HUMUS CONTENT AND PHYSICOCHEMICAL PROPERTIES OF PODZOLIZED CHERNOZEM DEPENDING ON FERTILIZATION

Abstract

The aim of the article was to determine the impact of long-term (15 years) application of different types and rates of mineral fertilizers and their combinations in a field crop rotation on the humus content and physicochemical indicators of podzolized chernozem. A stationary field experiment has been conducted on the experimental field of Uman National University since 2010, located in the Mankivka natural-agricultural district of the Right-Bank Forest-Steppe. The soil under study is heavy loam podzolized chernozem on loess (classified as Phaeozems according to FAO/WRB, 2022). The texture, by FAO classification, is defined as silt clay loam with a high proportion of silt (63–65%) and clay (33–35%) and a negligible sand content (2.1–2.5%). The field crop rotation (winter wheat, corn, spring barley, soybeans) is simultaneously deployed across four fields with a total area of 2 hectares. The experiment has three replications, with a sequential arrangement of the variants. The size of the experimental plots is 110 m², and the harvest plots are 25 m². Fertilizers in the form of granular superphosphate and potassium chloride were applied before deep autumn tillage, while ammonium nitrate was applied during pre-sowing cultivation and as early spring top-dressing. Non-marketable plant residues (straw, stalks) were shredded and left in the field. The long-term application of different fertilization systems, including the unfertilized control, did not significantly affect the humus content, which remained within the range of 3.7–4.1%. The minor fluctuations in humus content can be explained by the practice of leaving the non-marketable residues of all crops in the rotation on the field. It was found that in the experimental variants N110P60 and N110P30–60K40–80, compared to the unfertilized plots, there was a slight (7–8%) increase in Cation Exchange Capacity (CEC). This can be attributed to a greater input of organic matter into the soil from post-harvest and root residues. The structure of the CEC of the studied podzolized chernozem is close to optimal and, under the influence of the 15-year application of different mineral fertilizer systems combined with leaving non-marketable crop residues in the field, did not undergo significant changes. The share of calcium and magnesium in the CEC composition was within optimal limits – 69.5–75.8% and 10.9–12.8%, respectively. A slight decrease in the proportion of calcium in the soil of the fertilized plots can be explained by its return to the surface with the upward movement of water through soil capillaries. The Ca2+ : Mg2+ ratio in the soil's CEC structure was 7.7 before the experiment, and after the long-term fertilizer application, depending on the variant, it ranged from 5.8 to 6.5, being the lowest in the unfertilized plots. The Mg2+ : K+ ratio before the experiment was established was 3.5, and after the long-term use of the soil without mineral fertilizer application, it increased to 4.8. A significant increase in the Mg2+ : K+ ratio to 4.4 also occurred in the N110P60 experimental variant, indicating a potential potassium deficiency in plant nutrition.