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

Changes in the project were required in 2007 due to the identification of the Potato Cyst Nematode (PCN) and the resulting quarantine provisions in Southeastern Idaho. The field samples collected in 2006 were discarded and new soils were collected to meet the quarantine restrictions. Fifty-four fields were surveyed/sampled by working with growers and industry personnel to get actual field yield data, tuber quality information and post storage measurements. The field pairs were selected by choosing fields with similar soil type, topography, and management with the exception of rotation history. Fields with short rotation had potatoes every other year with small grains typically as the rotation crop; the long rotation fields had potatoes every four years, again with small grains as the rotation crops. Nematode and in-field soil assessments have been completed. Soil borne pathogen, insect, and weed assessments are in process. The greenhouse container study has been initiated on soil samples collected in 2007 and is nearing completion. Growers seem to be very interested in lengthening rotation and moving towards increased sustainability (as determined by surveys of attending growers showing a 42% shift in attitude from five years ago). This interest is due to somewhat widespread problems with various pests and pathogens (such as pink rot, nematodes, etc.) and has increased substantially with the PCN discovery.

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 conc.
*soil depth, density & 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

Changes in the project were required in 2007 due to the identification of the Potato Cyst Nematode (PCN) in Southeastern Idaho and the resulting quarantine provisions. Therefore, field soil samples collected in 2006 were discarded and new samples were collected in 2007 to meet the PCN quarantine restrictions and allow samples to be brought to Brigham Young University and University of Idaho R&E Centers for analyses and greenhouse work. 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.

In-field measurements were completed at the time of soil collection in 2007 and nematode analysis also is completed. Results from the nematode analyses have been interpreted and are being distributed to growers winter 2007/2008. Ten different nematode species were identified; however, there were no nematode species which were detected in all 27 of the short-rotation fields. Root lesion nematode was the only species detected in 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 six species: Cyst Heterodera viable, larvae, and eggs, Northern Root Knot, Columbia Root Knot, Stunt, Pin, and Golden Nematode. 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.

A greenhouse container study using soil collected from the paired fields has been initiated with an expected completion date of May 2008 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 2006 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) are 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.

No statistical analysis is available yet due to the small sample size for this survey (statistical analysis will be performed at the end of the three year trial, when enough data will be available to make the sample size large enough to accurately detect differences).

Impacts and Contributions/Outcomes

Few definitive impacts have been made to date as this project is 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. Surveys conducted at and after these workshops show over 21,000 acres of potatoes (31 growers) moving towards longer rotations as a direct result of the workshops. Idaho’s agricultural statistics are showing a substantial tend on more acres than this towards 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 states involved in this study, the Sustainable Agriculture Research and Education (SARE) 20th Anniversary Conference and other workshops, seminars, etc.

Collaborators: