The importance of Si fertilization in rice (Oryza sativa L.) and sugarcane (Saccharum
spp.), among other crops, has already been demonstrated by Okuda &
Takahashi (1964) in Japan; Ayres (1966) and Halais (1968) in Mauritius;
Gascho (1978), Snyder et al. (1986), and Anderson et al. (1987) in
Florida; and Korndörfer et al. (2002) in Brazil. The critical
sufficiency levels of this element in the soil and plants are currently
being established in Brazil (Korndörfer et al., 1999; 2002). It is
therefore necessary to identify the most promising, potentially
available Si sources to plants.
residues, such as rice hulls and sugarcane bagasse, are sometimes used
as Si sources. In addition to the fact that they are slow-release Si
sources, these residues have other uses, such as the generation of
steam, and are insufficient to meet the demand for Si in agriculture.
On the other hand, there are Si-rich metallurgic slags which could meet
this demand. The high temperatures used in iron industry release Si
from crystalline form to reactive and consequently more soluble forms.
results of 23 field experiments, during the 1992-1996 period,
Korndörfer et al. (2001) observed increase in grain yield of irrigated
rice - 1,007 kg ha-1 - in plots receiving Si as Ca silicate.
On the other hand, accumulated Si in rice plants could reduce
transpiration rate, by decreasing water intake (Marschner, 1995 and
Takahashi, 1996). Results by Faria (2000) corroborate this assertion;
when soil moisture was at 80% of field capacity, no increases in grain
yield were observed. Conversely, under a lower soil humidity value -
60% of field capacity - grain yield increased were linearly with
increasing Si rates, an indication that Si plays important role on
increasing tolerance of rice plants to water stress.
most important characteristics of a Si source for agricultural use are:
high soluble Si content, suitable physical properties, easy mechanized
application, ready availability for plants, low cost, balanced ratios
and amounts of calcium (Ca) and magnesium (Mg), and absence of heavy
metals. Many iron metallurgy slags possess these traits, and some of
them are promising sources of Si (Korndörfer et al., 2002).
the lack of information and the great demand for agronomically
efficient and economically viable Si sources for agriculture purpose,
the objective here was to evaluate several Si-rich materials (slags,
silicates, thermophosphates etc.) with regard to their ability to
supply this element to plants.