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

2003 Annual Report for SW01-023

Project Type: Research and Education
Funds awarded in 2001: $134,317.00
Projected End Date: 12/31/2005
Matching Non-Federal Funds: $54,912.00
Region: Western
State: Utah
Principal Investigator:
Brad Geary
Brigham Young University

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

Summary

Biofumigant Summary 2003, second year

In high lime fields, biofumigants did not raise P and N onion concentrations and had little effect on early development. Fumigation stunted early growth and tended to reduce stands. Metam sodium lowered Mycorrhizae colonization, root length, and pink root severities. In low lime soils, onion yields were not significantly different. Weed control differed only among weed management programs. Fertilizer effects and interactions between fumigation and fertilization were rare, indicating that the compensation by P fertilizer for a lack of mycorrhizae was only partial. Soil quality measurements showed no improvement except for Colonel, which improved aggregate stability over the check.

Objectives/Performance Targets

Biofumigant Objectives

Objective 1 – Evaluate a mustard and oil radish cultivar for the ability to reduce onion production problems, and compare them to soil fumigated with Metam Sodium and not fumigated.

Objective 2 – Evaluate summer-fall biofumigant crop effects on both P and N availability to subsequent onions.

Objective 3 – Evaluate and compare soil properties.

Objective 4 – Determine if a biofumigant crop positively or negatively impacts root populations of Mycorrhizae and Phoma terrestris (pink root).

Objective 5 – Determine if the use of biofumigant crops in onion production has potential to reduce the use of synthetic fumigants and herbicides applied for weed control by reducing weed germination and growth.

Objective 6 – Evaluate treatment effects on nematode populations and subsequent nematode damage to onions.

Objective 7 – Disseminate information by conducting research on growers’ farms and presenting data at field days, workshops, and annual growers meetings.

Accomplishments/Milestones

Biofumigant Accomplishments

Objective 1 — Evaluate a mustard and oil radish cultivar for the ability to reduce onion production problems, and compare them to soil fumigated with Metam Sodium and not fumigated.

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

Objective 2 — Evaluate summer-fall biofumigant crop effects on both P and N availability to subsequent onions.

The biofumigants tended to have higher P and N concentrations when no P was previously applied as compared to the highest P rates, probably due to greater biomass and nutrient dilution with adequate P. “Colonel” had significantly higher P and N concentrations than “Idagold” at higher P rates, but “Idagold” tended to have higher total P and N content due to greater biomass (Table 1). Mineralized N increased as the growing season progressed. Increased biomass with previously applied P at 225 lbs/A did not significantly affect mineralized N when compared to the same fumigation treatment at 0 lbs/A of P. The biofumigants “Idagold” and “Colonel” did not have appreciably greater N mineralization during the onion season than the fallow or fumigated plots (Tables 2 and 6). Onion stands tended to be reduced if P was not applied and tended to be lower where biofumigants were grown. Stands were highest where the soil was fall fumigated using Metam sodium. Early season onion growth was stunted by the previous fall fumigation and nutrient contents were reduced. Onion plant P concentrations were significantly higher with previously applied P. Biofumigants did not affect early season onion growth or nutrient concentrations. Previously applied P did not affect dry biomass of onions near maturity nor N and P content, except for the fumigated treatment where previous P increased plant P concentrations. Marketable yield was significantly reduced with fall fumigation, and to a less extent with biofumigants.

Objective 3 — Evaluate and compare soil properties.

Soil quality measurements were made in the weed-free treatment of the study. The addition of plant dry matter contributes to the organic matter in the soil. Organic matter is a principle component of soil structure and contributes to water-holding capacity and porosity. The organic matter was measured in each treatment to determine the contribution that the addition of green manure made to the soil. Bulk density measurements were made early in the season when the onions were 25 cm tall. The bulk density was measured on the surface 15 cm of soil using the standard core sample method. Aggregate stability was also measured using a dry sieves method. Soil aggregates were collected from the surface of the soil and sieved to determine the number of aggregates at each size. Each of the samples was then sieved again to determine the difference among the sieved weights.

The addition of the green manure did not increase the organic matter in the soil. There was no increase in %OM from the check or metam sodium treatment to the three green manure treatments. Climatic conditions may have been such that the OM from the green manure was immediately broken down or that the contribution of OM to the soil from the treatments was there but not significant after one year (only one year at each location). Continuous green manure application may indeed increase %OM over time. There were also no differences in the bulk density measurements. The values were not different from those expected in the area. Additions of green manure to the soil did not change the bulk density from the check. This may be related to the OM content of the soil but it also may be related to the intense tractor traffic that onion production receives. There were significant differences among the treatments with respect to aggregate stability. However, there was no difference between two of the green manure treatments and the check. Only the oil radish showed any improvement of aggregate stability over the check after the second sieving.

