Film Mulching with Low Phosphorus Application Improves Soil Organic Carbon and Its Decomposability in a Semiarid Agroecosystem

Soil organic carbon (SOC) storage and decomposability are crucial for soil quality. Film mulching phosphorus (P) application important agricultural practices on the semiarid Loess Plateau. This study analyzed combined effects of film P SOC, its fractions, mineralization kinetics under alfalfa (Medicago sativa L.). The six-year field experiment incorporated randomized blocks split-plot design with two treatments (no flat planting ridges furrows) as main plots four levels (P0: 0 kg ha−1, P1: 9.73 P2: 19.3 P3: 28.9 ha−1) subplots. Mulching increased SOC content, fractions (light heavy fraction C, microbial biomass dissolved C), mineralization. After six years, content by 2.18, 2.60, 2.37, 0.17 g kg−1 at P0, P1, P2, P3, relative to no mulching. With increasing levels, but initially then decreased P1 displayed highest utilization efficiency stability. Kinetic models divided into an active a slow pool, latter showing lowest stability in Overall, low level, especially 11.9 ha−1 fertilizer, promoted Plateau due high C decomposability.