Effects of Organic Amendments on Soil Humic Substances Content and Physiological Properties of Water-Stressed Zea mays and Glycine max

Project Overview

Project Type: Graduate Student
Funds awarded in 2004: $9,793.00
Projected End Date: 12/31/2005
Grant Recipient: Virginia Tech
Region: Southern
State: Virginia
Graduate Student:
Major Professor:
Greg Evanylo
Virginia Tech

Annual Reports


  • Agronomic: corn, rye, soybeans


  • Crop Production: biological inoculants, municipal wastes, nutrient cycling, organic fertilizers, tissue analysis
  • Education and Training: demonstration, extension
  • Production Systems: general crop production
  • Soil Management: organic matter, soil analysis, soil quality/health


    Field research determined that continuous application of various types and rates of compost elicited no greater plant physiological responses to environmental stress than than did annual applications of commercial fertilizer or uncomposted poultry litter. Compost rates designed to supply the nitrogen requirement for corn produced yields and seed quality as high as those with the fertilizer and litter. Benefits of compost on crop physiological responses are more easily observed in drought sensitive species grown in containers where the biologically active constituents are maintained in the root zone.

    Tables, figures or graphs mentioned in this report are on file in the Southern SARE office.
    Contact Sue Blum at 770-229-3350 or
    sueblum@southernsare.org for a hard copy.


    Water stress is the most critical environmental factor limiting crop production in the Piedmont soil physiographic province, which extends from Maryland to Alabama (Southeast Regional Climate Center, 2003a). Short-term crop water stress is common during summer months due to high evapotranspiration rate. Although often temporary, moisture stress usually reduces yield potential of crops such as corn and soybean because adequate moisture is essential for optimal growth and development during the sensitive reproductive stage of summer crops.

    Periodically, summer crops in the region sustain prolonged water deficits. The National Drought Mitigation Center issued ‘severe’ and ‘extreme’ drought indices for the Virginia Piedmont during the summers of 1999 and 2002 (National Drought Mitigation Center, 2003). Precipitation was 14% and 24% less in 1999 and 2002, respectively, than precipitation occurring in a normal year (Southeast Regional Climate Center, 2003b). Corn and soybean yields in 1999 and 2002 were 35% to 57% and 11% to 43% lower, respectively, than average yields produced in the region (National Agricultural Statistics Service, 2003).

    During water stress, overall photosynthetic efficiency is compromised and excessive concentrations of reactive oxygen species are generated within the chloroplast. Reactive oxygen species are partially reduced forms of oxygen that are capable of unrestricted oxidation of cellular components including the thiol and iron-sulfur clusters of peptides in the DNA bases (Mano, 2002). Reactive oxygen species also cause lipid peroxidation of the chloroplast membrane (as measured by malondialdehyde concentration) (Yan et al., 1996; Hung and Kao, 1997) and eventually cause cell death. Reactive oxygen species are naturally generated due to the intrinsic inefficiencies of photosynthesis. Plants have evolved an antioxidant scavenging system to effectively remove excessive reactive oxygen species from the chloroplast and maintain their concentrations at steady-state levels (Asada, 1994). It has been well documented that an up-regulation of antioxidant activity during stress increases the stress tolerance of plants (Longo et al., 1993; Li et al., 1994; Jiang and Zhang, 2001; Du et al., 2005; Ge at al., 2005). Pastori and Trippi (1993) observed greater antioxidant activity in more drought resistant plants than in the less resistant ones. Some plants have evolved an alternative photosynthetic pathway to prevent the formation of reactive oxygen species such as the of C4 metabolism of corn (Mittler, 2002). Stepien and Klobus (2005) observed lower reactive oxygen species generation and greater antioxidant efficiencies of stressed corn than in wheat.

    Increased antioxidant activity has also been documented to retard the natural process of leaf senescence (Lin et al., 1988; Pastori and Trippi, 1993). Prochazkova et al. (2001) observed greater antioxidant activity over a longer period in a later maturing corn cultivar than in a relatively early maturing one. The authors concluded that the earlier decrease in antioxidant activity in the faster maturing cultivar contributed to an earlier senescence.

