ABSTRACT
The soil biota, which promote soil aggregation and regulate nutrient mineralization and trace gas emissions, are also strongly in¢uenced by N fertilizer applications, although the direction of change for particular taxa is often difŸcult to predict. For example, increases, decreases, and no change in microbial biomass following fertilizer applications have been detected (O’Donnell et al., 2001; Ramirez et al., 2010), and the duration of reported changes varies (Ryan et al., 2009; Singh and Ghoshal, 2010). Similarly, synthetic N application in agricultural systems can increase soil CO2 emissions and soil C loss (Al-Kaisi et al., 2008; Russell et al., 2009; Kwon and Hudson, 2010), but responses remain difŸcult to predict (Taylor and Townsend, 2010), and reports showed accumulation (Al-Kaisi et al., 2008; Reay et al., 2008; Poirier et al., 2009), loss (Hofmann et al., 2009; Khan et al., 2007; Mulvaney et al., 2009), or no change in soil C (Halvorson et al., 2002).
