Evaluation of the AM400 Soil Moisture Data Logger to Aid Irrigation Scheduling.

Malheur Experiment Station

Information for Sustainable Agriculture

Evaluation of the AM400 Soil Moisture Data Logger to Aid Irrigation Scheduling.

Irrigation Association, 2001 Proceedings of the International Irrigation Show, p 111-116

Clint Shock, Annie Corn, Scott Jaderholm, Lynn Jensen, and Cedric Shock

Malheur Experiment Station
Oregon State University
Ontario, OR, 2001
E-mail clinton.shock@orst.edu

Summary

Growers need rapid and convenient ways to monitor soil moisture status to improve their irrigation scheduling. We examined AM400 Soil Moisture Data Loggers with Graphic Display (M.K. Hansen Co., East Wenatchee, WA) to see if they would aid irrigation scheduling using data from granular matrix sensors ("GMS", Watermark Soil Moisture Sensors, Irrometer Co., Inc. Riverside, CA). For simplicity, we refer to the AM400 Soil Moisture Data Logger with Graphic Display, as "Hansen unit". Each Hansen unit was wired to six GMS and one temperature probe. Hansen units were installed in 14 crop fields as aids to irrigation scheduling during the 2000 season. The practical usefulness of the loggers and their data are presented.

Introduction

Crop yields and quality in Malheur County Oregon are directly related to the quality of irrigation management using GMS. The term "granular matrix sensor" or GMS is used because there is granular matrix in the sensor which has variable electrical resistance as a function of soil water potential (Shock et al. 1998b).

Soil water potential data from GMS has been used by potato growers for irrigation scheduling in Malheur County since the late 1980's (Eldredge et al. 1996, 1992; Shock et al., 1993) and that use has expanded to onions and other crops. Onion yield and grade improves with careful irrigation scheduling based on GMS (Shock et al. 2000, 1998a). The growth of poplar trees is also closely related to the maintenance of soil water potential (SWP) within narrow bounds by careful irrigation scheduling (Shock et al, 2002).

Growers and fieldmen can make GMS readings with hand held 30 KTCD meters (Irrometer Co., Inc. Riverside, CA), and record the data manually. The GMS data is graphed manually or transferred to computer files to be graphed by computer. The data is graphed to demonstrate whether the SWP was wetter or drier than the irrigation criteria for that particular crop. It is easier for the grower to see the SWP in graphical form, because the relative position (wet or dry) is clearer and the rate of drying over time makes more sense as a graph.

Soil moisture data loggers with graphic displays ("Hansen unit", AM400 Soil Moisture Data Logger with Graphic Display M.K. Hansen Co., East Wenatchee, WA) were tested for ease of interpretation for irrigation scheduling at the Malheur Experiment Station and in growers fields. The Hansen unit reads the GMS three time a day and automatically graphs the data for each GMS individually.

Materials and Methods

Set up in 2000. Six GMS were installed at 10- or 12- inch depth in 14 fields (Table 1). By 10-inch depth, this refers to the depth to the bottom of the sensor. The GMS were installed directly in the center of the crop rows for furrow-irrigated and drip-irrigated onions and sugar beets. For potatoes, the sensors were located at 10-inch depth, and between two plants, 4 inches off of the center of the hill. Sensors were installed with the aid of a 7/8 inch diameter soil probe. The sensor was pressed to the bottom of the soil probe hole with an insertion rod, 2 oz of water were poured into the hole, soil was gently packed above the sensor, and the soil left level with little trace of installation except the wires coming out of the soil.

An additional 50 to 125 feet of wire was added to each GMS before installation and the wire was attached to the Hansen units. This wire allowed the grower to spread the sensors over a wider area of the field. Insulation was stripped off of the GMS wire and the GMS was connected to 18 gauge wire using a butt connector adapter (4*260-5,3M Highland) and shrink tubing, (3KH56-7, W.W. Grainger). The other end of the wire was connected to the Hansen unit. Six GMS and one temperature probe were connected to the Hansen unit starting at the double portal reading number 1 and the temperature probe was connected to portal number 7.

The Hansen units were mounted on 4 ft high 4x6 inch wooden posts, and set facing to the north. The posts themselves were placed on the edge of the field along an area which was judged to be representative of the entire field.

Calibration equations in the Hansen unit and 30 KTCD meter. The GMS calibration equations of the Hansen unit and 30 KTCD meter were compared using 12 GMS at 20⁰C, three each at -10, -30, -50, and -70 kPa. Each sensor was read with each of two wire thicknesses and 5 wire lengths using both meters at 20⁰C. The readings for each individual sensor, wire and meter combination were repeated three times.

Results and Discussion

Calibration equations in the Hansen unit and 30 KTCD meter. The magnitude of the water potential readings with the Hansen unit were essentially identical to the readings using the 30 KTCD meter. This is consistent with each manufacturers' intention to match equation 8 from Shock et al. (1998b) from -10 to -70 kPa.

Ease of use for irrigation scheduling. Since the GMS were wired to the Hansen unit, the reading of the sensors was very rapid. The outside cover of the Hansen unit was removed, and the red button, located in the center of the unit was pressed. After the button was pressed, the screen showed the data for GMS sensor #1, including the temperature and the SWP in centibars or kilo Pascals (1 cbar = 1 kPa). Data from the last five weeks was displayed on the screen. The most recently logged data was displayed on the right side of the screen. The lower the trace on the screen, the drier the soil.

