THE EFFECTS OF HUMIC SUBSTANCES ON CROP PRODUCTION, SOIL, AND

WATER QUALITY

Mir-M. Seyedbagheri

University of Idaho Elmore County Extension

Mountain Home, Idaho

ABSTRACT

Soil organic matter has declined drastically in farmlands worldwide since 1900 as a result

of carbon turnover and cropping systems. Humic substances, a major constituent of soil organic

matter, are important for their influence on soil physical, chemical and biological properties that

are essential to soil health and plant growth, including chelation, mineralization, buffer effect,

clay mineral-organic interaction, and cation exchange. For the past 18 years we have evaluated

commercial humic acid products derived from lignite and leonardite in different cropping

systems. Research trials were established from 1990 through 2008 to evaluate the efficacy of

different humates products in potatoes in Western Idaho. Data from humic acids trials showed

that different cropping systems responded differently to different products in relation to yield and

quality. Important qualifying factors included source; concentration; processing; chelating or

complexing capacity of the humic acid products; functional groups (Carboxyl -CO2H; Phenol -

Ohp; Hydroxyl -Oha; Ketone -C=O; Ester O=C-O-R; Ether –C-O-C-; Amine –NH2,-NH,-N);

rotation and soil quality factors; consistency of the product in enhancing yield and quality of

crops; mineralization effect; and influence of the product on fertilizer use efficiency.

Collectively, the consistent use of good quality products in our replicated research plots in

different years resulted in a yield increase from 11.4 percent to the maximum of 22.3 percent.

Over the past decade, there has been a major increase in the quality of research and development

of organic and humic acids by some well-established manufacturers. Our experimentations with

these commercial products showed an increase in the yield and quality of crops.

INTRODUCTION

Today soil OM is becoming an important element for agricultural environment and

energy. Humic substances (HS), the major fraction of OM, are ubiquitous in the environment,

and have been documented to interact in some manner with over 50 elements from the periodic

table. The importance of HS in soil science and agriculture has been acknowledged for over 150

years, but scientists have encountered major challenges in understanding humic acid

functionalities.

Soil is a living system, in which the interaction of the various metabolic processes is

regulated in much the same way cellular processes are regulated: feedback inhibition; induction

of enzymatic activity; secretion and impact of pH; ionic strength; temperature; and the presence

and absence of inhibitors. Soil OM is composed of plant and animal debris in various stages of

decomposition by soil microorganisms. Humus is fully decomposed organic matter. Brown or

black in color, humus makes up 65-80 percent of the total organic matter in soil.

Humus-mineral complexes are components of the conglomerate soil colloids which

contain oxyhroxides and humus materials associated to present reactive seats of fertility in soils.

Due to its low specific weight and high surface area, humus has a profound effect upon the

physical properties of mineral soils with regard to improved soil structure, water intake and

reservoir capacity, ability to resist erosion, and the ability to hold chemical elements in a form

readily accessible to plants.

Humic substances (HS) are the product of humification, the biological process whereby

organic matter is converted into humic substances via transformation of plant lignin and cell

polyphenols by microbial synthesis in the soil. HS are composed of three major fractions: humic

acid (HA), fulvic acid (FA) and humin. Humic acids constitute the largest of the three fractions,

and are one of the most important constituents of fertile soils because of their profound direct

and indirect modes of action on soil chemical, physical, and biological properties.

Direct modes of action of HS on plant growth:

Effects on membranes resulting in improved transport of nutritional elements.

Enhanced protein synthesis.

Plant-hormone-like activity.

Enhanced photosynthesis.

Indirect Effects of HS on enzyme activity:

Solublization of microelements (e.g. Fe, Zn, Mn) and some macroelements (e.g.

K, Ca, P)

Reduction of active levels of toxic elements.

Enhancement of microbial populations.

Chemical-physical effects of HS on plant growth:

Combines soil particles in structural aggregates.

Favors the mineralization of the chemical substances which releases SO4, PO4,

NH4, NO3.

High exchange capacity.

