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The Ins and Outs of Biological Crop Stimulants
Carl Rosen Department of Soil, Water, and ClimateUniversity of Minnesota
Indiana CCA ConferenceDecember 12, 2017
Topics Addressed Definition of crop biostimulants
Types of crop biostimulants Application methods Research methodology Possible modes of action
Do they work in the field? Case studies
Potatoes Corn
What are Crop Biostimulants? Currently no legal definition
More popular in Europe than in the U.S. Definition is evolving
European Biostimulants Industry Council Definition
“Plant biostimulants contain substance(s) and/or microorganisms whose function when applied to plants or the rhizosphere is to stimulate natural processes to enhance/ benefit nutrient uptake, nutrient efficiency, tolerance to abiotic stress, and crop quality.”
What are Crop Biostimulants? Another definition:
“Substances/microbes provided in minute quantities that promote plant growth” (du Jardin, 2015) Not fertilizers Not pesticides Not soil conditioners
Various products have been marketed for many years Regional committee developed in 1980 to test claims of
biostimulants and other nonconventional products NCR-103; NCERA 103 http://extension.agron.iastate.edu/compendium/index.aspx
Categories of Biostimulants Humic substances` Amino acids and other N compounds
Chitosans
Seaweed extracts
Beneficial microorganisms Bacteria – plant growth promoting rhizobacteria Fungi – often mycorrhizae
Applied individually or in combination; promoted as “natural”
Humic Substances (HS) Constituents of soil organic matter
Decomposition products of plants, animals, microbes Occur naturally in soil (OM breakdown) Categorized by molecular weight
Commercial HS Products Sources of commercial humic substances
Peat soils Composts Leonardite (oxidized lignite or compressed peat)
http://oceanagrollc.com/standard-humic-acid-testing-protocols-a-review/
Humic substances
Application methods Soil application – with starter fertilizer Foliar application
Studies to determine mode of action Usually conducted in the greenhouse Often using hydroponic techniques Effects found in the greenhouse do not necessarily translate
to an effect in the field
Reported Modes of Action for HS Under conditions of adequate nutrition in solution
Stimulation of root growth – length and secondary growth Complex metal cations (iron, zinc etc) Increase in membrane permeability Stimulation of nutrient uptake
Foliar application Some indication of increased root and shoot growth
In general, effects of HS on plant growth are not consistent and depend on a number of factors
HS Meta-Analysis (Rose et al., 2014)
Response to HS was affected by: Source of HS (compost HS > lignite HS) Rate of application Lesser extent crop type & growing conditions
HS increased shoot and root growth by 15-25% Half the studies failed to increase growth by 5% High variation increases risks to farmers Rates in meta analysis that promoted growth were much
higher than rates recommended for commercial HS products used in the field
Amino Acids and Other N Compounds Amino acids and peptides are protein breakdown
products Often termed protein hydrolysates Protein is split with acid, alkakli or enzymes Formed from animal or plant waste material
Amino Acids and Other N Compounds Protein hydolysates have multiple uses:
Media for animal and plant cell culture Animal feeds Dietary supplement for humans Crop production
Source of nitrogen that is easier to digest than protein For animals
Plants can use inorganic N Effect in plants is not due to the N supply
Amino Acids and Other N Compounds Reported Modes of Action
Some amino acids have a chelating effect Increase micronutrient availability and acquisition Decrease heavy metal toxicity
Regulate enzymes involved in N assimilation Antioxidant activity – scavenge free radicals
Increase tolerance to stress – salt, heat, chilling
Indirect effect – increase microbial biomass and nutrient cycling
Most effects are based on greenhouse studies Soil and foliar application methods
Effects on Plant Growth -Amino Acids Commercial products are available, but consistent
crop responses are not common
Amino acids are a readily available source of N for microbes Direct effects of amino acids or other small N compounds
on plant growth in the field are questionable; more likely indirect by stimulating microbes
Foliar application Repeated application has been reported to increase yield
in some horticultural crops
Chitosans Linear polysaccharide composed of glucosamine
Made by treating the shells of shrimp (chitin) with sodium hydroxide
Uses: Cancer treatment Dietary supplement (weight loss?) Wine making Agriculture
Effects and Reported Modes of Action for Chitosans
Effects on plants Seed treatment or foliar application Aids in defense of pathogens – biocontrol of fungi and
nematodes – biopesticide registered by EPA Stimulates growth; increases photosynthesis; stimulates
nutrient uptake
Modes of action Affects cell membranes; alters DNA; activates defense
genes
Field Research with Wheat – Hadwiger, 2013
“The conditions that enabled chitosan to increase wheat yield were so influenced by environmental or cultural practice that in a given year the chitosan benefits could deviate both up and down from the average 10% yield increase and reflected on the product credibility…”
“On the plus side, chitosan can also increase yields and is edible, without being allergenic, mutagenic, or carcinogenic. Thus, the application of chitosan directly to the plant part to be consumed is not of major concern.”
