In response to human population increase, the utilization of acid sulfate
soils for rice cultivation is one option for increasing production. The main
problems associated with such soils are their low pH values and their
associated high content of exchangeable Al, which could be detrimental to
crop growth. The application of soil amendments is one approach for
mitigating this problem, and calcium silicate is an alternative soil
amendment that could be used. Therefore, the main objective of this study was
to ameliorate soil acidity in rice-cropped soil. The secondary objective was
to study the effects of calcium silicate amendment on soil acidity,
exchangeable Al, exchangeable Ca, and Si content. The soil was treated with
0, 1, 2, and 3 Mg ha
Soils are the key to understanding the earth system as they control the hydrological, biological, geochemical, and erosional cycles (Smith et al., 2015; Decock et al., 2015; Keesstra et al., 2012). Moreover, the soil system is damaged by millennial use and abuse of soil resources, and the soils are failing to supply humankind with goods and services due to the degradation of soil structure, loss of soil quality, and loss of soil fertility (Dai et al., 2015; Masto et al., 2015; Zhao et al., 2015; Cerda, 1998; Costa et al., 2015). Pollution is one of the triggering factors of soil degradation and it is a worldwide problem (Wang et al., 2015; Roy and Mcdonald, 2015; Mahmoud and Abd El-Kader, 2015). Therefore, this is why it is necessary to develop a new strategy to restore and rehabilitate the soils, which can be based on the use of amendments (Riding et al., 2015; Hu et al., 2015; Yazdanpanah et al., 2016; Tejada and Benitez, 2014; Prosdocimi et al., 2016).
Acid sulfate soils are widespread in Malaysia, occurring almost exclusively
along its coastal plain (Shamshuddin and Auxtero, 1991; Shamshuddin et al.,
1995; Muhrizal et al., 2006; Enio et al., 2011). In these areas, the alluvial
sediments are intermittently inundated by seawater during low and high tides.
These soils are dominated by pyrite with high acidity (soil
pH < 3.5) (Shamshuddin, 2006) and are produced when the
pyrite-laden soils in the coastal plains are opened up for crop production
and/or development. This scenario leads to the release of large amounts of Al
into the soil environment (Shamshuddin et al., 2004), which affects crop
growth. For example, it affects oil palm growth (Auxtero and Shamshuddin,
1991) and cocoa production (Shamshuddin et al., 2004). In Peninsular
Malaysia, acid sulfate soils are used for rice cultivation with mixed
success. At times, rice cultivation in these soils is successful; but most
often, the rice yield each season is very low (< 2 t ha
The application of soil amendments to acid sulfate soil is a common approach for improving fertility. Suswanto et al. (2007), Shamshuddin et al. (2009), Shazana et al. (2013), Elisa et al. (2014), Fernandez-Sanjurjo (2014), Rabileh et al. (2015), and Rosilawati et al. (2014) reported that the infertility of acid sulfate soils can be ameliorated by application of lime, basalt, gypsum, biochar, controlled-release fertilizer, organic fertilizer, and/or their combination at an appropriate rate. Application of these ameliorants increased soil pH and reduced Al toxicity, resulting in improved rice growth. In addition to these improvements, these ameliorants also supply calcium (Ca) and magnesium (Mg), which are needed for crop growth and development.
Besides Ca and Mg, silicon (Si) is also important for rice growth. It has a
positive effect on the growth of crops such as tomato (Peaslee and Frink,
1969), barley, and soybean (Hodson and Evans, 1995; Nolla et al., 2006), and
many others (Liang et al., 2007; Nolla et al., 2012). The application of Si
may reduce the severity of fungal diseases such as blast and sheath blight of
rice (Farnaz et al., 2012); powdery mildew of barley, wheat, cucumber,
muskmelon, and grape leaves; and vermin damage of rice by plant hopper
(Crooks and Prentice, 2012; Ma et al., 2001; Menzies et al., 1992; Bowen et
al., 1992; Datnoff et al., 2001). In addition, Si can effectively reduce Al
toxicity (Barcelo et al., 1993). Calcium silicate application could be a
source of Si for soils. This material is available in Peninsular Malaysia.
