The Impact of the Farming System and Forecrops on Selected Soil Quality Indicators and Oat Yield

A field experiment was conducted in 2020–2022 at the Czesławice Experimental Farm (Lublin Voivodeship, Poland) to investigate the chemical properties and enzymatic activity of loess soil under oat cultivation, as well as crop productivity (grain yield and grain protein content). The first experimental factor was the farming system: (A) an organic system, without chemical plant protection products or NPK mineral fertilization (only the Humac Agro fertilizer, approved for organic farming, was applied); and (B) a conventional system, with chemical plant protection and NPK mineral fertilization at rates recommended for oat. The second factor comprised different forecrops for oat: potato, spring barley, narrow-leafed lupine, oat, and winter wheat. The organic system had a more fa-vorable effect on the soil contents of organic carbon (by 0.08 percentage points, pp), mag-nesium (by 10%), boron (by 13%), and zinc, manganese, and copper (by 5.5%, 18%, and 7%, respectively), and promoted higher soil enzymatic activity, with increases ranging from 9–14% (for alkaline phosphatase, urease, dehydrogenase) to 32–39% (for acid phos-phatase and protease). In contrast, the conventional system favored soil nitrogen, phosphorus, and potassium contents (increases of 0.02 pp, 12%, and 25%, respectively). The total sorption capacity of the soil was significantly higher under the organic system (by approximately 6%), particularly in interaction with potato as the forecrop (40.9 cmol(+) kg⁻¹). The forecrops such as potato and narrow-leafed lupine had a more beneficial effect on soil quality and oat productivity than the cereal forecrops. Oat grain yield under the organic system was, on average, only 8% lower than under the conventional system. When favorable root-crops and legume forecrops were used, the productivity of organically grown oat matched that of oat grown conventionally after cereal forecrops. Organic oat cultivation resulted in a significantly higher grain protein content.