Phytohormones are chemical substances that regulate plants growth, reproductive processes, longevity, development, and even death. One of the most common representatives of this group is indole-3-butyric acid (IBA), which is widely applied in various branches of agriculture. Taking into consideration that the conversion of conventional herbicides into ionic liquids leads to the enhancement of their biological activity, we decided to implement the same strategy for selected phytohormone. Hence, we synthesized a homologous series comprising alkylated choline cations and indole-3-butyrate anions. The new biobased ionic liquids (ILs) were characterized in terms of physicochemical properties (thermal stability, phase transitions, solubility, surface activity, density, and viscosity) and susceptibility to biodegradation according to the OECD 301 F test. Subsequently, their activity as a growth stimulator was evaluated for butterhead lettuce (Lactuca sativa L.) as a test plant. Additionally, the nutrient assimilation by the test plants was analyzed. The study revealed that the IL containing cations with octyl groups, at the optimal concentration of 0.5 ppm, enhanced lettuce biomass production by approximately 21% compared to that of the control. Moreover, the lettuce was enriched with valuable micro- and macroelements, such as P, K, Ca, Mg, Na, and Mn. These findings comply well with the concept of sustainable agriculture focused on utilizing environmentally friendly compounds derived from sources of natural origin while exhibiting enhanced efficacy.

The nitrogen requirements of flowering Chinese cabbage are unknown. Our study aimed at investigating the effect of varied nitrogen nutrition levels (including 50, 70, 90, 110, and 130 mg N per dm3, described as N-50 to N-130, respectively) on the yield of flowering Chinese cabbage (Brassica campestris L. ssp. chinensis var. utilis Tsen et Lee) grown in two varied soilless cultivation systems (substrate and hydroponic) and seasons (spring and autumn). We confirmed that the intensity of the nitrogen nutrition modified the yield of plants within a range of 50 to 90 mg N; the yields were increased; however, the higher N concentrations were not effective. In both cultivation systems, the content of K, Ca, and Fe in leaves was higher in autumn compared to spring. Nitrogen nutrition improved the weight of plants—an effect that varied depending on the system of cultivation—and increased the phenolic content. N-90 was the optimal level of nitrogen nutrition. More intensive N-nutrition did not significantly modify plant yields or phenolic content. We Concluded that N fertilisation might be an effective tool to obtain plants with high bioactive compound content.

Flowering Chinese cabbage (Brassica campestris L. ssp. chinensis var. utilis Tsen et Lee) is an original leafy vegetable from China, and it is a valuable source of bioactive compounds. In the literature, there are no practical recommendations for the cultivation and fertilization of this species. Our study aimed to investigate the effect of nitrogen nutrition levels (70 and 90 mg N per dm3) and various foliar treatments (Se, Si, Li, V, and SA—salicylic acid) on the quantity of the yield and the quality of flowering Chinese cabbage grown in two varied soilless cultivation systems: under pot cultivation (mixture of peat and sand) and hydroponic culture. In conducted studies, we have confirmed the hypothesis that the intensity of nitrogen nutrition and the application of foliar spraying modify the yield of plants, both the quantity and the quality aspects. The factors under analysis had a diversified and multidirectional influence on the yield, growth, and quality of the plants. The results varied between the two cultivation systems. This was proved by the PCA (principal component analysis). Generally, the plants grown in the hydroponic system were characterized by higher yields than those grown in pot cultivation. This was found to be a stimulating effect of N nutrition on the content of that nutrient in the aerial parts of the plants. Plants sprayed with Si and Se were characterized by a high content of Chl a, Chl b, carotenoids, and relatively high antioxidant activity. Finally, the samples subjected to different foliar spray treatments could be classified into appropriate groups based on the quality parameters.

The aim of our study was to determine the effect of various nitrogen sources (NH4NO3 (N, 34%), Ca(NO3)2 (N, 15.5%; Ca, 18%), Mg(NO3)2 (N, 11%; Mg, 12%), NaNO3 (N, 15%; Na, 25%) and urea (N, 46%)) and increasing the intensity of N nutrition with these fertilisers (50, 70, and 90 mg N·dm−3) on the yield and quality of flowering Chinese cabbage (Brassica campestris L. ssp. chinensis var. utilis Tsen et Lee). The plants were grown in two different soilless systems, namely pot cultivation (substrate system—mixture of peat and sand) and hydroponic cultivation. The quality of plants was expressed as macro- and microelement contents, pigment contents, antioxidant activity and phenolic content. It was observed that the yield of flowering Chinese cabbage was about 43–70% higher in the hydroponic system than in the substrate. The N source and N nutrition affected the yield volume. The highest mean yield was observed in pot cultivation after fertilisation with Mg(NO3)2 and in hydroponics with Ca(NO3)2. We found a rather high tolerance of flowering cabbage to sodium and an excessive content of ammonium in the nutrient solution. The nitrogen source and N doses modified plant contents of macro- and microelements (N, P, K, Ca, Mg, Na, Fe, Mn, Zn and Cu) and other quality parameters of plants. In pot cultivation, the highest element contents as well as the highest antioxidant activity were obtained after fertilisation with Mg(NO3)2 at N-70 and N-90. The highest pigment contents (chlorophylls and carotenoids) were obtained in the samples treated with urea at the N-90 dose. Those samples were also characterised by a high Mn content. Generally, the pigment content in the pot system positively correlated with the Mn content in leaves, the microelement which is involved in the process of photosynthesis, but it did not correlate with colour coordinates. In the hydroponic system, the highest pigment contents were observed in the samples treated with Mg(NO3)2 at the N-70 dose. Generally, in hydroponics, chlorophyll levels positively correlated with Ca levels in the aboveground parts of the plants. Additionally, the content of Chl b inversely correlated with L* and b* values. In hydroponic systems, the highest DPPH (2,2-diphenyl-1-picrylhydrazyl) activity was observed after treatment with NH4NO3 at the N-70 and N-90 doses and it did not correlate with phenolic content but rather with pigment content. In conclusion, both the intensity of N nutrition and the fertiliser applied can significantly modify the yield of plants and their quality parameters. For pot cultivation, the most effective fertiliser was Mg(NO3)2 at the N-70/N-90 doses, while for hydroponic cultivation, it is difficult to indicate the most effective fertiliser as the responses varied depending on the method of fertilisation.