The Effect of Different Doses of N Fertilization on the Parameters of Soil Organic Matter and Soil Sorption Complex

Mineral N fertilizer application may have an effect on soil organic matter and other soil parameters. Therefore, we studied the effects of different doses of N fertilization on soil organic matter and chemical properties of Haplic Luvisol in the locality of Dolná Malanta (Slovakia) during 2014–2016. Soil samples were collected from the plots exposed to the following treatments: 1. N0 – no N fertilization as control during 2014–2016, 2. N40 – N fertilizer at the rate of 40 kg N ha^–1 in 2014 and 2016, 3. N80 – N fertilizer at the rate of 80 kg N ha^–1 in 2014 and 2016, 4. N160 – N fertilizer at the rate of 160 kg N ha^–1 in 2015, and 5. N240 – N fertilizer at the rate of 240 kg N ha^–1 in 2015. The results showed that in N80 the soil organic carbon (SOC) content increased by 32% in comparison to N0. The addition of 80 kg ha^-1 of N significantly decreased the humic substances (HS) content in the soil by 16% compared to N0. The higher doses of N fertilization 80 rather than 40 kg ha^-1 as well as 240 rather than 160 kg ha^-1 significantly decreased humus stability. The addition of N fertilization decreased the average values of soil pH. Values of hydrolytic acidity (Ha) increased by 41% and 46% in N40 and N80, respectively than N0, but on the other hand, this one decreased by 36% and 27% in N160 and N240, respectively in comparison to N0. Positive statistically significant correlations were determined between soil pH and SOC in N40 and N80 treatments. The increase of soil pH was connected with higher humus quality in N160 and N240. Negative correlations between humic acids (HA) and sum of basic cations (SBC) and cation exchange capacity (CEC) were observed in N80 < N160 < N240 treatments. Higher values of fulvic acids corresponded with lesser CEC in N80 and N160 treatments. In N160, with increased humus quality, CEC significantly decreased. The same effect was observed in N240. In addition, in N240, we also observed that with increased HA:FA ratio SBC and base saturation significantly decreased.