Effects of Humic Substances on Soil Microbes

By Richard Lamar, PhD
Senior Director of Humic Research
Bio Huma Netics, Inc.

Most of the work on agricultural applications of humic substances (HS) has focused on their biostimulant effects on plants. Far less work has been conducted on the effects of HS on soil microbial populations. It’s not surprising to learn, from the few studies that have been published, that HS also stimulate the growth of soil bacteria, even the bacteria that inhabit earthworm digestive tracts. One of the most important discoveries is that many species of soil bacteria are able to grow on humic acid (HA) as their sole carbon source (Tikhonov et al., 2010).

These findings have important implications for the roles played by soil bacterial communities—including those residing in the guts of soil fauna, such as earthworms—in the humification process (i.e., the process of conversion of dead plant tissues to humic substances). This means that these bacteria are consuming HS and modifying HS by metabolizing humic molecules and using the metabolized molecules to produce proteins, fats, and other types of molecules. When the bacteria die, they are in turn consumed by other microbes and those molecules created from metabolized humic molecules wind up being included as HS.

The other important piece of information that has come out of the work on bacterial-HS interactions is that, in addition to being potential carbon sources, HS can also act as soil bacterial growth stimulants or growth regulators (Tiknonov et al., 2010). This was demonstrated in a study in which a number of soil isolated bacterial species were grown on a medium that contained glucose as the carbon source (10 mg/ml) and humic acid (1 mg/ml). Thus, the humic acid was 10X lower than the glucose. Growth of the bacteria on this medium was compared with the growth of bacteria on a medium that did not contain the humic acid. The growth of 41% percent of the bacterial species (these were isolated from earthworm digestive tracts) were stimulated by the inclusion of the humic acid. The authors of the study concluded that, because the concentration of glucose was so high and the increase in available carbon from the addition of 1 mg/ml humic acid was insignificant, the humic acid acted as a growth stimulant to the 41% of bacteria whose growth was increased.

These types of studies have demonstrated that HS can stimulate the growth of plant-growth-promoting rhizobacteria (aka PGPR bacteria, for which the “rhizo” stands for rhizosphere or the area of soil that is intimately associated with plant roots). One of the most well-known PGPR bacteria are Pseudomonads, strains of which have been found to be able to solubilize phosphate, produce siderophores (important for Fe uptake), ammonia, and the plant-growth-regulator auxin (Gupta, 2008; Selvakumar et al., 2009).

REFERENCES

Gupta, A. and M. Gopal. 2008. Siderophore production by plant growth promoting rhizobacteria. Indian J. Agric. Res. 42(2):153–156.

Salvakumar, G., P. Joshi, S. Nazim, P. K. Mishra, J. K. Bisht and H. S. Gupta. 2009. Phosphate solubilization and growth promotion by Pseudomonas fragi CS11RH1 (MTCC8984), a psychrotolerant bacterium isolated from a high-altitude Himalayan rhizosphere. Biologia, 64(2)239-245

Tikhonov, V. V., A. V. Yakushev, Y. A. Zavgorodnyaya, B. A. Byzov, and V. V. Demin. 2010. Effect of humic acids on the growth of bacteria.  European Soil Science, 43 (3):305–313.

Huma Gro® Turf Amendments Reduce Nitrogen and Phosphorus Leaching

Summary

This research report demonstrates the effect of HUMA GRO® TURF products X-TEND®, FERTIL HUMUS®, MULTI-PURPOSE™, and ZAP® in the reduction of nitrogen and phosphorus leaching in fine sand soils.

The leaching of nitrogen and phosphate fertilizers presents an on-going problem in Florida soils. Agricultural amendments that reduce leaching when applied to soils or when mixed with nitrogen and phosphate fertilizers present a potential solution to this problem. Retaining a greater amount of nutrient in the crop root zone is economically beneficial to the grower. Four Huma Gro® Turf amendments were applied to Immokalee fine sand soil to evaluate their respective effect on nutrient leaching and increasing nutrient levels in crop root zones.

In simulated irrigations, nitrogen and phosphorus and Huma Gro® Turf amendments were applied to columns of soil, with the leachate being drained away. A total of 15.5 inches water was applied over 60 days, after which the soil columns were analyzed for nitrate nitrogen and phosphate.

Results

The combinations of fertilizer plus the Huma Gro® Turf amendments lost only 15.6% of the nitrogen and 15.0% of the phosphate. The control lost 40.6% of the nitrogen and 35.6% of the phosphate. In the top 18″ of soil, the combination of fertilizer plus the Huma Gro® Turf amendments resulted in an increased nitrogen level of 76.1% and an increased phosphate level of 31.2% compared to the control.