Therefore, this study is relevant because calcium silicate could be used to
alleviate Al toxicity of soil from the Merbok granary area located in the
northern state of Kedah, Peninsular Malaysia. Certain regions of the rice
cultivation area are classified as acid sulfate soils and the average rice
yield in these areas is less than 2 t ha
The experiment was conducted at the Field 2 Glasshouse at Universiti Putra Malaysia, Serdang, Malaysia. The soil used in this study was obtained from Merbok, Kedah, Peninsular Malaysia. The soil sampling site was a rice-cropped area and the sampling was performed 1 month prior to rice cultivation (dry conditions). A composite soil sample of approximately 2500 g was taken from 0–15 cm depth using an auger. The sample was taken within a 0.5 ha region of the rice-cropped area. Afterward, the soil was crushed, passed through a 2 mm sieve, and mixed thoroughly prior to incubation.
Five hundred grams of soil was used to fill a plastic pot, which was then
incubated for 120 days. The treatments included 0 (CS0), 1 (CS1), 2 (CS2),
and 3 (CS3) Mg ha
The soils were mixed thoroughly with the added calcium silicate prior to the
addition of water. Tap water was added regularly and the water levels were
maintained at approximately 5 cm (height) above the soil surface. The
composition of the tap water in relation to phosphorus (P), potassium (K),
aluminum (Al), calcium (Ca), iron (Fe), magnesium (Mg), and silicon (Si) was
0.74, 10.62, 0.14, 19.78, 0.03, 1.00, and 5.18 mg L
Soil samples were air-dried, ground, and passed through a 2 mm sieve prior
to chemical analyses. Soil pH was determined in water at a ratio of
Statistical analysis for means comparison was performed using Tukey's test in SAS version 9.2 (SAS Institute Inc., Cary, NC).
Effects of calcium silicate application on soil pH under submerged
conditions. Means marked with the same letter for each incubation day are not
significantly different at
Initial soil pH and exchangeable Al were 2.90 and
4.26 cmol
Figure 1 shows the effect of calcium silicate application on soil pH under
submerged conditions. It shows that soil pH increased in line with the
incremental increases in the calcium silicate application rate. The highest
soil pH increase was from 2.90 (initial) to 3.95 due to the application of
3 Mg ha
Figure 2 shows the effect of calcium silicate application on exchangeable Al.
It shows that as the calcium silicate rate increased, the exchangeable Al
decreased from 4.26 to 0.82 cmol
Effects of calcium silicate application on exchangeable aluminum.
Means marked with the same letter for each incubation day are not
significantly different at
Figure 3 show that the application of calcium silicate increased exchangeable
Ca. There was a significant effect among the treatments after 30 days of
incubation. At 60, 90, and 120 days of incubation, soil treated with 2 and
3 Mg ha
Effects of calcium silicate application on exchangeable calcium.
Means marked with the same letter for each incubation day are not
significantly different at
Application of calcium silicate increased the Si content of the soil, as
shown in Fig. 4, from 14 to 74 %. At 30 days of incubation, soil treated
with 2 and 3 Mg ha
From this study, it was found that calcium silicate can neutralize H
During the incubation period, there was a strong relationship between calcium
silicate and soil pH at D30 (
Effects of calcium silicate application on silicon content. Means
marked with the same letter for each incubation day are not significantly
different at
It was observed that the soil pH was slightly lower for CS0, CS1, and CS2 at
D60 and D90 compared to that at D30 and D120. The decrease in soil pH is
believed to be due to the release of protons as pyrite in the soil was
oxidized during the incubation period. Shamshuddin et al. (2004) reported
that after 12 weeks of incubation, soil pH in the Cg horizon of acid sulfate
soil was lowered by 1 unit. The results from the current study are consistent
with those from other studies on acid sulfate soils (Shamshuddin and Auxtero,
1991; Shamshuddin et al., 1995, 2014). The oxidation of pyrite, which
produces acidity, may have taken place according to the following reactions
outlined by van Breemen (1976):
Relationship between exchangeable Al and soil pH (
The reduction in exchangeable Al is explained as follows. It is possible that soil Al can be reduced by the reactions of Si-rich compounds. By such reactions, Datnoff et al. (2001) postulated five mechanisms of Al reduction: (1) monosilicic acids increase soil pH (Lindsay, 1979); (2) monosilicic acids are adsorbed on Al hydroxides, reducing their mobility (Panov et al., 1982); (3) soluble monosilicic acid forms slightly soluble substances with Al ions (Lumsdon and Farmer, 1995); (4) mobile Al is strongly adsorbed on silica surfaces (Schulthess and Tokunaga, 1996); and (5) mobile silicon compounds increase plant tolerance to Al (Rahman et al., 1998). All of these mechanisms may work simultaneously, with one perhaps prevailing under certain soil conditions (Dantoff et al., 2001).
