Long-Term Effects of Fertilization and Subclover Seeding on Northern California Annual Range

Abstract

The long-term effects of P and S fertilizers and subclover seeding on northern California annual range production and composition were measured during a 20-year study. Following an initial calibration period, two pastures were seeded and fertilized; pasture A prior to the 1968 growing season and pasture B prior to the 1973 growing season. After treatment pasture A produced significantly more forage annually. It also produced significantly more winter forage, and winter and annual forage N than either of two adjacent untreated control pastures during the period from 1973 to 1979. This was due primarily to an increase in native legumes because subclover averaged only 7% of cover. Treatment on pasture B gave similar responses, but the relative increases in forage production were larger (annual production increased about 2,000 kg/ha compared to 1,200 kg/ha on pasture A), and winter forage N concentrations were significantly higher than on pasture A. This was due to the greater subclover component (36%) on pasture B. The significant increases in forage production and protein indicate that subclover seeding and appropriate fertilization are practical ways of improving utilization of northern California annual range.