Changes During Conversion

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The transition from conventional to organic and low-input farming is accompanied by changes in an array of soil chemical properties and processes that affect soil fertility. Fundamental differences, both qualities and quantitative, in the flow and processing of nutrient result from the use of cover crops, manure and compost applications, and reduction or elimination of synthetic fertilizers and pesticides. These changes affect nutrient availability to crops either directly by contributing to nutrient pools or indirectly by influencing the soil chemical and physical environment.

Few studies were reported with regards to conversion from conventional to organic farming (Werner 1997; Tu et al. 2006; Melero et al. 2007; Gopinath et al. 2008). Yield reduction in organic farming due to nutrient limitation and pest incidence in the early stages of transition from conventional to organic systems is a major concern for organic farmers, and is thus a barrier to implementing the practice of organic farming. Therefore, study related to transition strategies is important for facilitating the implementation of organic practices.

Microbial biomass and respiration rate were more sensitive to changes in soil management practices than total C and N. In the first 2 years, the organic management was most effective in enhancing soil microbial biomass C and N among the transition strategies, but was accompanied with high yield losses. By the third year, soil microbial biomass C and N in the reduced-input transition strategies were statistically significantly greater than those in the conventional. Soil microbial respiration rate and net N mineralization in all transitional systems were statistically significantly higher than those in the conventional, with no differences among the various transition strategies. The study suggested that the transitional strategies that partially or gradually reduce conventional inputs can serve as alternatives that could potentially minimise economic hardships as well as benefit microbial growth during the early stages of transition to organic farming systems (Tu et al. 2006). Axelsen and Elmholt (1998) estimated that a transition to 100% organic farming in Denmark would increase microbial biomass by 77%, the population of springtails by 37% and the density of earthworms by 154% as a nationwide average. Conversion to organic farming provides opportunities to significantly increase biological activity of the soil as well (Axelsen and Elmholt 1998). During conversion from conventional to organic farming, Melero et al. (2007) reported gradual increase in dehydrogenase, protease, b-glucosidase and alkaline phosphatase. In a 2-year conversion period, most of the enzymatic activities were more in organically managed soils than mineral-fertilized soils (Gopinath et al. 2008).

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