Biofumigants in Commercial Onion Production to Enhance Soil Nutrient Availability, Soil Quality, and Control of Weed, Nematode, and Disease Pests

Biofumigants in Commercial Onion Production to Enhance Soil Nutrient Availability, Soil Quality, and Control of Weed, Nematode, and Disease Pests

Summary

Phosphorus and N contents of onion tissue samples were higher in plots where the biofumigants “Idagold” and “Colonel” had been raised and tilled into the soil. However, the slight increase in nutrient availability from biofumigants did not result in higher yields over the metam sodium plots. In the weed control section, onion yields were greater with the fallow and metam sodium treatments. When no herbicide was applied, metam sodium treated plots produced more onions than the fallow or biofumigant treated plots. In general, biofumigants did not affect weed densities or weed biomass. Metam sodium treatments in both locations of this project had significantly lower Mycorrhizae colonization and pink root severities than the fallow, “Idagold” and “Colonel” biofumigants. “Sunrise” did not lower the severity of pink root but it did lower the amount of Mycorrhizae colonization when compared to the other biofumigants and the fallow treatment.

Objectives/Performance Targets

Objective 1. Evaluation and comparison of the biofumigants, fallow and chemical fumigant on onion production is best described in objectives 2 – 7 and will not be repeated here in objective 1.

Objective 2. The mustard “Idagold” tended to have higher P and N content when 0 lbs/A of P205 was applied when compared to P applications of 50, 130 and 210 lbs/A. The reverse was true for “Colonel,” it tended to have higher P and N content when P applications were 50 lbs/A or higher. When comparing “Idagold” to “Colonel” at 0 lbs/A of applied P, “Idagold” had significantly more P and N content, but it also had twice the amount of dry matter. Mineralized N from the biomass of the treatments increased as the growing season progressed. Phosphorus applied at 210 lbs/A increased the mineralized N when compared to the same fumigation treatment at 0 lbs/A of P. The biofumigants “Idagold” and “Colonel” tended to higher mineralized N rates than the fallow or fumigated plots. Stands were significantly lower in plots where 210 lbs/A of P was applied. However, the rates of P and N increased in onion tissue at bulbing stage when there was 210 lbs/A of P. However, the increase in P and N did remain when the bulbs were sampled at maturity. Total yields in A1 were higher in the metam sodium plots than in the other treatments. This result followed the pattern of total yields in E4. When 300 lbs/A of P and 80 lbs/A of N was applied in A1 the yields were better, but they were not much better than 50 or 130 lbs/A of P and 0 lbs/A of N was applied.

Objective 3. Soil property analysis is currently underway and the results for 2002 are not available, but will be included in the progress report at the end of 2003.

Objective 4. Metam sodium significantly reduced root colonization up 10 weeks after planting (Figures 1-4). After June 14, Mycorrhizae colonization was able to multiply and catch up with the treatments fallow, “Idagold” and “Colonel.” Surprisingly the biofumigant treatment “Sunrise” also had a negative impact on Mycorrhizae colonization (Figure 1-2). Suggesting that the glucosinolate levels are not responsible for the control of soil microbial populations. Root densities / volume of soil sampled did not vary among treatments therefore, the root densities data is no shown.

In field E4, pink root severity was significantly reduced by metam sodium when compared to the fallow, “Idagold,” “Sunrise” and “Colonel” treatments. This corresponds with data from field A1 where pink root severity was also reduced with the metam sodium treatment. However, in A1 the addition of P fertilizer appears to increase the amount of pink root severity.

Objective 5. Visual evaluations of weed control revealed that metam sodium increased control of redroot pigweed compared to the fallow or “Idagold” treatment (Table 8). Common lambsquarters control was higher with metam sodium compared to the fallow and oil radish treatments. Metam sodium had greater annual grass control than all other treatments except “Sunrise.” For all weed species, the high input herbicide treatment had greater weed control than the low input treatment. Weed density and weed biomass were not significantly affected by the fumigation treatments (Table 9). This is contradictory to the visual weed control evaluations. Both the low and the high input herbicide treatments reduced weed biomass compared to the weedy check, except that kochia biomass with the low input herbicide treatment was lower than the high input treatment and similar to the weedy check. Average weed density was reduced by the high input herbicide program but not by the low input program.

Onion stand was determined for each plot by counting the number of onions in 10 feet of rows 2 and 4. Onion yield was determined by harvesting 25 feet of the center 4 rows of each plot. Onion stand was significantly reduced by all green manures compared to the metam sodium treatment (Table 10). Onion density with metam sodium or “Idagold” was similar to the fallow treatment. The “Sunrise” and “Colonel” treatments had significantly lower stands than the fallow. The reduced stand may have resulted from volunteer canola and oil radish plants that sprouted in their respective plots and competed with onions prior to their removal. The mustard and oil radish volunteers averaged 1.0 and 0.25 plants/yd2, respectively. A significant fumigant by herbicide interaction was present for onion yields. Onion yields were greater with the fallow and metam sodium treatments under all levels of weed control except for the weedy check. When no herbicide was applied, metam sodium treated plots produced more onions than the fallow or green manure treated plots. Whether the metam sodium reduced the competitiveness of weeds or increased the ability of the onions to compete cannot be proven. Onion yield was related to both onion stand and weed control. Onion yields increased with increasing onion stand under low levels of weed competition. However, under extreme weed competition onion stand does not increase onion yield to the same degree.
In general, green manures did not affect weed densities or weed biomass. They did have a negative impact on onion stand and a correlated negative impact on onion yields. In future research it will be important to control volunteer green manure plants so that competitive effects on onion stand and yield can be eliminated.

Objective 6. Nematode samples were collected on December 7, 2001. Samples were again collected in May of 2002, but the data is not available. Root lesion, stunt, spiral and ring nematodes were assayed. There were no significant differences among the treatments and nematode populations. Nematodes are not a major pathogen of onions, but can cause quality problems. There were no apparent nematode symptoms in either field in 2002.

Objective 7. This research project was presented to growers at two field days and to the Idaho Eastern Oregon Onion Research Committee. Since this is the first year of the project, only the project was discussed at the field days and preliminary data was discussed with the onion research committee.

Accomplishments/Milestones

From a previous study here at the Parma Research and Extension Center it was believed that metam sodium reduced Mycorrhizae populations in the soil and subsequently in onion roots. The lack of Mycorrhizae colonization in onion roots decreased P availability to onions grown in high lime soils. This research project has proven that metam sodium does lower Mycorrhizal infections of onion roots.
This research project was presented to growers at two field days and to the Idaho Eastern Oregon Onion Research Committee. Since this is the first year of the project, only the project was discussed at the field days and preliminary data was discussed with the onion research committee.

Impacts and Contributions/Outcomes

Biofumigants in commercial onion production is just finishing it’s first year of research. Therefore, no impacts or contributions have yet to be made. It is anticipated that this research will help commercial onion growers to better manage their soils and soil microbial populations for optimum and sustainable onion production.

Collaborators: