Carbon dioxide emission and humus status of Albic Stagnic Luvisol under different fertilization regimes

The increase in the carbon dioxide content in the atmosphere, which enhances the greenhouse effect and leads to climate change, is the fundamental scientific problem of nowadays. Modern approaches to fertility management technologies of acid soils based on the principles of resource conservation and environmental safety are presented. They are based on the results of the study of carbon dioxide emission intensity, humus status, and crop rotation productivity in a classic long-term agricultural experiment under the influence of long-term use of various fertilizer systems with the application of ameliorant doses calculated by pH buffering capacity and hydrolytic acidity. The organo-mineral fertilizer system with the addition of 10 t of manure per ha of crop rotation area + N65P68K68, liming with a CaCO3 dose calculated according to pH buffering capacity (2.5 t/ha) contributes most to the optimization of soil processes. At the same time, it ensures the rational use of fertilizers and ameliorants, preservation of fertility, optimizes the processes of humus formation and carbon dioxide release. A high level of productivity of Albic Stagnic Luvisols forms under these conditions – 7.38 t/ha of grain units. Application of 1.0 and 1.5 lime norms calculated according to soil hydrolytic acidity with organic-mineral and mineral fertilizer systems on Albic Stagnic Luvisols in a short four-field crop rotation is not only a high-cost measure. However, it causes significant carbon loss in the form of CO2 due to additional mineralization. It is accompanied by calcium leaching and creates environmental problems in the conditions of the periodic washing-off water regime. Therefore, liming by CaCO3 dose calculated according to acid-base buffering capacity should be carried out before each of the following rotations in order to harmonize the environmental and productive functions of Albic Stagnic Luvisols in the short crop rotation. The obtained research results will be used to improve the methodology for determining carbon dioxide emissions and predicting the effect of various fertilizer and liming systems on its balance in the soil.

Impact of different fallow durations on soil aggregate structure and humus status parameters

Soil aggregate structure and soil organic matter are closely interrelated and commonly considered as key indicators of soil quality. The aim of this study was to evaluate the effects of different fallow durations on indices of soil structure and humus status indicators. Studies were conducted on abandoned agricultural fields (15, 20 and, 35 years after abandonment). As a reference site, we used a cultivated field in the area. The experimental soil fields are classified as Gleyic Cambisols. Soil macroaggregates were separated with the sieve (dry sieve) to seven aggregate size fractions, i.e.> 10, 10–5, 5–2, 2–1, 1–0.5, 0.5–0.25 and < 0.25 mm. The humus status parameters of soils included the following indicators: soil organic carbon (C_org), humus reserves (Q_H), the degree of humification of organic matter (SOM_dh), fractions of humic acids (HA) (free and bound with monovalent cations and Al₂O₃, Fe₂O₃, bound with Са²⁺ which forms humates, bound with clay minerals), fulvic acids (FA) (free aggressive) and ratio of HA to FA (C_HA: C_FA). After a fallow period of more than 20 years on the surface formation of a sod layer. A long-term fallow period had an impact on the mean weight diameter of the aggregates (MWD) and agronomically valuable aggregates (AVA). Fallow soils have a significantly better structure than soils under a cultivated field. Long-term cultivation leads to the deterioration of soil structure and the formation of large aggregates (>10 mm). The C_org content remains at the level of the background content when the soils are left fallow for less than 15 years and increases over time. The C_org in the upper 0–20 cm soil layer has been shown to increase from 3.55 to 8.74% on arable land that has been fallow for 35 years and has been largely associated with significant accumulation of organic matter within the plant root mass. Mature sites are characterized by an increase of fulvic acids in the humus composition in comparison with their arable analogues. The abandonment of soil agricultural use and the cessation of mechanical tillage results in the restoration of the natural structure of soils and the improvement of their agrophysical properties. Such studies have not been previously conducted in the Primorsky region of the Russian Far East.