Enhancing Post-harvest Soil Fertility and Nutrient Sustainability through Nano-DAP Integrated Fertilization in African Marigold (Tagetes erecta L.)

Abstract

Sustainable nutrient management in ornamental crops requires practices that improve productivity while maintaining residual soil fertility. The present study evaluated the post-harvest soil fertility status of African marigold (Tagetes erecta L.) under integrated Nano-DAP fertilization during 2022–23 and 2023–24 at the Experimental Farm, Assam Agricultural University, Jorhat. The experiment was conducted in factorial randomized block design with three planting dates and nine fertilizer treatments comprising conventional NPK and different combinations of reduced phosphorus with Nano-DAP root dip and foliar spray. Post-harvest soil samples (0–15 cm) were analysed for soil pH, organic carbon and available N, P₂O₅ and K₂O. The results showed increases in soil organic carbon (6.45%) and available N, P₂O₅ and K₂O (4.71, 5.59 and 5.46%, respectively) over the initial soil status. Among the treatments, F₉ (NPK 9:4.5:12 g m⁻² + Nano-DAP root dip 5 mL L⁻¹ + foliar spray 10 mL L⁻¹) recorded the highest post-harvest soil pH (5.18), organic carbon (0.68%), available N (289.17 kg ha⁻¹), P₂O₅ (30.23 kg ha⁻¹) and K₂O (154.39 kg ha⁻¹). The interaction D₁F₉ recorded the highest available N, P₂O₅ and K₂O of 290.50, 30.28 and 154.50 kg ha⁻¹, respectively. Correlation analysis showed positive relationships among major soil fertility parameters, while principal component analysis separated Nano-DAP integrated treatments from conventional fertilizer and control treatments. The study indicates that Nano-DAP integration can improve post-harvest nutrient availability and contribute to sustainable nutrient management in African marigold cultivation.