Vol 73, No 3 (2018)

Agriculture in the northern Meshchera lowlands is experiencing considerable difficulties due to both natural causes and the socioeconomic situation in Vladimir oblast. Some properties of reclaimed (drained) sod-podzolic soils remain sufficiently stable, including the considerable thickness of the arable horizon and the relatively high humus content. From the mid-1990s, a decrease in soil nutrient content and an increase in soil acidity have been observed. In recent years, state authorities have not allocated financial means for soil liming. The increase in precipitation in Northern Europe may lead to enhanced gleying in soil profiles and the subsequent transformation of sod-podzolic soils into sod-gley-podzolic. The article presents recommendations on land use.

Soluble forms of silicon affect a number of physical, chemical, and biological soil properties. Optimization of silicon nutrition enhances plant tolerance to biotic and abiotic stresses. Current climate change and anthropogenic impacts can alter the soil silicon state. Model laboratory experiments conducted with upper horizons of sod-podzolic soil, gray forest soil under different plant associations, chernozem, paddy soil, and red subtropical soil showed that insufficient soil moistening led to a reduction in soil monosilicic acid by 15 to 36% and simultaneous increases in polysilicic acid by 9 to 45%. Soil cultivation resulted in a decrease in plant-available soil silicon. An increase in NaCl concentration in the soil caused an increase in both monomers and polymers of silicic acid by 6 to 79%. The mobile equilibrium and lability of the numerical values of the parameters of the silicon state of the soil–plant system are revealed. These factors should be taken into account when implementing the 4R-STRATEGY for optimizing mineral nutrition in agricultural crops.

Prokaryotic communities of soils in oases of East Antarctica were studied at a model experiment with application of the succession approach. The total number of prokaryotes and filtered forms of prokaryotes, as well as the taxonomical diversity of the saprotrophic bacterial complex, were determined in two soil samples differing in organic matter content at temperatures of 5 and 20°C. We fixed the maximum total number of bacteria on the 14th day and the minimum number on the 1st and 160th (the end of the experiment) days in all variants. The amount and percentage of filtered forms of prokaryotes were the highest at the start of the experiment and the smallest on the 14th day. It is assumed that revival of Antarctica soils by humidification and incubation at temperatures above zero favors activation of dormant cells and their transition to viable status. Filtered forms of prokaryotes can be assigned to the pool of cells, which makes it possible to preserve bacteria at extremely low temperatures and without available water and nutrients. The succession approach enables more complete characterization of the taxonomic diversity of the saprotrophic bacterial complex and isolation of a wider genera of gram-negative bacteria than with a single inoculation of soil kept frozen. So it can be recommended for studying the prokaryotic community of Antarctica soils in model experiments.

Hysteresis of the soil water retention curve (SWRC), manifested as a difference between equilibrium curves of soil wetting and drying (hysteresis loop), is a phenomenon specific to soil hydrology, which is of practical importance for calculating irrigation norms. We have attempted to derive a model of the wetting curve from the drying curve. Modeling was based on parameters proposed by van Genuchten [6] and certain soil physical characteristics. SWRC hysteresis characteristics were obtained experimentally using capillarimetric measurements for wetting and drying curves at soil water pressures ranging from 0 to –800 cmH₂O. Two models, М-1 and М-2, based on the hypothesis of dissimilarity of parameters α for wetting (α_w) and drying (α_d) and the constancy of other parameters of the van Genuchten SWRC approximation for both curves of the hysteresis loop, have been developed for wetting curve assessment based on the drying curve. The M-1 error (RMSE = 0.05 cm^–1) was less than that of M-2 (RMSE = 0.06 cm^–1), which used clay content and soil density as predictors, as well as that of the well-known model proposed by Kool and Parker [11]. This approach to derive the wetting curve from the drying curve for a presumed correlation between the values of one parameter and equal values of the other parameters, can be used to predict an estimate of the SWRC hysteresis for a specific soil.