Seaweed Extracts Seaweed used in agriculture for thousands of years
Nutrient source; compost
Process developed in the 1950s to produce liquid extracts Mostly made from brown seaweeds
Ascophyllum nodosum, Fucus, Laminaria, Sargassum, & Turbinariaspp.
Proprietary process includes: Includes extracting with water, acids, alkalis with or without heating Physical disruption – low temperatures; high pressure
Seaweed Extracts
http://www.seaweed.ie/uses_ireland/irishseaweedmeal.php
https://www.indiamart.com/proddetail/seaweed-extract-liquid-zyme-solution-3815782562.html
Seaweed Extract Composition
Polysaccharides (long chain sugars)
Carrageenans (polysaccharides with sulfur) Flucoidan, alginates, laminarin
Macro and micronutrients
Various plant hormones – auxins, gibberellins, cytokinins, etc.
Seaweed Extract Uses Like amino acids – extracts are also
consumed by humans as a dietary supplement
Applied to soil or directly to the plant as a foliar application
Generally applied with the seed or as a foliar application; often combined with fertilizer 1.5 – 2 qts/A
Seaweed Extracts -Reported Effects
Enhanced root development
Stimulates nutrient uptake
Improved stress tolerance Drought, salinity, temperature
Increased microbial biomass & diversity when applied to soil
Seaweed Extracts -Mode of action Rates applied are too low to be of direct nutrient
benefit
Rates applied are also too low to have direct plant hormone effects
Some evidence that foliar application stimulates production of hormones within the plant, which in turn may affect growth and stress tolerance
Seaweed Extracts -Effects on field grown plants Many commercial products
As with other biostimulants results are inconsistent
Like amino acids, compounds in seaweed extract are a readily available nutrient source for microbes Any bioactive effects of the extracts would be
short-lived for soil applied products, but may stimulate microbes
Beneficial Microorganisms Practice of microbial inoculation has been used
for centuries Rhizobium for legumes; Nitrogen fixation
Often termed microbial inoculants Classified as biopesticides or biofertilizers Grey area as some are considered biocontrol agents
Fastest growing segment of the biostimulantindustry New DNA techniques for analyzing the soil microbiome Interest in more sustainable practices
Types of Microbial Inoculants Free living bacteria, fungi, mycorrhizal fungi
Isolated from soil, plants, plant residues, composted manure, and water Most isolated from the rhizosphere
http://plantsinaction.science.uq.edu.au/content/421-rhizosphere
Development of Inoculants
Factors to consider: Plant species (root
exudates) Reproducibility over
environments Commercial formulation –
must survive and be effective
Compatibility with fertilizers and pesticides
Bashan, et al., 2014
Beneficial Fungi
Fungi have co-evolved with plants for millions years Symbiosis to parasitism
Fungal endophytes Mycorrhizae – beneficial symbiosis with over 90% of all
terrestrial plants Associated with increased P uptake, Zn uptake, protects against
some diseases, increases drought tolerance Extends the root system to explore more soil (similar to root hairs)
Other fungal endophytes e.g. Trichoderma Transfer nutrients and also have biopesticidal activity
Roy-Bolduc and Hijri, 2011
