INFLUENCE OF NITROGEN FERTILIZATION AND STRAW RETURNING ON NITROGEN UPTAKE IN UPLAND SOILS: INSIGHTS FROM PHYSICOCHEMICAL PROPERTIES

This study investigated the effects of nitrogen fertilization and straw returning on soil physicochemical properties, enzymatic activities, and soybean yield in upland soils.A field experiment was conducted using three straw-returning levels T0, T1 no straw returning, and T2, combined with four nitrogen application rates N0, N1, N2, and N3.Under T2 + N3, soil total nitrogen reached 1.52 g kg, available potassium was 174.3 mg kg, and alkaline phosphatase activity measured 323.65 U L.With higher straw and nitrogen inputs, urease and phosphatase activities were enhanced, while sucrase activity declined.Agronomic traits improved under T2 + N3, with plant height at 89.67 cm, pods per plant at 73.08, seeds per plant at 171.21, hundred-seed weight at 16.04 g, and yield at 2726.34 kg ha.These findings demonstrate that combining higher straw returns with increased nitrogen fertilization effectively enhances soil fertility, enzyme-driven nutrient cycling, and soybean productivity in upland agricultural systems, compared to the low return conventional fertilization regime.