The Effect of Different Rates of Biochar and Biochar in Combination with N Fertilizer on the Parameters of Soil Organic Matter and Soil Structure

Since biochar is considered to be a significant source of carbon, in this work we have evaluated the changes in soil organic matter (SOM) and soil structure due to application of biochar and biochar with N fertilization, and have considered the interrelationships between the SOM parameters and the soil structure. The soil samples were collected from Haplic Luvisol at the locality of Dolná Malanta (Slovakia) during 2017. The field experiment included three rates of biochar application (B0 – no biochar, B10 – biochar at the rate of 10 t ha^-1, B20 – biochar at the rate of 20 t ha^-1) and three levels of N fertilization (N0 – no nitrogen, N160 – nitrogen at the rate of 160 kg ha^-1, N240 – nitrogen at the rate of 240 kg ha^-1). The rate of biochar at 20 t ha^-1 caused an increase in the organic carbon (C_org) content. The combination of both rates of biochar with 160 and 240 kg N ha^-1 also caused an increase in C_org. In the case of B20 the extractability of humic substances carbon (C_HS) was 17.79% lower than at B0. A significant drop was also observed in the values of the extraction of humic acids carbon (C_HA) and fulvic acids carbon (C_FA) after the addition of biochar at a dose of 20 t ha^-1 with 160 kg N ha^-1. However, both rates of biochar had a significant effect at 240 kg N ha^-1. After application of 20 t ha^-1 of biochar the content of water-stable macro-aggregates (WSA_ma) significantly increased compared to control. This rate of biochar also increased the mean weight diameter (MWD_W) and the index of water-stable aggregates (Sw) and decreased the coefficient of vulnerability (Kv). The biochar at a rate of 20 t ha^-1 with 240 kg N ha^-1 the value of MWD_W increased and value of Kv decreased significantly. The contents of C_org and C_L correlated positively with WSA_ma, MWD_W and Sw and negatively with WSA_mi and Kv. The extraction of C_HA and C_FA was in negative relationship with MWD_W. We conclude that the application of biochar and biochar combined with N fertilizer had a positive influence on SOM and soil structure.