Biochar is a widely known soil amendment. In the presented study, we aimed to evaluate the effect of biochar produced from Swedish willow ((Salix schwerinii x S. viminalis) x S. viminalis), ground into three different size fractions (<125µm, 125µm-2 mm and >2 mm) on selected hydrophysical properties of silty loam soils. Biochar was applied in the amount of 1.5% per weight of dry matter and the results were compared with pure silty loam soil (control). Data of biochar application impact on the selected hydrophysical properties of silty loam soil were statistically analyzed. In general, our results suggest that applied different size fractions of biochar does not have a statistically significant effect on particle density, however does have an effect on bulk density, porosity and saturated hydraulic conductivity of silty loam soil. With regard to bulk density, a statistically significant decrease (p<0.05) was observed compared to the control and it ranged from 4.18 to 8.13% from the smallest to the largest biochar fraction. The decrease of bulk density further led to a statistically significant increase (p<0.05) in porosity of all three treatments. Saturated hydraulic conductivity tended to increase as the size fraction of the biochar used was progressively reduced. This increase ranged from 63.77% (for biochar with size fraction >2 mm) to 112.42% (for biochar with size fraction <125µm) compared to pure silty loam soil (control).

Soil water content is an important factor influencing crop yield quantity and quality. Extreme meteorological events are more frequent in our geographical conditions in last years and they affect soil water storage. Biochar is an organic material and one of its properties is soil water holding for a longer time. This is one of great benefits during non-precipitation days. Our study is focused on soil water content changes with biochar amendment in comparison to soil without biochar. In addition, we analyzed biochar repeated application as well. It means addition another biochar dose into the soil where the biochar had been applied previously. Our results confirmed positive effect of biochar application and repeated application on soil water content. The soil water regime with biochar repeated application was the most stable in 2020 in comparison to other variants of experiment.

We compared two methods of modeling soil water retention curves used by scientists in Slovakia. The first modeling was done using the GENRET program and the second using the RETC program. Samples of pure sandy soil and sandy soil with applied biochar in three different particle sizes were used for the simulation. Sandy soil has a very low retention capacity therefore the modeling of soil water retention curves is not easy. Our results showed that the GENRET program can model the curve even at high pressures, which the RETC program modeled only in one variant, but the RETC program had better agreement with measured data. The most significant differences between the programs were at the lowest and highest pressures.

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