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.

If we want to develop farming on soil effectively and ecologically, we have to know the soil characteristics, the reasons for the potential low fertility and the ways how to eliminate them. Only this approach allows the rational utilization of the soil fund and achievement of the high effectiveness of the costs needed for the stabilization and increase of fertility and land capability. Recently, many scientific teams have focused their attention on the biochar, a lot of recommendations have been published which are dealing with its application into soil. However, the principal attention has been drawn to the impact of biochar on the particular soils and under the particular conditions. Far less information has been presented about the mutual interactions between the further significant agronomical factors in the combination with biochar. In this primary study, we analyze two new experiments established in the southwest part of Slovakia at the 1 Dolná Streda (sandy soil) and 2 Veľké Uľany (loamy soil) Localities. We discussed (1) the impact of the individual factors on the changes of soil characteristics, and (2) the impact of the individual interactions, such as: soil class-fertilization-biochar on the changes of the soil characteristics. The results indicated that the most significant factor, which influences the monitored soil parameters, is the soil class. The fertilization proved to be a factor which has a negative impact on the humus parameters; on the other hand, it improved the soil sorption. Biochar increased the content of the organic substances in soil and also its environmental effect of retention and immobilization of harmful elements and its positive effect on the soil structure was indicated. The highest frequency of the interactions between the monitored parameters related to the changes of soil characteristics was recorded in the combination fertilization x biochar, and also the soil class x fertilization x biochar.

The effects of biochar and biochar combined with N-fertilizer on the content of soil organic matter in water-stable aggregates were investigated. 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 levels of nitrogen fertilization on silt loam Haplic Luvisol (Dolna Malanta, Slovakia), in 2014. The N doses of level 1 were calculated on required average crop production using balance method. Level 2 included additional 100% of N in year 2014 and additional 50% of N in year 2016. The effects were investigated during the growing seasons of spring barley and spring wheat in 2014 and 2016, respectively. Results indicate that the B20N2 treatment significantly increased the proportion of water-stable macro-aggregates (WSAma) and reduced water-stable micro-aggregates (WSAmi). Aggregate stability increased only in the B20N1 treatment. The B20N2 treatment showed a robust decrease by 27% in the WSAma of 0.5-0.25 mm. On the other hand, an increase by 56% was observed in the content of WSAma with fractions 3-2 mm compared to the B0N0 treatment. The effect of N fertilizer on WSAma was confirmed only in the case of the B10N2 treatment. The proportion of WSAma with fractions 3-2 mm decreased by 42%, while the size fraction of 0.5-0.25 mm increased by 30% compared to the B10N0 treatment. The content of WSAma with fractions 1-0.5 mm decreased with time. On the contrary, the content of WSAma with particle sizes above 5 mm increased with time in all treatments except the B10N2 and B20N2 treatments. A statistically significant trend was identified in the proportion of WSA in the B10N2 and B20N2 treatments, which indicates that biochar with higher application levels of N fertilizer stabilizes the proportion of water-stable aggregates. In all treatments, the content of soil organic carbon (SOC) and labile carbon (CL) in WSAmi was lower than those in WSAma. A considerable decrease of SOC in the WSAma >5 mm and an increase of SOC in WSAmi were observed when biochar was applied at the rate of 10 t ha-1. Contents of SOC in WSAmi increased as a result of adding biochar combined with N fertilizer at first level. CL in WSA significantly increased in all size fractions of WSA.References Abiven S., Hund A., Martinsen V., Cornelissen G., 2015. Biochar amendment increases maize root surface areas and branching: a shovelomics study in Zambia. Plant Soil, 342, 1-11. Agegnehu G., Bass A.M., Nelson P.N., and Bird M.I., 2016. Benefits of biochar, compost and biochar–compost for soil quality, maize yield and greenhouse gas emissions in a tropical agricultural soil. Sci. Tot. Environ., 543, 295-306. Angers D.A., Samson N., Legere A., 1993. Early changes in water-stable aggregation induced by rotation and tillage in a soil under barley production. Can. J. Soil Sci., 73, 51-59. Atkinson Ch.J., Fitzgerald J.D., Hipps N.A., 2010. Potential mechanisms for achieving agricultural benefits from biochar application to temperate soils: a review. Plant Soil, 337, 1-18. Balashov E., Buchkina N., 2011. Impact of short- and long-term