Integrated Soil and Crop Management for Organic Potato Production

Integrated Soil and Crop Management for Organic Potato Production

Summary

The yield and quality of a potato crop are the result of complex interactions amongst crop nutrition, cultural practices, and pest damage. In this project we are developing a participatory process to share knowledge, experience, and farmer innovation; to illuminate new strategies for farmer-identified problems in whole farm systems; and to enhance their adoption and adaptation. This project aims to enhance the ability of farmers to: 1) identify and manage pest and nutrient problems, 2) keep on-going records and enterprise budgets, 3) synthesize “systems” information, and 4) plan and evaluate alternative management strategies, both individually and in collaboration with other farmers.

Objectives/Performance Targets

1. Pilot a participatory approach to learning and adaptation of novel farming systems strategies.
2. Evaluate the effects of soil management on tuber insect pests and diseases, weeds, nitrogen availability, and profitability.
3. Extend project findings to a larger audience of farmers.

Accomplishments/Milestones

Objective 1. Pilot a participatory approach to learning and adaptation of novel farming systems approaches.

2007
Two farmer meetings were held in 2007: a one-day meeting in February before the growing season and a final two-day meeting in December.

The goals of the February meeting were to evaluate the first year’s field data and to review the budget and make future decisions regarding project direction and field trials. During the meeting, Jeff McMorran, OSU Extension Seed Certification Specialist, gave a presentation on potato seed certification and seed handling in response to interest voiced by project farmers. Additionally, Al Mosley, OSU Emeritus Potato Specialist who is very popular with this group of farmers, provided a lively question and answer period.

Researchers presented a comprehensive range of options for 2007 field trials in areas farmers had previously identified as important. These areas included variety trials, a late blight spray trials, nitrogen management, and flea beetle and wireworm management. Budget ramifications for each option were also included and considered. From the range of options the farmers were able to pick which trials they would like conducted on their farms in 2007. The following is a list of these decisions:

· Seven farms chose to test fourteen different varieties of potatoes.
· Five farmers requested a late blight spray trial to evaluate organically approved materials
· Seven farms chose to repeat the zero nitrogen trials on their farms.
· All farmers requested research on flea beetle management. Five farms chose to test hilling and mulching, and 3 farms chose to evaluate nematode applications for biological control of flea beetles.

The group discussed enterprise budgets and case studies. Farmers shared their existing potato enterprise budgets at a previous meeting. The pros and cons of enterprise budget formats were discussed with researchers; the group concluded that OSU staff would help farmers take appropriate data if interested. It was decided that case studies would conducted in future projects, possibly as part of a graduate class at OSU.

The project budget was discussed and priorities were set for the remaining funds.

The meeting was ended with a brief, general, oral evaluation of the meeting in which growers expressed satisfaction at the format and outcomes of the meeting. Farmers reiterated the value of “the whole production approach” of the farmer presentations by project farmers at past meetings and expressed a strong desire to present the OSPUD Project at future conferences.

The December 17-19 meeting was the project’s final farmer meeting. The objectives of the meeting were to present the results of the 2007 field trials, evaluate the value and outcomes of the project, determine a schedule for farmer outreach, and discuss possibilities for further group collaboration and research.

The meeting also included a potato variety tasting and an open forum with Jeff McMorran, Al Mosley, and Oscar Gutbrod, all OSU potato specialists, brought back by popular demand to discuss seed certification and quality.

For the field trial presentations, each researcher partnered with a farmer for their presentation. The researcher presented his or her results, and the farmer presented his or her interpretations of the work and its meaning to his/her farming operation.

The farmers created an outreach schedule and some farmers volunteered to present at each event. Farmers will be compensated for their outreach activities. Farmers and project staff will present at 5 conferences (4 local and one national) and two farmer meetings over the next year.

Farmers were given draft copies of three of the Extension documents created from this project: What’s Wrong with my Potato Tubers, Flea Beetle Management for Organic Potatoes, and Estimating Nitrogen Mineralization in Organic Potato Production and comments were solicited.

