Mitigating water stress effects on Roselle production: effects of Conocarpus biochar and nitrogen fertilizer on soil nutrients and yield

Aims The objective of this study was to determine the effects of different levels of irrigation water depth, nitrogen fertilizer, and Conocarpus biochar on the quantitative and qualitative characteristics of Roselle plants and their irrigation water use efficiency (IWUE) and soil nutrition. Methods The experimental treatments included three levels of nitrogen fertilizer (N1: 100, N2: 150, N3: 200 t ha −1 ), three levels of irrigation water depth (I1: 50, I2: 75, I3: 100% of plant water requirement), and three levels of biochar (B1: 0, B2: 10, B3: 20 t ha −1 ). Results The research findings indicated that the effects of irrigation water depth, nitrogen fertilizer, and biochar were significant on all measured parameters at a 1% and 5% probability level. The highest yield (710.58 kg ha −1 ) was achieved under the B3N2 treatment. The highest IWUE was observed under the I2N3 treatment (0.125 kg m −3 ). Applying biochar at all levels increased the total nitrogen content, organic matter, and microbial carbon biomass while reducing nitrate leaching in the soil. The total nitrogen, organic matter, and microbial carbon biomass increased by 82.92%, 47.31%, and 61.75%, respectively. Conclusions Considering the region’s water scarcity, applying 75% of the water requirement (I3) can help conserve water. Additionally, using 75% of the nitrogen content (N2) and applying 20 t ha −1 of biochar (B3) can improve Roselle’s quality and mitigate drought stress’s negative impacts. Furthermore, using Conocarpus waste and other agricultural residues as biochar can increase organic matter levels in dry soil areas while preventing environmental pollution.