Mycorrhizal non-Mycorrhizal
Is Inoculation with Mycorrhizae Beneficial? Depends on the situation
In most field studies – no effect on yield Soils have high populations of native mycorrhizae High soil P inhibits mycorrhizal infection
Exceptions are if the soil is fumigated
Beneficial effects in potted media
Sometimes co-inoculated with bacteria Improves uptake of micronutrients
Beneficial Bacteria Two types of bacteria isolated
Plant growth promoting bacteria (PGPB) Plant growth promoting rhizobacteria (PGPR)
Mechanisms reported for stimulating plant growth and nutrient uptake Asymbiotic nitrogen fixation (free living) Nutrient solubilization (esp. phosphorus) Production of chelating agents Production of volatile organic compounds Production of growth hormones
Examples of Beneficial Bacteria Free living nitrogen fixers
Azospirillium Azobacter Bacillus polymyxa Clostridium pasteurianum
Azospirillium is found in close contact with roots Can supply 7-12% of N for wheat
Phosphorus solubilizers Pseudomonas spp., Azospirillium, Bacillus spp., etc. Produce organic acids and phosphatase enzyme
http://agriculturers.com/azospirillum-la-bacteria-del-suelo-como-bio-fertilizante-en-la-agricultura/
Examples of Beneficial Bacteria Iron transport chelators
Bacillus, Pseudomonas, Streptomyces Siderophore production
Volatile organic compounds Paenibacillus, Bacillus strains Alcohols, ketones, hydrocarbons Biocontrol properties Growth stimulation increased auxin production
Production of plant growth regulators Azospirillium spp. – produces auxin & gibberllins Bacillus subtlis – increases cytokinin
Lateral root formation by VOCs emitted by Bacillus pumilus(Delaplace, et al., 2015)
Is Inoculation with Bacteria Beneficial?
Field studies with microbes and other biostimulants so far have been inconsistent
Each teaspoon of field soil contains over 1 billion bacteria
Beneficial microbes must compete with the existing microbial community They often lose out
Field Studies with Biostimulants
Humic acid, Calcium, and Foliar carbon (sugars) study on potato
Treatments:1. Starter only (30 lb N/A)2. Reduced N (135 lb N/A as MAP + Urea)3. Reduced N + Humic Acids + Calcium (HA + Ca @ planting)4. Reduced N + Humic Acids + Foliar carbon (HA @ planting)5. Recommended N (240 lb N/A as MAP + Urea)
HA applied at 2 gal/A; Ca at 5 gal/A; Foliar C at 16 oz/A
Field Studies with Biostimulants - Humic acids
0
100
200
300
400
500
30 lbs N/A 135 lbs N/A 135 lb N/A +HA + Ca
135 lb N/A +HA + foliar
carbon
240 lbs N/A
Mar
keta
ble
Yeild
, cw
t/A
Treatment
d
ab bc c
Biostimulants had a slight negative effect on yield
Field Studies with Biostimulants N Fixers + Microbial enhancer potato study (2 yrs)
Treatments:1. Starter only (30 lb N/A)2. Reduced N (150 lb N/A as MAP + Urea)3. Reduced N + N fixers (Azotobacter + Clostridium) 4. Reduced N + N fixers + Microbial enhancers5. Recommended N (225 lb N/A as MAP + Urea)6. Recommended N + N fixers (Azotobacter + Clostridium)7. Recommended N + N fixers + Microbial enhancers
Microbial Enhancers = amino acids, chitin, chitosan, glucosamine N fixers and ME each applied at 2.6 quarts/A in furrow @planting + 2 wks
after emergence
Field Studies with Biostimulants - Potato
b
300350400450500550600650
Tota
l Yie
ld, c
wt/
A
