Changes in Soil Properties and Carbon Content Following Compost Application: Results of On-farm Sampling

Abstract

A field survey was conducted to quantify the benefits of applying compost to agricultural soils in California. Soil samples were collected from farm sites with a history of compost use. Soils were analyzed for total organic carbon and nitrogen, Mehlich III extractable nutrients, bulk density, microbial activity (measured as CO₂ evolution), water infiltration rate and gravimetric water at 1 bar tension. Across all sites, compost application increased soil organic carbon by 3× in comparison to control soils. Significant changes were also observed in soil microbial activity (2.23 × control), gravimetric water (1.57 × control), and bulk density (0.87 × control). Nutrient availability in compost amended soils was similar to availability in conventionally managed soils. Infiltration times were significantly reduced in compost amended soils in comparison to control soils. High rates of compost application showed more significant benefits in comparison to low rates of compost application and control soils. At lower application rates, compost amended soils were statistically similar to controls for most variables. Increases in water holding capacity were significant in coarser textured soils in comparison to finer textured soils. Results from this sampling confirm results from replicated field trials on benefits associated with compost use in agricultural soils.