Project farmers brainstormed and prioritized suggestions for a future group projects similar to OSPUD. They identified important elements of OSPUD that they would like to see in future collaborations, including a focus on a particular crop as well as participatory and multidisciplinary approaches to solving the problems associated with that crop. Farmers decided that they would like to focus on either Alliums or Brassicas in the next project. Regardelss of the crop, they would like to conduct variety trials and tastings, and maintain a strong focus on organic soil management. The farmers agreed to take these ideas back to their farmer-to-farmer exchange meeting this winter. They would discuss and evolve these project ideas with this larger group of organic vegetable farmers, identify which crop family to focus the project on, and recruit additional farmers to bring into the project. OSU staff will then work with this larger group of farmers to develop the next integrated participatory crop-focused project.

2006
Before the first meeting, growers were sent a potato production survey in which they described all aspects of their production system from seed sourcing to market. All group participants received all surveys before the meeting. During the first and second meetings in December 2005, farmers and the project team collaboratively 1) identified and prioritized the issues reducing potato production profitability, 2) identified and discussed any known solutions, 3) generated hypotheses to be tested during the first growing season in on-farm trials, and 4) identified who would participate in on-farm trials. Staff met monthly from December through August to plan, trouble-shoot and discuss project activities, and bi-weekly from August through December to interpret data and plan the December 2006 meeting. Before each December meeting, draft agendas were drafted by staff for grower review; the agenda for the December meeting was finalized after incorporating grower input. On-farm reports (whole group and farm-specific) were sent to each participant before the meeting. At the meeting, staff presented research reports with considerable interaction from farmers and staff. One farmer presented his potato enterprise budget and the group discussed the production surveys in the context of the enterprise budgets. In the final morning session, farmers and staff prioritized research issues for summer 2007 and evaluated the year’s work and the meeting process. Staff are now drafting research and extension activities to address those priorities with farmer input when needed; these proposals will be presented to the group at the second winter meeting in February 2007. The last winter meeting will be held in December 2007, when second year and final project results will be presented and discussed. All participants are surveyed before each December meeting to track changes in knowledge and attitudes.

Objective 2. Evaluate the effects of soil management on insect dynamics, tuber disease, and nitrogen availability.

A. Nitrogen Management
Nitrogen Management – 2007
Nitrogen (N) release by the soil was estimated for organic farms in Oregon and Washington. Methods included an aerobic laboratory incubation technique and zero-applied N plots located on the farms. In 2006, the median net mineralization rate for summer-collected soil was 0.7 ppm per day for 12 farms, and in 2007, 0.6 ppm per day for seven farms during the 63-day incubation at room temperature. The N-supplying capacity of the soils is estimated at 100 to 140 lb/acre for 2000-degree days (base 0°C) assuming a sample depth of 6 inches and soil bulk densities of 1.0 to 1.3 g cm-3. The uptake of N by the potato in zero-N plots at harvest ranged from 74 to 212 lb N/acre with a median of 138 lb N/acre in 2006 with six farms participating, and 66 to 276 lb N/acre with a median 169 lb N/acre in 2007 with seven farms participating. This indicates a high amount of N mineralization was taking place on some of the participating farms. Our results suggest that farms with a longer history of organic farming management practices had higher levels of nitrogen availability to the potato plants. Plant tissue samples and soil nitrate-N monitoring during the growing season help to confirm this. Farms with higher relative N uptake by the potato plants recorded higher petiole-N levels and higher levels of nitrate-N in the soil. Dependent on yield goals, our findings suggest that the application quick-release forms of N can be reduced on fields that have a history of organic amendments, with only maintenance applications of organic matter required to maintain available plant nutrients.

Nitrogen Management – 2006

On-farm data on nitrogen and yield were collected in 2006, including: pre-plant soil testing, laboratory soil incubations, potato petiole nutrient analysis, potato nitrogen uptake from on-farm fertilized and unfertilized plots, end of season 3-ft soil nitrate sampling, irrigation water nitrate, and fresh tuber yield.

