was a linear effect of Wollastonite application in the above-ground
part of plants and grain, i.e., the higher the Si dose applied, the
higher the concentration in the tissues (Figure 1).
sources were compared, differences were observed between them. The
phosphorus slag elicited the highest Si concentration in the
above-ground part of plants, followed by Wollastonite and the electric
furnace slag, which did not differ between themselves, for both
above-ground part and grain. The stainless steel slag, LD3 and AOD only
differed regarding Si content in the above-ground part. The source
showing the smallest Si content was silicate clay, which did not differ
from the control treatment, followed by AF2, AF1, schist ash, schist,
and LD4 (Table 2).
slags (LD, AOD, electric, and stainless steel furnaces) had higher Si
availability than blast furnace slag, and those slags also showed
solubility differences among themselves, depending on the type of steel
produced and type of furnace used to produce steel (Table 2). Similar results were also obtained by Kato & Owa (1997).
The soil Si content determined by both extractors also increased with Wollastonite doses (Figure 2),
but extraction in acetic acid was higher. With regard to results of
soil Si and Si accumulated by plants, no significant correlations were
found (Figure 3).
The AF2 slag was the source with the highest Si release by acetic acid (Table 3),
but it was not, however, the treatment with the greatest uptake by the
plant; actually, the opposite occurred. This happened due to Si
solubility in the source itself by acetic acid. A similar fact occurs
with phosphorus extracted by double acid in soils where natural
phosphate is applied. Results overestimate this element because of the
insoluble phosphorus solubilization in the soil by the acid (Raij,
1991). On the contrary, high correlation between soil Si extracted in
acetic acid and plant-absorbed Si was observed when Wollastonite was
applied, since it is practically insoluble in weak acid (Pereira et
al., 2003). In this case, Si determined in the soil corresponds to the
amount of Si actually released by the source.
the Si in the soil, extracted by showed better correlation when
compared to the acetic acid, contradicting results of Korndörfer et al.
(1999) who, working with a single Si source, concluded that acetic acid
is superior to calcium chloride. Some Si sources show solubility in
acetic acid but not in CaCl2. Therefore, acetic acid could
solubilize the material applied to the soil, which is not available for
plants, overestimating Si availability. This was demonstrated in
another paper by Korndörfer & Gascho (1999). When different doses
of Wollastonite and phosphorus slag were applied, the authors observed
greater Si accumulation in rice with Wollastonite, while the source
with the highest Si release in the soil was phosphorus slag.
With respect to dry matter yield, Wollastonite showed linear increase with increasing Si doses (Figure 4).
This reinforces the idea that Si is indeed beneficial to rice. However,
the only difference between sources occurred for grain yield between
the stainless steel (highest yield) and silicate clay treatments
(lowest yield) (Table 4). Maybe the 125 kg ha-1
dose was not sufficient to reveal more expressive differences between
sources. In the case of Wollastonite, the response was linear and
positive with increasing doses, with the application of 500 kg ha-1 Si showing the highest yield (Figure 4).
With regard to Si extraction by plants, Wollastonite also showed linear increases with increasing doses (Figure 5).
Between sources, P slag also accumulated the most Si, followed by
Wollastonite, which differed in Si accumulation in the grain, and by
electric furnace slag, which differed in Si accumulation in dry matter.
These two sources, however, did not differ regarding total Si uptake (Table 5).
steel slag was the source allowing the higher Si acumulation in grain
due to its higher productivity, and was the source ranked fourth
regarding total Si uptake, followed by LD1, LD3, AOD, LD2, and LD4. The
sources extracting the smallest amount of Si were, again, silicate clay
and AF2, which also did not differ from the control, followed by
schist, schist ash, and AF1 (Table 5).
the efficiency of the sources with regard to total Si accumulation was
considered in comparison to the standard, P slag was the only source
superior to the standard. Stainless steel slag and electric furnace
slag were seemingly as efficient as the standard, while the other iron
metallurgy slags (LD1, LD3, AOD, and LD2) showed a behavior where
reduced doses of the standard, between 10 and 20%, would be enough to
provide the same amount of Si as the 125 kg ha-1 Si doses
provided by those sources. The other sources showed equivalent doses
well below that value; the least efficient was again silicate clay,
where the supplying of only 7 kg ha-1 Si provided by the standard would be sufficient to show the same effect as 125 kg ha-1 Si provided by this source.