agricultural use of chernozem on its quality indicators. Int. Agrophys., 25, 1-5. Barrow C.J., 2012. Biochar: potential for countering land degradation and for improving agriculture. Appl. Geogr., 34, 21-28. Barthes B.G., Kouakoua E.T., Larre-Larrouy M.C., Razafimbelo T.M., De Luca E.F., Azontonde A., Neves C.S.V.J., De Freitas P.L., Feller C.L., 2008. Texture and sesquioxide effects on water-stable aggregates and organic matter in some tropical soils. Geoderma, 143, 14-25. Benbi D.K., Brar K., Toor A.S., Sharma S., 2015. Sensitivity of labile soil organic carbon pools to long-term fertilizer, straw and manure management in rice-wheat system. Pedosphere, 25, 534-545. Benbi D.K., Brar K., Toor A.S., Singh P., Singh H., 2012. Soil carbon pools under poplar-based agroforestry, rice-wheat, and maize-wheat cropping systems in semi-arid India. Nutr. Cycl. Agroecosys., 92, 107-118. Blanco-Canqui H., Lal L., 2004. Mechanisms of carbon sequestration in soil aggregates. Crit. Rev. Plant Sci., 23, 481-504. Brevik E.C., Cerda A., Mataix-Solera J., Pereg L., Quinton J.N., Six J., Van Oost K., 2015. The interdisciplinary nature of SOIL. SOIL, 1, 117-129. Brodowski S., John B., Flessa H., Amelung W., 2006. Aggregate-occluded black carbon in soil. Eur. J. Soil Sci., 57, 539-546. Bronick C.J., Lal R., 2005. The soil structure and land management: a review. Geoderma, 124, 3-22. Chenu C., Plante A., 2006. Clay-sized organo-mineral complexes in a cultivation chronosequece: revisiting the concept of the “primary organo-mineral complex”. Eur. J. Soil Sci., 56, 596-607. Dziadowiec H., Gonet S.S., 1999. Methodical guide-book for soil organic matter studies.  Polish Society of Soil Science, Warszawa, 65p. Elliott E.T., 1986. Aggregate structure and carbon, nitrogen, and phosphorus in native and cultivated soils. Soil Sci. Soc. Am. J., 50, 627-633. Fischer D., Glaser B., 2012. Synergisms between compost and biochar for sustainable soil amelioration, In: Kumar S. (ed.): Management of Organic Waste, In Tech Europe, Rijeka, 167-198. Glaser B., Lehmann J., Zech W., 2002. Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal - a review. Biol. Fertil. Soils., 35, 219-230. Heitkotter J., and B. Marschner, 2015. Interactive effects of biochar ageing in soils related to feedstock, pyrolysis temperature, and historic charcoal production. Geoderma, 245-246, 56-64. Herath H.M.S.K., Camps-Arbestain M., Hedley M., 2013. Effect of biochar on soil physical properties in two contrasting soils: an Alfisol and an Andisol. Geoderma, 209-210, 188-197. Hillel D., 1982, Introduction to soil physics. Academic Press, San Diego, CA , 364 p. Chenu C., Plante A., 2006. Clay-sized organo-mineral complexes in a cultivation chronosequence: revisiting the concept of the “primary organo-mineral complex”. Eur. J. Soil Sci., 56, 596-607. IUSS Working Group WRB., 2014. World reference base for soil resources 2014. International soil classification system for naming soils and creating legends for soil maps. World Soil Resources Reports, 106, FAO, Rome., 112p. Jeffery S., Verheijen F.G.A., Van der Velde M., Bastos A.C., 2011. A quantitative review of the effects of biochar application to soils on crop productivity using meta-analysis. Agr. Ecosys. Environ., 144, 175-187. Jien S.H., Wang Ch.S., 2013. Effects of biochar on soil properties and erosion potential in a highly weathered soil. Catena, 110, 225-233. Kammann C., Linsel S., Goßling J., Koyro H.W., 2011. Influence of biochar on drought tolerance of Chenopodium quinoa Willd and on soil-plant relations. Plant Soil, 345, 195-210. Kodesova R., Nemecek K., Zigova A., Nikodem A., Fer M., 2015. Using dye tracer for visualizing roots I pact on soil structure and soil porous system. Biologia, 70, 1439-1443. Krol, A., Lipiec, J.,  Turski, M., J. Kuoe, 2013. Effects of organic and conventional management on physical properties of soil aggregates. Int. Agrophys., 27, 15-21. Kurakov A.V., Kharin S.A., 2012. The Formation of Water-Stable Coprolite Aggregates in Soddy-Podzolic Soils and the Participation of Fungi in This Process. Eur. Soil Sci., 45, 429-434. Loginow W., Wisniewski W., Gonet S.S., Ciescinska B., 1987. Fractionation of organic carbon based on susceptibility to oxidation. Pol. J. Soil Sci., 20, 47-52. Lynch, J.M., and E. Bragg, 1985. Microorganisms and soil aggregate stability. Adv. Soil Sci., 2, 133-171. MHYPERLINK "about:blank"unkholm L.J., Schjonning P., Debosz K., Jensen H.E., Christensen B.T., 2002. Aggregate strength and mechanical behaviour of a sandy loam soil under long-term fertilization treatments. Eur. J. Soil Sci., 53, 129-137. Paradelo R., Van Oort F., Chenu C., 2013. Water-dispersible clay in bare fallow soils after 80 years of continuous fertilizer addition. Geoderma, 200-201, 40-44. Purakayastha T.J., Kumari S., Pathak H., 2015. Characterisation, stability, and microbial effects of four biochars produced from crop residues. Geoderma, 239-240, 293-303. Rees F., Germain C., Sterckeman T., Morel J.L., 2015. Plant growth and metal uptake by a