Pre-plant soil testing
Eleven farms had complete soil nutrient testing prior to the growing season. Results and interpretations were distributed to the farms. None of the results were unusual for organic farms with compost-based nutrient management.

Laboratory soil incubations
Soil was collected for laboratory incubations in spring prior to planting and again in the summer. Approximately 500 g soil on a dry weight basis was added to Ziploc bags and then incubated at 22 C for 9 weeks. Soil was subsampled in three week intervals and extracted with 2M KCl and analyzed for nitrate nitrogen. The results suggest that the mineralization rates of organic farms in our study groups are high, with an average of 0.8 mg nitrate-N/ kg soil/ day at 22 C from the spring sample.

Potato Petiole Values
Potato petioles were collected at most farms during tuber growth. Our 2006 petiole nitrate-N values were below published recommended ranges for Russet Burbank potatoes grown in the Columbia Basin.

Crop Nitrogen Uptake
Crop nitrogen uptake (vines + tubers) was measured weekly during tuber growth to determine typical N uptake rates using normal grower fertilization practices. During mid-season (40 to 100 days after planting), crop N uptake averaged 2 lb N per acre per day. Six farms also participated in an unfertilized N uptake study, in which a field plot was marked off before planting and no compost or other fertilizers were added. Crop N uptake in the absence of current season fertilization ranged from 100 to 200 lb N per acre.

At harvest, soil samples down to three feet in 1-ft increments were collected from most of the farms. Most fields had low to medium levels of nitrate-N at harvest, suggesting that overall N supply from was not excessive.
Tuber Yields at our farms ranged from 15 to 25 tons/acre for fresh tuber yield, based on 36 inch spacing between hills.

Summary of N management findings
In this season the project quantified plant uptake, yield, nitrogen mineralization, petiole nitrate values and soil nitrate testing at different times during the growing season. This information was new to both farmers and researchers. The largest source of nitrogen for the potato crop appears to come from in-season mineralization of N from decaying soil organic matter.

B. Tuber Insect Pests
Early on in the first year of the project, after a number of discussions with the participant growers, regional potato experts, and some preliminary sampling on project farms, it was determined that the most likely insect pest groups were flea beetles and wireworms (click beetles as adults). Five farms were then intensively sampled for the incidence, arrival/movement patterns, and damage levels of the species in these two pest groups throughout the course of that season.

Flea Beetles – 2007
After discussing the 2006 season data during the December 2006 project meeting, the growers voted on priorities for insect potato pest management for the 2007 growing season. The strategies they were most interested to investigate in on-farm experiments were entomopathogenic nematodes, and covering the base of the potato plants with soil or a mulch to prevent oviposition. It was also agreed that we would monitor tuber flea beetle overwintering sources and how far and how quickly they move to potato fields that were planted on different dates. They were also interested in differences in insect damage among various available varieties, and so these differences were assessed for flea beetle and wireworm damage.

Materials and Methods
Experiments with replicated blocks of treatments were performed at 5 of the project farms. Finely chopped barley straw mulch and nematodes were tested at SHF, GTF, 47th and PF, chopped leaf mulch was tested at SHF and GTF, and extra high hilling at the base of the plants was tested at WGF.

All mulches and high hills completed within a week after the first overwintering tuber flea beetles were seen, so that the base of the plants would be covered by the time these beetles had mated and were ready to lay eggs for the next generation. All mulch was at least 3” high at the base of the plants, and the extra high hills were twice as high as the normal hills, covering much of the base of the plants. Mulches were applied with a compost spreader at SHF and GTF, and by hand at PF and 47th.

Two species of nematodes (Steinernema carpocapsae and Heterhabditis bacteriophora) purchased from Biologic Company were applied by watering can at a rate of 45.3 million infective juveniles per acre on two occasions starting at least one month after planting (so that we could see if the they could affect at least partially-established flea beetle larval populations). Soil samples from all nematode plots and a nearby control plot were taken on two occasions at the end of the season, and used for a bioassay with sentinel waxworm larvae in the lab to see if nematode-treated plots contained viable nematodes.

