Regulation of Lettuce Growth and Calcium-Magnesium Nutrition by Sheep Wool-Derived Hydrolyzed Keratin Under Natural and LED Light Spectra

Abstract This study investigates the effects of hydrolyzed keratin (HK) on the growth and Ca and Mg uptake of lettuce plants under natural and light-emitting diode (LED) lighting conditions in cocopeat and soil environments. Lettuce plants were grown under natural light in cocopeat and soil, and simultaneously under blue (B), blue + far-red (B + FR), red (R), R + B, R + FR, R + B + FR, and white (W) light conditions. The fertilizer treatments consisted of control, HK, Ca + Mg, and HK + Ca + Mg. The highest fresh and dry weights of lettuce plants were observed with HK treatment in cocopeat, and HK + Ca + Mg treatment in soil. Among different LED light sources, the highest fresh and dry weights were recorded under the R light, followed by R + B + FR, R + B, and W, with the weakest growth observed under B + FR, R + FR, and B. Regardless of light source, HK and Ca + Mg treatments improved fresh and dry weights compared to the control. All treatments increased Ca and Mg concentrations compared to the control, with the highest Mg concentration observed under HK + Ca + Mg treatment and the highest Ca concentration is found with HK + Ca + Mg and Ca + Mg treatments. The highest N concentrations were observed in cocopeat with HK treatments and in soil with HK + Ca + Mg, compared to the control. The Ca concentration was higher under B + FR and R + FR, and Mg concentration was highest under R and R + B. HK, Ca + Mg, and HK + Ca + Mg treatments consistently improved the nutritional status of lettuce plants, making HK a promising organic amendment for enhancing plant growth and nutrient uptake in both soil and soilless cultivation systems.