EFFECT OF FERTILIZER RATE ON THE FORMATION OF ROOT CHICORY YIELD AND INULIN YIELD

Abstract

Purpose, to determine the effect of different rates of mineral fertilization on root mass formation, yield, inulin content, and inulin harvest of root chicory, as well as to identify the optimal nutrient level that ensures high productivity without a negative effect on yield and inulin accumulation. Methods. Field studies were conducted in 2021–2024 on gray forest soils using the root chicory cultivar Tsezar. The experimental design included an unfertilized control and six NPK rates, ranging from N30P25K40 to N180P150K240. Phosphorus and potassium fertilizers were applied before primary soil tillage, while nitrogen fertilizers were applied before sowing. At the stage of biological maturity, plant density, yield, inulin content, and inulin harvest per hectare were recorded. Statistical analysis was performed in R using multifactorial analysis of variance and Tukey’s HSD0.05 test. Results. It was established that fertilizer rate was the leading factor determining root mass, yield, and inulin harvest, whereas weather conditions had a greater effect mainly on inulin content. A gradual increase in the level of mineral nutrition up to N120P100K160 promoted a stable increase in root mass during the growing season and provided the best combination of productivity and quality indicators. The highest root mass (249.8 g), yield (36.7 t/ha), and inulin harvest (5.66 t/ha) were obtained at this fertilization rate. The N90P75K120 treatment also ensured high productivity, with root mass reaching 230.7 g, yield 34.3 t/ha, and inulin harvest 5.16 t/ha; however, these values were lower than those recorded for the optimal treatment. A further increase in fertilizer rate to N150P125K200 led to a decline in these indicators, despite the highest inulin content of 15.5%. The most negative effect was observed at the maximum rate of N180P150K240, where root mass decreased to 86.2 g, yield to 11.73 t/ha, and inulin harvest to 1.78 t/ha. This indicates that increasing the concentration of nutrients beyond the optimal level did not enhance productivity but, on the contrary, suppressed plant growth and reduced stand density. Correlation analysis confirmed a very strong positive relationship between root mass, yield, and inulin harvest, whereas the relationship between yield and inulin content was weak. Findings. The optimal fertilization rate for root chicory grown on gray forest soils is N120P100K160, which provides the maximum yield and inulin harvest. Exceeding this rate causes a decrease in productivity, which may be associated with excessive osmotic stress on plants.