Alternatives to methyl bromide soil fumigation for vegetable and floriculture production
Location: Subtropical Plant Pathology Research
Title: Effect of anaerobic soil disinfestation on weed seed germination
| Muramoto, Joji - UC SANTA CRUZ |
| Shennan, Carol - UC SANTA CRUZ |
| Fitzgerald, Alicia - UC SANTA CRUZ |
| Koike, Steve - UC COOPERATIVE EXT. |
| Bolda, Mark - UC COOPERATIVE EXT. |
| Daugovish, Oleg - UC COOPERATIVE EXT. |
| Butler, David |
Submitted to: Proceedings of International Research Conference on Methyl Bromide Alternatives
Publication Type: Proceedings
Publication Acceptance Date: October 11, 2011
Publication Date: October 1, 2008
Citation: Muramoto, J., Rosskopf, E.N., Burelle, N.K., Shennan, C., Fitzgerald, A., Koike, S., Bolda, M., Daugovish, O., Butler, D.M. 2008. Effect of anaerobic soil disinfestation on weed seed germination. Proceedings of International Research Conference on Methyl Bromide Alternatives. 109:1-3.
The project goal is to optimize anaerobic soil disinfestation (ASD) as an alternative to methyl bromide fumigation using strawberry in coastal California and pepper/eggplant double crop in southeast Florida as model systems (Shennan et al., 2007). In preparation for field experiments, a series of pot experiments were conducted to examine effect of ASD with varying plastic tarps, soil types, carbon sources, and temperature conditions on weed seed germination and the soil-borne pathogen, Verticillium dahliae. Results on weed seed germination are reported in the present paper.
A split plot experimental design with temperature as the main plot (15 or 25 ºC), type of tarp (none, regular green, regular white/black (both 1.25 mil regular plastic films for mulching strawberry beds), VIF (1.25 mil embossed black tarp), or pit tarp (8 mil black/white tarp)), and soils (Watsonville sandy clay loam or Moss Landing sandy loam) as split plots, was performed with two replicates. A soil was mixed with10 ton/ha equivalent of wheat bran and was packed into a PVC pot (15cm x 20 cm). Two nylon mesh packets, each containing 50 weed seeds of either annual bluegrass (Poa annua), or common purslane (Portulaca oleracea), which are common weeds in California, were placed at 15 cm depth in each pot. Water was applied to saturate soil, with excess water drained through the bottom holes of the pot. After covering the soil surface with a plastic tarp, pots were placed in incubators for three weeks. Soil Eh and temperature at 15 cm depth in each pot were monitored throughout the experiment. After three weeks, buried weed seeds were retrieved and the germination was visually assessed within 24 hours, as well as three and seven days after the retrieval.
A strong to moderate anaerobic condition (Eh -200 to 100 mV) was developed within one week in all treatments except for the no tarp treatment. Cumulative Eh values below 200 mV during the entire incubation period were similar among all tarp types, indicating a regular plastic film for strawberry mulch may be sufficient for ASD. Germination rates of retrieved weed seeds were also similar across varying tarp types; 32-36% for annual bluegrass and 62 to 69% for common purslane. This suggests that the potential of ASD in controlling common weeds in California strawberry fields may be low.
Using locally-available carbon sources from FL and a sandy soil from Fort Pierce, FL, an experiment was performed to evaluate 10 different carbon sources (none, wheat bran 10 tons/ha, molasses 10 tons/ha, molasses 20 tons/ha, 1% ethanol solution 100 mm, broiler litter 20 tons/ha, broiler litter 20 tons/ha + molasses 10 tons/ha, broiler litter 20 tons/ha + molasses 20 tons/ha, broiler litter 20 tons/ha + 1% ethanol solution 100 mm, and broiler litter 20 tons/ha + molasses 20 tons/ha + 1% ethanol solution 100 mm) with treatments replicated four times. An ABS pot (7.7cm x 20 cm) was packed with the soil mixed with carbon source(s), and a mesh bag containing four tubers of yellow nutsedge (Cyperus esculentus) was buried 15 cm deep. Water was added to saturate the soil and allowed to drain naturally through the mesh-bottom of the pot. The soil surface was covered with a rubber cap and pots were incubated in a growth chamber for three weeks. Temperature of the chamber was set to simulate a diurnal change of soil temperature under plastic in the summer of southeast Florida (32 to 41 ºC). Soil Eh at 15 cm depth was monitored during the incubation. After three weeks, nutsedge tubers were retrieved and germination was visually examined immediately as well as three weeks after the retrieval. A strong to mild anaerobic condition (Eh -250 to 100 mV) was observed within one week in most treatments including no carbon source. Further, none of the retrieved yellow nutsedge tubers germinated regardless of treatment.
To examine the cause of dead nutsedge tubers, a factorial experiment was performed with burial depths of yellow nutsedge (2 cm or 15 cm deep) and use of mesh bags for enclosing nutsedge tubers (with or without) as treatments (four reps). The same methods as the previous experiment were used but no carbon sources were added to any plots in this experiment. Soil Eh at 15 cm deep indicated the development of a strong anaerobic condition from the 5th day of incubation in all pots (Eh -200 mV). None of the retrieved nutsedge tubers buried at 15 cm deep germinated, whereas 66% of tubers buried at 2 cm depth germinated (P<0.0001). The higher germination rate at the shallow depth, where the soil is slightly dryer, indicates that the lack of oxygen at the deeper depth might be the cause of nutsedge tuber mortality. The retrieved tubers were rotten and not considered viable. Use of the mesh bag increased the average nutsedge germination rate from 50% to 60% (P=0.04), probably by providing slightly more void spaces around tubers. The C/N ratio of the sandy soil is as high as 17 and the soil appears to contain carbon sources that can create an anaerobic condition when the soil water content remains above the field capacity under relatively high temperature with limited O2 supply. Based on above and other pot experiments, field trials are in progress in Santa Paula, CA, Moss Landing, CA and Fort Pierce, FL, to optimize ASD in each area.