Abstract
Rice grown on an acid sulfate soil is subjected to Al3+ and Fe2+ toxicity. The stress encountered by the rice plant is usually alleviated by applying ground magnesium limestone (GML). A study was conducted to explain how rice planted on acid sulfate soils can overcome the stress caused by Al3+ and Fe2+ toxicity. The rice variety tested in this study was MR 219. Seed (under H+ and/or Al3+ stress) germination experiments were conducted in the laboratory in which root length, root surface area and organic acids excretion were determined. This study was followed by a liming trial in the field. The results from the laboratory experiments showed that high Al concentration in the water severely affected root length of rice seedlings and caused the release of organic acids by rice roots. Field trial results showed that when GML was applied under flooded condition at the rate of 4 t ha-1, water pH increased from 3 to 4.5. The pKa of Al was 5 and Al concentration was still high in the water, which was most probably existed in the form of Al3+. Although under stress, the rice was able to grow and consequently produced a reasonable yield. This was probably due to excretion of citric, oxalic and malic acids when Al3+ was on the surface of the roots, which subsequently chelated the Al3+, thus enabling the rice to defend itself against Al3+ toxicity. Rice defends itself against Fe2+ via another mechanism. The pKa of Fe is 3. Due to liming at 4 t GML ha -1, the pH of the water increased to pH above 3. The Fe was precipitated as brown crust, coating the surface of the rice roots, and subsequently prevented or reduced the uptake of Fe2+, thus the overall effect of Fe2+ toxicity on rice plant was less severe. To grow rice on acid sulfate soils, it is recommended that GML should be applied at the rate so that water pH is increased to above 5 to get rid of Al3+ and Fe2+ although it might be costly.
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Claims 9
Claim · model-written summary
High aluminum concentration shortened rice seedling roots.
- Taxon
- rice
Oryza sativae0 - Treatment
- high Al concentratione0
- Outcome
- root lengthe0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“high Al concentration in the water severely affected root length of rice seedlings”
Claim · model-written summary
High aluminum concentration caused rice roots to release organic acids.
- Taxon
- riceOryza sativae0
- Organ / stage
- rice rootse0
- Treatment
- high Al concentratione0
- Outcome
- release of organic acidse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“high Al concentration in the water severely affected root length of rice seedlings and caused the release of organic acids by rice roots”
Claim · model-written summary
GML at 4 t ha-1 increased flooded field water pH from 3 to 4.5.
- Taxon
- RiceOryza sativat0
- Treatment
- GML was applied under flooded condition at the rate of 4 t ha-1e0
- Outcome
- water pHe0
- Direction
- increasede0
- Value
- 3 to 4.5e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“when GML was applied under flooded condition at the rate of 4 t ha-1, water pH increased from 3 to 4.5”
t0“Rice defense mechanisms”
Claim · model-written summary
Aluminum concentration remained high in the water after liming.
- Taxon
- RiceOryza sativat0
- Outcome
- Al concentratione0
- Direction
- still highe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Al concentration was still high in the water”
t0“Rice defense mechanisms”
Claim · model-written summary
Rice under stress grew and produced a reasonable yield.
- Taxon
- riceOryza sativae0
- Outcome
- grow and consequently produced a reasonable yielde0
- Qualifier
- under stresse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Although under stress, the rice was able to grow and consequently produced a reasonable yield”
Claim · model-written summary
Excretion of organic acids probably chelated aluminum and enabled rice defense against toxicity.
- Taxon
- riceOryza sativae0
- Compound
- citric, oxalic and malic acidse0
- Outcome
- defend itself against Al3+ toxicitye0
- Qualifier
- probablye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“This was probably due to excretion of citric, oxalic and malic acids when Al3+ was on the surface of the roots, which subsequently chelated the Al3+, thus enabling the rice to defend itself against Al3+ toxicity”
Claim · model-written summary
Liming raised water pH above 3.
- Taxon
- RiceOryza sativat0
- Treatment
- liming at 4 t GML ha -1e0
- Outcome
- pH of the watere0
- Direction
- increasede0
- Value
- pH above 3e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Due to liming at 4 t GML ha -1, the pH of the water increased to pH above 3”
t0“Rice defense mechanisms”
Claim · model-written summary
Precipitated iron coated rice roots and probably reduced iron uptake and toxicity.
- Taxon
- riceOryza sativae0
- Organ / stage
- rice rootse0
- Outcome
- uptake of Fe2+e0
- Direction
- prevented or reducede0
- Qualifier
- Fe was precipitated as brown cruste0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The Fe was precipitated as brown crust, coating the surface of the rice roots, and subsequently prevented or reduced the uptake of Fe2+, thus the overall effect of Fe2+ toxicity on rice plant was less severe”
Claim · model-written summary
GML should raise water pH above 5 for rice on acid sulfate soils.
- Taxon
- riceOryza sativae0
- Outcome
- GML should be applied at the rate so that water pH is increased to above 5e0
- Qualifier
- although it might be costlye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“To grow rice on acid sulfate soils, it is recommended that GML should be applied at the rate so that water pH is increased to above 5 to get rid of Al3+ and Fe2+ although it might be costly”
The same questions in other papers
magnesium atom · soil: chemistry · Oryza sativa (rice)Results agree
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- positive
calcium oxide · soil: chemistry · Oryza sativa (rice)Results agree
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- positive
lime · soil: chemistry · Oryza sativa (rice)Results differ
34 papers in the same direction as this paper · 3 in the opposite direction
- negative
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See all 38 papers →flooding · soil: chemistry · Oryza sativa (rice)Positive and negative results
12 papers in the same direction as this paper · 1 in the opposite direction
- negative
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See all 14 papers →Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.