Improving the soil physical properties and relationships between soil properties in arable soils of contrasting texture enhancement using biochar substrates: Case study in Slovakia

In the agricultural sector, the soil's physical and hydrological properties become a limiting factor in achieving sufficient crop yields. Biochar has emerged as a significant source of organic carbon and a tool for its sequestration and there are identified significant relationships between soil agricultural properties induced by biochar application with that of soil physical and hydrological properties. However, underlying mechanisms for changes in some physical and hydrological properties of the soil are not fully understood due to insufficient data resulting in a poor understanding of the interconnection among properties in biochar substrates amended soils. Therefore, we studied the impact of two different biochar substrates (BS: BS1 - biochar blended with farmyard manure, and BS2 - biochar blended with farmyard manure and digestate) at two rates (10 and 20 t ha-1) combined alone and with additional fertilization (F) on two contrasting soils. The two contrasting soils included a sandy Arenosol, and a loamy Chernozem in south-western Slovakia. The changes in soil physical properties and interrelationships between soil pH, sorption capacity, soil organic matter (SOM), humic substances (HS), and physical properties was regularly monitored in the field for a three-year period (2018-2020). The results showed that biochar substrates had different effects with dependence on soil textures. In sandy soil, BS improved soil properties such as pore size distribution, soil-air content, and water regimes, including water retention capacity (WRC), and soil structure. The most significant effects were determined in the case of BS compared to BS + F, and in the case of 20 than 10 t ha-1 as well as in BS1 than BS2 in sandy soil. In loamy soil, compared to the control, the volume of non-capillary pores (Pnc) values decreased significantly (by 29%) in the BS1 10 t ha-1 treatment, while in the case of BS + F a significant decrease in Pnc was observed after application of both rates of BS1 compared to the fertilized control. For the BS1 + F, compared to the fertilized control, the soil water storage (SWS) increased significantly by 15 and 14% at 10 t ha-1 and 20 t ha-1, respectively. Overall, the soil structure was better in loamy than sandy soil and therefore the effect of BS was not as pronounced in loamy soil as it was in sandy soil. The number of correlations between soil pH, sorption capacity, SOM, HS, and soil physical properties decreased in the following order: loamy soil > sandy soil; BS + F > BS treatments; BS1 > BS2, and at a rate of 20 t ha-1 > at a rate of 10 t ha-1.