Integrated Soil and Crop Management for Organic Potato Production

OBJECTIVE ONE. Pilot a participatory approach to learning and adaptation of novel farming systems approaches.
2006
Before the first meeting, growers were sent a potato production survey in which they described their production system from seed sourcing to market. Group participants received 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 then drafted research and extension activities to address those priorities with farmer input when needed; these proposals were presented to the group at the second winter meeting in February 2007.

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 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.
• 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.
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 17-19th 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, 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 (4 local conferences, 1 national conference, 2 farmer meetings).

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. Regardless 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.
OBJECTIVE TWO: 2. Evaluate the effects of soil management on tuber insect pests and diseases, weeds, nitrogen availability, and profitability.
A. INSECT PEST MANAGEMENT
Flea Beetles – First year
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 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 was 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 initially at field edges, 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 – First year
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.
Flea beetles – Second year
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, ‘high damage’, 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 within 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 in general.
B. LATE BLIGHT MANAGEMENT
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 plan to grow Defender in the future.

Materials for LB management: The three copper products (Cuprofix, Nordox 75WP, and Kocide 3000), 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.

C. NITROGEN MANAGEMENT
Nitrogen Objective 1: Evaluate the balance between N supplied and N utilized by a potato crop under a variety of organic management regimes.

The median soil N mineralization rate (soil samples collected midseason; incubated at 22oC in laboratory) was 0.7 ppm N per day across 12 farms studied. 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 (six farms), and 66 to 276 lb N/acre with a median 169 lb N/acre in 2007 (seven farms). This indicates a high amount of N mineralization was taking place on many of the participating farms.

On-farm N monitoring results showed a wide range of N availability that appeared to be primarily related to long-term management practices (years in organic production, typical rates of N inputs from fertilizer, compost and cover crops). The rate of current season compost application had little effect on N availability. Several farms had consistently high soil and plant N, illustrating an oversupply of N relative to plant needs. Over-application of rapidly-available N sources (e.g. fish, feather meal) during the current season appeared to be the main reason for N oversupply. Several other farms had consistently low soil and plant N, suggesting that N deficiency limited tuber yields. One farmer was surprised to learn irrigation water (well water with N = 15 ppm) was an important N source at his farm. Substantial amounts of crop N uptake in the absence of current season N inputs (zero N plots) demonstrated that mineralization of N from soil organic matter was a major source of N at these farms.

Nitrogen Objective 2:
Determine the most reliable methods for assessing crop N status within an organic farming system
Based on monitoring data from the two years, we recommend the following methods for assessing N sufficiency on our organic farms:
1. Vine + tuber N uptake by an unfertilized potato crop is the best measure of N mineralized from soil organic matter. This measurement incorporates site-specific factors, and is a low technology method that has credence with organic growers (Sullivan and McQueen, 2008).
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.
Nitrogen Objective 3: Develop typical system values (N inputs and N outputs) for planning crop N budgets
From our monitoring data, 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).
Objective 3. Extend project findings to a larger audience of farmers
(see NINE: Outreach)

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