EFFECTS OF A BIOLOGICAL AMENDMENT ON CHEMICAL AND BIOLOGICAL PROPERTIES AND MICROBIAL DIVERSITY IN SOILS RECEIVING DIFFERENT ORGANIC AMENDMENTS

Authors: PARK, KEECHOON - KOREA; Kremer, Robert

Submitted to: Korean Journal of Soil Science and Fertilizer
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2007
Publication Date: 12/31/2007
Citation: Park, K., Kremer, R.J. 2007. Effects of a biological amendment on chemical and biological properties and microbial diversity in soils receiving different organic amendments. Korean Journal of Soil Science and Fertilizer. 40:234-241.

Interpretive Summary: The organic matter content in soil is a source of nutrients for plants, made available through the action of microorganisms, and provides structure to the mineral soil particles for optimum movement of air and water. A concern with many current intensive crop production systems is depletion of soil organic matter (SOM) due to retention of less crop residue (source of organic matter) and use of high rates of chemical fertilizers that aid in rapid decomposition of SOM. Management practices for improving SOM include adding organic materials (i.e., composts, manures) to soils or “growing organic matter in place” by using crops planted after harvesting the main crop to add organic matter through roots and above-ground growth. The latter strategy is most often referred to as “cover cropping” because the soil surface is covered by vegetation during the period when the main crops have been harvested. We investigated the effects of selected organic amendments and cover crops on improving biological activity and chemical properties of a soil previously cropped to soybean or corn grown continuously for several years. The organic amendments were poultry litter and a municipal compost (yard waste + milled gypsum board + wood ash) applied to soil at 14 and 6.7 tons per acre; the cover crops were red clover and spring oats, which were mowed in late spring and the clippings allowed to remain on the soil surface. A biological product containing a variety of selected microorganisms with beneficial properties (i.e., nitrogen fixation, plant growth regulator production, pathogen antagonism) was also applied by spraying to half the treatments. Both chemical (SOM, pH, and the nutrients K, P, Mg, Ca) and biological (measured as microbial enzyme activities) properties were variable across seasons during a two-year sampling period. We found that the individual organic amendment and soil moisture regime influenced the level of biological activity. Also, the biological product increased soil biological activity or selected chemical properties only with certain organic amendments. A dry period experienced during the second year of testing greatly reduced effects on soil activity regardless of treatment. The results demonstrate the dynamic characteristics of soil microbial activity are affected by seasonal changes, and effects on soil properties need to be evaluated frequently in long-term studies (5+ years). The current studies have implications for other scientists, extension personnel, and farmers because results suggest that effects of practices devised to improve soil organic matter may not be readily detected in a short (< 2 years) period; use of biological product in addition to standard organic amendments may not provide consistent effects; and environmental variables such as rainfall and soil moisture must be considered in interpreting effects observed in the field.

Technical Abstract: Biological fertilizers consisting of suspensions of selected microorganisms are often used in conjunction with various organic materials for amending soils to improve soil quality and plant growth. The effects of a biological fertilizer on chemical and biological properties of soil were investigated alone and when combined with different organic materials including municipal compost (MC), poultry litter (PL), and cover crops [red clover (RC) and spring oats]. A liquid preparation of the biological amendment called Effective Microorganisms (EM) was sprayed on test plots three times over a two-year period. Effective Microorganisms alone did not influence pH, K, or organic matter content in soil. However, increases in P in PL-treated soils in fall of both years and Ca in MC-treated soil in fall 2001, and decreases in Ca, Mg, and cation exchange capacity (CEC) in RC-planted soil were associated with EM. Increased dehydrogenase (DH) activities associated with EM were only detected in July (P=0.0222) and October (P=0.0834) for RC-planted soils in the first year. Fluorescein diacetate (FDA) hydrolysis appeared to be enhanced by EM in soils untreated or treated with MC and oats but only sporadically during the sampling period. FDA hydrolysis in both PL-and RC-treated soils as well as DH activity in PL-treated soils decreased with EM treatment. Effective Microorganisms did not influence substrate utilization patterns expressed by the BIOLOG assay. We concluded that EM effects on soil chemical and biological properties varied depending on the added organic materials. Effective Microorganisms periodically increased soil DH activity and FDA hydrolysis with RC with MC plus oats, respectively.