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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).

Biochar application to agriculture soil has been recommended as a strategy to reduce increasing CO2 emission in the atmosphere and mitigate climate change. In this study, we evaluated the impact of two doses of biochar (10 and 20 t.ha−1) applied in 2014 and reapplied in 2018 combined with three fertilization levels (N0, N1, N2) on carbon dioxide emissions and selected physical and chemical soil properties in field conditions during spring season (April–June) in 2020. The field site is situated in the Nitra region of Slovakia (Malanta). The soil in the field was classified as a silt loam Haplic Luvisol. In this field research it was found that biochar application mostly in all treatments decreased cumulative CO2 emissions in rage from 4.2% to 30.4% compared to controls (B0N0, B0N2), except treatments where biochar was applied with lower level of N-fertilizer (N1) and treatment B20N0. According to our study results, it was confirmed that biochar can be a promising material for improving soil physical and chemical properties. Mainly, it has very good impact on soil pH, even after seven years of field experiment established. However, the response of soil CO2 fluxes to biochar application were regulated mainly by experiment length, biochar application rate, biochar properties, giving a new perspective for more comprehensive understanding on biochar.

Biochars, depending on the types of feedstocks and technological conditions of pyrolysis, can vary significantly in their properties and, therefore, it is difficult to predict biochar-induced effects on nitrous oxide (N2O) emissions from various soils, their physical properties and water availability. The objectives of this study were (1) to quantify effects of slow pyrolysis biochar (BC) and fast pyrolysis biochar (PYRO) on physical and hydro-physical properties of sandy soil (Haplic Arenosol) and clayey loam soil (Gleyic Fluvisol), and (2) to assess corresponding N2O emissions from these two soils. The study included a 63-day long laboratory investigation. Two doses of BC or PYRO (15 t ha−1 and 30 t ha−1) were applied to the soils in combination or without nitrogen fertilizer (NH4NO3, 90 kg N ha−1). The obtained results have shown a significant decrease in the bulk density of sandy soil after it was amended with either rate of BC or PYRO. Water retention capacity of the soils in all the treatments with BC or PYRO increased considerably although no changes was found in the soil water-filled pore space (WFPS) which was higher than 60%. BC was increasing N2O emission rates from the sandy soil treated with N fertilizer, and reducing N2O emission rates from the clayey loam soil treated with N fertilizer. PYRO was more efficient and was reducing N2O emissions from both fertilized soils, but for the sandy soil the reduction was statistically significant only at higher dose (30 t ha−1) of the biochar.

Biochar can affect CO2 emission and C sequestration from soils, but little is known about the effects of its re-application and interaction with easily accessible substrates. Since most agricultural soils are continuously reworked, understanding the mechanics of CO2 evolution as affected by soil amendments and their combinations may have important lessons for the global effort to combat climate change. In this study carried out in a controlled environment, we tested the short-term effects of biochar, and its re-application at different rates, on the production of CO2 emission and C accumulation in samples of arable soils. We used a loamy Haplic Luvisol as the substrate and added varying amounts of biochar and sources of easily accessible N and C. We observed CO2 evolution for 20 days at optimal temperature and moisture conditions. We found that in the control treatment with no biochar, the total potential respiration after the addition of (NH4)2SO4 (N) and glucose (G) was increased compared to basal respiration. The addition of biochar reduced CO2 emission in the control, N- and G-stimulated treatments by 12–22, 13‒24 and 2‒21%, respectively. Conversely, the application of biochar increased CO2 emission in the combined NG treatment. Application of biochar at a higher rate, as well as its re-application, increased soil organic carbon content and reduced emission of CO2 into the atmosphere.

