Estimation of phytomass reserves and fertility of gray soil assets

Abstract

Purpose of the study. To assess phytomass structure and production, as well as gray soil (Greyzemic Phaeozems (Aric) fertility of abandoned arable land under different land use in the forest-steppe.

Location and time of the study. The study was carried out at three sites: 1)abandoned arable land under natural revegetation, 2) abandoned arable land used for haymaking and 3) abandoned arable land once more ploughed for grain crops pproduction) in the Krasnoyarsk and Achinsk-Bogotol forest-steppe of the Krasnoyarsk Krai (Russia) from 2011 to 2016.

Methodology. In all key study sites the general structure of aboveground phytomass and fertility indicators of gray soils were determined. The data were analyzed statistically, and the differences and correlation coefficients were considered statistically significant at P ≤ 0.05.

Main results. Revegetation succession of the abandoned arable land in the forest- steppe zone displayed transition from the rhizome to the bunch stage. The vegetation of the Krasnoyarsk forest-steppe abandoned site was represented by the phytocenosis of grasses and forbs with 30% of ruderal species. The flora of the Achinsk-Bogotol forest-steppe abandoned site had greater plant species richness with increased contribution of legumes and 30% of ruderals. Plant species richness at both study sites depended on water regime. The productive soil water content at the the Achinsk-Bogotol site was significantly higher than at the Krasnoyarsk site. The use of abandoned land for haymaking was found to accelerate the bunch stage of vegetation succession, substituting herbs and grasses by grasses and forbs due to soil compaction because of haymaking. The above-ground phytomass of the abandoned, but once more used for grain crop production, being dominated by the respective crops (oats and wheat), had an increased contribution of herbs andgrasses due to ruderal species.

The total aboveground phytomass stocks were estimated to be maximal (P ≤ 0.05) at the abandoned sites under natural revegetation in both regions. The site cropped to oats was an exception, as oats increased its aboveground phytomass during the growing season, resulting in the drastic increase from the summer to the autumn sampling dates. Due to their optimal soil water regime, the abandoned sites in the Achinsk-Bogotol forest-steppe were more productive, while the sites under haymaking were less productive and practically similar in both regions.

Intensive biogenic accumulation was found to be characteristic for the abandoned arable lands. However, the renewed arable use was shown to decrease significantly soil potential fertility. The actual soil fertility, as judged by the nitrate and ammonium nitrogen content, was shown to depend on land use, as ploughing increases soil organic matter mineralization and hence soil nitrate and ammonium content. The closer positive correlation between the aboveground phytomass and soil actual and potential fertility indicators in the Achinsk-Bogotol forest-steppe was most likely resultant from the optimal soil water regime there.

Soil fertility of abandoned lands was shown to depend on their subsequent land use. Natural revegetation significantly improved soil agrochemical properties and biogenic indicators.

Conclusion. The maximal aboveground phytomass was found to develop under natural revegetation during transition from rhizome to bunch stage of vegetation succession, which leads to biogenic accumulation and hence increased soil fertility. Grasses and herbs dominate in the aboveground phytomass. Haymaking at the abandoned revegetating sites results in decreased phytomass production and increased contribution of grasses, which accelerates successional changes towards the bunch stage and decreases soil fertility. The renewed use of the abandoned land for grain crtop production decreases phytomass production and biogenic accumulation.