Applying organic fertilisers improves soil health and plant growth by improving the soil organic matter, soil structure, nutrient uptake and water‐holding capacity. Small‐plot stationary field experiments on four different soils in Central Europe evaluate the long‐term effect of organic amendments and/or mineral fertilisers on the soil organic matter quality under conventional tillage and the potato/maize–winter wheat–spring barley crop rotation. Soil samples were collected after the spring barley harvest in 2022. A total nitrogen dose of 330 kg N·ha −1 over 3 years was applied in all fertilised treatments; organic fertilisers were applied after the barley harvest. The E4/E6 absorbance ratio showed significant correlations with the C‐HA/C‐FA ratio, humification index and proportion of humic acid carbon. However, when assessing the effects of fertilisation, treatments within a single homogeneous field, the E4/E6 ratio did not prove to be a reliable indicator of soil organic matter quality. Application of farmyard manure resulted in higher values of the C‐HA/C‐FA ratio, humification index and percentage of humic acid carbon compared to mineral fertilisation (N, NPK). In contrast, sewage sludge application was less effective in increasing the C‐HA/C‐FA ratio and proportion of humic acid carbon than the combination of mineral nitrogen fertilisation with straw. Regardless of weather conditions during stem elongation and flowering, higher yields of spring barley and winter wheat were recorded when nitrogen was applied in mineral fertilisers compared to manure or sewage sludge.
Sedlář et al. (Thu,) studied this question.