Biochar application into soil has potential as a means for reducing soil greenhouse gas emissions and climate mitigation strategy. In this study, we evaluated the impact of two doses of biochar (10 and 20 t.ha−1) applied in 2014, combined with three fertilization levels (N0, N1, N2) on carbon dioxide (CO2) in field conditions during the growing season (April – October) in 2018. The field site is located in the Nitra region of Slovakia – Malanta. The soil in the field was classified as a silt loam Haplic Luvisol. There was not found any statistically significant (P 2 emissions, while the CO2 emissions increased with additional N-fertilizer. Biochar decreased (insignificantly) the daily and cumulative CO2 emissions only in the treatments without N-fertilization and in the treatment fertilized with higher level of biochar application (20 t.ha−1) and N-fertilizer (80 kg.N.ha−1). According to these results it can be concluded that the biochar applied to soil is not able to reduce CO2 emissions after four years of its application when it is combined with usual agriculture practices which include N-fertilization.

Current biochar application in the global agronomic practice focuses firstly on economic profits. In this paper, we would like to draw attention to our results and experience from the economic assessment of the agronomic effect of applied biochar through the generated crop yields. The results come from a field experiment (locality Dolná Malanta, Slovakia, silt loam Haplic Luvisol – the most intensively used soil in the Slovak Republic for agricultural purposes), where a biochar experiment was established in 2014. Based on our data, it is evident that both the application of biochar and its application in combination with N-fertilisation in field conditions at current realization prices of commodities in individual years and high input costs are still unprofitable. However, we emphasize that from an economic point of view of the stand ard agronomic practice.

The paper presents evaluation of the calibration method using side-by-side direct gravimetric and indirect time domain reflectometry (TDR) for soil moisture measurements to improve TDR measurement accuracy. Measurements were carried out at the experimental site Dolná Malanta (Slovakia) in 2017. Two non-fertilized treatments – without biochar (B0 + N0) and with biochar at 20 t·ha−1 (B20 + N0) – and two fertilized treatments – with biochar at 20 t·ha−1 and N fertilizer at dosages of 160 kg·ha−1 (B20 + N160) and 240 kg·ha−1 (B20 + N240) – were used in this study. The study also investigates the relationship between both used methods of soil water content determination. A strong correlation between both methods was observed. In case of (B0 + N0); (B20 + N0); (B20 + N160); and (B20 + N240), it was 0.93; 0.97; 0.97; and 0.98, respectively. However, it is assumed that the TDR probe may show errors in the results without prior calibration. It was observed that the accuracy of TDR device was lower for fertilized treatments in contrast to the gravimetric method and non-fertilized treatments. It is assumed that the higher measurement inaccuracy might be increased by salt concentration in the soil as a result of applied N fertilizer.

The objectives of the study were to: (1) assess the strength of associations of direct CO2 and N2O emissions with the seasonal variations in the relevant soil properties under both tillage systems; 2) evaluate how CT and RT affect magnitudes of seasonal CO2 and N2O fluxes from soil. Field studies were carried out on plots for conventional tillage (up to 0.22–0.25 m) and reduced tillage (up to 0.10–0.12 m) during the growing season and post-harvest period of red clover. The results showed that daily CO2 emissions significantly correlated only with soil temperature during the growing season under conventional and reduced tillage. Soil temperature demonstrated its highest influence on daily N2O emissions only at the beginning of the growing season in both tillage systems. There were no significant inter-system differences in daily CO2 and N2O emissions from soil during the entire period of observations. Over the duration of post-harvest period, water-filled pore space was a better predictor of daily CO2 emissions from soils under CT and RT. The conventional and reduced tillage did not cause significant differences in cumulative N2O and CO2 fluxes from soil.

