Soil organic carbon content and stock in the abandoned lands in the forest-steppe of the Southern Cis-Urals

Abstract

Purpose of the study was to analyze soil organic carbon (SOC) content and stocks in the abandoned lands of the Southern Cis-Ural, which are used as hayfields and pastures or are under spontaneous forest revegetation.

Location and time of the study. Russian Federation, Republic of Bashkortostan, Mishkinsky district, «Eurasian carbon polygon», May-October 2023.

Methods. Soil samples were taken layer by layer (every 10 cm to a depth of 60 cm) from the abandoned (for 20–25 yrs) lands of the carbon polygon occupied by birch forests, hayfields and pastures. The samples were used to determine the content of organic carbon, alkali-hydrolyzable nitrogen, mobile phosphorus and exchangeable potassium, as well as pH (water) and salts.

Main results. The SOC content both under forest and grasslands in the 0–30 cm layer in gray forest soil was 3.2%, (in the 30–60 cm layer – 1.9%); SOC stock was estimated as 94–102 t/ha (in a layer of 0–60 cm – 162–179 t/ha). The SOM content in the dark-gray forest soil under a birch forest was 8.8% in the 0–30 cm layer (6.4% in the 30–60 cm layer), and its stocks were 257 t/ha (492 t/ha in the 0–60 cm layer). The SOC content in the 0–30 cm layer of grasslands used as hayfields and pastures was 5.1–5.7% in the 0–30 cm layer and 3.9–4.3% in the 30–60 cm layer. The respective SOC stock was estimated as 167–187 t/ha in the 0–30 cm layer and 319–343 t/ha in the 0–60 cm layer.

Conclusion. The SOC content and stock in the gray forest soil under communities of herbs and grasses were 1.6–1.9 times less than in the dark-gray birch forest soil, where the content and SOC stock were 50–70% higher than in hayfields and pastures. Thus abandonment of the arable lands in the forest-steppe in the southern Cis-Urals region decreased the excessive percentage of ploughed land, stopped the low-profitable agricultural production and started spontaneous restoration of ecosystems and their soils in the direction of adjacent virgin ones, decreasing erosion hazards. The SOC and its stock values of the abandoned soils being between the respective ones for the arable and virgin soil, suggest that further on with course of time these properties may significantly increase.