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□ Latin America

□ North America

FIGURE 17.1 Hectares in organic food production and number of organic farms on a global basis.

a combination of changes in the microbial community and a physical redistribution of SOM fractions (Wander and Traina, 1996; Clark et al., 1998). In the long term, soils under organic management will tend to increase in SOM. In addition, organically managed soils also have increased levels of biologically active SOM, which promotes an active microflora. This is why organically managed soils have a greater microbial biomass, more active microbial respiration, and a higher rate of N mineralization than conventionally farmed soils (Reganold et al., 1993; Clark et al., 1998).

Since organic systems are often low nutrient input systems, with respect to N, P, and K, the cycling of SOM by microorganisms is important because plants rely on nutrients solely from SOM. These systems may work due to an increase in microbial biodiversity as transition to organic management occurs. Organic systems have higher catabolic activity and nutrient cycling stability as the microbial diversity increases. However, this increase in diversity and its relationship to soil function are poorly understood, leading others to conclude that microbial biodiversity is not the primary regulator of SOM dynamics. The mechanistic basis of the microbial diversity-soil function relationship with respect to C and N cycling needs further study.

There are scant scientific studies on the nutritional benefits of organically grown foods; however, higher levels of vitamin C, flavonoids, and nutrient elements Ca, Mg, and Fe and superior taste are commonly cited. Comparatively, in conventionally fertilized soils it has been shown that excess N can decrease the nutritional quality and taste of crops and make plants more susceptible to diseases and insects. Excess N is also responsible for decreasing the vitamin C of crops. The most often cited benefits of organically grown foods are probably what may not be on and in the foodstuffs, such as herbicide and pesticide residues and high concentrations of nitrates. In addition, no genetically modified (GM) crops or ingredients are allowed in organic foods, and in animal production there is no routine use of antibiotics.

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