All plots were 150 square feet in size, replicated four times, and replicated control plots of the same size were set up as well. All plots were placed on the edges of the fields to maximize the chance for flea beetle infestation, and flea beetle adults were monitored in each plot on a weekly basis to keep track of the potential for differential flea beetle pressure in each plot/treatment.

Tuber damage was assessed once at 90 DAP and once at 105 DAP, covering most of the normal range of harvest dates, and allowing a comparison of the potential effect of additional damage in control plots if tubers are left in the ground longer. Tubers were rated for tuber flea beetle damage.

In addition to the experiments, the timing of emergence of tuber flea beetles from potential overwintering sources on each farm was monitored by sweeping and yellow sticky traps in winter/early spring potato fields, patches of solanaceous weeds, and cull piles/volunteers.

Results and Discussion/Milestones
GTF and SHF farms had relatively moderate to heavy levels of flea beetle damage overall, and both the straw and leaf mulch plots, and the nematode-treated plots, had appreciably less total flea beetle damage (ranging from 15-45% relative reductions in damage), as well as appreciably less damage in the FB3 category (ranging from 41-81% relative reductions in damage). PF and 47th farms had relatively low flea beetle damage overall, and no appreciable differences were seen among treatments and the control for total flea beetle damage as well as for all flea beetle damage categories. No appreciable differences were seen in the amount of flea beetle damage between high hill plots and control plots at WGF, but flea beetle adult pressure in the high hill plots was three times higher than that for the control plots. All soil samples from nematode-treated plots contained viable nematodes.

Tuber flea beetles were generally not found any earlier in cull piles or in patches of solanaceous weeds compared to the winter/early spring potato fields present at two of the farms, so they may have been overwintering among sheltered locations throughout the farm. One other interesting observation is that the two farms that had relatively high flea beetle damage (GTF and SHF), were the same two farms that had winter/early spring potato fields within a few hundred feet of the main potato field. Tuber flea beetles tended to arrive to the edges of the potato fields 2-3 weeks after planting.

Tuber Insect Pests – 2006
After a number of discussions with the participant growers, regional potato experts, and some preliminary sampling on project farms, it was determined that the most likely insect pest groups were flea beetles and wireworms (click beetles as adults). Five farms were sampled for insect pest incidence and damage.

Flea Beetles – 2006
The three flea beetle species in the Willamette Valley that are capable of inflicting economic damage on tubers are the tuber flea beetle (Epitrix tuberis), the tobacco flea beetle (E. hirtipennis), and the western potato flea beetle (E. subcritina). The first two of these species were found in the potato fields on all five of the sampled farms, and the third species was present in very low numbers at a few of the farms. Tuber flea beetle numbers were about twice as high as those of tobacco flea beetles.

Flea beetle populations increased at the edges of the potato fields more rapidly than at the inner areas of the fields. This indicates that flea beetles initially came from overwintering sites outside of the potato fields, and gradually spread into the inside of the fields from the edges. The ‘edge’ area of the field was defined as potato plants within 5 meters of the outside edge of the field.

The extent of tuber damage in each of the five fields relative to flea beetle populations and the timing of their arrival was also assessed. Three of the fields showed the expected higher or lower amount of damage with higher or lower flea beetle populations respectively, but two of the fields showed the opposite trend, with high populations yet comparatively little tuber damage. There are many possible management and/or biological factors in these fields that could cause the large flea beetle populations to not reach their typical damage potential, and this also shows that the beetle population levels are not always reliable predictors of damage in a field.

Since tubers are more susceptible to damage from increasing numbers of flea beetle larvae as the season progresses, the time of arrival of the beetle adults to a field in the spring could also be an indicator of the extent of damage in a given field. The timing of arrival of flea beetle adults also turned out to not be a reliable predictor of tuber damage, but the sampling at the beginning of spring may not have been intensive enough to catch the first individuals. The plan for year 2 is to increase the intensity of flea beetle sampling in the early spring to confirm the actual timing of arrival, as well as to provide biofix information for predictive tuber and tobacco flea beetle degree day phenology models that are being developed.

