Can an enhanced soil biological community improve availability of plant nutrients in organic systems?
It is often assumed that the soil biological community will be enhanced in response to organic management, developing a greater capacity to supply plants with nutrients from poorly soluble inorganic and organic sources (Ritz et al 1997). However, if organic systems do not include larger inputs of organic matter than conventional counterparts, or if organic production is limited by low fertility, the soil biological community and its activity will not be enhanced relative to conventional systems (Ryan 1999). Indeed, soil organic matter contents have been reported as higher (Reganold 1988; Wander et al 1994; Liebig and Doran 1999), lower (Ltzow and Ottow 1994; Petersen et al 1997) or to not differ (Derrick and Dumaresq 1999) in organic compared to conventional systems. This variety reflects different crop sequences and/or addition of different amounts and types of organic inputs (Robertson and Morgan 1996). Higher addition of organic matter in either system is naturally followed by a lar
