Co-application of mustard oil cake and chemical fertilizers increased yield and quality of betel leaf (Piper betle L. cv. Mahanali) in sub-tropical floodplain soil

Nutrient management is crucial for sustainable betel leaf production in subtropical floodplain soils; however, the effects of co-applying mustard oil cake (MOC) with mineral fertilizers have not been well studied in Bangladesh. This study evaluated graded N-substitution ratios of MOC and urea to identify the most productive and profitable nutrient management strategy for betel leaf (Piper betle L., cv. Mahanali) across Rabi and Kharif seasons using a randomized complete block design with three replications. The experiment consisted of six treatments, viz, T0 (Control), T1 (N300P100K100 kg ha-1), T2 (25% N from MOC + 75% N from urea), T3 (50% N from MOC + 50% N from urea), T4 (75% N from MOC + 25% N from urea), and T5 (100% N from MOC). The findings revealed that nutrient management significantly improved betel leaf growth and yield across seasons. T3 produced the highest Rabi yield (2.76 t ha-1), increasing yield by 94.83% over the control (1.42 t ha-1), while T4 produced the highest Kharif yield (5.78 t ha-1), increasing yield by 79.37% over the control (3.23 t ha-1). Post-harvest soil fertility also improved, with maximum increases in SOC from 0.74 to 0.81%, total N from 0.06 to 0.08%, available P from 8.30 to 9.85 ppm, exchangeable K from 0.34 to 0.41 meq 100 g-1 soil, and available S from 6.27 to 6.92 ppm, corresponding to increases of 8.6, 33.3, 18.7, 20.6, and 10.4%, respectively. Moreover, the highest BCR (1.37) was calculated from T3. Co-applying MOC with urea, particularly at 50–75% N substitution from MOC, improves betel leaf yield and soil nutrient status, with T3 best for profitability and T4 best for soil improvement.