Influence of Different Cow Manure Application Rates on the Growth, Yield and Indigo Blue Color of Indigofera suffruticosa Mill

Background: Indigo is a key ingredient in the natural dyeing of fabrics. However, the conventional use of chemical fertilizers in indigo cultivation has led to an increase in production costs and soil degradation. Low-fertility soils further compromise the growth and yield of indigo plants. To address these challenges, employing manure is recognized as a sustainable approach for indigo cultivation. The use of manure enhances soil nutrient levels, improves soil structure and mitigates production costs. In this study, our objectives were to compare different rates of cow manure in relation to indigo growth, yield and the effect of cow manure rate on the value of indigo blue color. Methods: The experiments were carried out at the Plant Science Field from June to October 2022. Employing a randomized complete block design (RCBD), the study featured four treatments with four replications each. The treatments included: Treatment 1: no fertilizer (control); Treatment 2: cow manure at a rate of 3,125 kg/ha; Treatment 3: cow manure at a rate of 6,250 kg/ha; and Treatment 4: cow manure at a rate of 9,375 kg/ha. Data collection included plant height, canopy width, number of branches, plant weight, indigo blue weight and indigo blue color value. The CIE color system (Commission International de l’Éclairage) determined the color value. Result: The application of cow manure at a rate of 9,375 kg/ha resulted in the highest plant height and canopy width, with the corresponding number of branches of 150.73 cm, 46.45 cm and 31.73 cm, respectively. As compared to the other treatments, these values were statistically different. The color that was associated with the indigo finished product was dark blue and the yield; plant weight and indigo blue weight were recorded as 15,663.44 kg/ha and 2,540.44 kg/ha, respectively. The color value of indigo blue showed that the L* values of 24.94, a* -9.32, b* -2.44 and C* 9.63 were not significant but h* 194.66 was statistically significant.