Low-level Substitution of Urea Fertilizer with Organic Manure and Its Advantages in Wheat Cultivation under Subtropical Conditions in Bangladesh

Abstract

Inorganic-organic integrated soil fertility management is often suggested to improve soil health, reduce environmental risks, and strengthen the resilience of agroecosystems. However, limited research has focused on the effect of inorganic-to-organic nitrogen (N) fertilizer substitution on the growth, yield and nitrogen use efficiency (NUE) of wheat under the subtropical monsoon climatic conditions of this region. Therefore, seven quintuplicated treatments were established in a pot culture system with varying levels of N-equivalent substitution between chemical fertilizer (urea) and organic manure (OM) to assess their benefits in wheat cultivation during the winter season of 2023-2024 following a completely randomized design (CRD) at the research field of Sher-e-Bangla Agricultural University, Dhaka. The treatments were N0=zero N fertilizer (control); N1=120 kg N ha⁻¹ from urea; N2=100 kg N ha⁻¹ from urea + 20 kg N ha⁻¹ from OM; N3=80 kg N ha⁻¹ from urea + 40 kg N ha⁻¹ from OM; N4=60 kg N ha⁻¹ from urea + 60 kg N ha⁻¹ from OM; N5=40 kg N ha⁻¹ from urea + 80 kg N ha⁻¹ from OM; and N6=120 kg N ha⁻¹ from OM. Despite sources, N fertilization significantly improved plant height, leaf area index (LAI), effective tillering, yield-contributing attributes and yield of wheat. The tallest plant (89.33 cm) was observed from the N1 treatment, which was 19.6% greater than the control treatment. The plants with N1 treatment also produced 54.4% greater LAI at heading. Total chlorophyll content of the flag leaf was highest under N1 treatment, and differences among N2, N3, and N4 treatments were non-significant. The N1, N2, N3, N4, N5, and N6 treatments increased total dry matter accumulation in plants by 111.67%, 97.2%, 93.9%, 84.4%, 73.3%, and 69.4%, respectively. The maximum effective tiller (1.60 plant⁻¹) and thousand grain weight (45.7 g) were observed under N1 treatment, which was 14.3% and 43.9% greater than the control but statistically identical with N2 and N3 treatments. The highest grain yield (345.56 g m⁻²) and highest harvest index (45%) of wheat were recorded under the N1 treatment, which was statistically similar to the N2 treatment. The highest NUE of wheat (28.8 g g⁻¹) was recorded with the N1 treatment, which was statistically identical with the N2 treatment. Current results suggest that up to 33% of N-equivalent urea fertilizer substitution with organic manure could serve as a suitable eco-friendly alternative to sole reliance on chemical fertilization for wheat farming in this region.