Sampling and diagnostic methods for flea beetles were tested and developed, and these have been summarized in an identification and monitoring worksheet for use in the field. Sweep netting of potato plants was more efficient than simple visual observation for assessing beetle numbers in the crop field. Yellow sticky traps yielded some information on flea beetle numbers, but they were not as efficient as sweep netting, and are probably more useful for assessing the timing arrival of the first flea beetles rather than population levels. Since flea beetle populations were shown to increase at field edges first, monitoring efficiency can be increased by focusing on these parts of the field. A flea beetle damage rating system was also developed to quantify damage for the consistent diagnosis of flea beetle damage.

Wireworms – 2006
Since wireworms have a 4-5 year life cycle, fields that were planted to potatoes in the 2005 season were also sampled in addition to the 2006 potato fields at each of the 5 farms. Adult beetles of the wireworms were sampled with pitfall traps, white sticky traps and pheromone ground traps for two invasive species from Europe (Agriotes lineatus and A. obscurus), which have a reputation for causing more consistent damage to tubers and other crops than the other local wireworm species. Wireworm larvae were sampled with underground bait traps of germinating grain.
Several different species of wireworms were obtained at the 5 farms, but efforts for species-level identification and confirmation focused on the two invasive species due to their economic importance in British Columbia and Washington State over the past several decades. In 2005 the known distribution of these two species in Oregon consisted of only a few nurseries and ports near the Columbia River, which were reported in a survey by the Oregon Department of Agriculture (ODA). One of the project farms in this same area near the Columbia River had A. lineatus adults in the pheromone traps. Another farm about 15 miles south of this area also had A. lineatus in the pheromone traps, and this was a new county record of this invasive species that was reported to the ODA.

Although species-level identity of the other wireworm species was not confirmed in most cases, the extent of overall wireworm damage relative to overall wireworm and adult numbers in a given field was recorded. As for the flea beetles, numbers of wireworms were not always associated with the extent of wireworm damage in a given field. Wireworm damage in general was not as prevalent as flea beetle damage among project participants.

Pitfall traps and white sticky traps trapped very few wireworm adults, but the pheromone traps and larval bait traps were useful for wireworm monitoring and should be continued in project fields where wireworms are a concern. As was done for the flea beetles, a wireworm damage rating system was developed for consistent diagnoses, and discussions with the growers provided them with information about how to tell that damage apart from the damage of other insect and other tuber skin problems.

C. Late blight (LB) management
Late Blight Management – 2007
All farm fields were scouted for late blight and any other diseases. No farms in southern and eastern OR, one farm in the Willamette Valley, and one farm in NW WA experienced LB epidemics in 2007; the differences in farm incidence are related to differences in temperature and rainfall patterns in these distinct regions – LB is more prevalent in cooler, moister environments. In addition, NW WA is a major potato growing region with high inoculum potential. Farms in LB-conducive regions use cultural methods such as wide row spacing, row orientation, irrigation management, and destruction of inoculum sources (e.g. cull piles) to manage LB. Only one farmer collaborator applies copper fungicides. The LB epidemics in the Willamette and Skagit Valleys occurred late in the season. Copper fungicide applications (Nordox 75 WP) effectively controlled the epidemic in the Skagit Valley. No materials were applied to the Willamette Valley crop, and all foliage was destroyed within approximately 2 weeks at that location.

Resistant varieties: OSPUD identified 3 commercially available LB resistant cultivars in 2006: Island Sunshine (IS), Jacqueline Lee (JL), and Defender. These were grown in non-replicated trials on 5 cooperating farms in 2006 as well as in inoculated replicated trials at the OSU research farm. Defender was highly resistant to foliar LB and IS and JL were somewhat to moderately resistant in on-farm and research station trials in 2006. Ozette, a PNW Slow Food potato clone, is also reported to be resistant to foliar LB (Vales/Yilma OSU potato LB clonal evaluations). Project farmers grew Jacqueline Lee and Ozette in variety trials in 2007 and they were productive, marketable, and performed well in taste evaluations; most farmers intend to grow these clones if high quality organic seed is available. In addition, at least two project farmers will grow Defender in the future. The OSU/PNW potato programs continue to evaluate specialty potato germplasm (commercially-available and research clones) for LB resistance; Alex Stone will continue to partner with them to identify emerging LB resistant clones with organic market potential and will extend this information to regional organic potato growers.

