NANO-DAP-MEDIATED NITROGEN AND PHOSPHORUS USE EFFICIENCY, NUTRIENT UPTAKE, GROWTH AND FLOWER PRODUCTION OF AFRICAN MARIGOLD (TAGETES ERECTA L.) CV. SERACOLE

Abstract

A two-year field experiment (2022 and 2023) was conducted at Assam Agricultural University, Jorhat, to determine whether Nano-DAP integrated with reduced conventional phosphorus could improve nutrient acquisition, nutrient-use efficiency, growth and flower production of African marigold cv. Seracole across three planting dates (15 February, 15 April and 15 June). Nine fertilizer treatments were evaluated in a factorial randomized block design with three replications. The integrated treatment F₉ [NPK 9:4.5:12 g m⁻² + Nano-DAP root dip (5 mL L⁻¹) + foliar spray (10 mL L⁻¹)] produced the highest pooled flower yield (259.72 q ha⁻¹), N uptake (78.82 kg ha⁻¹), P uptake (14.22 kg ha⁻¹) and K uptake (70.55 kg ha⁻¹) at 90 DAT. Relative to full recommended NPK (F₃), F₉ increased pooled flower yield by 9.6% while using approximately half the conventional soil-applied P₂O₅. Using the Nano-DAP nutrient composition specified for the notified IFFCO liquid formulation (8% N and 16% P₂O₅, w/v) for derived calculations, F₉ achieved a P partial factor productivity of 573.9 kg flowers kg⁻¹ P₂O₅ compared with 263.2 under F₃, and an apparent P recovery efficiency of 38.8% compared with 4.8% under F₃. Across planting dates, D₁F₉, D₂F₉ and D₃F₉ exceeded the corresponding full-RDF treatment F₃ by 7.0, 6.6 and 15.9%, respectively, for flower yield. Nutrient uptake at 90 DAT was positively associated with flower yield across the 27 pooled treatment means (r=0.63 for N, 0.65 for P and 0.66 for K). The results demonstrate that Nano-DAP can support high flower production with reduced conventional phosphorus input, although derived nutrient-use-efficiency indices should be interpreted as treatment-mean estimates and confirmed using replicate level efficiency calculations and the exact nutrient analysis of the Nano-DAP formulation used in the experiment.