Agriculture Reference
In-Depth Information
microbes immobilize soil nutrients. With time, the enhanced availability of
soil nutrients in organic farming can dominate such deficiencies and hence
increase the rate of crop production. Microbial activities in soil can
significantly influence soil productivity when transitioning to organic farming
(Widmer et al., 2006).
Conventional farming can adversely affect soil microbial activities
(Menendez et al., 2001). Agricultural practices including use of chemical
fertilization and tillage can diminish the diversity and population of AM fungi
in soil. For example, soil tillage can negatively affect the network structure of
AM hyphal decreasing AM fungi activity and population. In addition, soil
tillage can move AM spores to the deeper depths delaying the process of root
colonization. These all decrease plant growth and yield production (Evans and
Miller, 1990; Kabir et al., 1998; 1999; Kabir, 2005). Hence, use of no- or
reduced tillage is very recommendable as such tillage methods can increase
the rate of colonization and plant nutrient uptake (Galvez et al., 2001).
Among different soil nutrients, P is the nutrient that can decrease AM
fungi activities in soil. It is because AM fungi can enhance plant P uptake in
soils with low or medium level of P. In addition, excess P can also adversely
affect P transporters gens. Due to excess use of P fertilization and with respect
to the low solubility of P in soil usually P can build up in soil (Kahiluoto et al.,
2001; De Clerck et al., 2003; Kogelmann et al., 2004). Different researchers
have indicated the positive effects of organic farming on AM root colonization
and number of propagules including spores and AM fungal diversity (Galvez
et al., 2001; Ryan et al., 2004). The following practices can adversely affect
the performance of AM fungi under organic farming: 1) controlling weeds by
mechanical tillage, 2) use of bare follows, 3) planting non-mycorrhizal crops,
and 4) use of herbicides with copper. However, to improve the performance of
AM fungi under organic farming the following practices are suggested: 1) low
use of chemical fertilization, although the low soluble ones are
recommendable, 2) no or minimum use of fungicides, and 3) use of diverse
and suitable rotations (Ryan and Graham, 2002). It can also be very beneficial
if AM fungi inoculum is used for plant inoculation under organic farming.
Most of the experiments regarding the effects of AM inoculation on plant
growth have been performed under greenhouse conditions, however, there are
also examples of field inoculation (Alkaraki et al., 2004; Miransari et al.,
2006; Daei et al., 2009).