Humin serves to stabilize soil organic matter by a) encapsulation of small polar

molecules (physical sequestration), b) binding of functionalized biomarkers (chemical

sequestration), and c) selective preservation of aliphatic biopolymers.

Figure 1. Stable Humus vs Productivity Figure 2. Clay-Organic Acid Nutrient Exchange

Sustainable cropping systems call for the protection of organic carbon (C), a major

component of HS. Over a one-year period, 32 to 98 percent of C in soil and plant residues is lost

as CO2. Results of various investigators concluded that 32 to 98 percent of soil humus present in

agricultural soils was in organo-mineral complexes. Pure culture studies have indicated that clays

may increase the efficiency of conversion of substrate C to biomass (Figure 3).

Figure 3. Clay-humic association via

Binding HS to clay by cationic bridges

Low levels (<2 percent) of elements that influence plant nutrition are one of the most

important constraints to crop growth. New technologies are needed for OM manipulation to

overcome current agronomic practices of organic matter (OM) maintenance in the soil. For over

17 years we established research trials in farmers’ fields in Western Idaho to scientifically

evaluate the efficacy of different humates products on crop yield and quality in potato

production. We evaluated over 30 different commercial humic substances derived from lignite

and leonardite. Collectively, the consistent use of good quality products in our replicated

research plots in different years resulted in a yield increase from 11.4 percent to the maximum of

22.3 percent.

METHODS

For each research trial, HA treatments were arranged in a randomized complete block

design,with four replications. HA treatments were applied as soil amendment, top-dressed, side-

dressed, or foliar, in accordance with standard commercial practices. For each top-dressed, side-

dressed, or foliar application, the hills were opened above the potato seeds for pre-emergence

treatments prior to application of the products. Liquid humic products were applied with solo-

pack sprayers to the opened furrow in accordance with manufacturers‘ recommendations.

Furrows were closed immediately after application of different commercial HA treatments. In

different trials, granular humates were weighed (40.48 kg.ha-1) and spread as evenly as possible

to treated rows according to block design randomizations. At the end of the crop season, potato

plots were harvested, graded, weighed, and quality parameters were evaluated. Data from these

years were subjected to analysis of variance of regression.

RESULTS AND DISCUSSION

Data from HA trials showed that different cropping systems responded differently to

different products in relation to yield and quality. Collectively, the consistent use of good quality

products in our replicated research plots in different years resulted in a yield increase from 11.4

percent to the maximum of 22.3 percent. Humic acid products enhanced nitrogen mineralization

in early season by an average of 9.6 percent. Research studies done by my colleagues, Drs. Jeff

Stark and Bryan Hopkins, reflect favorable findings regarding the impact of humics on yield and

quality (see Table 1). Over the past decade, there has been a major increase in the quality of

research and development of organic and humic acids by some well-established manufacturers.

Our experimentations with these commercial products showed an increase in the yield and

quality of crops (Figure 4).

Figure 4. Effects of Humic Acid Rate on Potato Yield

Table 1. Yield, specific gravity, petiole P and gross return in Russet Burbank

Potatoes under different rates of 10-34-0 Fertilizer

Bryan Hopkins and Jeff Stark, University of Idaho Aberdeen Research Station

O5

(kg/ha)

Humic

Acid

(L/ha)

Total US

No.1

>283g Sp.

gravity

Petiole P

(% dwt)

Gross

Return

(US$/ha)

0 0 394 225 146 1.077 0.24 4523

67.36 0 431 260 177 1.079 0.29 5110

67.36 14 444 279 186 1.080 0.31 5390

134.7 0 438 261 179 1.079 0.30 5187

134.7 28 446 278 193 1.079 0.32 5402

LSD @

1%

48 33 23 0.003 0.03

336

358

368

385 385

346

300

325

350

375

400

0 1 2 4 8 16

Yie

ld (

cw

t/acre

)

Humic acid (gal/acre)

Y = 343.4 + 12.01X-0.746X2

R2 = 0.92 ***

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