Skip to main content
ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research Unit » Research » Publications at this Location » Publication #119923
Title: SOIL SOLARIZATION REDUCES ARBUSCULAR MYCORRHIZAL FUNGI AS A CONSEQUENCE OF WEED SUPPRESSION

Author
item Schreiner, Roger - Paul
item IVORS, KELLY - USDA-ARS-HCRL
item Pinkerton, John

Submitted to: Mycorrhiza
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2001
Publication Date: 9/15/2001
Citation: 11: 273-277

Interpretive Summary: A two year field study was conducted in 1995 and 1996 to determine the impact of soil solarization (the process of heating soil by covering fields with clear plastic) on beneficial, mycorrhizal fungi. The effects of solarization were compared to fumigation with vapam (a common replacement for methyl bromide) at two rates and to fumigation with methyl bromide at a asingle rate. Treatments were applied during the mid-summer when solar radiation is maximal. Infective propagules of arbuscular mycorrhizal (AM) fungi (spores and other fragments of the fungi that initiate root colonization) were monitored before and after solarizing or fumigating field plots by using a greenhouse bioassay. AM fungi were also monitored the following spring, 8 months after treatments were applied. Solarizing soil did not reduce AM fungi immediately after the solarization period in either year. However, AM fungi were greatly reduced in solarized soil the following spring in both years. The reduction in AM fungi that had occurre over winter was associated with a large reduction in winter annual weed populations in solarized plots. Fumigation of soils with vapam or methyl bromide reduced or eliminated AM fungi immediately after treatment. Therefore, solarizing soil may not directly harm AM fungi, but can indirectly reduce AM fungi as a consequence of suppressing weeds that maintain AM-fungal populations during the winter. Solarization should not be followed by a long-fallow period to ensure that AM fungi are not reduced by a lack of host plants (weeds in our study) that maintain AM-fungal populations in soil.

Technical Abstract: Soil solarization, the process of heating soil by covering fields with clear plastic, is a promising method to reduce the populations of soilborne pests and weeds without the use of pesticides. However, the destruction of beneficial organisms like arbuscular mycorrhizal (AM) fungi may also occur and reduce the positive effects of solarization. We tested the effects of solarization as compared to chemical fumigants on the survival of infectiv propagules of AM fungi in 1995 and 1996. AM fungi were monitored before and after the solarization period using a greenhouse bioassay with Sorghum bicolor for both years. AM colonization of roots was also monitored in the field 8 months after the solarization period in 1995. Weed densities were measured for the 1996 trial 8 months after treatment. Solarization increased the average daily soil temperature by 6-10 deg C and the daily maximum temperature by 10-16 deg C (5-20 cm depth). Solarization did not reduce viable propagules of AM fungi immediately after the solarizatio period in either year. However, AM-fungal propagules were greatly reduced in solarized plots 8 months after the solarization period (over winter) for both years. Fumigation with vapam at 930 L ha-1 (330 kg ha-1 actual) or 230 L ha-1 reduced AM-fungal propagules in both years, and fumigation with methyl bromide at 800 kg ha-1 eliminated AM fungi. Solarization was just as effective as methyl bromide and vapam at the high rate in controlling winter annual weeds measured 8 months after treatment. Solarization apparently reduced AM-fungal propagules in soil indirectly by reducing weed populations that maintained AM fungi over the winter, while fumigation with vapam or methyl bromide directly reduced AM-fungal propagules.