Chemical Properties of Soil in Four-Field Crop Rotations under Organic and Conventional Farming Systems

In agriculture, the farming system significantly affects chemical soil properties. The organic system, which is based among others on the use of natural (organic) fertilizers, promotes increased soil contents of humus, organic C, and micronutrients. The conventional system, in turn, may cause soil acidification if high rates of mineral (particularly nitrogen) fertilization are used. The crop plant species also modifies soil chemistry by providing different (quantitatively and qualitatively) crop residues. The study was conducted over the period 2013–2016 in Czesławice (Lublin Region, Poland). The aim of this study was to determine the content of some chemical components determining the quality of loess soil on which four plant species were grown under organic and conventional farming systems. This research involved the determination of some parameters of the chemical composition of the soil: soil pH, total sorption capacity, humus content, macronutrient (P, K, Mg) and micronutrient (B, Cu, Mn, Zn) content, organic carbon, and total nitrogen content. The content of different forms of nitrogen, N-NO₃ and N-NH₄, was also determined. The experimental design included two crop rotations (organic and conventional) in which identical plant species were grown: potato—winter wheat—field bean—spring barley. The experiment was established on loess soil with the grain size distribution of silt loam and classified as good wheat soil complex (soil class II). It was carried out as a split-plot design in three replicates, and the area of a single plot was 80 m². Soil samples were taken using a soil sampling tube from an area of 0.20 m² (from the 0–25 cm layer) in each plot at the end of the growing season of the specific crops grown. Over the four year study period, it was found that the organic system contributed to an increased soil content of magnesium, boron, copper, manganese, zinc, organic carbon, and total nitrogen. Moreover, organic cropping promoted more favorable soil pH and higher soil humus content. Organic cropping significantly improved the total sorption capacity of the soil compared to conventional cultivation. Moreover, the organic system contributed to a higher soil content of nitrogen in the form of N-NH₄ and its lower content in the form of N-NO₃. Under the conventional system, in turn, a higher soil phosphorus and potassium content was observed. To sum up, the study confirmed the assumed hypothesis that the organic farming system would contribute to an improvement in the chemical quality indicators of loess soil. Regardless of the cropping system, potato and field bean had the most beneficial effect on soil chemistry, whereas cereal crops showed the weakest effect. Winter wheat and spring barley had an effect on significantly lower total sorption capacity of the soil and a significantly lower soil content of N-NO₃ and N-NH₄.