Agriculture Reference
In-Depth Information
has been recognized as one of the main limiting factors for upland rice production
in many parts of the world (Sahrawat et al.
2001
). This situation requires an
extensive research in order to manage the fertilizer application in aerobic rice,
especially phosphorus nutrient management.
9.2.2.1 Phosphorus
Phosphorus indeed is a primary essential nutrient for rice production. It stimulates
various physiological activities such as root and shoot growth, promotes vigorous
seedling growth, advances crop maturity, and plays a vital role in plant metabolism
such as cell division, breakdown of sugar, nutrient transport within the plant,
regulation of metabolic pathways,
and other biochemical
characteristics
(Theodorou and Plaxton
1993
; Khan et al.
2009
).
Phosphorus deficiency is a common problem in many soils; globally, about 5.7
billion ha of land has been found to contain too little available P for sustaining
optimal crop production. Phosphorus ion concentration in most of the soils ranges
from 0.1 to 10
M, while P in soil should range from 1 to 5
M for the optimal
μ
μ
growth of grasses and 5-60
M for high-demand crops such as tomato and pea
(Hinsinger
2001
). Malaysian soils are generally poor in P, and a substantial amount
of Malaysia's income (RM 55 billion) was expected to be derived from agricultural
activities in 2010. Demand of phosphate fertilizer in the world has increased from
40.6 million tons in 2011 to 41.5 million tons in 2012, at a growth rate of 2.4 %. It is
expected to reach 45 million tons in 2016 at a growth rate of 2 % per year. Of the
overall increase in demand for a total of 3.5 million tons P
2
O
5
between 2012 and
2016, 58 % would be in Asia, 24 % in America, 11 % in Europe, 4 % in Africa, and
3 % in Oceania. Among the Asian countries, about 25 % of growth in world demand
of P is expected in India, 14 % in China, 4 % in Pakistan, and 3 % in Indonesia,
Malaysia, and Bangladesh. West Asia accounts for 5 % of the increase in consump-
tion, of which Turkey, Iran, and Syria have the bulk of the share (FAO
2012
).
μ
9.3 Phosphate-Solubilizing Bacteria
Soil microorganisms have ability to convert insoluble phosphatic compounds into
soluble P form for uptake by the crops (Panhwar et al.
2011
). There are many
rhizosphere microorganisms, which are able to dissolve insoluble P (Henri
et al.
2008
; Hameeda et al.
2008
). Microorganisms play an important role in
agriculture by supplying nutrients to the plants and reduce the demand of chemical
fertilizers ( ¸ akmak¸ı et al.
2006
). It has been found that the poorly soluble P is
usually dissolved by microorganisms, which can then be converted into soluble
forms by the process of acidification, chelation, and exchange reactions (Chung
et al.
2005
). The quantity of PSB, involved in solubilization process, is more
abundant in the rhizosphere than non-rhizosphere soil and is metabolically more
