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Nutrient Management Research Database
General Information
Research Title
Research Specifications
Authors
Summary/Abstract from Original Source
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 gkg–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 8C. 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;
HAwas applied to the soil at a rate simulating a field application of 2.2 kgha–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 kgha–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.
Research Highlights
Design and Methods
This study assessed the effect of five different commercial formulations of humic acid (HA) on seedling emergence, soil microbial activity, seedling emergence, early growth, nutrient uptake, and crop yield. The trade names for the humic acids were:
- Actagro humic acid
- Actagro liquid humus
- Organo liquid hume
- Quantum-H
- ESP-50
The study was conducted using laboratory, greenhouse, and field experiments on lettuce and processing tomato. A laboratory incubation was implemented to assess the impact of HA on microbial respiration and microbial community structure. The greenhouse study focused on the effects of HA on lettuce seedling emergence, growth, and P uptake. Soils used in the study were collected from fields under vegetable crops in California, and were chosen for their limited P availability. Field trials at UC Davis were also conducted to evaluate the effect of HA on processing tomatoes.
The HA was applied at an equivalent to the field rate of 2.2 kg ha-1
Results
Highlights of the results include:
- HA had no effect on lettuce emergence percentage, or speed of emergence in the greenhouse study.
- In a low organic soil HA application led to increased microbial activity in the short term.
- Positive growth response resulting from HA application occurred with lettuce in one of four soils and was not found with tomatoes.
Additional Information
Tags (links to other subject matter in database)
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