Abstract
As concern over NO 3 -N pollution of groundwater increases, California lettuce growers are under pressure to improve nitrogen (N) fertilizer efficiency. Crop growth, N uptake, and the value of soil and plant N diagnostic measures were evaluated in 24 iceberg and romaine lettuce ( Lactuca sativa L. var. capitata L., and longifolia Lam., respectively) field trials from 2007 to 2010. The reliability of presidedressing soil nitrate testing (PSNT) to identify fields in which N application could be reduced or eliminated was evaluated in 16 non-replicated strip trials and five replicated trials on commercial farms. All commercial field sites had greater than 20 mg·kg −1 residual soil NO 3 -N at the time of the first in-season N application. In the strip trials, plots in which the cooperating growers’ initial sidedress N application was eliminated or reduced were compared with the growers’ standard N fertilization program. In the replicated trials, the growers’ N regime was compared with treatments in which one or more N fertigation through drip irrigation was eliminated. Additionally, seasonal N rates from 11 to 336 kg·ha −1 were compared in three replicated drip-irrigated research farm trials. Seasonal N application in the strip trials was reduced by an average of 77 kg·ha −1 (73 kg·ha −1 vs. 150 kg·ha −1 for the grower N regime) with no reduction in fresh biomass produced and only a slight reduction in crop N uptake (151 kg·ha −1 vs. 156 kg·ha −1 for the grower N regime). Similarly, an average seasonal N rate reduction of 88 kg·ha −1 (96 kg·ha −1 vs. 184 kg·ha −1 ) was achieved in the replicated commercial trials with no biomass reduction. Seasonal N rates between 111 and 192 kg·ha −1 maximized fresh biomass in the research farm trials, which were conducted in fields with lower residual soil NO 3 -N than the commercial trials. Across fields, lettuce N uptake was slow in the first 4 weeks after planting, averaging less than 0.5 kg·ha −1 ·d −1 . N uptake then increased linearly until harvest (≈9 weeks after planting), averaging ≈4 kg·ha −1 ·d −1 over that period. Whole plant critical N concentration (N c , the minimum whole plant N concentration required to maximize growth) was estimated by the equation N c (g·kg −1 ) = 42 − 2.8 dry mass (DM, Mg·ha −1 ); on that basis, critical N uptake (crop N uptake required to maintain whole plant N above N c ) in the commercial fields averaged 116 kg·ha −1 compared with the mean uptake of 145 kg·ha −1 with the grower N regime. Soil NO 3 -N greater than 20 mg·kg −1 was a reliable indicator that N application could be reduced or delayed. Neither leaf N nor midrib NO 3 -N was correlated with concurrently measured soil NO 3 -N and therefore of limited value in directing in-season N fertilization.
Abstract from the paper’s OpenAlex record, shown for indexing and research. Copyright remains with the authors or the publisher. Read at the source ↗
The text the model read, with the source record’s inline markup (italics, sub- and superscripts) rendered and its character entities decoded; quote offsets refer to the raw text.
Claims 10
Claim · model-written summary
Cutting seasonal N application in strip trials by 77 kg·ha −1 caused no reduction in fresh biomass compared with the grower N regime.
- Taxon
- lettuce
Lactuca sativae0 - Treatment
- Seasonal N applicatione1
- Outcome
- fresh biomasse1
- Direction
- no reductione1
- Value
- 77 kg·ha −1e1
- Comparator
- grower N regimee1
- Setting
- field trialse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“evaluated in 24 iceberg and romaine lettuce ( Lactuca sativa L. var. capitata L., and longifolia Lam., respectively) field trials from 2007 to 2010”
e1“Seasonal N application in the strip trials was reduced by an average of 77 kg·ha −1 (73 kg·ha −1 vs. 150 kg·ha −1 for the grower N regime) with no reduction in fresh biomass produced”
Claim · model-written summary
Reduced seasonal N application produced only a slight reduction in crop N uptake (151 kg·ha −1) compared with the grower N regime.
- Taxon
- lettuceLactuca sativae0
- Treatment
- Seasonal N applicatione1
- Outcome
- crop N uptakee2
- Direction
- slight reductione2
- Value
- 151 kg·ha −1e2
- Comparator
- grower N regimee2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“evaluated in 24 iceberg and romaine lettuce ( Lactuca sativa L. var. capitata L., and longifolia Lam., respectively) field trials from 2007 to 2010”
e1“Seasonal N application in the strip trials was reduced by an average of 77 kg·ha −1 (73 kg·ha −1 vs. 150 kg·ha −1 for the grower N regime) with no reduction in fresh biomass produced”
e2“only a slight reduction in crop N uptake (151 kg·ha −1 vs. 156 kg·ha −1 for the grower N regime)”
Claim · model-written summary
In replicated commercial trials, an average seasonal N rate reduction of 88 kg·ha −1 was achieved with no biomass reduction.
- Taxon
- lettuceLactuca sativae0
- Treatment
- seasonal N rate reductione3
- Outcome
- biomasse3
- Direction
- no biomass reductione3
- Value
- 88 kg·ha −1e3
- Setting
- replicated commercial trialse3
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“evaluated in 24 iceberg and romaine lettuce ( Lactuca sativa L. var. capitata L., and longifolia Lam., respectively) field trials from 2007 to 2010”
e3“Similarly, an average seasonal N rate reduction of 88 kg·ha −1 (96 kg·ha −1 vs. 184 kg·ha −1 ) was achieved in the replicated commercial trials with no biomass reduction”
Claim · model-written summary
Seasonal N rates between 111 and 192 kg·ha −1 maximized fresh biomass in research farm trials on fields with lower residual soil NO 3 -N than the commercial trials.
