During the last decade, biochar has captured the attention of agriculturalists worldwide due to its positive effect on the environment. To verify the biochar effects on organic carbon content, soil sorption, and soil physical properties under the mild climate of Central Europe, we established a field experiment. This was carried out on a silty loam Haplic Luvisol at the Malanta experimental site of the Slovak Agricultural University in Nitra with five treatments: Control (biochar 0 t ha–1, nitrogen 0 kg ha–1); B10 (biochar 10 t ha–1, nitrogen 0 kg ha–1); B20 (biochar 20 t ha–1, nitrogen 0 kg ha–1); B10+N (biochar 10 t ha–1, nitrogen 160 kg ha–1) and B20+N (biochar 20 t ha–1, nitrogen 160 kg ha–1). Applied biochar increased total and available soil water content in all fertilized treatments. Based on the results from the spring soil sampling (porosity and water retention curves), we found a statistically significant increase in the soil water content for all fertilized treatments. Furthermore, biochar (with or without N fertilization) significantly decreased hydrolytic acidity and increased total organic carbon. After biochar amendment, the soil sorption complex became fully saturated mainly by the basic cations. Statistically significant linear relationships were observed between the porosity and (A) sum of base cations, (B) cation exchange capacity, (C) base saturation.
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.
Recent studies show that biochar improves physical properties of soils and contributes to the carbon sequestration. In contrast to most other studies on biochar, the present study comprise a long-term field experiment with a special focus on the simultaneous impact of N-fertilizer to soil structure parameters and content of soil organic carbon (SOC) since SOC has been linked to improved aggregate stability. However, the question remains: how does the content of water-stable aggregates change with the content of organic matter? In this paper we investigate the effects of biochar alone and in a combination with N-fertilizer (i) on the content of water-stable macro- (WSAma) and micro-aggregates (WSAmi) as well as soil structure parameters; and (ii) on the contents of SOC and labile carbon (CL) in water-stable aggregates (WSA).
A field experiment was conducted with different biochar application rates: B0 control (0 t ha–1), B10 (10 t ha–1) and B20 (20 t ha–1) and 0 (no N), 1st and 2nd level of nitrogen fertilization. The doses of level 1 were calculated on required average crop production using the balance method. The level 2 included an application of additional 100% of N in 2014 and additional 50% of N in the years 2015–2016 on silty loam Haplic Luvisol at the study site located at Dolná Malanta (Slovakia). The effects were investigated after the growing season of spring barley, maize and spring wheat in 2014,
2015 and 2016, respectively. The results indicate that the B10N0 treatment significantly decreased the structure vulnerability by 25% compared to B0N0. Overall, the lower level of N combined with lower doses of biochar and the higher level of N showed positive effects on the average contents of higher classes of WSAma and other soil structure parameters. The content of SOC in WSA in all size classes and the content of CL in WSAma 3–1 mm significantly increased after applying 20 t ha–1 of biochar compared to B0N0. In the case of the B20N1 treatment, the content of SOC in WSAma within the size classes >5 mm (8%), 5– 3 mm (19%), 3–2 mm (12%), 2–1 mm (16%), 1–0.5 mm (14%), 0.5–0.25 mm (9%) and WSAmi (12%) was higher than in B0N1. We also observed a considerably higher content of SOC in WSAma 5–0.5 mm and WSAmi with the B10N1 treatment as compared to B0N1. Doses of 20 t biochar ha–1 combined with second level of N fertilization had significant effect on the increase of WSAma and WSAmi compared to the B0N2 treatment. A significant increase of CL in WSA was determined for size classes of 2–0.25 mm and WSAmi in the B20N2 treatment. Our findings showed that biochar might have beneficial effects on soil structure parameters, SOC, CL in WSA and carbon sequestration, depending on the applied amounts of biochar and nitrogen.
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.