Dairy Manure and Cover Crops Effect on Soil Biological Properties, C Fractions, and Bulk Density.

No-till efficiency to improve soil quality for economic crop production can be improved by organic amendments. Since dairy manure supplies organic matter, N and other nutrients, it is likely that dairy manure will exert immediate and wide-ranging beneficial effects on more soil quality properties than chemical fertilizers alone. A randomized complete experiment was conducted to determine the seasonal effects of dairy manuring with or without cover crops on biological properties, C fractions, and bulk density of soil. Dairy manure was applied in fall of 2006 at 0, 3000 and 6000 gallons per acre to standing annual ryegrass and cereal rye with a bare field as control. Soil samples were randomly collected (at 0-15 and 15-30 cm depth) in late September 2006 (fall) prior to application of dairy manure, and March (winter), May (spring), and August (summer) of 2007, respectively after manure application. The 2-mm sieved field-moist soil samples were analyzed for microbial biomass, soluble and salt extractable C. A portion of the soil was air-dried and analyzed for antecedent moisture content, pH, Ec, active and total C, and bulk density. Results showed that dairy manure applied at 6000 gallons per acre significantly influenced Ec, salt extractable C (7 to 18%), microbial biomass (20 to 43%), and the proportion of microbial biomass in total C (21 to 41%) over 3000 gallons per acre and control treatments. A significant variation in Ec, pH, salt extractable an soluble C, microbial biomass, proportion of microbial biomass in total C, and active C was found in response to season. Greater microbial biomass was found during spring-summer compared to winter. Both active and salt extractable C was highest in fall and lowest in summer. However, soluble C was highest in spring. The effect of dairy manure was most pronounced fall-spring than winter-summer. Seasonal effect on microbial biomass was most pronounced at surface soil (0-15 cm depth) over subsurface depth (15-30 cm).