Materials for LB management: Most OSPUD farmers in western WA and northwestern OR have experienced late blight epidemics. In 2006 OSPUD emphasized cultural management strategies and identified and trialed LB resistant clones. However, farmers west of the Cascades can experience epidemics in spring or fall despite practicing best cultural management and growing resistant clones. For this reason, OSPUD farmers requested an LB spray trial in 2007. Requested materials included coppers, oxidizers, compost teas, and biologicals. The three copper products (Cuprofix, Nordox 75WP, and Kocide 3000), all applied at the highest labeled rate, reduced AUDPC by 88% with no significant difference amongst copper products. In epidemics initiated early in tuber bulking, this level of disease control would likely increase potato yield. A locally produced compost tea, although applied on dates different from those of all other treatments, reduced disease severity compared to the control (applied on different dates) by 60% and 28% at the 2nd and 3rd evaluation dates, respectively. Oxidate significantly reduced disease severity by 42% at the 2nd evaluation date but not on any other date. No other treatments (Sonata, horsetail tea, Maria Thun barrel compost tea) significantly reduced disease severity.

Late Blight Management – 2006
All farm fields were scouted for LB and any other diseases. No farms in southern and eastern OR, one farm in the Willamette Valley, and both farms in NW WA experienced LB epidemics in 2006; the differences in farm incidence are related to differences in temperature and rainfall patterns in these distinct regions – LB is more prevalent in cooler, moister environments. In addition, NW WA is a major potato growing region with high inoculum potential. Farms in LB-conducive regions use cultural methods such as wide row spacing, row orientation, irrigation management, and destruction of inoculum sources (e.g. cull piles) to manage late blight. Only one farmer collaborator has ever applied copper fungicides. Disease incidence in the one farm with LB in the Willamette Valley may have been due to row-covering of an early potato planting, a narrow in-row spacing, late afternoon irrigations, and late spring rainfall. One of the WA farms intends to investigate the use of copper fungicides for late blight control in 2007.

A European Union project (BlightMOP) investigating organic LB management strategies reported that the most promising strategy is to identify LB resistant germplasm. OSPUD identified 3 commercially available LB resistant cultivars: Island Sunshine (IS), Jacqueline Lee (JL), and Defender. These were grown in non-replicated trials on 5 cooperating farms in 2006 as well as in inoculated replicated trials at the OSU research farm. Defender was highly resistant to foliar LB and IS and JL were somewhat to moderately resistant in on-farm and research station trials in 2006. In general, the farmers who trialed the three cultivars considered them to be viable alternatives to the russet and yellow-fleshed cultivars they were currently producing and 7 farmers intend to evaluate them in on-farm trials in 2007. The OSU potato program continues to evaluate specialty potato germplasm (commercially-available and research clones) for LB resistance; OSPUD will continue to partner with them to identify LB resistant clones with organic market potential.

Variety Trial – 2007
Interest in variety selection, flavor and culinary attributes surfaced early on in the OSPUD project. The importance of variety was a recurring theme in discussions ranging from nitrogen demand to late blight resistance. During the February 2007 meeting, a variety trial investigation was requested by project farmers. Seven farms were involved in the evaluation of fourteen varieties, including currently grown favorites, as well as three unreleased varieties of interest (two with documented late blight resistance).

Varieties of interest were planted on each participating farm, with two reps per farm (except RGH, with three reps).

