REPORT TO THE RESEARCH SUBCOMMITTEE OF THE MAINE POTATO BOARD

January, 2006

Project Title: Optimizing Field-scale Potato Irrigation over Stable, Spatially Variable Soil Water Patterns

Executive Summary:

This Maine Potato Board supported irrigation research project has shown that field-scale soil water patterns are stable in time. Observed potato yield response to irrigation depends upon the relative soil water status of specific areas and fields. Yield data indicate strong positive response to irrigation for consistently drier areas within a field and neutral to negative response for wet areas. Additionally, the stable water pattern seems to depend on soil type, topography, and global position in a fairly predictable way.

Detailed soil type and topographic surveys were obtained for several fields under the barley-potato rotation of a collaborating grower. Soil water content was measured using a hammer driven probe throughout the growing season. Following spring tillage a newly developed “on-the-fly” method (see photo figure 1) for soil water mapping was also used. Yield data were obtained using both hand sampling and yield monitor. The time stability and spatial variability of soil water patterns, the stable component of soil water, and the yield data are being mapped for comparison. These data are being compared with the detailed soil and topographic data to evaluate the potential use of soil classifications and topographic attributes such as the “wetness index” for inferring the soil water pattern and irrigation requirements.

Results thus far suggest that with a traditional gun and reel “traveler” irrigation system (see photo figure 2), substantial water conservation can be achieved by answering the question of which transects to irrigate, when, and how much water to apply. Light, frequent applications of water are most beneficial for potato production but are difficult to achieve using a traveler. It appears that selecting which transects to apply water based upon stable soil water pattern is a viable option. Results indicate that measurements of soil water taken near the field edge can be used to rapidly assess the current crop water demands of a given transect. The level of precision that can be achieved is higher with center pivot and linear irrigation systems. A more detailed report is in preparation for publication and will be supplied to the research committee upon its completion.

Applicant

Gordon Starr of the USDA-ARS New England, Plant, Soil, and Water Laboratory

Relationship to MPB Priorities

This research project addresses the following priorities of the Maine Potato Board:

1. Increase irrigation research especially in developing efficient, environmentally sound irrigation practices.

2. Additional support structure for irrigation to provide technical assistance to growers.

3. New production techniques such as precision farming and irrigation.

Economic Benefit to Potato Industry

The projected economic benefit for the potato industry are through increased yield, reduced irrigation water requirements, and savings in time, energy, and equipment wear.

Explanation of the Project

Precision or site-specific farming is being promoted by private sector manufacturers and agribusinesses. Yield monitors with capabilities for mapping harvest variability across fields are supplied by farm equipment manufacturers. Irrigation systems with the capability of applying variable rates of water and chemicals are being developed and marketed by irrigation manufacturers. Maps of the stable components of the landscape such as topography and soil type are available to farmers from both public and private sources for managing their fields, crops, and natural resources. Efficient and cost effective means of utilizing these tools and information are needed.

Crop water availability has a profound influence on potato production. Additionally, field scale spatial patterns of soil water are much more stable in time than would be expected from random processes. Stated simply, the wetter areas remain relatively wet and the drier areas relatively dry. This pilot study of potato production in Maine provides a simple model for assessing the stable component of the water pattern and shows that this stable water pattern has a strong bearing on irrigation water requirements and yield. Soil type and topography play a role in determining the stable soil water patterns. Topographic attributes such as the “wetness index” could explain much of the observed soil water variability. Water patterns have been observed to vary on a spatial scale that is appropriate for the application of precision agriculture technology.

Precision agriculture has great potential to minimize production inputs while improving the environment. For instance, precision irrigation could minimize yield losses due to water stress and agricultural chemical leaching while improving water use efficiency. To achieve these benefits, more efficient management and production technologies will be required.

A particularly costly and problematic process for precision agriculture in general and water management in particular is real time assessment of spatial variability and adapting application technology to that assessment in real time. An unchanging map such as the stable soil water pattern could reduce or eliminate the burdensome processes of real time monitoring of spatial variability in water and real time adaptation of precision irrigation systems.

This research suggests that the stable component of the soil water pattern is linked with landscape and soil properties that change little with time, notably topography, soil type, and surface/sub-surface drainage pathways. Through continued research more is now known about the nature of these relationships and their implications for precision water management in Maine potato production. Despite advances in technology, soil water mapping at field scales is laborious. Thus, it is desirable that we have developed improved technologies that provide alternatives for assessing stable field scale patterns of irrigation water requirements. Once a stable pattern is determined, a form of precision agriculture (particularly precision water management) reflecting this pattern should be feasible.

Figure 1. Technicians Ben LaGasse and Peggy Pinette operating the “on the fly” soil water mapping system at the potato farm of collaborator Donald Fitzpatrick. Significant improvements were made to this system thanks to this Maine Potato Board research grant.

Figure 2. Traveler irrigation systems are slow moving and not particularly efficient, but much time and water can be saved by carefully choosing which transects to irrigate based upon soil water status.