ENVIRONMENTAL
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  COLUMN STUDIES

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    CARBON USE EFFICIENCY

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    LIGHT STUDIES

  TURFGRASS RESEARCH

RESEARCH: HUMIC SUBSTANCES

BACK TO RESEARCH

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.

• Humic and Fulvic Acids: Effects on Plant Nutrition and Growth
  Jason Tew (Master's Thesis)

Humic substances can improve nutrient uptake, with iron the most studied nutrient. Iron deficient plants become chlorotic, which reduces growth and yield. To determine if humic substances can reduce iron chlorosis, organic acids were tested on maize grown in sand columns at high pH. A 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, significantly reduced iron chlorosis (p<0.0001). It also increased fresh mass by 39 % and improved root growth. The other products, applied at low rates (0.05 ml per liter) did not significantly decrease iron chlorosis.

Humic substances can also improve plant growth. The effects of eleven dry granular humic products on tomato growth were studied in soil columns in a greenhouse. An experimental product from Horizon Ag Products (Modesto, CA), applied at 44.8 kg/ha (40 lbs/acre) significantly improved root growth, but there were not enough replications to show a statistically significant improvement in yield; however, increased root growth has the potential to improve plant growth in the field, particularly under nutrient or water stress conditions. Additional research is necessary to determine cost effective rates of humic products for specific crops, application methods, and soil conditions.

• 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.

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.

• The Use of  Humic Acid to Ameliorate Iron Deficiency Stress.
  Julie Chard and B. Bugbee - 2006

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.