PHOSPHORUS AVAILABILITY IN SOILS OF TEA PERENNIAL AGROCENOSES IN THE HUMID SUBTROPICS OF RUSSIA

The paper presents a retrospective assessment of available phosphorus in the soils under tea plantations according to the soil-agrochemical surveys conducted by tea-producing farms in Sochi. Plantations established in the 1950s contained on average 380–450 mg/kg of mobile P2 O5 by 1987–1992, which is optimal for the plant and 2.5–3 times higher than the natural level. By 1994–1997, the availability reached a high/ultra-high level (650–900 mg/kg in a layer 0–20 cm), 3–4 times higher than natural. In 2004–2006, many plantations showed signs of "overphosphating" with an excessively high content of P2 O5 (1 300–1 800/900–1 200 mg/kg in layers 0–20/20–40 cm), 8–12 times higher than natural. This was a consequence of the intensive use of mineral fertilizers in the 1970s – early 1990s. At the same time, the plantations established in the 1980s had an average soil availability (250–400/150 mg/kg). In 2009 and in 2018–2022, the soils under long-cultivated plantations, despite the absence of systematic fertilizers application since the mid-1990s, still had a very high or excessive phosphorus supply (from 700–800 to 900–1 200 mg/kg in a layer 0–20 cm); there were also clearly "overphosphated" soils. But according to data from different years for specific sites, a drop in the concentration of mobile phosphates (1 700 –> 900 –> 500 mg/kg) was observed in the absence of fresh receipts. Plantations abandoned more than 25 years ago had a low soil availability (200–250/50–100 mg/kg P2 O5 ). The change in the available phosphorus in soils depending on the doses and duration of fertilizers application, and then in their absence, is demonstrated by a special field experiment: soil "overphosphating" (1 200–1 300/800–950 mg/kg in a layer 0–20/20–40 cm) as a result of the introduction of 120 and 180 kg of active agent/ha, with a sharp increase in the content of mobile phosphates in the upper layer for 5–7 years and in 20 years, was deeper; in the absence of fertilizers, the content dropped by 1.5–2.0 times for 8–9 years.