BIOFERTILIZERS AS COMPLEMENTS TO SYNTHETIC AND ORGANIC FERTILIZATION - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 168

Strain 63-28 of Pseudomonas fluorescens functions as an activator of disease resistance
of plants by inducing the synthesis of callose in tomato (M'Piga et al. , 1997), while the
application of saprophyte fluorescent pseudomonads in beans resulted in increased lignin
content in the root (Anderson & Guerra, 1985).
Serratia plymuthica, strain R1GC4, sensitizes cucumber plants to react more quickly and
effectively against the attack by Pythium ultimum, through the formation of physical and
chemical barriers to impede the penetration of the fungi (Benhamou et al. , 2000).
Formation of Biofilms to Prevent the Entry to Pathogens
Frequently, bacteria live in the environment as biofilms, which are highly structured,
surface-attached communities of cells encased within a self-produced extracellular polymeric
substance matrix (O'Toole et al., 1999; 2000; Branda et al., 2005; Kolter & Greenberg, 2006).
Bacterial biofilms established on plant roots could protect the colonization sites and act as a
sink for the nutrients in the rhizosphere, hence reducing the availability of root exudate
nutritional elements for pathogen stimulation or subsequent colonization on the root (Weller
& Thomashow, 1994). Particularly some strains of Paenibacillus polymyxa can form biofilms
around the root tips of some plants to improve drought tolerance and to prevent the access to
pathogens (Timmusk et al., 2005; Singh et al., 2006).
I NTEGRATED P LANT N UTRITION S YSTEM (IPNS): C OMBINED U SE OF
B IOFERTILIZERS AND C HEMICAL OR O RGANIC F ERTILIZERS
One of the most important requirements in agriculture is the maintenance of soil fertility.
Traditionally, nutrient deficiency, especially of N, is corrected by adding fertilizers. However,
the high costs of these chemical products limit this practice, especially in developing
countries, where the need to increase food production is more urgent (Aguado-Santacruz et
al., 2012). It is estimated that crops absorb between 20-40% of the fertilizer applied because
the rest is lost in different ways, generating substantial economic losses and environmental
pollution such as eutrophication of water bodies, acid rain, destruction of the stratospheric
ozone layer and increased greenhouse effect (Duxbury, 1994). On the other hand, some other
sources, mainly organic fertilizers (compost, vermicompost and manures) and more
importantly the Nitrogen Biological Fixation (NBF), can also contribute significantly to the N
soil economy,
The IPNS basic concept is the adjustment of soil fertility for providing the optimal plant
nutrients in order to maintain high crop productive levels taking advantage of the benefits
from all of the possible sources of nutrients in an integrated manner (Jen-Hshuan, 2006). The
implementation of sustainable technologies, such as biofertilization, to complement and
enhance the assimilation of nutrients from chemical synthetic fertilizer and organic fertilizer,
has been assessed in different studies that report satisfactory performance of different crops
cultured under different environments emphasizing the necessity of considering
complementary nutritional sources and tools for augmenting the nutrient assimilation by
agricultural crops.