The magnitude of the scale on the Hansen unit screen changed with the range of the data. The graphs and instantaneous data for the other 5 GMS were viewed by repeatedly pressing the red button; each sensor being read in turn. When all the sensors had been read, the unit turned itself off.

Data for the entire season was successfully collected from the Hansen units using a laptop computer or palm pilot and a computer program written at the Malheur Experiment Station.

The soil water potential (SWP) from a sample of fields is presented below (Figures 1-4). The SWP irrigation criteria for alfalfa forage on silt loam is in the range of -60 kPa. Regular use of sensor readings allowed the average SWP to remain within the ideal range (Figure 1). The frequency of irrigation depended on the weather and the stage of growth of the alfalfa. Since the screen displayed data from the last 5 weeks, the information was easy to interpret.

The SWP criterion for drip-irrigated onions on silt loam is in the vicinity of -20 kPa (Shock et al. 2000). This criteria was rather carefully followed in a grower's drip-irrigated onion field (Figure 2).

The irrigation criterion for furrow or sprinkler irrigated potatoes on Malheur County silt loam is -50 to -60 kPa (Eldredge et al. 1996, 1992). This criteria can be closely followed (Figure 3).

The use of drip irrigation for sugar beets is entirely experimental. No locally verified irrigation criterion has been established (Figure 4).

Acknowledgments

Contributions towards drip irrigation scheduling from the Oregon Watershed Enhancement Board and EPA 319 funding through the Oregon Department of Environmental Quality are gratefully acknowledged.

Literature Cited

Eldredge, E. P., Z. A. Holmes, A. R. Mosley, C. C. Shock, and T. D. Stieber. 1996. Effects of transitory water stress on potato tuber stem-end reducing sugar and fry color. Am Potato J. 73:517-530.

Eldredge, E.P., C.C. Shock, and T.D. Stieber. 1992. Plot sprinklers for irrigation research. Agron. J. 84:1081-1984

Shock, C.C., E.B.G. Feibert, M. Seddigh, and L.D. Saunders. 2002. Water requirements and growth of irrigated hybrid poplar in a semi-arid environment in Eastern Oregon. Western Journal of Applied Forestry. In Press.

Shock, C. C., E. B. G. Feibert, and L. D. Saunders. 2000. Irrigation criteria for drip-irrigated onions. HortSci. 35:63-66.

Shock, C. C., E. B. G. Feibert, and L. D. Saunders. 1998a. Onion yield and quality affected by soil water potential as irrigation threshold. HortSci. 33:1188-1191.

Shock, C. C., J. Barnum, and M. Seddigh. 1998b. Calibration of Watermark soil moisture sensors for irrigation management. Irrigation Association. Proceedings of the International Irrigation Show. pp. 139-146. San Diego, CA.

Shock, C.C., Z.A. Holmes, T.D. Stieber, E.P. Eldredge, and P. Zhang. 1993. The effect of timed water stress on quality, total solids and reducing sugar content of potatoes. Am Potato J. 70:227-241.

Table 1. Hansen units were installed in 14 crop fields during the 2000 crop season. Malheur Experiment Station, Oregon State University, Ontario, OR.

Crop
1. Alfalfa 2. Alfalfa
3. Potatoes
4. Onions
5. Potatoes
6. Onions
7. Wheat
8. Sugar beets
9. Potatoes
10. Onions
11. Sugar beets
12. Potatoes
13. Onions
14. Onions
Irrigation system
Sprinkler
Sprinkler
Furrow
Drip
Sprinkler
Furrow
Drip
Furrow
Furrow
Drip
Drip
Sprinkler
Drip
Drip
Location
MES Field B2
MES Field A2
MES Field D-1a
Skyline Farms
Gressley Farms
MES B-8b
Ontario Farms
MES B-8a
MES D-1a
Ontario Farms
Ontario Farms
Teramura Farms
Komoto Farms
DeBoer Farms
Depth to the bottom of the 5 or 6 shallow sensors
12"
12"
10"
10"
10"
10"
10"
10"
10"
10"
10"
10"
10"
10"
Depth to the bottom of the single deep sensor
NA
NA
NA
14"
14"
14"
NA
14"
14"
14"
14"
14"
14"
14"

Figure 1. Soil water potential at 12-inch depth in sprinkler-irrigated alfalfa as measured by 6 GMS recorded by a Hansen unit, Malheur Experiment Station, Oregon State University, Ontario, OR 2000.

Figure 2. Soil water potential at 10-inch depth in drip-irrigated onion as measured by 6 GMS recorded by a Hansen unit in a grower's field, Malheur Experiment Station, Oregon State University, Ontario, OR 2000.

Figure 3. Soil water potential at 10-inch depth in a furrow-irrigated potato field as measured by 6 GMS recorded by a Hansen unit. The sixth sensor was at 14-inch depth. Malheur Experiment Station, Oregon State University, Ontario, OR 2000.

Figure 4. Soil water potential at 10-inch depth in a grower's drip-irrigated sugar beet as measured by 6 GMS recorded by a Hansen unit in a grower's field. The sixth sensor was at 14-inch depth. Malheur Experiment Station, Oregon State University, Ontario, OR 2000.