“Cultivation of Pakcoy Mustard (Brassica rapa L.) in a Hydroponic System in a Surabaya Vegetable Garden: Analysis of Plant Nitrogen Requirements: Budidaya Sawi Pakcoy (Brassica rapa L.) pada Sistem Hidroponik di Kebun Sayur Surabaya: Analisis Kebutuhan Nitrogen Tanaman” (2026) Procedia of Engineering and Life Science, 8(2). doi:10.21070/pels.v8i2.2520.