Reduction in Chemical Fertilizer Rates by Applying Bio-Organic Fertilizer for Optimization Yield and Quality of Hemerocallis citrina Baroni

In this study, we investigated if reducing the amount of chemical fertilizer by combining it with organic fertilizer in Hemerocallis citrina Baroni (H. citrina) cultivation could improve plant growth and photosynthetic capacity and, consequently, increase yield and quality. A continuous two-year field experiment was conducted at a research farm in Zhangzhou City, China, during 2021–2022. Six fertilization levels with two locally grown H. citrina cultivars, “Taidong 6” and “Shibage”, were tested. The results showed that 100% of the recommended dose of chemical fertilizer (RDF) with bio-organic fertilizer yielded superior effects in promoting both vegetative and reproductive growth in comparison to RDF alone. However, reducing the application rate of chemical fertilizers, especially by more than 40%, resulted in a significant decline in certain agronomic traits such as plant width, leaf width, and scape length. Compared to RDF, the use of 100% or 80% RDF in combination with bio-organic fertilizer significantly increased chlorophyll content, net photosynthetic rate, and transpiration rate as well as yield production, while excessive reductions in chemical fertilizer rate produced results that demonstrated an opposite trend. The co-application of chemical and bio-organic fertilizer enhanced the contents of soluble sugar and lowered total acidity, whereas excessive chemical fertilizer reduction decreased vitamin C, total flavonoids, and soluble protein levels. Utilizing radar chart analysis for a comprehensive assessment of yield and quality demonstrates that the application of bio-organic fertilizer with 80% RDF could be a better field fertilization regime for H. citrina cultivation.