Soil fertility transformation of abandoned soils along a catena in the Krasnoyarsk forest-steppe

Abstract

The aim of the study was to assess the transformation of some abiotic factors and soil fertility indicators, as well as erosion progress in the post-agrogenic dark-gray glei soil, undergoing spontaneous revegetation after abandonement, and after it was once again putt into agricultural use (ploughed)on a catena in the Krasnoyarsk forest-steppe.

Location and time of the study. The study was conducted in the Krasnoyarsk forest-steppe in 2017-2019 using 1) abandoned dark-gray glei soil and 2) the same abandoned soil after it was again put into agricultural use and tilled. The studied land, abandoned for 18 years prior to the beginning of the study, reached the quasi-steady state of succession with grasses, forbs and herbs, forming rhioms, turfs and bunches. In 2016 a portion of the abandoned land was ploughed, i.e. again turned into arable land.

Methods. Catenary approach to soil studies was used: at the east-exposed slope with 1.8˚ inclination a catena was chosen, composed of a summit, backslope and footslope. The abandoned land consisted of two sites: 1) abandoned land, AS, and 2) abandoned land that was again used as an arable one (ASA). At each catenary position soil profile morphology was described, genetic horizons characterized, soil bulk density and structural composition determined, the latter based on the agronomically valuable fractions (AVF). Soil temperature and moisture were measured in 0-10 and 10-20 cm soil layers from May till August. Mobile mineral nitrogen forms (N-NО₃ and exchangeable N-NH₄) were also measured. Using the so-called soil traps the possibility of water erosion flow and of the processes of fine earth and biota accumulation downward the catena was assessed. Soil samples were collected in triplicates, and all analyses were also performed with three replicates.

Results. All catenary position displayed fully developed soil profiles at the AS.  The soil was identified as dark gray post-agrogenic weakly podzolized glei clay soil, developed on the brown clay. The former arable layer (the so-called ploughed sole) could be clearly seen, thus confirming the post-agrogenic stage of land development. The ASA was found to be better heated due to less covered soil surface. At the summit the temperature was higher as compared with other positions of the catena. Soil water content over three years at the ASA site was significantly higher as compared with the AS one. High humus content and AVF share resulted in very small fraction of silt. Mechanical tillage of the abandoned soil (i.e. at the ASA site) did not decrease the lumpy fraction. The structure of all studied soils according to their AVF fraction could be characterized as good or excellent. The AVF were found to increase downward the ASA catena.

Due to heavier granulometric composition at the AS accumulative position the soil there was denser. After the AS site was ploughed, soil bulk density somewhat decreased at the transit and accumulative positions. The exchangeable N_NH4 content at both sites was rather low and did not differ. After ploughing the AS site, which had low nitrate content, the nitrate content increased by 1-2 grades at the ASA site.

Judging by the coefficients of soil transfer and accumulation, the former was much less at the ASA site. The backslope was characterized by higher soil mass accumulation as compared with the summit and the footslope. The biota share was rather high, especially at the AS backslope.

Conclusions. The difference in abiotic factors and fertility indicator of the dark-gray glei soil at the abandoned site and the adjacent site ploughed again is determined by the relief position. The maximal intensity of soil processed and regimes, as well as soil properties transformation, are characteristic for the foot slope of the abandoned land and the back slope of the abandoned and then ploughed land. So the set of soil fertility properties of the post-agrogenic dark-gray glei soil in the Krasnoyarsk forest steppe showed the possibility to turn the long-term abandoned land into arable.