|Yang, Yoo-Jeong - ENV SCI, UC RIVERSIDE|
|Valenzuela-Solano, Cesar - ENV SCI, UC RIVERSIDE|
|Crohn, David - ENV SCI, UC RIVERSIDE|
|Crowley, David - ENV SCI, UC RIVERSIDE|
Submitted to: Biology and Fertility of Soils
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 17, 2003
Publication Date: August 29, 2003
Citation: YANG, Y., DUNGAN, R.S., IBEKWE, A.M., VALENZUELA-SOLANO, C., CROHN, D.M., CROWLEY, D.E. 2003. EFFECT OF ORGANIC MULCHES ON SOIL MICROBIAL ACTIVITIES AND COMMUNITIES ONE YEAR AFTER APPLICATON. BIOLOGY AND FERTILITY OF SOILS. 38:273-281. Interpretive Summary: Recent attention on the toxicity impacts of agricultural chemicals has increased needs to develop reliable alternative methods to protect and conserve soils. One such method is the land application of mulch such as yard waste. With the over abundance of waste materials generated daily by human activities, there is great interest in using organic waste to improve our soils. The addition of organic waste to soils is an effective way of controlling soilborne pathogens and stimulating antagonistic bacterial growth. The proper use of many types of organic residues as mulches on agricultural soils is known to provide various minerals (e.g., N, P, and S) essential for proper plant nutrition, increase the soil organic matter content, and influence soil structure and many other related physical, chemical, and biological parameters. In addition, organic amendments also increase the size, biodiversity, and activity of microbial populations. This study demonstrated the many benefits derived from using organic mulches to increase soil quality by increasing bacterial diversity.
Technical Abstract: The application of organic mulches as a soil cover is effective in improving the quality of soil, however, very little information is available on the effect of mulches on the soil microbial community. In this study, we investigated the effect of various organic mulches on soil dehydrogenase activity (DHA) and microbial community structure at the soil surface and 5 cm below the soil surface one year after application of the mulches. DHA was only stimulated at the surface and at 5 cm in plots mulched with grass clippings. Fatty acid methyl ester (FAME) analysis and denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rDNA fragments were used to assess changes in the soil microbial community structure. Cluster analysis and principle component analysis of FAME profiles showed that only soil mulched with pine chips distinctively clustered from the other treatments. At the soil surface, bacterial DGGE profiles revealed that distinct shifts in several bacterial populations occurred in soils mulched with grass clippings and eucalyptus yardwaste, while DGGE profiles from 5 cm revealed no distinct changes. From the soil surface DGGE profile, the Shannon-Weaver index of diversity, H, was calculated. Compared to the control (H = 0.9), the grass clipping- and eucalyptus-treated soils showed slightly increased bacterial diversity, with an H of 1.1 and 1.0, respectively. These results indicate that the long-term effect of organic mulches on the soil microbial activity and community structure is highly dependent upon the type of mulch and soil depth.