- Taxon
- lettuceLactuca sativae0
- Treatment
- Seasonal N rates between 111 and 192 kg·ha −1e4
- Outcome
- fresh biomasse4
- Direction
- maximizede4
- Qualifier
- lower residual soil NO 3 -N than the commercial trialse4
- Setting
- research farm trialse4
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“evaluated in 24 iceberg and romaine lettuce ( Lactuca sativa L. var. capitata L., and longifolia Lam., respectively) field trials from 2007 to 2010”
e4“Seasonal N rates between 111 and 192 kg·ha −1 maximized fresh biomass in the research farm trials, which were conducted in fields with lower residual soil NO 3 -N than the commercial trials”
Claim · model-written summary
Lettuce N uptake was slow in the first 4 weeks after planting, averaging less than 0.5 kg·ha −1 ·d −1.
- Taxon
- lettuceLactuca sativae5
- Outcome
- N uptakee5
- Value
- less than 0.5 kg·ha −1 ·d −1e5
- Qualifier
- slow in the first 4 weeks after plantinge5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“evaluated in 24 iceberg and romaine lettuce ( Lactuca sativa L. var. capitata L., and longifolia Lam., respectively) field trials from 2007 to 2010”
e5“Across fields, lettuce N uptake was slow in the first 4 weeks after planting, averaging less than 0.5 kg·ha −1 ·d −1”
Claim · model-written summary
Lettuce N uptake increased linearly until harvest, averaging about 4 kg·ha −1 ·d −1.
- Taxon
- lettuceLactuca sativae5
- Outcome
- N uptakee6
- Direction
- increased linearlye6
- Value
- ≈4 kg·ha −1 ·d −1e6
- Qualifier
- until harveste6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“evaluated in 24 iceberg and romaine lettuce ( Lactuca sativa L. var. capitata L., and longifolia Lam., respectively) field trials from 2007 to 2010”
e5“Across fields, lettuce N uptake was slow in the first 4 weeks after planting, averaging less than 0.5 kg·ha −1 ·d −1”
e6“N uptake then increased linearly until harvest (≈9 weeks after planting), averaging ≈4 kg·ha −1 ·d −1 over that period”
Claim · model-written summary
The whole-plant critical N concentration was estimated as 42 − 2.8 times dry mass (Mg·ha −1) for lettuce.
- Taxon
- lettuceLactuca sativae0
- Outcome
- critical N concentratione7
- Value
- 42 − 2.8 dry masse7
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“evaluated in 24 iceberg and romaine lettuce ( Lactuca sativa L. var. capitata L., and longifolia Lam., respectively) field trials from 2007 to 2010”
e7“Whole plant critical N concentration (N c , the minimum whole plant N concentration required to maximize growth) was estimated by the equation N c (g·kg −1 ) = 42 − 2.8 dry mass (DM, Mg·ha −1 )”
Claim · model-written summary
Critical N uptake in commercial fields averaged 116 kg·ha −1, compared with 145 kg·ha −1 under the grower N regime.
- Taxon
- lettuceLactuca sativae0
- Outcome
- critical N uptakee7
- Value
- 116 kg·ha −1e7
- Qualifier
- 145 kg·ha −1e7
- Comparator
- grower N regimee7
- Setting
- commercial fieldse7
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“evaluated in 24 iceberg and romaine lettuce ( Lactuca sativa L. var. capitata L., and longifolia Lam., respectively) field trials from 2007 to 2010”
e7“critical N uptake (crop N uptake required to maintain whole plant N above N c ) in the commercial fields averaged 116 kg·ha −1 compared with the mean uptake of 145 kg·ha −1 with the grower N regime”
Claim · model-written summary
A soil NO 3 -N greater than 20 mg·kg −1 was a reliable indicator that N application could be reduced or delayed in lettuce.
- Taxon
- lettuceLactuca sativae0
- Compound
- NO 3 -Ne6
- Outcome
- reliable indicatore6
- Direction
- greater thane6
- Value
- 20 mg·kg −1e6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“evaluated in 24 iceberg and romaine lettuce ( Lactuca sativa L. var. capitata L., and longifolia Lam., respectively) field trials from 2007 to 2010”
e6“Soil NO 3 -N greater than 20 mg·kg −1 was a reliable indicator that N application could be reduced or delayed”
Claim · model-written summary
Leaf N and midrib NO 3 -N were not correlated with concurrently measured soil NO 3 -N and have limited value for in-season N fertilization.
- Taxon
- lettuceLactuca sativae0
- Organ / stage
- leafe6
- Outcome
- correlatede6
- Qualifier
- of limited value in directing in-season N fertilizatione6
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“evaluated in 24 iceberg and romaine lettuce ( Lactuca sativa L. var. capitata L., and longifolia Lam., respectively) field trials from 2007 to 2010”
e6“Neither leaf N nor midrib NO 3 -N was correlated with concurrently measured soil NO 3 -N and therefore of limited value in directing in-season N fertilization”
The same questions in other papers
nitrogen · growth · Lactuca sativa (garden lettuce)Results differ
59 papers in the same direction as this paper · 22 in the opposite direction · 3 reporting no difference from an alternative
- positive
- positive
- positive
81 papers more in this group
See all 85 papers →nitrogen · nutrient: content · Lactuca sativa (garden lettuce)Positive and negative results
16 papers in the same direction as this paper · 35 in the opposite direction
- positive
- positive
- positive
48 papers more in this group
See all 52 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.