Abstract
Abstract The effect of humic substances on P‐availability in soil is still debated. Therefore, the effect of model humic substances synthesized from hydroquinone on P, Fe, and Al solubility in a strong P fixing Oxisol and on P acquisition by red clover and ryegrass was investigated. After 4 months of incubation, P concentration of soil solution had increased by a factor of > 10 at the highest humic level (50 g humics kg −1 soil), accompanied by a similar increase in Fe and Al concentrations. Soil samples with 0, 10, 30, 50 g humics kg −1 soil were planted with red clover and ryegrass. Red clover showed a small increase of shoot yield and a moderate increase of P uptake after humics addition. High humics levels increased slightly Fe concentration in the shoots but strongly that of Mn leading to Mn toxicity. Ryegrass showed a strong increase in shoot yield after humics addition of about 150 % at the highest humics level compared to the control without humics. At each humic level, P application (100 mg kg −1 soil) had no effect on P uptake of red clover and a small effect on P uptake by ryegrass. The relatively small effect of humics and P application on shoot yield of clover compared to grass can be explained by chemical P mobilization of red clover via exudation of citrate (about 12 μmol citrate g −1 soil). This agrees with the finding that P solubility increased in the soil under red clover but not under ryegrass from the first to the second harvest, indicating that red clover mobilized P.
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Claims 12
Claim · model-written summary
Model humic substances increased soil solution P concentration by a factor of more than 10 at the highest humic level.
- Treatment
- highest humic levele1
- Outcome
- P concentration of soil solutione1
- Direction
- increasede1
- Value
- a factor of > 10e1
Not reportedTaxonComparator
Verbatim
e1“After 4 months of incubation, P concentration of soil solution had increased by a factor of > 10 at the highest humic level”
Claim · model-written summary
The highest humic level increased soil solution Fe and Al concentrations similarly to P.
- Treatment
- highest humic levele1
- Outcome
- Fe and Al concentrationse2
- Direction
- increasee2
- Qualifier
- similare2
Not reportedTaxonComparator
Verbatim
e1“After 4 months of incubation, P concentration of soil solution had increased by a factor of > 10 at the highest humic level”
e2“accompanied by a similar increase in Fe and Al concentrations”
Claim · model-written summary
Humics addition gave red clover a small increase in shoot yield.
- Taxon
- red clover
Trifolium pratensee3 - Treatment
- humics additione3
- Outcome
- shoot yielde3
- Direction
- small increasee3
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e3“Red clover showed a small increase of shoot yield and a moderate increase of P uptake after humics addition”
Claim · model-written summary
Humics addition gave red clover a moderate increase in P uptake.
- Taxon
- red cloverTrifolium pratensee3
- Treatment
- humics additione3
- Outcome
- P uptakee3
- Direction
- moderate increasee3
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e3“Red clover showed a small increase of shoot yield and a moderate increase of P uptake after humics addition”
Claim · model-written summary
High humic levels slightly increased shoot Fe concentration in the grown plants.
Not reportedTaxonComparator
Verbatim
e4“High humics levels increased slightly Fe concentration in the shoots but strongly that of Mn leading to Mn toxicity”
Claim · model-written summary
High humic levels led to Mn toxicity in the grown plants.
Not reportedTaxon
Verbatim
e4“High humics levels increased slightly Fe concentration in the shoots but strongly that of Mn leading to Mn toxicity”
Claim · model-written summary
Ryegrass shoot yield rose strongly, by about 150 %, after humics addition at the highest humic level compared with no humics.
- Treatment
- humics additione5
- Outcome
- shoot yielde5
- Direction
- strong increasee5
- Value
- about 150 %e5
- Qualifier
- at the highest humics levele5
- Comparator
- control without humicse5
LoliumOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e5“Ryegrass showed a strong increase in shoot yield after humics addition of about 150 % at the highest humics level compared to the control without humics”
Claim · model-written summary
P application had no effect on P uptake of red clover at any humic level.
- Taxon
- red cloverTrifolium pratensee7
- Treatment
- P applicatione6
- Outcome
- P uptakee7
- Direction
- no effecte7
- Qualifier
- At each humic levele6
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e6“At each humic level, P application”
e7“had no effect on P uptake of red clover”
Claim · model-written summary
P application had a small effect on P uptake by ryegrass.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a small effect on P uptake by ryegrass”
Claim · model-written summary
The effect of humics and P application on clover shoot yield was relatively small compared with grass.
TrifoliumOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The relatively small effect of humics and P application on shoot yield of clover compared to grass”
Claim · model-written summary
The relatively small clover shoot yield response is explained by chemical P mobilization of clover via exudation of citrate.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The relatively small effect of humics and P application on shoot yield of clover compared to grass”
e1“can be explained by chemical P mobilization of red clover via exudation of citrate”
Claim · model-written summary
P solubility in the soil increased under red clover but not under ryegrass from the first to the second harvest.
- Taxon
- red cloverTrifolium pratensee0
- Outcome
- P solubilitye0
- Direction
- increasede0
- Qualifier
- from the first to the second harveste0
- Comparator
- ryegrasse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“P solubility increased in the soil under red clover but not under ryegrass from the first to the second harvest”
The same questions in other papers
phosphorus · nutrient: content · Trifolium pratense (red clover)Positive and negative results
2 in the opposite direction
- positive
- positive
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.