During the growing season, plots were evaluated for (1) emergence / stand count; (2) PVY incidence; (3) general observations on general vigor and health

At harvest, plots were evaluated for
(1) yield
(2) size distribution {large (8 oz +), medium (3-8 oz), small (0-3 oz), culls}
(3) a subset of tubers (30 tubers/plot) were rated for
o Disease incidence (scab, black scurf, silver scurf)
o Flea beetle damage and severity
o Wireworm damage
o Moisture-related damage (elephant hide and cracking)
(4) a subset of tubers (50 tubers/plot) were stored and rated for degradation
(5) a subset of tubers were collected for taste testing to measure consumer acceptance for flavor, texture and appearance

Seed quality problems, including Fusarium dry rot, Erwinia and PVY incidence, were significant seedborne problems observed in several varieties across the farms. These seed quality problems adversely affected yields and led to in-depth discussions with OSU potato specialists (Jeff McMorran, Al Mosley and Oscar Gutbrod) during farmer meetings. A new seed source was identified which may potentially alleviate these seed problems.

Yields may have also been affected by planting date, with earlier plantings producing greater yields due to less heat and moisture stress at tuber set. Yield, insect damage, and disease incidence across varieties were variable on individual farms indicating additional data are required before making conclusions.

Objective 3. Extend project findings to a larger audience of vegetable farmers. The project intends to extend experiences and findings to a larger audience of diversified vegetable farmers through:

1) Project website:
www.OSPUD.org – which describes current and upcoming project activities.

2) Outreach workshops:
A. Workshop One: October 2006. A potato evaluation and tasting was held at one of the OSPUD farms in collaboration with the OSU potato breeding program. Approximately 50 organic potato farmers, retailers, chefs, processors, and researchers drafted organic potato germplasm selection criteria and evaluated approximately 25 potato cones for appearance, flavor, and texture (steamed, chipped and fried).
B. Workshop Two: Oregon Tilth 2008 Annual Conference (January 2008) including a potato variety tasting and an OSPUD farmer panel presenting “Micronutrient Uptake and Soil / Recent Potato Research”
C. Workshop Three: North Willamette Horticulture Society Meeting (January 2008)
D. Workshop Four: The 8th Annual Small Farms and Farm Direct Marketing Conference (February 2008). OSPUD collaborators presenting project results and impacts.
E. Workshop Five: NW Farmer to Farmer Exchange (February 2008). OSPUD farmers presenting project results and impacts as well as brainstorming where to go from here.
F. Workshop Six: Washington Tilth (Tentative: November 2008). OSPUD collaborators presenting project results and impacts.
G. Workshop Seven: Eco-Farm Conference (Tentative: January 2009). OSPUD collaborators presenting project results and impacts.

3) Extension publications:
1. What’s Wrong with my Potato Tubers (to be published January 2008)
2. Flea Beetle Management for Organic Potatoes (to be published January 2008)
3. Estimating Nitrogen Mineralization in Organic Potato Production (to be published January 2008)
4. Wireworm Management for Organic Potatoes (to be published March 2008)

Impacts and Contributions/Outcomes

2007
Objective 1. Pilot a participatory approach to learning and adaptation of novel farming systems approaches.

Outcome: At project meetings, growers and researchers have expressed enthusiasm for the participatory approach implemented in this project. The participatory approach has allowed the project group to adapt project activities to meet grower needs, and to evaluate project outcomes at each project meeting. A formal evaluation of project impacts on grower knowledge, intentions, and practices will be conducted during 2008.

Objective 2. Evaluate the effects of soil management on insect dynamics, tuber disease, and nitrogen availability.

2007
Nitrogen Management:
This project has (i)strengthened our knowledge of best methods for N monitoring, and has (ii) developed typical system values that can be used in planning crop N budgets and in modeling of the N cycle for organic potato crops. Overall, we found that soil N mineralization supplied most of the N needed by organic potato crops. This finding will assist growers in reducing expensive, rapidly available N inputs, and will likely reduce soil nitrate-N available for leaching to groundwater at the end of the growing season.
Best methods for N monitoring (best indicators of N available to the potato crop):

1. Vine + tuber N uptake by an unfertilized potato crop. An Extension publication was produced, telling growers and agricultural professionals how to perform crop N uptake measurements for potatoes, and why this measurement is helpful in developing reliable estimates of N mineralization from soil organic matter.