    There are three major antioxidants that quench free radicals. Superoxide dismutase (SOD) reduces superoxide to peroxide in the chloroplast (Asada, 1994) and is considered the first response antioxidant. Ascorbate peroxidase (APX) reduces peroxide to water in the chloroplast. Catalase (CAT), located in the peroxisome, also reduces peroxide to water. Researchers have observed that CAT activity in C4 species is predominately driven by the formation of reactive oxygen species in the chloroplast (Tolbert et al., 1969), though corn CAT activity has been documented to be unresponsive to changes in the intercellular redox status during stress (Alber and Scandalios, 1993). Catalase activity in C3 plant species appears to be driven by the oxidation of glycolate, a product of photosynthesis (Lyu-bimov and Zastrizhnaya, 1992).

    The soil-based application of organic amendments to field grown crops may have an ameliorating effect on drought stressed crops. Sahs and Lesoing (1985) observed higher sweet corn yields in plots amended with beef feedlot manure than those that were inorganically fertilized during drought years. Heckman et al. (1987) found that field grown soybeans fertilized with sewage sludge had increased drought resistance and nitrogen fixation than the control treatment.

    Improved drought tolerance of crops grown in organically amended soils has been linked to the maintenance of optimum leaf health. In five-week old water stressed maize seedlings, Xu (2000) recorded higher photosynthetic rates when the soils were organically amended. HuiLan et al. (1998) noted that the application of organic amendments increased water stress resistance of sweet corn leaves. In particular, stomatal and curticular conductances of the leaves were lower in these plants than in inorganically-fertilized plants. Researchers speculate that the hormone-like properties of humic substances may play a causal role in drought stress amelioration (Serdyuk et al., 1999; Kulikova et al., 2003; Chen et al., 2004; Quaggiotti et al., 2004; Zhang and Ervin, 2004).

    Humic substances are the major constituents of stable organic matter. These materials are naturally occurring, ubiquitous organic compounds that contain relatively high molecular weights, are yellow-black in color, and are formed by secondary synthesis reactions between plant and animal remains and microbial metabolites (Stevenson, 1994b). Humic substances are operationally defined, based on solubility. Fulvic acids represent about 20% of humic substances (Epstein, 1997), are relatively low in molecular weight (1000-4000 g/mol), and soluble in both alkali and acidic solutions (Stevenson, 1994b). Humic acids represent roughly 80% of humic substances (Epstein, 1997), have relatively large molecular weights (12,000-300,000 g/mol), and are insoluble in acidic solutions (Stevenson, 1994b).

    Humic substances have been shown to elicit ameliorative effects on drought stressed plants, but most experiments designed to elucidate such benefits were limited to foliar applications of humic substances in pot studies. Xudan (1986) foliarly applied fulvic acid to pot grown wheat plants prior to imposing a nine-day dry down period. These plants maintained greater stomatal conductances, contained greater chlorophyll contents and increased 32P uptake relative to the control. Yan and Schmidt (1993) applied a commercially available seaweed extract to pot grown drought stressed perennial ryegrass and observed increased cell membrane fluidity and permeability relative to the control treatment. Zhang and Schmidt (1999, 2000) foliarly applied a commercially available seaweed extract and humic acid solution to drought-stressed tall fescue, creeping bentgrass, and Kentucky bluegrass, and observed an increase in leaf water status and antioxidant activities relative to the control.

    Research exploring possible ameliorative effects of
    soil applied compost humic substances on drought stressed agronomic crops is lacking. Further investigation is required to discover whether organic matter fractions in compost may elicit plant physiological benefits under field conditions.

    Project objectives:

    The objectives of this field study were to compare the effects of repeated applications of inorganic fertilizer, poultry litter, and two composts on
    (1) soil physiochemical properties (i.e., nutrient concentrations, bulk density, water holding capacity, organic carbon, humic and fulvic acid carbon) and (2) physiological properties (i.e., chlorophyll content, leaf water potential, photochemical efficiency, leaf antioxidant activities, lipid peroxidation, leaf Delta T values, yield, seed quality) of corn and soybean grown in a Piedmont soil.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.