The silicate anion can also neutralize H
Furthermore, the application of calcium silicate to the acid sulfate soil
showed an immediate ameliorative effect, i.e., the Ca content increased from
1.68 (initial) to above the critical level of 2 cmol
In the current study, the Si content prior to the incubation was
21.21 mg kg
When the soil pH increased, the Si content of the soil also increased (Fig. 6). The Si content was positively correlated with soil pH at D30 and D60, likely due to the dissolution of calcium silicate. The ability of the soil to adsorb Si was higher at D30 and D60 than at D90 and D120. There was no correlation observed at D90 and D120, even though the Si content was higher, probably because the soil-exchangeable sites became fully occupied with Si through adsorption processes. This proves that the application of calcium silicate to soil, accompanied by an increase in soil pH, enhances the ability of soil to adsorb Si.
Relationship between Si content and soil pH throughout the
incubation period (
The positive effect of the presence of Si at D30 and D60 corresponds with the
early growth stage of rice, i.e., the active tillering stage. This means that
a rice plant can actively uptake Si during the tillering stage, hence
improving rice growth. Figure 7 shows the relationship between the
exchangeable Al and Si contents of the soil throughout the incubation period
after the application of calcium silicate. The reduction in exchangeable Al
corresponded directly with the availability of Si in the soil. This means
that as more Si is available in acid sulfate soil, a reduction in the
exchangeable Al content occurs. Exchangeable Al was negatively correlated
with Si content in the soil at D30 (
Relationship between exchangeable Al and Si content in the soil
throughout the incubation period (
Silicon is released from calcium silicate into the bulk soil solution and may
become absorbed by plants as Si (OH)
A prolonged incubation of soil not treated with calcium silicate might have
also influenced the changes in soil chemical characteristics. As such, CS0
(untreated soil) showed an increase in soil pH from 2.90 (prior to
incubation) to 3.63 at D30. A decrease in soil pH values was noted for D60
and D90, likely due to pyrite oxidation in the soil system, and no
significant effect was observed among the days of incubation. Meanwhile,
exchangeable Al decreased significantly with increasing incubation time. For
the first 2 months, exchangeable Al was above the critical level of
2 cmol
Cost of calcium silicate applied to a 1 ha area for rice production.
Farmers in the study area have applied GML to overcome soil fertility
problems associated with Al toxicity. As an alternative to GML application,
this study suggests that such farmers could benefit from the use of calcium
silicate as a soil amendment. Therefore, the costs of the input (calcium
silicate) and labor should be taken into account to better understand the
feasibility of such an approach for farmers in this region. Table 1 shows the
costs of applying calcium silicate to 1 ha area for rice production. The
costs for calcium silicate and labor were USD 407 and USD 45 t
Application of calcium silicate showed an ameliorative effect on acid sulfate
soil, i.e., an increase in soil pH, exchangeable Ca content, and Si content,
and a reduction in exchangeable Al. This suggests that calcium silicate
amendment is effective in alleviating Al toxicity in acid sulfate,
rice-cropped soils. Furthermore, it is an affordable soil amendment, with a
cost ranging from USD 452 to USD 1354 ha
We would like to acknowledge Universiti Putra Malaysia and Ministry of Higher Education Malaysia for technical and financial support (under LRGS Program-Food Security: enhancing sustainable rice production). Edited by: A. Cerdà