The effect of calcium nitrate on the agrochemical properties of agrogenically-modified soils under tea crop in the subtropics of Russia
The long-term use of mineral fertilizers when cultivating tea crop has led to significant agrogenic changes in the brown soils of the humid subtropics of Russia. The revealed degradation processes (acidification, increased mobility of biogenic elements, "overphosphating", inhibition of biological activity) lead to a decrease in the overall soil fertility level, which requires radical chemical reclamation during their further exploitation. This determines the relevance of testing various types of fertilizers in order to restore deficient elements, as well as regulating soil acidity and aluminum toxicity. The purpose of this work was to study the effect of calcium nitrate on the agrochemical properties and nutritional regime of agrogenically-modified acid brown forest soils under tea crop. Changes in the following soil parameters have been studied: рН<sub>KCl</sub>, the content of exchangeable calcium and aluminum, ammonia and nitrate forms of nitrogen, mobile phosphates, exchangeable potassium, as well as the elemental composition of mature tea leaves (N, P, K, Ca, Mg). It has been found that the use of calcium nitrate on tea plantations during summer feeding (at a dose of Ca150) replenished the reserves of exchangeable calcium in the soil, while reducing the content of exchangeable aluminum and the rate of its acidification. An increased concentration of calcium ions in the soil solution contributed to the consolidation of some mobile phosphates (due to the formation of less soluble forms with them), without significant effect on the bioavailability of this element. Taking into account the positive effect of calcium fertilizers on the chemical composition of agrogenically-modified soils, it is necessary to continue studying the effects from calcium fertilizers at different forms and concentrations on the agrochemical soil properties, as well as the functional state of the tea plant related to acidophytes.