Assessment and Demonstration of the Sustainability of Long vs. Short Potato Rotations

Assessment and Demonstration of the Sustainability of Long vs. Short Potato Rotations

Summary

Fifty-four paired potato fields were surveyed/sampled to get yield data, tuber quality and post storage measurements. Soil and tubers were collected at each site, completing the field survey portion of the project. The pairs were selected by choosing fields with similar soil type, topography, and management except for rotation history. Fields with short rotation had potatoes every other year; long rotation fields had potatoes every four years. All fields generally had small grains as rotational crops. Nematode, insect and fry quality assessments have been completed. Soil borne pathogen and weed assessments and a greenhouse container study are in process.

Objectives/Performance Targets

The objectives of this project are to quantify the effects and educate growers concerning the long-term impacts of short vs. long periods of time between potato crops with regard to potato yield and tuber quality parameters, all major potato pests and pathogens, as well as soil health parameters:

• nematodes

  wireworm

  bacteria:fungi ratios

  Rhizoctonia (Rhizoctonia solani)

  silver scurf (Helminthosporium solani)

  white mold (Sclerotinia sclerotiorum)

  pink rot (Phytophthora erythroseptica)

  Pythium leak (Pythium species)

  Verticillium wilt (Verticillium dahliae)

  powdery scab (Spongospora subterranea subsp. subterranea)

  weed seed bank/numbers

  herbicide-resistance development

  soil microbial activity

  soil carbon and inorganic nutrient concentration

  soil depth, density and aggregate stability

  water infiltration rate

  biomass yield

  tuber yield, size, grade, solids, and defects

  net economic return

  cost per rotational acre

  cost per potato acre and per cwt

Accomplishments/Milestones

The 27 pairs (54 total fields) of short- and long-potato rotation fields chosen and sampled are located across the predominant potato production areas of the Snake River Basin in southern Idaho and the Columbia Basin in eastern Washington and Oregon. Project personnel are working with growers and industry personnel to get actual field yield data, tuber quality information, and post storage measurements. Fields in each pair were selected because of proximity and by matching as closely as possible soil type, topography, and management history other than rotation length. The short rotation fields in each pair have a history of potatoes every other year with small grains typically as the rotation crop. The long-rotation fields have a history of potatoes no less than every four years with small grains, sugarbeets, and corn commonly grown in the rotation. All fields had potatoes growing in them for the 2008 season.

In-field measurements were completed at the time of soil/tuber collection in 2008. Nematode analyses conducted on the soils sampled have been finished; harvest sugar and fry color analyses were conducted immediately after tubers were sampled. A second run of fry quality analyses will be conducted May 2009 to assess storage quality and the ensuing effects. Results from the analyses completed have been interpreted and are being distributed to growers winter 2008/2009.

Nematode species detected, number of fields infected, and maximum and average counts per field are summarized in Table 1 below. Five different nematode species were identified; however, there were no nematode species which were detected in neither all 27 of the short-rotation fields nor all 27 of the long-rotation fields. Compared with the long-rotation fields, the short rotation fields had a numerically higher average nematode count per field of the following four species: Cyst Heterodera larvae, and eggs, Columbia Root Knot, and Stunt. Soil chemistry, pathology, and wireworm analyses are in progress; greenhouse weed I.D/germination/count and herbicide resistance studies are on schedule to be initiated the end of January 2008.

Fry color rating (bud end, stem end and USDA rating), mottling (severity and percent incidence), percent sugar ends and sugar content are summarized in Table 2 below. In general, the long-rotation fields had numerically higher values/scores on the fry quality parameters compared with the short-rotation fields. Overall, values for both rotation lengths were within the standard range. Further interpretation will be possible when the samples are removed from storage in a few months, allowing an assessment of storage quality.

Soil chemistry and pathology analyses and greenhouse weed I.D/germination/count and herbicide resistance studies are in progress. They are on schedule to be completed by late spring 2009.

Soil samples collected from both growing seasons are use being used in a greenhouse container study. The study on the 2007 soils has been completed and results have been interpreted. Results from this greenhouse study are being disseminated to growers winter 2008/2009. A greenhouse container study using soil collected from the 2008 paired fields has been initiated with an expected completion date of May 2009 to allow tubers to reach a reasonable size and to accrue maximum pathogen and pest pressure. The soils collected were placed in 5-gallon plastic containers and planted with 2 pre-sprouted Russet Burbank seed pieces from the 2008 growing season. SPAD, NDVI, and visual readings are routinely recorded to monitor plant health. After the plants start senescing severely, biomass readings (leaf, vine, root, and tuber) will be taken and tubers graded for quality. At that time, storage assessment will be conducted; pathology testing will be completed on the leaf, root, and tuber samples; and soil borne insect analysis will be concluded.

Results from the completed greenhouse study are summarized in Table 3 below. The plants grown in short rotation soils had numerically lower visual ratings and began senescence an average of 16 days earlier than the plants grown in long rotation soils. Total senescence was achieved 5 days later with the long rotation. Canopy scores indicating Russet Burbank potato canopy development and senescence for the greenhouse container study are summarized in Figure 1 below. The potatoes grown in long rotation soils also had numerically higher estimated tuber size, yields, and percentage of US No. 1 potatoes.

Statistical analysis is not available yet. All aspects of the project are on track for completion by late spring. Once all of the project components are finished, statistical analysis will be performed. At that time enough data will be available to make the sample size large enough to accurately detect differences. The final report will be submitted thereafter.

Impacts and Contributions/Outcomes

Few definitive impacts have been made to date as this project is still in progress. All of the fields have been sampled/surveyed and some of the analyses are still in progress. However, several workshops have been conducted and more are scheduled where growers will learn about the importance of rotation frequency and participation in this project. Idaho’s agricultural statistics are showing a substantial trend on more acres toward longer and more sustainable rotations. The final information from this project will be disseminated to the potato industry through extension publications and presentations at the annual potato conferences for each of the states involved in this study, the Sustainable Agriculture Research and Education (SARE) Conference and other workshops, seminars, etc.

Collaborators: