LAUSR

Abstract In organic farming, reduced tillage aims to maintain the natural fertility of the soil, including its microbiological diversity. Cultivation practices that change the properties of the soil environment determine conditions of plant growth and yield as well as the chemical composition of the biomass. The methods and dates of performing soil cultivation treatments in organic vegetable production were studied in southern Poland, in the years 2016–2018. The following cultivation combinations were applied: conventional autumn ploughing tillage (APT), spring ploughing tillage (SPT), spring rotary tillage (SRT), spring rotary tillage with polypropylene nonwoven (surface mass of 50 g m−2) mulch (SRTPM), and spring rotary tillage with fresh biomass mulch (SRTBM). The experiment was established on a site where a mixture of white clover (Trifolium repens L. cv. ‘RD 84’) and Italian ryegrass (Lolium multiflorum Lam. cv. ‘Gaza’) was grown for green manure, which constituted a forecrop for zucchini (Cucurbita pepo L.) cv. ‘Partenon’ F1. The fresh biomass of clover and grass was used to mulch the soil on the SRTBM plots. It was shown that the spring soil cultivation with a rotary tiller before planting zucchini plants resulted in a higher marketable yield of zucchini fruit compared to the ploughing performed in the spring (an increase by 34.3%) and the ploughing performed in the autumn (an increase by 25.3%), but these differences are not statistically confirmed. The date of ploughing did not significantly affect the extent of weed infestation on the experimental plots. Zucchini fruit harvested in the last year of study (2018) were characterized by the strongest antioxidant activity and contained the highest amount of total phenols. The study demonstrated a beneficial effect of the reduced tillage and mulching with fresh biomass (SRTBM) on bacterial population (1.56 × 109 CFU g−1 DW) in the soil.