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

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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.