Soil Microbial Biomass

Field and laboratory experiments have demonstrated that soil microbial activity can create soil conditions favourable to sustainable production (Andrade et al. 1998). Bolton et al. (1985) found that microbial activity and microbial biomass were higher under organic management systems. Soil microbial communities are strongly influenced by agricultural practices. Many farming practices such as intensive tillage, application of chemical pesticides and mineral fertilizers and monoculture are directly or indirectly harmful to soil microbes. Microbial population density and diversity are affected by the level of organic matter, which provides energy for soil micro-organisms. Peacock et al. (2001) reported that soil management practices that result in differential carbon inputs also affect the size and structural community of soil biomass. One such practice is the use of organic amendments and cover crops, which increase carbon availability to micro-organisms. Non-pathogenic and plant growth stimulating micro-organisms in the rhizosphere increase plant root exudation. This will in turn improve root growth and thereby plant nutrient availability. It has been shown to occur in the presence of free-living bacteria such as Azospirillium spp. and Azotobacter spp. and in the presence of symbiotic organisms such as myc-orrhizae (Lundegardh and Martensson 2003).

Dynamics of microbial communities during two growing seasons were significantly negatively correlated with amounts of soil mineral N in the conventional system, whereas they were positively correlated with mineral N in the organic system (Gunapala and Scow 1998). Another study showed that total bacterial biomass was highest in conventional field soils while the ratio of active to total bacterial biomass was highest in organic field soils (Glenn and Ristaino 2002). After long-term organic management, e.g. >40 years, microbial biomass C was higher than in conventionally managed farm soils (Schjonning et al. 2002). Carbon released from crop residues contributes to increasing soil microbial activity and so increases the likelihood of competition effects in the soil.

Organic Gardeners Composting

Organic Gardeners Composting

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