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The objectives of the research were to: (1) assess the strength of relationships between the soil thermal and hydrophysical properties, (2) evaluate the strength of association of evapotranspiration of spring wheat crop with soil thermal and hydrophysical properties, and (3) estimate the ranges of the thermal and hydrophysical properties of the sandy Haplic Podzol during the growing period of spring wheat in 2022. The study included instrumental simultaneous measurements of meteorological data, soil water retention curve, soil moisture content (SMC) and thermal properties. Actual evapotranspiration was calculated according to the Allen equation. Spearman’s rank correlation coefficients showed that the increase in SMC from 0.10 cm3 cm−3 to 0.26 cm3 cm−3 resulted in a significant increase in thermal conductivity (r = 0.81, p < 0.001), volumetric heat capacity (r = 0.93, p < 0.001) and thermal diffusivity (r = 0.94, p < 0.001). Actual evapotranspiration also rose with the increasing SMC (r = 0.91, p < 0.001) and matric water potentials (r = 0.61, p < 0.05). As a consequence of the changes in SMC, the Spearman’s rank correlation coefficients supported the strong positive relationships of actual evapotranspiration with volumetric heat capacity (r = 0.97, p < 0.001), thermal conductivity (r = 0.96, p < 0.001) and thermal diffusivity (r = 0.96, p < 0.001). Pearson correlation coefficients also supported the strong input of thermal inertia to the actual evapotranspiration (r = 0.88, p < 0.01). During the whole period of observations, actual evapotranspiration varied from 0.05 to 0.59 mm hr−1, soil thermal conductivity – from 0.225 to −1.056 W m−1 K−1, volumetric heat capacity – from 1.057 to 1.889 MJ m–3 K−1, heat diffusivity from 0.189 to 0.559 mm2 s−1, and thermal inertia – from 516 to 1412 J m−2 K−1 s−0.5.

It was shown that the use of biochar provides many benefits to agriculture by improving the whole complex of soil properties, including soil structure. However, the diverse range of biochar effects depends on its physicochemical properties, its application rates, soil initial properties etc. The impacts of biochar, mainly its reapplication to soils and its interaction with nitrogen in relation to water-stable aggregates (WSA) did not receive much attention to date. The aims of the study were: (1) to evaluate the effect of initial application (in spring 2014) and reapplication (in spring 2018) of different biochar rates (B0, B10 and B20 t ha−1) as well as application of biochar with N-fertilizer (40 to 240 kg N ha−1 depending on the requirement of the cultivated crop) on the content of WSA as one of the most important indicators of soil structure quality, (2) to assess the interrelationships between the contents of soil organic matter (SOM) and WSA. The study was conducted in 2017–2019 as part of the field experiment with biochar on Haplic Luvisol at the experimental station of SUA in Nitra, Slovakia. Results showed that initial application as well as reapplication of biochar improved soil structure. The most favorable changes in soil structure were found in N0B20B treatment (with biochar reapplication) at which a significantly higher content of water-stable macro-aggregates (WSAma) (+15%) as well as content of WSAma size fractions of > 5 mm, 5–3 mm, 3–2 mm and 2–1 mm (+72%, +65%, +57% and +64%, respectively) was observed compared to the control. An increase in SOM content, due to both, initial biochar application and its reapplication, significantly supported the stability of soil aggregates, while organic matter including humic substances composition did not.

Soils are one of the main sources of nitrous oxide (N2O) in agriculture. Soil management practices can significantly affect N2O emissions through changing soil physical, chemical and biochemical properties. Application of biochar to arable soils can be an option for N2O emission mitigation, but the effect of biochar can be different for soils with different fertility levels. The objective of this study was to evaluate the effect of biochar application on N2O emission, soil properties and barley yield from loamy sand Stagnic Luvisol with high and medium levels of fertility caused by high rates of farmyard manure and fertilizer application for 10 years. A small-scale field experiment was conducted during the growing season of 2012 in North-Western Russia. Four treatments were used in the experiment: 1) control (no biochar, no N-fertilizer), 2) biochar (12 t ha-1), 3) N-fertilizer (90 kg ha-1 N) and 4) biochar (12 t ha-1) + N-fertilizer (90 kg ha-1 N), in five replicates. Significant changes in water-holding capacity and the amount of available nitrogen (N) occurred in the soil with high fertility, and thus it emitted significantly more N2O for the growing season than the soil with medium fertility. Biochar application effect on N2O emissions depended on the soil management history and was reducing the emission from the soil with high fertility rich in mineral N and C but not from the soil with medium fertility if no nitrogen fertilizer was applied to the latter soil. The yield-scaled N2O emission was the highest from the control treatments for the soil with both fertility levels, and the soil with high fertility was always characterized by higher yield-scaled N2O emissions than the soil with medium fertility. Application of biochar reduced yield-scaled N2O emission from the soil with medium and high fertility levels showing that biochar application to the soil can improve N use by the plants. [ABSTRACT FROM AUTHOR]