Treatments
2016
300
350
400
450
500
550
600
650
Tota
l Yei
ld, c
wt/
A
Treatments
2015
c
bb ab ab abac
b bab ab aba
Significant effect of N fixers & ME at 150 lb N/A, but not at 225 lb N/A in 2016
Significant effect of N fixers at 225 lb N/A, but not at 150 lb N/A in 2017
Field Studies with Biostimulants - Corn Microbe and plant growth regulator
(PGR) study on corn
2 year (2016 & 17) study in Indiana (Lee and Camberato, 2017)
Five Purdue research farms: 17-55 acres SE, NE, Davis, Pinney, Throckmorton Purdue
Ag Centers; 4 to 6 reps/site; 17 to 55 acres/site Six treatments
No starter N-P Starter - 2x2 application (~10 to 16 gal/A) N-P Starter + 4 biostimulant treatments (applied
in furrow)
N rates: 191 to 220 lb N/A (2016); 175 to 215 lb N/A (2017)
Field Studies with Biostimulants - Corn
Biostimulants used: Bio-A (2016 & 17) @ 32 fl oz/A
Bacillus licheniformis, B. megaterium, B. pumilus PGR (2016 & 17) @ 6 fl oz/A
Cytokinin, Indole-3-butyric acid, Gibberellic acid Bio-B (2016 & 7) @ 32 fl oz/A
Rhodopseudomonas palustris, B. bravis, B. lichenifomis, B. megaterium, R. rhodochrus, Lactobacillus planetarium
Bio-C (2016 only) @ 0.16 fl oz/A Trichoderma harzianum; T. atoviride
Bio-D (2017 only) @ 16 g/80,000 seeds Bacillus amyloliquefaciens, Trichoderma virens
Field Studies with Biostimulants - Corn
General results for grain yield (based on 9 sites):
Comparisons based on starter treatments vs. biostimulant (10% probability):
Statistically positive response to biostimulants at 3 sites Positive response to Bio-A (1 site), Bio-B (1 site), PGR (2 sites),
Bio-D (2 sites)
Statistically negative response to biostimulants at 1 site Negative response to Bio-B (1 site)
Results at Throckmorton Ag Center
180
190
200
210
220
230
Control Starter BioA PGR BioB BioD
Grai
n Yi
eld,
bu/
ATreatment
TPAC 2017
180
185
190
195
200
Control Starter BioA PGR BioB BioC
Grai
n Yi
eld,
bu/
A
Treatment
TPAC 2016
* ++
** ** **
Bio-B – 3 bushel decrease in 2016; no effect in 2017Bio-A & PGR – no effect in 2016; 6 to 8 bu/A increase in 2017Bio-D – 8 bu/A increase in 2017 (was not tested in 2016)
Summary and Key Points Biostimulants are substances or microbes applied to
plants or plant roots in small amounts that promote growth
Modes of action for biostimulants vary Direct on plant or indirect effects by stimulating microbes Improved nutrient availability and uptake Act as a growth regulator or hormone Protect against diseases
Effects found in controlled lab experiments often do not translate to the field
Summary and Key Points Responses in the field are inconsistent at best
There are no silver bullets They come at a cost
Do not use biostimulants based on testimonials
Evaluation of biostimulants should be based on replicated field studies over multiple years Compare apples to apples
A more systematic approach is needed to define situations when a biostimulant may be beneficial
QUESTIONS???????
Field Studies with Biostimulants
Azospirillium (N Fixer) on potato study
Treatments:1. Starter only (30 lb N/A)2. Reduced N (180 lb N/A as MAP + Urea)3. Recommended N (240 lb N/A as MAP + Urea)4. Reduced N + Azospirillium at planting5. Recommended N + Azospirillium at planting
Azospirillium applied in furrow @ 12.8 oz/A
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