Dairy manure effects on soil quality properties and carbon sequestration in alfalfa-orchardgrass systems

Dairy manure, as a passive by-product of livestock, is an important source of nutrients and organic matter to soils that support forage production. A split-plot experiment was conducted to determine the long-term (19941999) effects of dairy manure and chemical fertilizer on soil quality properties and carbon (C) sequestration in an alfalfa (Medicago sativa L.) and orchardgrass (Dactylis glomerata L.) forage systems. Five years after initiation of the experiment, soil core samples were collected randomly from between the alfalfa-orchardgrass rows under different treatments and analyzed or incubated to determine selected soil biological, chemical and physical properties. Results show that long-term application of dairy manure slurries significantly increased total organic, microbial biomass, potentially mineralizable, extractable and labile C pools, respectively, and improved soil aggregate stability by associated decrease in specific maintenance respiration rates, and subsequently enhanced soil quality. Relatively smaller amounts of total, microbial biomass, extractable and labile C pools with an increase in specific maintenance respiration rates, and increase in soil acidity accompanied by a decrease in aggregate stability suggest that long-term and continuous use of inorganic fertilizers for forage production did not improve soil quality or enhance C sequestration. The continuous cover of forage species, especially alfalfa, significantly improved soil quality over time as compared to orchardgrass species. The beneficial effects of organic amendments are important for proper disposal and utilization of dairy manures in forage production systems with an accompanied improvement in soil quality and C sequestration.