BIOFERTILIZERS AS COMPLEMENTS TO SYNTHETIC AND ORGANIC FERTILIZATION - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 171

1 soil). The positive responses observed in the growth of inoculated plants may be due to the
provision of nutrients, especially nitrogen, and growth promoting hormones by Azospirillum
sp. and greater uptake of phosphorus and other nutrients due to mycorrhizal colonization
(Zaidi et al., 2004). The greater availability of nutrients can be attributed to organic manure
decomposition or transformation of inorganic substances into available forms by
microorganisms. The increased population of Azospirillum sp. , as well as spore density and
G. mosseae colonization could be related to the application of manure, which constitutes a
carbon source for microbes.
C ONCLUSION
The information presented in this chapter shows that plant growth promoting
microorganisms can be successfully used as complementary tools to organic and chemical
fertilization for improving plant nutrition. It is clear that the confidence of the studies
conducted under field conditions will largely depend not only on our knowledge of the
nutrient and biological charge of the soil and composts or manures employed as organic
fertilizers, and the growth promoter activities of the microorganisms employed as
biofertilizers, but also on their particular interactions. This knowledge will be instrumental in
the implementation of successful, low-environmental impact and more profitable agriculture
production systems (organic or conventional).
Current and predicted costs of chemical fertilizers and cumulative evidence of negative
effects of agrochemicals on the environment and human health will follow redirecting the
efforts of crop research to look for the implementation of an integrated plant nutrition system
in the agricultural production systems. Certainly, environmental and health, but mainly
economic concerns will greatly impulse this approach in the next years.
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