Change in the soils’ fertility level of tea agrocenoses in the transition to cultivation without mineral fertilizers in the humid-subtropical zone of Russia

Research was carried out on the basis of preserved field multifactor experiment on tea crop (Camellia sinensis (L.) Kuntze) in the conditions of the Sochi Black Sea coast. The application of NPK fertilizers in different doses and combinations according to the experimental scheme was carried out annually from 1986 to 2011. Since 2012, the use of fertilizers has been completely discontinued. The fertility indicators of long-fertilized brown forest acidic soils (in layers 0-20/20-40 cm) were compared with those after 7-8 years of fertilizer withdrawal. During the period of fertilizers’ application, the level of soils’ nitrogen supply significantly exceeded the control (by 30-75/30-56 mg/kg depending on the doses of nitrogen fertilizers). After the fertilizers’ discontinuity, nitrogen supply level equalization occurred in all experimental options. The content of labile phosphorus in soils previously fertilized with high phosphorus doses (120 kg P2 O5 ha-1 year-1 and more), during the period of experiment’s conservation decreased by 450-500/350-450 mg/kg, but exceeded the control in 2-2.5 times; in soils previously fertilized by low doses, the indicators have not changed significantly. In soils highly supplied with labile potassium, the content of the element decreased by 70-140 mg/kg. The yield of tea in 2019-2020 was equally low (12-26 cwt/ha) on all options, 2.2-3 times lower than fertilized plantations. After the fertilizers’ withdrawal, there was a decrease in acidity (an average increase in pH by 0.18-0.24/0.12-0.20 units) of agrogenic-acidized soils and an increase in their oppressed respiratory activity (on average by 1.6 times). These changes reflect the tendency of soil self-restoration after the removal of the fertilizers’ load.