Abstract
Low rice yields following intermittent loss of soilwater saturation are believed to involve, on occasions, P deficiency but the possible mechanisms have not been studied in detail. In the present pot experiments, two acid lowland soils from Cambodia (Koktrap -black clay soil and Prateah Lang- sandy soil) were treated with P either before or after flooding to investigate the effect of the timing of P application on its effectiveness for upland rice growth. Phosphate fertiliser (45 mg P/kg soil) was added to both soils before flooding for periods of 0, 1, 2 and 4 weeks, or after drying the flooded soils. After air-drying and crushing, the soils were wet to field capacity and the upland rice grown in them for six weeks. The addition of P 4 weeks before flooding decreased shoot dry matter in the sandy soil and in the black clay soil after only 1 week of flooding. But when P was added after drying the soils, shoot dry matter was not decreased regardless of the period of prior soil flooding. Soil pH increased and redox potential (Eh) decreased during flooding, resulting in an increase in acetate extractable Fe and the phosphate sorption capacity of soils. There was a close relationship between P sorbed and acetate extractable Fe (r2=0.96–0.98). Olsen and Bray-1 extractable P strongly correlated with shoot dry matter and shoot P concentrations indicating that P, the availability of which was controlled by the period of prior flooding, limited the growth of upland rice. It was concluded that phosphate fertiliser added before flooding was relatively ineffective in increasing growth in the upland rice. This was attributed to the increase in occlusion of P within ferric oxyhydroxides formed during subsequent oxidation of the soils. Decrease P availability may also have been associated with a greater phosphate sorption capacity of the soils during flooding and drying of soils. The implications of this for P supply to rice in intermittently flooded lowlands, and for P fertilizer requirements of pre- and post-rice upland crops are discussed.
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Claims 11
Claim · model-written summary
Adding P 4 weeks before flooding decreased upland rice shoot dry matter in the sandy soil.
- Taxon
- upland rice
Oryza sativat0 - Treatment
- P 4 weeks before floodinge0
- Outcome
- shoot dry mattere0
- Direction
- decreasede0
- Qualifier
- sandy soile0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“upland rice”
e0“The addition of P 4 weeks before flooding decreased shoot dry matter in the sandy soil and in the black clay soil after only 1 week of flooding”
Claim · model-written summary
Adding P 4 weeks before flooding decreased upland rice shoot dry matter in the black clay soil after only 1 week of flooding.
- Taxon
- upland riceOryza sativat0
- Treatment
- P 4 weeks before floodinge0
- Outcome
- shoot dry mattere0
- Direction
- decreasede0
- Qualifier
- black clay soil after only 1 week of floodinge0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“upland rice”
e0“The addition of P 4 weeks before flooding decreased shoot dry matter in the sandy soil and in the black clay soil after only 1 week of flooding”
Claim · model-written summary
When P was added after drying the soils, upland rice shoot dry matter was not decreased regardless of the period of prior flooding.
- Taxon
- upland riceOryza sativat0
- Treatment
- P was added after drying the soilse0
- Outcome
- shoot dry mattere0
- Direction
- not decreasede0
- Qualifier
- regardless of the period of prior soil floodinge0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“upland rice”
e0“when P was added after drying the soils, shoot dry matter was not decreased regardless of the period of prior soil flooding”
Claim · model-written summary
Soil pH increased during flooding of the soils.
Not reportedTaxonTreatmentComparatorQualifier
Verbatim
e0“Soil pH increased”
Claim · model-written summary
Soil redox potential (Eh) decreased during flooding of the soils.
Not reportedTaxonComparator
Verbatim
e0“redox potential (Eh) decreased during flooding”
Claim · model-written summary
Flooding resulted in an increase in acetate extractable Fe and in the phosphate sorption capacity of the soils.
- Treatment
- floodinge1
- Outcome
- acetate extractable Fe and the phosphate sorption capacity of soilse0
- Direction
- increasee0
Not reportedTaxonComparator
Verbatim
e0“resulting in an increase in acetate extractable Fe and the phosphate sorption capacity of soils”
e1“during flooding, resulting”
Claim · model-written summary
There was a close relationship between P sorbed and acetate extractable Fe in the soils (r2=0.96-0.98).
Not reportedTaxonDirection
Verbatim
e0“There was a close relationship between P sorbed and acetate extractable Fe (r2=0.96–0.98)”
Claim · model-written summary
Olsen and Bray-1 extractable P strongly correlated with upland rice shoot dry matter and shoot P concentrations.
- Taxon
- upland riceOryza sativat0
- Compound
- Olsen and Bray-1 extractable Pe0
- Outcome
- shoot dry matter and shoot P concentrationse0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“upland rice”
e0“Olsen and Bray-1 extractable P strongly correlated with shoot dry matter and shoot P concentrations”
Claim · model-written summary
The authors concluded that phosphate fertiliser added before flooding was relatively ineffective in increasing upland rice growth.
- Taxon
- upland riceOryza sativat0
- Treatment
- phosphate fertiliser added before floodinge0
- Outcome
- growthe0
- Direction
- relatively ineffective in increasinge0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“upland rice”
e0“phosphate fertiliser added before flooding was relatively ineffective in increasing growth in the upland rice”
Claim · model-written summary
The authors attributed the ineffectiveness of P added before flooding to increased occlusion of P within ferric oxyhydroxides formed during subsequent oxidation of the soils.
- Taxon
- upland riceOryza sativat0
- Compound
- ferric oxyhydroxidese1
- Outcome
- growthe0
- Qualifier
- increase in occlusion of Pe1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“upland rice”
e0“increasing growth in the upland rice”
e1“This was attributed to the increase in occlusion of P within ferric oxyhydroxides formed during subsequent oxidation of the soils”
Claim · model-written summary
Decreased P availability may also have been associated with a greater phosphate sorption capacity of the soils during flooding and drying.
Not reportedTaxon
Verbatim
e0“Decrease P availability may also have been associated with a greater phosphate sorption capacity of the soils during flooding and drying of soils”
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