Submitted to: Korean Society of Soil Science and Fertilizer
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/19/2011
Publication Date: N/A
Citation: Interpretive Summary: Maintaining and improving organic matter in soils is central to achieving sustainability in agricultural production systems. Soil organic matter improves physical processes of water infiltration and soil aggregation that reduces erosion and water runoff; improves chemical characteristics for retaining nutrients for plant growth and neutralizing potentially toxic, synthetic chemicals; and promotes biological activity critical for transforming nutrients into plant available forms and suppressing plant disease agents. Soil organic matter can be improved through the addition of various organic materials including composts and animal wastes as well as growing various crops specifically for adding carbonaceous materials via root exudation and returning vegetative growth to the soil. To better understand conditions affecting the contributions of various organic amendments toward soil organic matter buildup in soil, we tracked the soil biological activity after addition of various amendments during the growing seasons over a two-year period. We measured soil enzymes as an indicator of microbial activity and microbial diversity as an indicator of potential changes in the soil environment caused by organic amendment. The organic amendments evaluated included municipal compost prepared from lawn clippings and tree leaves, poultry manure, and oat and red clover cover crops. We found that biological activity was affected by organic amendment type with municipal compost gradually increasing in activity during the season and sustaining this high activity through the end of the two-year period while other amendments appeared slower in building up overall soil organic matter. The cover crops accommodated a highly diverse soil microbial community, likely due to continuous inputs of readily available nutrient sources during active root growth, that could lead to greater diversity in beneficial functions provided in the soil. However, regardless of organic amendment, microbial activity and diversity were greatly affected by seasonal environmental conditions especially under dry weather extremes. These results are important to other scientists, extension personnel, and farmers because they characterize various organic amendments available for soil improvement to help guide selection in regard to rates of organic matter buildup and insight to the diversity of biological activity that might be provided. They also show that these functions are susceptible to environmental stresses, suggesting that other management practices such as irrigation might be included to realize the full effect of organic amendments.
Technical Abstract: Soil microbial activity and diversity fluctuate seasonally under annual organic amendment for improving soil quality. We investigated the effects of municipal compost (MC), poultry litter (PL), and cover crops of spring oats and red clover (RC) on soil enzyme activities, and soil bacterial community-level physiological profiling (CLPP) in a Mexico silt loam in Central Missouri, USA. Temporal patterns of these parameters were observed by periodic soil sampling from spring to fall during 2001-2002. MC increased soil dehydrogenase (DH) activity consistently beginning about three months after MC application; fluorescein diacetate (FDA) hydrolytic activity significantly increased by September 2001 but fluctuated during the remaining experimental period. DH activity responded more directly to the amount or properties of organic residues in soils while FDA hydrolysis and CLPP were generally influenced by composition of organic sources. Enzyme activities and CLPP showed seasonal variation, which depended on organic sources and soil moisture. MC and cover crops may be useful organic sources for enhancing general soil microbial activity and altering soil microbial diversity, respectively. Because microbial activities and diversity are dynamic and subject to seasonal changes, the effects of organic amendments on these parameters should be investigated frequently during a growing season.