non-hyperaccumulating species (Lolium perenne) and a Cd-Zn hyperaccumulator (Noccaea caerulescens) in contaminated soils amended with biochar. Plant Soil, 395, 57-73. Saha D., Kukal S.S., Sharma S., 2011. Land use impacts on SOC fractions and aggregate stability in typic Ustochrepts of Northwest India. Plant Soil, 339, 457-470. Six J., Bossuyt H., Degryze S., Denef  K., 2004. A history of research on the link between (micro)aggregates, soil biota, and soil organic matter dynamics. Soil Till. Res., 79, 7-31. Six J., Elliott E.T., Paustian K., 2000. Soil macroaggregate turnover and microaggregate formation: A mechanism for C sequestration under no-tillage agriculture. Soil Biol. Biochem., 32, 2099-2103. Soinne H., Hovi J., Tammeorg P., Turtola E., 2014. Effect of biochar on phosphorus sorption and clay soil aggregate stability. Geoderma, 219-220, 162-167. Simansky V., 2013. Soil organic matter in water-stable aggregates under different soil management practices in a productive vineyard. Arch. Agron. Soil Sci., 59(9), 1207-1214. Simansky V., Jonczak J., 2016. Water-stable aggregates as a key element in the stabilization of soil organic matter in the Chernozems. Carp. J. Earth Environ. Sci., 11, 511-517. Simon T., Javurek M., Mikanova O., Vach M., 2009. The influence of tillage systems on soil organic matter and soil hydrophobicity. Soil Till, Res., 105, 44-48. Tiessen H., Stewart J.W.B., 1988. Light and electron microscopy of stainedmicroaggregates: the role of organic matter and microbes in soil aggregation. Biogeochemistry, 5, 312-322. Tisdall J.M., Oades J.M., 1980. The effect of crop rotation on aggregation in a red-brown earth. Austr. J. Soil Res., 18, 423-433. Vadjunina A.F., Korchagina Z.A., 1986. Methods of Study of Soil Physical Properties. Agropromizdat, Moscow, 415p. Vaezi A.R., Sadeghi S.H.R., Bahrami H.A., Mahdian M.H., 2008. Modeling the USLE K-factor for calcareous soils in northwestern Iran. Geomorphology, 97, 414-423. Von Lutzow M., Kogel-Knabner I., Ekschmitt K., Matzner E., Guggenberger G., Marschner B., Flessa H., 2006. Stabilization of organicmatter in temperate soils:mechanisms and their relevance under different soil conditions a review. Eur. J. Soil Sci., 57, 426-445.

In recent years, the importance of biochar application in world´s soils have increased tendency mainly due to its opposite effects. Therefore, the effort of many companies is based on the development of soil amendment which together improve properties and crop productivity in lot of soils. In this short study, we have verified the effectiveness of biochar blended with farmyard manure named Effeco on soil properties and crop yields in different textural soils (1. sandy soil in Dolná Streda and 2. loamy soil in Veľké Uľany). Our results showed that the Effeco increased soil pH in both soils. In sandy soil, the Effeco more significantly affected sorptive parameters and soil organic carbon content than in loamy soil. Water retention in capillary pores after Effeco application in sandy and loamy soils was higher by 22% and 4%, respectively compared to control. On the other hand, more significant effect of Effeco application on soil structure was observed in loamy soil. The total crop productions in sandy and loamy soils due to the Effeco application were higher by 82% and 16%, respectively, compared to control plots. All in all, we concluded that the effects of biochar blended with farmyard manure differ mainly on soil texture.

Scientific studies show that the efficiency of biochar can be improved by its combination with other fertilisers. For this reason, fertiliser manufacturers are working to create products that combine biochar with other soil fertility enhancers suitable for different soil-climatic conditions. In this study, two types of biochar substrates (1. biochar blended with farmyard manure, and 2. biochar blended with farmyard manure as well as with digestate) at rates of 10 and 20 t/ha were applied alone or in combination with other manure and mineral fertilisers. These were added to Arenosol (sandy soil, Dolná Streda, Slovakia) and Chernozem (loamy soil, Veľké Úľany, Slovakia) to evaluate the soil physical properties to test the potential of these amendments for soil amelioration in texturally different soils. The results showed that the application of biochar substrates alone increased soil moisture, the volume of capillary pores, and decreased aeration and volume of non-capillary pores. The application of biochar substrates with mineral fertilisers increased aeration, content of water-stable macro-aggregates (WSAma), total porosity, and decreased soil moisture and the content of water-stable micro-aggregates (WSAmi) in sandy soil. In loamy soil, when compared to unfertilised control, the biochar treatments increased content of WSAma, content of dry-sieved macro-aggregates, and decreased content of WSAmi and content of dry-sieved micro-aggregates. The combination of biochar substrates together with manure had no effect on changes in the physical properties of loamy soil.