2. Soil nitrate-N and petiole nitrate-N samples collected at 45, 60, and 75 days after planting. Soil nitrate values are easier to interpret than petiole values, as soil nitrate values are not strongly affected by cultivar.

3. Nitrate analysis of irrigation water. We had one farm with very low soil nitrate, low petiole nitrate, but good yields. At this farm, irrigation water (15 ppm nitrate-N) was a very important N source.

Caveats in interpreting N monitoring data:
We found that potato petiole nitrate-N values were not always a reliable indicator of crop N status because of differences in typical petiole values among varieties. We found that soil organic matter content was not a reliable indicator of soil N mineralization potential. Potato crops are capable of continued growth with very low soil nitrate-N and petiole-N values, when N is supplied by mineralization or by irrigation water.

We developed typical system values that can be used in planning crop N budgets and in modeling of the N cycle for organic potato crops:
1. A typical crop N uptake value is 200 lb N/acre (for yields ranging from 15 to 30 ton/acre).
2. Median N uptake by an unfertilized potato crop was approximately 150 lb N per acre from typical western Oregon soils.
3. The typical rate of crop N uptake for unfertilized potato crops during tuber growth was 2 lb N per acre per day
4. Median net mineralized N in laboratory incubations (0.7 ppm N per day in 9-wk incubations at 22oC) was approximately equivalent to seasonal crop N uptake (150 lb N/acre) measured in the field (taking into account incubation time and temperature).

Grower responses. Many of the collaborating farmers expressed surprise at the nitrogen results. According to the growers, they have placed their emphasis of supplying adequate N through fertilizers without appreciating the amount of N released by the soil in their systems. As a result of our findings, some of the growers intend on reevaluating their N fertilizer regimes to see if they need to reduce an over-supply of N. The growers were pleased to hear that their methods of applying organic sources of N have likely increased the level of N release by the soil through mineralization.

Late Blight Management: Identified at least 3 commercially available potato cultivars with LB resistance and good market quality for organic fresh market production; demonstrated that copper fungicides effectively controlled LB.

Tuber Insect Pests:
– The tuber flea beetle was identified and confirmed as the most important insect pest in Western OR and WA.
– Monitoring and tuber damage assessment methods were developed and methods that growers can use are described in an extension publication

Improved strategies for monitoring beetles and preventing damage to tubers were developed by the project. Specifically:
1. Field placement (early and late season crops on same farm) is important. Beetles move from early spring potato crops to nearby main summer-season potato fields
2. Tuber flea beetle monitoring and corrective management activities should focus on field edges early in the season
3. Mulching potato hills reduced flea beetle damage levels when compared to control plots
4. Adding nematodes reduced flea beetle damage levels when compared to control plots

2006
1) developed and evaluated a participatory process for this group of farmers and researchers – a process which will continue to evolve over the next 11 months
2) identified at least 2 commercially available potato cultivars with LB resistance and good market quality for organic fresh market production;
3) measured the balance between N supplied by different sources (mineralization of soil organic matter and irrigation water) and crop N uptake. During mid-season (40 to 100 days after planting), unfertilized crop N uptake averaged 2 lb N per acre per day. At 100 days after planting, unfertilized crop N uptake averaged 150 lb N per acre. Potato yields of 20+ ton/acre were produced at farms with relatively low levels of soil nitrate–N throughout the year. Petiole nitrate-N associated with typical yields was much lower than suggested by PNW Extension publications. These findings are being incorporated into a worksheet to assist growers in managing the supply of nitrogen for their potatoes.
4) identified tuber flea beetle (TFB) as the most important insect pest in western OR and WA; wireworm is a significant problem only on fields with a rotational history including long-term sod. TFB is an intractable pest, requiring further research on cultural, biological, chemical, and integrated control methods.
All of these findings in the long term will contribute to improving the economic and environmental sustainability of organic potato/diversified vegetable production in this region.

Objective 3. Extend project findings to a larger audience of vegetable farmers. The project intends to extend experiences and findings to a larger audience of diversified vegetable farmers.
This phase of the project is just beginning. Six workshops will feature OSPUD participation by the end of February, 2008.

Collaborators: