Abstract
Poor response of rice to phosphorus (P) fertilization and low phytoavailability of soil P have been reported in sandy rainfed fields in northeast Thailand. In order to evaluate the effects of mild soil drying on the uptake of P by rainfed lowland rice, we carried out nutrient omission trials for nitrogen (N) and P at Ubon Ratchathani Rice Research Center under rainfed and flooded conditions. The surface soil was classified as sandy loam. To avoid severe soil drying and drought stress in the rainfed field, soil water potential at a depth of 20 cm was maintained at the field capacity (> −20 kPa) by flush irrigation. The effects of flooding and drying on the soil properties were also evaluated in the laboratory using soils with diverse textures in and around the center. In the field experiments, the above-ground biomass of rice plants (RD6) did not respond significantly to P fertilization in the rainfed field, although it responded positively to N fertilization. Root length in the surface 10 cm under the rainfed condition was significantly smaller than that under the flooded condition due partly to the increased soil hardness upon drying, but this could not quantitatively explain the large discrepancy of P uptake observed between the rainfed and flooded conditions. Under the rainfed condition, the P uptake did not increase significantly, even when the concentration of soil Bray P was tripled by transferring the surface soil from the flooded to the rainfed field. From the laboratory experiments, it was further suggested that soil P was supplied mainly by diffusion and that the effective diffusion coefficient for P can become less than one-tenth of the value in the flooded field when the sandy soil with clay at around 10% dried to −100 kPa. Our results suggest that the uptake of P by the rainfed lowland rice grown in sandy soil can be limited physically by mild soil drying that reduces the supply of P to roots by diffusion rather than the chemical extractability of soil P.
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Claims 5
Claim · model-written summary
Rice biomass did not respond significantly to phosphorus fertilization in the rainfed field.
- Taxon
- rice plants
Oryza sativae0 - Material
- RD6e0
- Treatment
- P fertilizatione0
- Outcome
- above-ground biomasse0
- Direction
- did not respond significantlye0
- Setting
- rainfed fielde0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the above-ground biomass of rice plants (RD6) did not respond significantly to P fertilization in the rainfed field”
Claim · model-written summary
Rice biomass responded positively to nitrogen fertilization in the rainfed field.
- Taxon
- rainfed lowland ricet0
- Treatment
- N fertilizatione0
- Outcome
- it responded positivelye0
- Direction
- positivelye0
Not reportedComparatorSetting
Verbatim
e0“although it responded positively to N fertilization”
t0“rainfed lowland rice”
Claim · model-written summary
Surface root length was significantly smaller under rainfed than flooded conditions.
Verbatim
e0“Root length in the surface 10 cm under the rainfed condition was significantly smaller than that under the flooded condition”
t0“rainfed lowland rice”
Claim · model-written summary
Tripling soil Bray P did not significantly increase phosphorus uptake under rainfed conditions.
- Taxon
- rainfed lowland ricet0
- Treatment
- transferring the surface soil from the flooded to the rainfed fielde0
- Outcome
- P uptakee0
- Direction
- did not increase significantlye0
- Qualifier
- soil Bray P was triplede0
- Setting
- rainfed fielde0
Not reportedComparator
Verbatim
e0“Under the rainfed condition, the P uptake did not increase significantly, even when the concentration of soil Bray P was tripled by transferring the surface soil from the flooded to the rainfed field”
t0“rainfed lowland rice”
Claim · model-written summary
Mild drying of sandy soil was interpreted to limit rice phosphorus uptake by reducing diffusion to roots.
Verbatim
e0“the uptake of P by the rainfed lowland rice grown in sandy soil can be limited physically by mild soil drying that reduces the supply of P to roots by diffusion rather than the chemical extractability of soil P”
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