average from 119 and 88 to 766 and 628 µg/kg, that is, 6.4-fold and 7.1-fold. The accumulation of nitrates, on the contrary, decreased (р ≤ 0.05) by 13 % in annual and 11 % in perennial grasses.