Abstract
During winter, when light intensities are low, high nitrate concentrations often occur in leafy vegetables which are undesirable from the viewpoint of public health. The effects of low lighting during the night in combination with various nutrient solutions and solution temperatures on the nitrate concentration of lettuce cv. Panvit plants grown in a nutrient film technique system were studied. The experiment showed that lettuce heads could be grown during winter under glass with a nitrate concentration as low as 2900 mg/kg FW, which is much lower than the maximum permissible concentration for winter-grown lettuce in the Netherlands of 4500 mg/kg. The lowest nitrate concentration, without negative effects on yield or quality, was obtained by growing the crop on recirculating nutrient solutions with an initial ammonium:nitrate ratio of 0.25, with a change to a ratio of 1.0 for the last 2 weeks. The addition of chloride did not affect the nitrate concentration. Raising the temperature of the nutrient solution at night from 6 to 10 degrees C in combination with a minimum air temperature of 6 degrees stimulated growth, but also increased the lettuce nitrate concentration by an average of 360 mg/kg. Supplying light of a low intensity at a photon flux density of 27 micro mol m-2s-1 (400-700 nm) at night for up to 8 nights before harvest did not further reduce the nitrate concentration on a FW basis because the dry matter percentage increased.
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Claims 7
Claim · model-written summary
Winter glasshouse lettuce reached nitrate concentration of 2900 mg/kg FW.
- Taxon
- lettuce
Lactuca sativae0 - Outcome
- nitrate concentratione0
- Direction
- as low ase0
- Value
- 2900 mg/kg FWe0
- Setting
- under glasse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“lettuce heads could be grown during winter under glass with a nitrate concentration as low as 2900 mg/kg FW”
Claim · model-written summary
Changing ammonium:nitrate ratio from 0.25 to 1.0 in the last two weeks yielded the lowest nitrate without harming yield or quality.
- Taxon
- lettuceLactuca sativat0
- Treatment
- recirculating nutrient solutions with an initial ammonium:nitrate ratio of 0.25, with a change to a ratio of 1.0 for the last 2 weekse0
- Outcome
- nitrate concentratione0
- Direction
- loweste0
- Qualifier
- without negative effects on yield or qualitye0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The lowest nitrate concentration, without negative effects on yield or quality, was obtained by growing the crop on recirculating nutrient solutions with an initial ammonium:nitrate ratio of 0.25, with a change to a ratio of 1.0 for the last 2 weeks”
t0“lettuce”
Claim · model-written summary
Added chloride did not change nitrate concentration.
- Taxon
- lettuceLactuca sativat0
- Treatment
- addition of chloridee0
- Outcome
- nitrate concentratione0
- Direction
- did not affecte0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The addition of chloride did not affect the nitrate concentration”
t0“lettuce”
Claim · model-written summary
Raising night nutrient-solution temperature stimulated growth.
- Taxon
- lettuceLactuca sativat0
- Treatment
- Raising the temperature of the nutrient solution at night from 6 to 10 degrees Ce0
- Outcome
- growthe0
- Direction
- stimulatede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Raising the temperature of the nutrient solution at night from 6 to 10 degrees C in combination with a minimum air temperature of 6 degrees stimulated growth”
t0“lettuce”
Claim · model-written summary
Raising night nutrient-solution temperature increased nitrate by 360 mg/kg on average.
- Taxon
- lettuceLactuca sativae0
- Treatment
- Raising the temperature of the nutrient solution at night from 6 to 10 degrees Ce0
- Outcome
- lettuce nitrate concentratione0
- Direction
- increasede0
- Value
- 360 mg/kge0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Raising the temperature of the nutrient solution at night from 6 to 10 degrees C in combination with a minimum air temperature of 6 degrees stimulated growth, but also increased the lettuce nitrate concentration by an average of 360 mg/kg”
Claim · model-written summary
Low-intensity night lighting for up to eight nights did not further reduce nitrate on a fresh-weight basis.
- Taxon
- lettuceLactuca sativat0
- Treatment
- Supplying light of a low intensity at a photon flux density of 27 micro mol m-2s-1 (400-700 nm) at night for up to 8 nights before harveste0
- Outcome
- nitrate concentration on a FW basise0
- Direction
- did not further reducee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Supplying light of a low intensity at a photon flux density of 27 micro mol m-2s-1 (400-700 nm) at night for up to 8 nights before harvest did not further reduce the nitrate concentration on a FW basis because the dry matter percentage increased”
t0“lettuce”
Claim · model-written summary
Low-intensity night lighting increased dry matter percentage.
- Taxon
- lettuceLactuca sativat0
- Treatment
- Supplying light of a low intensity at a photon flux density of 27 micro mol m-2s-1 (400-700 nm) at night for up to 8 nights before harveste0
- Outcome
- dry matter percentagee0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Supplying light of a low intensity at a photon flux density of 27 micro mol m-2s-1 (400-700 nm) at night for up to 8 nights before harvest did not further reduce the nitrate concentration on a FW basis because the dry matter percentage increased”
t0“lettuce”
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