Optimizing Nitrogen and Phosphorus Application for the Growth and Seed Yield of Katwa Amaranth (Amaranthus spp.)

Abstract

A field experiment was conducted at the Agronomy Farm of Sher-e-Bangla Agricultural University, Dhaka, Bangladesh, during December 2022 to March 2023 to evaluate the effect of nitrogen and phosphorus levels on the growth and seed yield of Katwa amaranth (Amaranthus spp.). A factorial experiment with two factors was laid out in a Randomized Complete Block Design (RCBD) with three replications. Four levels of nitrogen—N₀ (0), N₁ (27.6 kg/ha), N₂ (55.2 kg/ha), and N₃ (82.8 kg/ha)—and four levels of phosphorus—P₀ (0), P₁ (12 kg P₂O₅/ha), P₂ (24 kg P₂O₅/ha), and P₃ (36 kg P₂O₅/ha)—were combined to form sixteen treatment combinations. Data were collected on morphological and yield-related parameters. Results revealed that nitrogen and phosphorus levels significantly affected most growth and yield traits, including plant height, number of leaves and branches, stem diameter, spikes per plant, and seed yield. The tallest plants (168.72 cm) and highest seed yield (3.56 t/ha) were recorded under N₃, representing a 61.8% increase over the control. Similarly, phosphorus at 36 kg P₂O₅/ha produced 3.15 t/ha seed yield, which was 18% higher than P₀. The combined treatment N₃P₃ resulted in superior performance for all parameters, with plant height (171.60 cm), number of branches (22.67), and seed yield (3.80 t/ha) showing respective increases of 13.6%, 27.9%, and 90.0% over the control (N₀P₀). The highest benefit–cost ratio (1.90) was also recorded in N₃P₃. These findings indicate that the integrated application of 82.8 kg N/ha and 36 kg P₂O₅/ha can be recommended for achieving optimum growth, higher seed yield, and economic profitability in Katwa amaranth cultivation under Bangladesh conditions.