Abstract
Soil application of humic acid (HA), generally derived from leonardite shale, is a common practice in California vegetable production. Five commercial HA formulations were evaluated for their effects on soil microbial activity, seedling emergence, crop productivity, and nutrient uptake when applied to representative agricultural soils. Two soils differing in organic matter content (8 and 25 g·kg −1 ) were wetted to field capacity moisture content with solutions of water, nitrogen and phosphorus (P) fertilizer, HA, or fertilizer + HA and incubated aerobically at 25 °C. In the lower organic matter soil, a synergistic effect of fertilizer and HA was observed after 7 days of incubation on both microbial respiration and the amount of phospholipid fatty acids detected; these stimulatory effects were not observed in the higher organic matter soil. In a greenhouse pot study, the effects of HA on seedling emergence, dry mass accumulation, and P uptake of romaine lettuce ( Lactuca sativae L.) were evaluated in four soils of low P availability; HA was applied to the soil at a rate simulating a field application of 2.2 kg·ha −1 a.i. HA had no significant effect on emergence rate or percentage, or P uptake, in any soil; plant dry mass was increased in one soil. Field trials were conducted in 2008 and 2009 evaluating the effects of pre-transplant soil application of HA at 1.1 or 3.4 kg·ha −1 a.i. on growth, nutrient uptake, and fruit yield of processing tomato ( Lycopersicon esculentum Mill.). In neither year was macro- or micronutrient uptake increased with HA. Similarly, there was no significant HA effect on plant dry mass accumulation or fruit yield. We conclude that, at typical commercial application rates in representative field soils, HA is unlikely to significantly improve vegetable crop nutrient uptake or productivity.
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
Fertilizer plus HA stimulated microbial respiration in lower organic matter soil after seven days.
- Taxon
- Vegetable Cropt0
- Treatment
- fertilizer and HAe0
- Outcome
- microbial respiratione0
- Qualifier
- lower organic matter soile0
Not reportedComparatorDirection
Verbatim
t0“Vegetable Crop”
e0“In the lower organic matter soil, a synergistic effect of fertilizer and HA was observed after 7 days of incubation on both microbial respiration and the amount of phospholipid fatty acids detected”
Claim · model-written summary
Fertilizer plus HA stimulated detected phospholipid fatty acids in lower organic matter soil.
- Taxon
- Vegetable Cropt0
- Treatment
- fertilizer and HAe0
- Outcome
- amount of phospholipid fatty acids detectede0
- Qualifier
- lower organic matter soile0
Not reportedComparatorDirection
Verbatim
t0“Vegetable Crop”
e0“In the lower organic matter soil, a synergistic effect of fertilizer and HA was observed after 7 days of incubation on both microbial respiration and the amount of phospholipid fatty acids detected”
Claim · model-written summary
These stimulatory effects were absent in higher organic matter soil.
- Taxon
- Vegetable Cropt0
- Treatment
- fertilizer and HAe1
- Outcome
- stimulatory effectse0
- Direction
- not observede0
- Qualifier
- higher organic matter soile0
Not reportedComparator
Verbatim
t0“Vegetable Crop”
e0“these stimulatory effects were not observed in the higher organic matter soil”
e1“fertilizer and HA”
Claim · model-written summary
HA did not significantly affect romaine lettuce emergence rate or percentage.
- Taxon
- romaine lettuce
Lactuca sativa var. longifoliae1 - Treatment
- HAe0
- Outcome
- emergence rate or percentagee0
- Direction
- no significant effecte0
- Qualifier
- any soile0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“HA had no significant effect on emergence rate or percentage, or P uptake, in any soil”
e1“romaine lettuce ( Lactuca sativae L.)”
Claim · model-written summary
HA did not significantly affect romaine lettuce P uptake.
- Taxon
- romaine lettuceLactuca sativa var. longifoliae1
- Treatment
- HAe0
- Outcome
- P uptakee0
- Direction
- no significant effecte0
- Qualifier
- any soile0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“HA had no significant effect on emergence rate or percentage, or P uptake, in any soil”
e1“romaine lettuce ( Lactuca sativae L.)”
Claim · model-written summary
HA increased lettuce dry mass in one soil.
- Taxon
- romaine lettuceLactuca sativa var. longifoliae1
- Treatment
- HAe2
- Outcome
- plant dry masse0
- Direction
- increasede0
- Qualifier
- one soile0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“plant dry mass was increased in one soil”
e1“romaine lettuce ( Lactuca sativae L.)”
e2“HA had no significant effect”
Claim · model-written summary
HA did not increase tomato macro- or micronutrient uptake in either year.
- Taxon
- processing tomatoe1
- Treatment
- HAe0
- Outcome
- macro- or micronutrient uptakee0
- Direction
- In neither year wase0
Not reportedComparator
Verbatim
e0“In neither year was macro- or micronutrient uptake increased with HA”
e1“processing tomato ( Lycopersicon esculentum Mill.)”
Claim · model-written summary
HA had no significant effect on tomato dry mass accumulation.
- Taxon
- processing tomatoe1
- Treatment
- HAe0
- Outcome
- plant dry mass accumulatione0
- Direction
- no significante0
- Qualifier
- fruit yielde0
Not reportedComparator
Verbatim
e0“there was no significant HA effect on plant dry mass accumulation or fruit yield”
e1“processing tomato ( Lycopersicon esculentum Mill.)”
Claim · model-written summary
HA had no significant effect on tomato fruit yield.
Not reportedComparator
Verbatim
e0“there was no significant HA effect on plant dry mass accumulation or fruit yield”
e1“processing tomato ( Lycopersicon esculentum Mill.)”
Claim · model-written summary
Typical commercial HA application is unlikely to significantly improve vegetable nutrient uptake or productivity.
Verbatim
t0“Vegetable Crop”
e0“at typical commercial application rates in representative field soils, HA is unlikely to significantly improve vegetable crop nutrient uptake or productivity”
The same questions in other papers
other · nutrient: content · Lactuca sativa (garden lettuce)Positive and negative results
3 papers in the same direction as this paper · 32 in the opposite direction
- positive
- positive
- positive
32 papers more in this group
See all 36 papers →other · nutrient: content · Solanum lycopersicum (tomato)Positive and negative results
3 papers in the same direction as this paper · 44 in the opposite direction
- positive
- positive
- positive
44 papers more in this group
See all 48 papers →other · growth · Lactuca sativa (garden lettuce)Positive and negative results
65 papers in the same direction as this paper · 12 in the opposite direction
- no effect
- negative
- no effect
74 papers more in this group
See all 78 papers →other · yield · Solanum lycopersicum (tomato)Positive and negative results
12 papers in the same direction as this paper · 117 in the opposite direction
- positive
- positive
- positive
126 papers more in this group
See all 130 papers →other · growth · Solanum lycopersicum (tomato)Positive and negative results
17 papers in the same direction as this paper · 157 in the opposite direction
- positive
- positive
- positive
171 papers more in this group
See all 175 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.