Nowadays, there are various methods of plant biomass assessment available for the purposes of plant growth analysis. Visual plant coverage assessment is often subjective; the other methods are destructive or require purchasing some special devices. This paper presents the assessment of the possibilities and limitations of using digital images made by conventional digital cameras for the purposes of monitoring of the plant canopy development and weed distribution during a vegetation period using the example from the field experiment established on agricultural land in Malanta at the experimental site of the Slovak University of Agriculture. The study is focused on assessment of the effect of biochar application on gas emission, hydrophysical soil properties as well as plant response and yields and it was established in the spring of 2014. Downward images of corn (Zea maysL.) were taken during four sampling campaigns in the vegetation season 2015. Images were analysed by the BreedPix software that could estimate the portion of green fraction (count of green pixels) and thus the image-derived vegetation index (IDVI). According to the image analysis of photos taken during different sampling dates, it could be concluded that biochar addition had a positive effect on the plant growth (above ground biomass) since all treatments resulted in higher IDVIs at the end of the vegetative growth in comparison to control. Further, we assume that the increasing trend in the crop canopy growth was partially limited by competitive presence of weeds at the beginning of the study. According to our experience, we can recommend the software for temporal and spatial monitoring of agricultural crops development. The usage is limited to early growth stages. Moreover, it can be also used for assessment of the weed coverage.

An important method of investigating N2O emissions from cropland is model simulation. The measured data of N2O emissions under conventional tillage (CT) and reduced tillage (RT) with (N1) and without (N0) N fertilizer application were used to test the DNDC model during the year 2012 (April-December) in Slovakia. There was found a good agreement with seasonal N2O emissions only for CTN0 treatment, but in case of other treatments DNDC overestimated the emissions. The relative deviation between observed and simulated total seasonal N2O emissions (kg N ha−1) from four treatments were 46%, 164%, 346% and 321% for CTN0, CTN1, RTN0 and RTN1, respectively. Also, some discrepancies were found between observed and simulated emissions when evaluating the daily N2O emissions, especially when looking at the magnitude of N2O emissions peaks. The correlation between observed and simulated daily N2O emissions (N = 38) in case of conventional tillage was quite high and significant with r = 0.48 (P r = 0.45 (P r = 0.22 (P >0.01) and r = 0.39 (P >0.01), for RTN0, RTN1, respectively.

The effect of fertilisation on C and N, P, K nutrients distribution in the Rendzic Leptosol in locality Nitra-Dražovce was studied. We evaluated the following treatments of fertilisation: (1) G (non-fertilised), (2) FYM (farmyard manure – dose 40 t/ha), (3) G+NPK3 (grass + 3rd intensity of fertilisation for vineyards), and (4) G+NPK1 (grass + 1st intensity of fertilisation for vineyards). The soil samples were taken in spring during the years 2008–2015. Obtained results showed that the content of organic carbon (Corg) decreased in the following order: G+NPK1 > FYM > G > G+NPK3 and content of total nitrogen (Nt) decreased in the following order: FYM > G+NPK3 > G+NPK1 > G. The application of NPK in the 1st intensity of fertilisation for vineyards and added FYM build up a Corg at an average rate of 370 and 229 mg/kg/year, respectively. On the other hand, contents of Nt due to fertilisation declined in FYM, G+NPK3 and G+NPK1 at an average rate of 53, 22 and 20 mg/kg/year, respectively. Available P and K contents were also increased after the fertilisation of FYM and NPK. Added fertilisers (G+NPK3) significantly build up a P at an average rate of 10.2 mg/kg/year.

One-year field experiment with spring barley (Hordeum vulgare L.) was carried out to evaluate the effect of biochar amendment on the pH of Orthic Luvisol at the research site located in western Slovakia (lat. 48° 19′ 00″; lon. 18° 09′ 00″). Biochar with higher pH (8.8) was applied to slightly acidic soils with the initial pH at 5.6. The field experiment consisted of control, 10 and 20 t ha−1 (B0, B10, B20) of biochar application to soils combined with three levels of nitrogen fertilization (0, 40 and 80 kg N ha−1) (N0, N40, N80). The soil pH (KCl) at depth 0–10 cm was measured once a month (March – October, 2014). Application of both biochar rates (10 and 20 t ha−1) increased pH (in all months) with the magnitude of 0.13–1.09 units in all three fertilization levels (0, 40 and 80 kg N ha−1) compared to the control one. However, the significant increase (p