Micronutrient dynamics and morphological performance of African marigold (Tagetes erecta L.) under North Bihar agroclimatic conditions

Abstract

African marigold (Tagetes erecta L.) is an economically important ornamental crop in North Bihar, India. There are fertiliser recommendations for commercial cultivation of marigolds, but systematic information on leaf micronutrient composition and its relationship with floral performance remains limited. A three-year (2021–2024) randomised block design (RBD) field trial was conducted with nine micronutrient treatment combinations involving soil and foliar applications of Zn, Mn, Fe and B, with leaf micronutrient profiling in African marigold (Tagetes erecta L. cv. Arka Abhi) under the humid subtropical conditions of North Bihar, India. Results of the analysed data showed significant phenotypic variation in micronutrient levels of the following from lower to upper range, i.e., Fe (555–847 ppm), Mn (61–130 ppm), Zn (14.7–44.4 ppm), Cu (10.6–26.5 ppm) and B (29–67 ppm). Strong positive correlations were observed between Fe-Mn content and flower yield (r = 0.70) and flowering duration (r = 0.74). Zinc showed a positive association with plant height (r = 0.61), while boron correlated with the shelf life of the flower (r = 0.59). Among the treatments, the combined application of micronutrients including soil application of Zn (2.5 kg/ha) + Mn (2.5 kg/ha) + B (1 kg/ha) + Fe (1.25 kg/ha) at planting and Zn-ethylenediaminetetraacetic acid (EDTA) + Mn-EDTA + B + Fe-EDTA (0.2 % each) foliar application, exhibited optimal micronutrient balance with highest yield (762.55 g/plant), tallest plants (126.2 cm), longest flowering (81.66 days) and best shelf life (5.88 days), representing 78.9 % yield advantage over the check. The findings suggest that maintaining Fe (600–700 ppm), Mn (90–110 ppm), Zn (25–30 ppm) and B (45–60 ppm) in leaf tissue is crucial for superior floral performance under North Bihar's humid subtropical conditions. Maintaining optimal leaf levels of Fe (600–700 ppm), Mn (90–110 ppm), Zn (25–30 ppm) and B (45–60 ppm) is crucial for superior floral performance. Balanced micronutrient ratios rather than high individual levels drive crop performance and support effective, site-specific nutrient management in alkaline alluvial soils.