Based on previous studies by UI researchers and others it is anticipated that continued green manure applications will increase OM in the soil and thus improve soil physical characteristics.

Objective 4 — Determine if a biofumigant crop positively or negatively impacts root populations of Mycorrhizae and Phoma terrestris (pink root).

Mycorrhizae counts were collected by taking a core of soil 6 inches deep by 2.5 inch diameter with the onion at the center. The samples from low lime soils were collected in all main treatment plots but only from the weed free sub-treatment plots. In high lime soils, the samples were only taken from the main treatment plot of 0 P, 80 lbs N, and the combined application of 8- lbs N with 225 lbs P2O5. Each sample was washed on a 500 micrometer sieve to remove soil. Then the roots were washed again on a 25 micrometer sieve. The onion roots were then placed in 70% ethanol. The root density / gram of soil was calculated and the Mycorrhizae were stained and counted according to vesicular colonization and hyphal colonization. Mycorrhizae sampling dates were April 24, May 7, May 22 and June 4.

Mycorrhizae colonization of onion roots

Low Lime Plots 2003
All data for low lime soil plots were analyzed as a randomized complete block with fumigation and fate as treatment factors. There was considerably more colonization in Replicate 1 and Replicate 2 than in the other two replicates (Table 7). This effect may be due to different histories for the two halves of the experimental area. No fumigation effects were detected. The probabilities for F values were P=0.21 and P=0.33, respectively, for the fumigation factor and for the fumigation-by-date interaction for AC. Corresponding values for HC were P=0.58 and P=0.10. The replicate effect may have precluded the detection of any differences in colonization among fumigation treatments in 2003. Changes in colonization with time were evident (Table 8).
Root length per shoot was not affected by replicate (P=0.35) or fumigation (P=0.25), and there was no fumigation-by-date interaction (P=0.92), but root length increased (P<0.001) with time (Table 8). Shoot P concentration (P=0.06), shoot mass (P=0.25), and shoot P content (P=0.07), were not affected by fumigation treatment, but they all increased (P<0.001) with time (Table 9). There were no interactions of Shoot P concentration, shoot mass, and shoot P content with time (P=0.32, P=0.55, and P=0.11, respectively). High Lime Plots 2003
All data for high lime plots were analyzed as a split-plot experiment in five blocked replicates with fertilizer as the main plot factor at three levels: check, N, and NP, where N was applied at 225 lb N acƒo1 and P was applied at 225 lb P2O5 acƒo1. Fumigation was the split-plot factor at four levels: fallow, Vapam, Idagold, and Colonel.
Vapam significantly (Table 10) reduced root length and mycorrhizal colonization (Table 11).Vapam fumigation also reduced shoot P concentration and shoot dry mass at various harvests, and the combination of these effects significantly (Table 12) reduced shoot P content at the last two harvests (Table 13). Fertilizer effects and interactions between fumigation and fertilization were rare (Tables 10 and 12), indicating that the compensation for lack of mycorrhizae in onion offered by P fertilizer was only partial. For example, shoot P content in the Vapam treatment on the 6 June was 106 ƒªg P shootƒ{1 in the check and 205 ƒªg P shootƒ{1 in the NP treatment, compared to between 288 and 347 ƒªg P shootƒ{1 in the fallow and biofumigant treatments given NP fertilization. The significant interaction between fumigation and fertilization for shoot P content at the third harvest did not show any meaningful pattern in relation to treatments and was likely generated as a chance event, which is prone to happen one time in twenty for the 5% probability level.
These results show that chemical fumigation reduces mycorrhizae of onion and that P fertilizer is only partly effective to offset this effect in the early season. Further, the biofumigant treatments do not inhibit the growth of mycorrhizae and are associated with early season growth and P nutrition of onion that was essentially indistinguishable from that of the fallow treatment.

Pink Root
Pink root samples were collected in August, and were estimated by placing the onions in 6 classes based on the infection of the roots. Class 1 was 0%, 2 = 1-3%, 3 = 4-6%, 4 = 7-10%, 5 = 10-15%, and 6 = 16-30%. In low lime plots, pink root severity was not significantly different among the treatments (Table 14). In high lime plots, pink root severity was significantly reduced with the metam sodium treatment.

Objective 5 — Determine if the use of biofumigant crops in onion production has potential to reduce the use of synthetic fumigants and herbicides applied for weed control by reducing weed germination and growth.

