Soil carbon and nitrogen dynamics following application of pig slurry for the 19th consecutive year: I. Carbon dioxide fluxes and microbial biomass carbon

Agricultural soils often receive annual applications of manure for long per iods. The objective of this study was to quantify the effects of 19 consecu tive years of pig (Sus scrofa) slurry (PS) application on CO2 emissions and soil microbial biomass. Soil temperature, soil moisture, sad extractable s oil C were also determined to explain the variations in CO2 emissions and s oil microbial biomass. Long-term (19 Sr) treatments were 60 (PS60) and 120 Mg ha(-1) yr(-1) (PS120) of pig slurry and a control receiving mineral fert ilizers at a dose of 150 kg ha(-1) yr(-1) each of N, P2O5, and K2O. Very hi gh CO2 emissions (up to 1.5 mg CO2 m(-2) s(-1)) occurred during the first 2 d after PS application. Following that peak, decomposition of PS was rapid , with one-half the total emissions occurring during the first meek after s lurry application. The rapid initial decomposition was exponential and was attributed to the decomposition of the labile fraction. of the slurry C. Th e second phase was linear and much slower and probably involved more recalc itrant C material. Cumulative annual decomposition was proportional to the application rate, with 769 and 1658 kg C ha(-1) lost from the 60 and 120 Mg ha(-1) doses, respectively. Pig slurry application caused a rapid increase in soil microbial biomass (from approximate to 100 to up to 370 mg C kg(-1 ) soil), which coincided with a peak in the concentration of extractable C and in CO2 emissions. Field estimates of the microbial specific respiratory activity suggested that the difference in soil respiration between the two slurry treatments was due to differences in the size of the induced microb ial biomass rather than to differences in specific activity.