REPORT TO THE RESEARCH SUBCOMMITTEE OF THE MAINE POTATO BOARD

January, 2005

Project Title: Improving Soil Conservation in Potato Systems

Executive Summary:

Two trials were initiated to evaluate the use of polyacrylamide (PAM) for preventing soil erosion. In one on-farm observation study, a simple injection system was constructed for applying PAM in a liquid formulation (Soilfix LDP) through hose reel and center pivot systems. Initial tests were made with both hose-reel and center pivot systems working with Mr. Keith LaBrie of St. Agatha. In preliminary runs, the system worked well on the center pivot system. On the hose-reel system it appeared to slow down the reel speed so injection was discontinued until a port could be put in the system behind the control unit. However, rainfall brought an end to the study before the modifications could be made.

In a second on-farm trial PAM was applied to the soil after potato harvest to see whether or not it would help stabilize the soil and decrease erosion. Replicated plots were set out with application rates of 25 lbs per acre of PAM as Soilfix Polybeads. Landscape cloths were set out in the fall to trap soil erosion from treated and untreated portions of the field. The cloths will be removed in the spring and the amount of erosion from each plot measured.

Budget Requested: $ 9,340

Budget Approved: $ 5,900

Personnel: Peter Sexton (principal investigator) UMCE Presque Isle

Matt Williams UMCE Houlton

Chris Reberg-Horton UMCE Orono

John Jemison UMCE Orono

Tim Griffin USDA-ARS Orono

Gordon Starr USDA-ARS Orono

Cooperators: Laurie Osher MAFES Orono

John Halloran USDA-ARS Orono

Objectives:

1.) Develop useful methods of decreasing soil erosion following the potato crop. Avenues to be evaluated are: broadcast seeding barley immediately prior to potato harvest; use of mulch after potato harvest; application of polyacrylamide.

2.) Evaluate the use of polyacrylamide in irrigation systems in Maine.

Decreasing soil erosion following potato harvest.

A solid formulation of PAM (Soilfix Polybead, Ciba Specialty Chemicals Corp. Suffolk, VA) was applied in strips along with mulch on a sloping field near Houlton at a rate of 25 lbs per acre. The trial was set up on a field with a fairly uniform slope in a randomized complete block design with four replications. Fabric traps were placed at the base of each plot. The traps will be lifted in the spring and the amount of soil in each trap will be weighed to obtain an estimate of soil erosion from each plot.

Polyacrylamide injected into irrigation systems.

An LMI high-viscosity injection pump (model C711-75 HV, LMI Milton Roy Inc., Acton, MA, USA), rated to a pressure of 150 psi, was mounted on a trailer along with a small generator powered by a gas engine. A quick-attach connector was placed on the irrigation port with a matching connector on the end of the high-pressure hose coming from the injection pump. The pump was primed with crop oil and then the intake line was placed in a container of liquid (reverse emulsion) PAM (Soilfix LDP, Ciba Specialty Chemicals Corp. Suffolk, VA). The pump was initially calibrated under a non-pressurized system. Based on this calibration a target injection rate of 10 qts per hour, and 4 quarts per hour, was set for the center pivot and hose-reel systems respectively. The goal was to keep at least 10 ppm of PAM in the flow of irrigation water, and deliver about 3 lbs of PAM per acre.

The system was set up on the farm of Mr. Keith LaBrie and was used in trial runs during the first week of August. However, very little area was irrigated (less than 20 acres) before rainfall occurred. Rainfall was such that soil moisture did not approach the stress threshold during the season (Fig. 1) and no further irrigation was practiced on this farm. In the trial run on the center pivot system the injection unit appeared to work well. On the hose-reel the injection unit was able to pump PAM into the high-pressure stream of water, but the control unit on the irrigation unit was adversely affected by the PAM – it slowed down shortly after the unit was started, and so the injector was shut down. For future use with hose-reel systems the injection port should be placed downstream of the control unit.

Fig. 1. Soil moisture versus day of the year for the field where the PAM study was conducted at St. Agatha, Maine, in 2004. Note that soil moisture never dropped below the stress threshold in 2004, and that average values only crossed the irrigation threshold of –40 centibars for a total of four days (July 31, and August 6-7, and August 29) in the whole season. The PAM study was initiated in the drying cycle around August 6, but the occurrence of rain brought an end to the effort.

Winter rye variety trials.

This component was not funded and so work in this area was not conducted in northern Maine.

Request for further funding.

No further funding is requested for these studies at this point. Further work with solid PAM applied after potato harvest will be carried forward as part of another grant to Matt Williams that has already been funded. Work with liquid PAM injected into irrigation lines will also not require further funding. The injection pump and generator will be mounted on the trailer again for work in the coming season. We propose to make the unit available to growers who want to use it, but we do not propose intensive data collection or any further expenditures on equipment.