Role of Intercropping, Herbicides and Fungicides in Compensating for the Lack of Crop Rotation in Long-Term Continuous Cropping of Two Potato Cultivars

Continuous potato cropping is usually associated with a reduction in tuber yield and deterioration in crop structure, resulting in a decrease in the proportion of marketable produce. The effect of crop rotation, cultivar selection, the range of chemical plant protection, and the periodic introduction of an intercrop on potato (Solanum tuberosum L.) yield was studied in a field experiment at the Production–Experimental Station in Bałcyny near Ostróda, belonging to the University of Warmia and Mazury in Olsztyn, where potatoes have been continuously cultivated since 1973. Results from 2015 to 2023, corresponding to the 43rd–51st year of continuous potato cropping, were compared to a six-course crop rotation (potato—oat—flax—winter rye—faba bean—winter triticale). The study discusses the yield of two potato cultivars (Catania and Red Sonia) across two periods: 2015–2018 and 2019–2023. In the first period, potatoes were grown according to the general experimental design, whereas in 2019–2023, the cultivation included an additional intercrop of oil radish (Raphanus sativus L.) cv. Rolterra In both series of studies, the experimental factors included potato cultivation without the use of plant protection products (object O) and objects with the application of herbicides (H) and herbicides and fungicides (H + F). The introduction of intercropping into continuous potato cropping was more effective than the application of pesticides and limited the scale of yield decline in relation to crop rotation. In the case of the Catania cultivar, the mean difference in yield between crop rotation and continuous cropping in the first series of tests (without intercropping) was 50.4%, and in the second series (after introducing intercropping), it decreased to 22.3%. The corresponding mean differences for the Red Sonia cultivar were 45.5% in the first series and 12.9% in the second series. Furthermore, in the second series of studies (thanks to the introduction of intercropping), the mean share of marketable yield in continuous cropping increased from 35.1% to 51.9% (for the Catania cultivar) and from 23.6% to 35.8% (for the Red Sonia cultivar). In summary, the introduction of oil radish as an intercrop was the most effective factor (more effective than the choice of potato cultivar and use of chemical crop protection products) to limit the negative aspects of long-term continuous potato cropping, improving yield, yield stability, and the share of marketable tubers.