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The formation of soil aggregates, including water-stable aggregates, is linked to soil organic matter (SOM). Biochar (B) is carbon-rich, which, in addition to storing carbon in a stable form for many years, has important benefits for soils and plants, but the mechanisms of soil structure formation after B and mineral fertiliser application are not sufficiently studied. For this reason, the study aimed to answer the following questions: How (1) the rate of B and (2) varying levels of nitrogen fertiliser (N) being applied to the soil affect the dynamics of soil aggregation due to the increase in the content of soil organic carbon, labile carbon in the bulk soil and in the content of water-stable aggregates (WSA) size-fractions. In 2014–2021, in Dolná Malanta (experimental site of Slovak University of Agriculture on silty loam Haplic Luvisol) during the growing seasons, soil samples were collected from all the B (0, 10 and 20 t ha–1) and N (0, 1st and 2nd level of N fertilisation) treatments. The results have shown that the highest values of many variables were associated with B20 treatment for all the N fertilisation levels. B compared to N more significantly affected the content of almost all the size-fractions of WSA. In all the treatments, the content of WSAma >5 mm, 5–3 mm, 3–2 mm and 1–0.5 mm in size was increasing over time – a yearly increase from 0.31 to 2.14% for 8-years. Based on the changes in the SOM content, WSA were divided into 3 groups: 1) Water-stable microaggregates (WSAmi < 0.25 mm), 2) Smaller size-fractions of water-stable macroaggregates (WSAma 1–0.25 mm), and 3) Medium and large fractions of WSAma (WSAma ≥1 mm).

Wheat is one of the modern world's staple food sources. Its production requires good environmental conditions, which are not always available. However, agricultural practices may mitigate the effects of unfavorable weather or poor-quality soils. The influence of environmental and crop management variables on yield can be evaluated only based on representative long-term data collected on farms through well-prepared surveys. The authors of this work analyzed variation in winter wheat yield among 3868 fields in western and eastern Poland for 12 years, as dependent on both soil/weather and crop management factors, using the classification and regression tree (CART) method. The most important crop management deficiencies which may cause low wheat yields are insufficient use of fungicides, phosphorus deficiency, non-optimal date of sowing, poor quality of seeds, failure to apply herbicides, lack of crop rotation, and use of cultivars of unknown origin not suitable for the region. Environmental variables of great importance for the obtaining of high yields include large farm size (10 ha or larger) and good-quality soils with stable pH. This study makes it possible to propose strategies supporting more effective winter wheat production based on the identification of characteristics that are crucial for wheat cultivation in a given region. [ABSTRACT FROM AUTHOR]