Humus content and balance in the soil with different doses and ratios of mineral fertilizers in field crop rotation

Abstract

Purpose. To evaluate direction of content change in humus content and reserves in podzolized hard-loam chernozem of the Right Bank Forest-Steppe with different doses and ratios of mineral fertilizers in short crop rotation against the background of ploughing non-commodity part of the crop. Methods. The research was conducted in crop rotation of experimental field of the Uman National University of with the following alternating crops: winter wheat, corn, spring barley, and soybean. The total humus content in the soil was determined in accordance with the State Standard 4289 and its balance according to Baliuk S. A. et al. (2011) Results. It has been monitored the balance of humus in the soil for 2011–2018 at various doses and ratios of mineral fertilizers in field crop rotation. With full mineral fertilizer (N110P60K80) for eight years, the humus content in the 0–20 cm layer of chernozem increased by 10 % compared with the areas with no fertilizers (from 3.71 to 4.09 % on average in four fields of crop rotation). In the soil layer of 20-40 cm, the changes were unreliable. The humus reserves in the 0–20 cm layer of soil have most decreased with no fertilizers and under P60K80 and N110K80 fertilization (by 2.0–4.2 t/ha), and the most increase in humus reserves in this soil layer as compared to the initial level was noted in variants of the experiment with N110P60K80 and N110P60K40 fertilization (by 6.9 and 5.8 t/ha, respectively). Conclusions. The direction of soil formation processes and the level of soil fertility depend on fertilizer types, doses, and ratios. The most humus loss in the soil layer of 0–20 cm occurred in areas with no fertilizers (by 3 %) and in the experiment variant N110K80 (by 4 %). The N55P30K40, N110P30K40, and N110P30K80 fertilizer systems generally provide for the restoration of humus content in soil layer of 0–40 cm, but the most increase in soil humus content was observed in the experiment variant N110P60K80 and N110P60K40 at which humus reserves increased by 6.4–8.1 t/ha. Non-commodity part of the crop in plant mass composition entering the soil after harvesting crops is 47–51 % depending on the fertilizer and is an important source of restoring the humus content.