Cartographic modeling of humus content dynamics in the soils of Zdolbuniv district of Rivne region

Abstract

Soil agrochemical testing allows us to make optimal decisions to restore soil fertility, use fertilizers and pesticides efficiently, increase agricultural productivity and preserve the environment. Among the main agrochemical properties of soils, an important place belongs to the humus content, which is the organic part of the soil formed as a result of the decomposition of plant and animal residues and products of organisms' vital activity. This organic matter is a class of chemical compounds whose main components are carbon, as well as nitrogen, phosphorus, sulfur, and other elements. The main importance of humus in the soil is as follows: it helps to increase water absorption and air permeability; increases the level of dissolved macro- and microelements; and supports biological activity. Based on the results of the IX–XI rounds (2007–2017) of the planned agrochemical certification of the lands of Zdolbuniv district of Rivne region, conducted by the State Soil Protection Service, a corresponding database was created and thematic maps of soil humus content were constructed. The author's maps were developed for different years at a scale of 1 : 250 000 using ArcMap software, using the Gauss-Kruger projection and the Pulkovo 1942 GK Zone 5 coordinate system, with cartograms as the main method of depiction. The maps, in the context of the territories of former village councils (before the administrative-territorial reform of 2020), provide qualitative and quantitative information on humus content using a standard color scale and appropriate symbols. On the territory of Zdolbuniv district, which covers an area of 66.1 thousand hectares, the most common among the surveyed agricultural lands are light gray podzolized slightly stony (16.8 %), dark gray podzolized (13.8 %), light gray and gray podzolized medium-washed (11.7 %) and gray podzolized slightly washed (10.3 %) soils. The presented thematic maps show the spatial distribution of humus content in the soil by former village councils. This makes it possible to identify areas with different values of the indicators and to identify possible problematic or potentially fertile lands. The maps also show specific quantitative weighted average values of soil humus content for village councils, which makes it possible to determine changes in the indicator over the period in question for individual territorial units. In this regard, the best indicators are observed on the lands of Mizotska and Pyatihirska councils (the average humus content increased by 0.9–1.0 %), and the worst on the lands of Buderazhska council (the average humus content decreased by 0.3 %). As a result of the research, it was found that the generalized average humus content in the soil in the surveyed area for each tour ranged from 2.2 % to 2.6 %. According to classification criteria, this corresponds to lands with an average humus content (2.1–3.0 %). In the context of village councils, the weighted average humus content during this period ranged from 1.5 % to 3.1 %, meaning that the land belonged to 3 groups of land: low, medium, and high humus content. Low humus content in the soil is an indication of insufficient retention of organic matter, which can usually be the result of improper tillage, limited use of fertilizers, erosion processes, and suboptimal crop rotation. The average humus content is a sign of moderate farming, a certain stability of the soil's ecological condition, but still requires certain measures to maintain its fertility. Soils with high humus content are quite fertile and favorable for crop production. In case of small volumes or absence of manure application, peat use, plowing green manure, straw application can stabilize the state of biologization of agriculture to some extent. The thematic maps and diagrams created in this way allow, with the help of other additional and more detailed data, to become the basis for making informed management decisions on optimizing the humus content in the soil, growing crops, modeling changes in soil cover properties, and making agrochemical forecasts. Keywords: humus, agrochemical properties, cartographic modeling, thematic maps, cartograms.