Gray forest soils peculiarities of loess islands in Polissia and Left-Bank Wooded Steppe of Ukraine

Abstract

The article reviews the achievements in gray forest soils study, reveals the main tenets of their formation and the results of authors’ research. The authors were induced to carry out the research, stated in the article, by the necessity to convert from the generalized characteristics of gray forest soils to the differentiated ones, as it is very important with regard to sustainable use of soils fertility and developing their stabilization measures. The article deals with the peculiarities of gray forest soils in left-bank Ukraine from the aspect of these soils characteristic features discreteness within the area stretching from the Podillia to Central Russian Upland. The research was carried out in two provinces – in Chernihiv region, in the transition zone from Polissia (woodlands) to Wooded Steppe, where gray forest soils occur on loess islands and in northern part of Wooded Steppe in the valley terraces of the Desna and Dnipro rivers, and also in Kharkiv region in droughty Eastern Wooded Steppe of Ukraine. It is shown that gray forest soils of loess islands of Polissia (woodlands) and northern part of Wooded Steppe were formed mainly on loessivated sandy loams and partly on loessial loam soils. Among the analogs from other regions they have the shortest humus part of the profile. By the way, humus coloration of the profile increases maximally in the soils of the most humid regions in the Podillia Upland, and in the northern part of the Central Russian Upland. In Polissia (woodlands) and the adjacent (northern) belt of Wooded Steppe gray forest soils contain a very little amount of humus (1,2–1,6 %), have high acidity, contain few nutrients, especially nitrogen. Though, in husbandries of durable optimal arable farming culture rather fertile soils are formed, even on loess sandy loams. They contain 2,4–2,7 % of humus, are saturated with bases by 90–93 %, are characterized by the close to neutral condition reaction, have high content of phosphorus and potassium, and sufficient content of nitrogen. The soils of droughty Eastern Wooded Steppe adjoining to right banks of river valleys, mostly along the edges of plateau terraces, were formed on heavy loamy loesses. The biggest tract is situated around the city of Kharkiv (Kharkiv refugium). They contain more humus (over 2 %), have a deeper dark-gray coloration of the profile, have a less lack of bases and are more saturated with nutrients, though have substantial acidity. It is stated, that in the virgin gray forest soils (in groves) a rather high level of fertility is formed, active accumulation of humus, nitrogen and ashy elements, which are very important for soils fertility, takes place in particular. This is proved by the conclusions of S. V. Zonn and A. P. Travleev about the fact that a broad-leaved forest is not only the cause of leaching and podzolizing. But the factors of fertility decrease rapidly in arable soils. It is caused by stressful aeration while mechanical tilling, which is resulted in intensive mineralization of organic matter. All the above-mentioned peculiarities of gray forest soils properties are the necessary base of regional adaptive-landscape agriculture planning. As for the improvement of gray forest soils classification, the necessity of singling out gray forest soils subtypes according to natural zones and facies is proved, including singling out the above introduced subtype of gray forest soils and the subtype of gray wooded steppe soils.