Percent Increase of N & P Over the Control in Top 18″ Soil

% Increase vs Control Nitrogen Phosphate
Fertilizer
+ Huma Gro®
76.1% 31.2%

Percent Loss of Nitrogen & Phosphate in 36″ Soil Profiles

Nitrogen % Loss Phosphate % Loss
Fertilizer
+ Huma Gro®
15.6% 15.0%
Control 40.6% 35.6%

 

Fertilizer complexed with Huma Gro® Turf amendments to the soil significantly reduced leaching. With Huma Gro® Turf amendments, more nitrogen and phosphate remained in the top 18″ of soil.

Product Summary

FERTIL HUMUS® (24-0-0 + Fe, Zn, Mn) complexed with our proprietary Micro Carbon Technology®* (MCT) contains the nutrients necessary to feed beneficial fungal activity in the soil and to increase carbon and nutrient availability in the root zone. FERTIL HUMUS® enhances aerobic decomposition of organic matter and builds a humus-rich soil, which releases nutrients tied up in organic matter. FERTIL HUMUS® also helps buffer the plant from the effects of heavy metals and toxic substances in the soil.

MULTI-PURPOSE™ (5-0-0 + Fe,Zn,Mn) with our proprietary MCT* base, improves soil structure and feeds the beneficial bacteria activity in the soil. This balances the carbon-oxygen ratio, creating a carbon-rich soil that allows the soil and rhizosphere interface to be more active.

X-TEND®  (6-2-0) is a concentrated MCT* product with high levels of organic acids and nutrients. X-TEND® is formulated to be blended in liquid fertilizers or to be impregnated onto dry fertilizers, which extends the effectiveness of the fertilizer or fertilizer solutions.

ZAP® (8-0-0 + Fe,Zn,Mn,S) complexed with MCT* is an organic–based formulation of nutrients for feeding the native beneficial soil biological balance. ZAP® feeds a strong, vigorous soil biology which indirectly results in the natural improvement of soil health.

* Huma Gro®  Turf products with Micro Carbon Technology® rapidly deliver essential nutrition to crops for optimal growth, fruiting, and vigor. The results are higher quality harvests, increased crop yields, and maximum profit.

 See the complete Research Report.

Contact us for a free quote.

Research Report: FERTIL HUMUS® Soil Amendment Trial for Water Infiltration

Summary

The following research report compares increased moisture infiltration with the use of FERTIL HUMUS® at different rates and timings. It was conducted in the southern portion of the Columbia Basin in Washington State. The field, which had sandy loam soil, was pivot-irrigated as a broadcast spray, incorporated. All treatments were replicated four times in a complete randomized-block plot design. The time it took for a measured acre-inch of water to penetrate into the soil was recorded for each replication in each treatment. The times for each replication were averaged so that the influence of the treatments could be compared.

Results

Chart of average time for water infiltration

  • Trt 1: 1 pint/acre FERTIL HUMUS
  • Trt 2: 2 pint/acre FERTIL HUMUS®
  • Trt 3: 4 pint/acre FERTIL HUMUS®
  • Trt 4: 2 pint/acre FERTIL HUMUS®, followed 2 weeks later by another 2 pints/acre
  • Trt 5: The Grower Standard Treatment (Untreated Check)

Conclusion

Application of FERTIL HUMUS® reduces the amount of time required for water to enter the soil surface, which is beneficial in terms of reducing the risk of soil erosion, fertility movement, and evaporation loss. It also aids soil aeration and moisture uniformity within the field.

Product Summary

FERTIL HUMUS® (24-0-0 + Fe, Zn, Mn) is a unique blend of nutrition and enzymes with our proprietary Micro Carbon Technology®* base. It has been developed to deliver the nutrients necessary to feed beneficial fungal activity in the soil and increase carbon and nutrient availability in the root zone. FERTIL HUMUS® enhances aerobic decomposition of organic matter and builds a humus-rich soil, which releases nutrients tied up in organic matter and improves soil condition. It also helps buffer the plant from the effects of heavy metals and toxic substances in the soil.

Benefits of use:

  • Aids in the decomposition of organic residues in soils
  • Increases recycling of nutrients tied up in organic matter
  • Helps to buffer harsh chemicals and degrade toxic compounds in soil
  • Increases soil water retention
  • Stimulates root growth

Apply Fertil Humus® where there is:

  • Poor or imbalanced soil biology.
  • Slow breakdown of organic matter.
  • Sandy soil needing stabilization by humus formation.
  • Poor water penetration or retention.
  • Chemical or toxic compound residues in the soil.

* Huma Gro® Turf products with Micro Carbon Technology® rapidly deliver essential nutrition to crops for optimal growth, fruiting, and vigor. The results are higher quality harvests, increased crop yields, and maximum profit.

See the complete Research Report.

Contact us for a free quote.

 

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