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RESEARCH: HUMIC SUBSTANCES |
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There
is a long history of using humic and fulvic acids to improve
nutrient uptake. Previous studies in this laboratory have shown that
humic acid can improve iron uptake in wheat (Mackowiak, Grossl, and
Bugbee, 2001. Soil Sci. Soc. Am. J. 65:1744-1750). More recent
studies have been examined the use of humic products to improve
phosphorous and Iron uptake from soils. Recent studies indicate
that uptake of both of these elements can be increased by humic
products. The mechanism appears to be associated with the ability
of these products to reduce the rate of precipitation of P and Fe
supplements when humic products are added with the nutrient
supplement.
The humic products are particularly effective when added with banded
fertilizer at the time of planting. We are continuing our studies
to determine the most cost effective rates.
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Humic
and Fulvic Acids: Effects on Plant Nutrition and Growth
Jason Tew (Master's Thesis)
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Humic substances
are reported to improve plant growth and nutrient uptake, with
iron the most studied nutrient. The most common forms of iron in
soils are iron oxides, which are stable under aerobic conditions and
unavailable for plant uptake. Iron deficient plants become chlorotic, which reduces growth and yield. To determine if humic
substances can reduce iron chlorosis, five commercially available
organic acids were tested on maize grown in sand columns at high
pH. The dry granular humic acid from Aldrich Chemical company
applied at 84.4 g/ liter of sand by volume
(5 % by mass) and 1 g/ liter added with irrigation water,
significanlty reduced iron chlorosis (p<0.0001). It also
increased fresh mass by 39 % and improved root growth. The other
products, applied at 50 µl/ liter did not significantly affect
chlorosis or plant growth.
A second objective was to
determine if humic substances improve plant growth and yield. The
effects of eleven commercially available dry granular products on
tomato growth were studied in soil columns in a greenhouse. A
product from Horizon Ag Products (Modesto, CA), DGX FeZnMn Blend at
a rate of 44.8 kg/ha (40 lbs/acre) significantly improved root
growth, but not shoot growth or yield.
In another study, ten
commercially available liquid products from Horizon Ag Products were
tested. Treatments were applied at 50 ml/liter mixed with
irrigation water. Treatment BA6.6% increased fruit number, fruit
dry mass and plant dry mass. Treatments QH6.6% and Charger
increased plant dry mass. Treatments QH6.6%, Hydra-Hume6% and
F-6000 increased fruit dry mass. However, when the application rate
was reduced to 4.6 µl/liter, there were no significant beneficial
effects. Most application rates reported in the literature are
considerably higher than economic rates applied in the field. The
results of these studies indicate beneficial effects on plant
nutrition and growth at high rates but limited effects when at low
rates.
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Beneficial effects of humic acid on micronutrient availability to wheat.
Cheryl Mackowiak, P. Grossl, and B. Bugbee - 2001
Soil Science Society of America Journal 65(6): 1744-1750.
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ABSTRACT Humic
acid (HA) is a relatively stable product of organic matter
decomposition and thus accumulates in environmental systems. Humic
acid might benefit plant growth by chelating unavailable nutrients
and buffering pH. We examined the effect of HA on growth and
micronutrient uptake in wheat (Triticum aestivum L.) grown
hydroponically. Four root-zone treatments were compared: (i) 25 muM
synthetic chelate N-(4-hydroxyethyl)ethylenediaminetriacetic acid
(C10H18N2O7) (HEDTA at 0.25 mM C); (ii) 25 muM synthetic chelate
with 4-morpholineethanesulfonic acid (C6H13N4S) (MES at 5 mM C) pH
buffer; (iii) HA at I mM C without synthetic chelate or buffer; and
(iv) no synthetic chelate or buffer. Ample inorganic Fe (35 muM Fe3+
) was supplied in all treatments. There was no statistically
significant difference in total biomass or seed yield among
treatments, but HA was effective at ameliorating the leaf
interveinal chlorosis that occurred during early growth of the
nonchelated treatment. Leaf-tissue Cu and Zn concentrations were
lower in the HEDTA treatment relative to no chelate (NC), indicating
HEDTA strongly complexed these nutrients, thus reducing their free
ion activities and hence, bioavailability. Humic acid did not
complex Zn as strongly and chemical equilibrium modeling supported
these results. Titration tests indicated that HA was not an
effective pH buffer at I mM C, and higher levels resulted in HA-Ca
and HA-Mg flocculation in the nutrient solution.
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The Use of Humic Acid to Ameliorate Iron Deficiency Stress.
Julie Chard and B. Bugbee - 2006
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ABSTRACT
Most soils contain ample inorganic iron for plant growth but in
alkaline, calcareous soils the concentration of plant-available iron
(Fe2+ and Fe3+ in the soil solution) is
extremely low. Humic compounds (humic and fulvic acids) can
incorporate insoluble iron into chelated complexes that enable its
uptake by plants. We tested the ability of a leonardite-derived
granular humic acid (HA) to alleviate iron stress in corn plants.
Individual corn plants were grown in columns filled with sand and
amended with varying amounts of HA. In Trial #1 calcium carbonate
was mixed in to the sand to buffer the pH around 8. In Trial #2 the
effect of high pH buffering was investigated by replicating all
treatments with and without the addition of calcium carbonate. The
plants in both trials were watered with a dilute nutrient solution
that provided all the necessary plant nutrients except iron. Low
chlorophyll content (chlorosis) of young leaves is the most obvious
visible symptom of iron deficiency. As the amount of HA per
treatment increased, chlorosis decreased, indicating that HA
provided iron to the corn plants. However, the necessary HA
application rate to provide ample iron was more than 20 times the
recommended application rate of commercially-available HA.
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