Methods
Weed control programs included a weedy check, low herbicide inputs, high herbicide inputs, and a weed-free check. The low input herbicide program consisted of Buctril (0.19 lb ai/acre) plus Goal (0.094 lb ai/acre) applied to 2-leaf onions on May 16, Buctril (0.25 lb ai/acre) plus Goal (0.125 lb ai/acre) plus Poast (0.19 lb ai/acre) applied to 3 to 4-leaf onions on May 27, and Goal (0.25 lb ai/acre) applied to 4 to 6-leaf onions on June 9. The high input herbicide treatment was the same as the low input but included a preemergence application of Roundup (0.375 lb ai/acre) and Prowl (1.0 lb ai/acre) on April 7 and the addition of Prowl (0.5 lb ai/acre) to the last postemergence application on June 9. All herbicide applications were made with a 4-wheeler mounted sprayer calibrated to deliver 30 gpa of water at 30 psi. Weed control was evaluated using weed counts, visual weed control ratings, and weed biomass samples. Weed counts were taken from 10 feet of rows 2 and 4 in each plot on May 13, June 8, and June23. On July 11, weed control was evaluated visually and on July 16 weeds biomass samples were harvested from 5 feet of one row of each plot, separated by species, dried, and weighed. Following sampling, weeds were removed from all plots to allow for harvesting in September. Because of reduced stands in the first replication that were unrelated to treatment, the first replication was removed for the analysis of onion stand and yield data.

Weed Control
On May 8, weed counts revealed a significant number of volunteer oil radish (Colonel) plants (35 plants/yd2). The canola (Sunrise) also volunteered but not in significant numbers. These same species volunteered when this trial was conducted in 2002. The hot mustard (Idagold) did not volunteer in either year. Early weed counts also revealed that the hot mustard treated plots had kochia densities similar to the fallow treatment and greater than any other treatments. Hairy nightshade densities were higher in the fallow than with any fumigant treatment. The higher number of nightshade in the fallow may be due to nightshade plants that grew and produced seeds the previous fall during the time the biofumigants were growing and competing with the nightshade. Weed counts on June 8 and June 23 demonstrated that weed control input level was the most significant factor affecting weed densities (data not shown). Visual evaluation of weed control revealed that fumigant treatment had no effect (Table 15). The high herbicide input treatment increased control of pigweed, kochia, and annual grass compared to the low input treatment. For weed biomass measurements, both low and high input weed control programs reduced biomass of pigweed and hairy nightshade compared to the untreated plots (Table 16). However, the low input treatment produced kochia, annual grass, and total weed biomass similar to the untreated plots. The low input weed control program controlled pigweed and hairy nightshade, and removal of these species may have allowed the surviving kochia and grass to grow without competition. Weed biomass samples also included a significant amount of volunteer canola that must have emerged after its initial removal.

Onion Stand and Yield
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 not affected by either fumigant or weed control level (Table 17). Onion yield also was not affected by fumigant treatments. Onion yields were increased with both the low and the high input weed control treatments compared to the untreated plots, and the low and high input treatments were similar to the hand-weeded plots. Based on the weed biomass samples we would have expected less onion yield in the low herbicide input treatment compared to the high input treatment. The fact that yields were not different between the low and high input weed control treatments may be due to the late onset of weeds in the low input treatment (weeds not controlled are burned back and re-growth generally occurs after the last herbicide application) and the earlier removal of weeds from the plots (July 16). In addition, extreme heat conditions during July and August may have limited the maximum potential of onion yields and thus limited the differences among treatments. Onion stand loss due to volunteer biofumigants that was observed in 2002 was not observed in 2003 because the volunteer biofumigants were removed early in the season. The potential of biofumigants to volunteer in subsequent onion crops needs to be addressed before they could be incorporated into a viable onion production system.

Objective 6 — Evaluate treatment effects on nematode populations and subsequent nematode damage to onions.

Nematode samples were collected in November 2002, and again on June 9, 2003. 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 2003.

Objective 7 — Disseminate information by conducting research on growers’ farms and presenting data at field days, workshops and annual growers meetings.

This research project has been presented to growers at four field days, the annual Idaho Eastern Oregon Onion Growers meeting, the international meeting of Molecular Biology and Biotechnological Applications of Mycorrhizal Fungi, the Idaho Association of Plant Pathologists, and to the Idaho Eastern Oregon Onion Research Committee.

Impacts and Contributions/Outcomes

Biofumigant Contributions

This research project has been presented to growers at four field days, the annual Idaho Eastern Oregon Onion Growers meeting, the international meeting of Molecular Biology and Biotechnological Applications of Mycorrhizal Fungi, the Idaho Association of Plant Pathologists, and to the Idaho Eastern Oregon Onion Research Committee.

Collaborators:

Ernie Chandler

Chandler Farms
ID 83672
Larry Nelson

Nelson Farms
Parma, ID 83660
Saad Hafez

Univ of Idaho
ID 83660
Corey Ransom

Oregon State Univ
OR 97914
Terry McGonigle

mcgotere@isu.edu
Idaho State University
Pocatello, Id
Office Phone: 2084780266
Brad Brown

Univ of Idaho
ID 83660