Malheur Experiment Station Information for Sustainable Agriculture

Granular Matrix Sensors

What is a Granular Matrix Sensor?

Granular matrix sensors (GMS) represents an option for measuring soil water to schedule irrigation. Irrigation of crops highly sensitive to water stress, like potatoes, onions, and many other horticultural crops require precision irrigation scheduling, determining both irrigation frequency and duration.

SOIL WATER POTENTIAL: An expression of the energy level of water in the soil system. This is contrasted to the amount of water present in the system for which water content is the fundamental parameter. The soil water potential is of direct importance to plants because it is the force necessary to remove water from the soil.   Soil water potential is usually expressed in centibars, cb, or kilo Pascals, kPa.  The scientific units, kPa, were conveniently defined so that 1 kPa = 1 cb.

SOIL WATER TENSION: Soil water tension is numerical similar to soil water potential with the opposite sign.  For example a "soil water tension" of 20 cb would be a "soil water potential" of -20 cb.

SOIL WATER CONTENT: The amount of water present in a given volume of soil.

A Granular matrix sensor for electronically measuring soil water has been patented (Larson, 1985) and is marketed as the Watermark sensor (Irrometer Co., Riverside, CA). Granular matrix sensor technology reduces the problems inherent in gypsum blocks (i.e., loss of contact with the soil by dissolving, and inconsistent pore size distribution) by use of a granular matrix mostly supported in a metal or plastic screen. Granular matrix sensors operate on the same electrical resistance principle as gypsum blocks and contain a wafer of gypsum embedded in the granular matrix . The electrodes inside the GMS are embedded in the granular fill material above the gypsum wafer. The gypsum wafer slowly dissolves, to buffer the effect of salinity of the soil solution on electrical resistance between the electrodes. According to Larson (1985), particle size of the granular fill material and its compression determines the pore size distribution in GMS and their response characteristics.

For many soil types, growers have found that GMS are a useful tool to schedule irrigations. as plants use water from the soil, the soil dries and water is drawn out of the sensor. Sensor resistance increases. Upon irrigation or rainfall, the GMS takes up water and the resistance decreases.

Granular matrix sensors have been calibrated to soil water potential and used to estimate soil water potential for irrigation decisions. GMS can substitute for tensiometers in irrigation management when irrigation criteria based on soil water potential have been established. Because GMS do not require periodic maintenance during the growing season, they are ideally suited for sensing soil water potential to automatically start an irrigation system as we have been doing since 1995. GMS have advantages of low unit cost and simple installation procedures, similar to those used for tensiometers. Data acquisition with GMS can be remote from the measurement site by use of electrical wires, so the plants and soil at the measurement site remain relatively undisturbed.

Shock, C.C., A.B. Pereira, and E.P. Eldredge. 2007. Irrigation Best Management Practices for Potato. In C. Rosen and M. Thornton (Eds.). Symposium on Best Management Practices for Nutrients and Irrigation: Research, Regulation, and Future Directions. Submitted to Amer J Potato Res. 84:29-37.

Shock, C.C., A.B. Pereira, B.R. Hanson, and M.D. Cahn. 2007. Vegetable irrigation. p. 535--606. In R. Lescano and R. Sojka (ed.) Irrigation of agricultural crops. 2nd ed. Agron. Monogr. 30. ASA, CSSA, and SSSA, Madison, WI.

Shock, C.C., R.J. Flock, E.B.G. Feibert, C.A. Shock, A.B. Pereira, and L.B. Jensen. 2005. Irrigation monitoring using soil water tension. Oregon State University Extension Service. EM 8900 6p. <http://extension.oregonstate.edu/catalog/pdf/em/em8900.pdf>

Shock, C.C. R. Flock, E.B.G. Feibert, C.A. Shock, A.B. Pereira y L. Jensen. 2006. El control del riego mediante la tensión matricial del suelo. Oregon State University Extension Service, Corvallis. EM 8900-S-E. 8p. <http://extension.oregonstate.edu/catalog/pdf/em/em8900-s-e.pdf>

Pereira, A.B., C.C. Shock, E.B.G. Feibert, R.J. Flock, L.A. Lima, and N. Fernandes. 2006. Monitoramento da irrigação por meio da tensão da água do solo.  Editora UEPG, Ponta Grossa, Paraná, Brasil. ISBN: 85-86941-78-6. 20p.

Shock, C.C., E.B.G. Feibert, A.B. Pereira, and C.A.Shock. 2005. Automatic Collection, Radio Transmission, and Use of Soil Water Data. Oregon State University, Malheur Experiment Station, Special Report 1062:211-222.

Pereira, A.B., C.C. Shock, C.A. Shock, and E.B.G Feibert. 2005. Use of Irrigas® for Irrigation Scheduling for Onion under Furrow Irrigation. Oregon State University, Malheur Experiment Station, Special Report 1062:223-229.

Shock, C.C. and C.A. Shock. 2004. Comparison of the AM400 and Watermark Monitor for precise irrigation scheduling. Oregon State University Agricultural Experiment Station, Special Report 1055:257-260.

Shock, C.C., 2003. Soil water potential measurement by granular matrix sensors.  In Stewart, B.A. and Howell, T.A. (eds) The Encyclopedia of Water Science. Marcel Dekker. p 899-903.

Shock, C.C., K. Kimberling, A. Tschida, K. Nelson, L. Jensen, and C.A. Shock. 2003. Soil Moisture Based Irrigation Scheduling to Improve Crops and the Environment. Oregon State University, Malheur Experiment Station, Special Report 1048:227-234.

Shock, C.C., A. Akin, L. Unlenen, E.G.B. Feibert, K. Nelson, and A. Tschida. 2003.  A Comparison of Soil Water Potential and Soil Water Content Sensors. Oregon State University, Malheur Experiment Station, Special Report 1048:235-240.

Shock, C.C., E.B.G. Feibert, and L.D. Saunders. 2003. Micro-irrigation Alternatives for Hybrid Poplar Production, 2002 Trial. Oregon State University, Malheur Experiment Station Special Report 1048:110-118.

Shock, C.C., E.B.G. Feibert, and L.D. Saunders. 2003. Irrigation Frequency, Drip Tape Flow Rate, and Onion Performance. Oregon State University, Malheur Experiment Station, Special Report 1048:64-70.

Shock, C.C., A. Corn, S. Jaderholm, L. Jensen, and C.A. Shock. 2002. Evaluation of the AM400 Soil Moisture Data Logger to Aid Irrigation Scheduling. Oregon State University, Malheur Experiment Station, Special Report 1038:252-256.

Shock, C.C., Feibert, E.B.G., and S. Jaderholm. 2002.  A Comparison of Six Soil Moisture Sensors. Oregon State University, Malheur Experiment Station, Special Report 1038:262-267.

Shock, C.C., A. Corn, S. Jaderholm, L. Jensen, and C.A. Shock. 2001. Evaluation of the AM400 Soil Moisture Data Logger to Aid Irrigation Scheduling.  Irrigation Association, 2001 Proceedings of the International Irrigation Show, p 111-116.

Shock, C.C., E.B.G. Feibert, and L.D. Saunders. 2000. Irrigation management for hybrid poplar production, 1997-1999. Oregon State University, Malheur Experiment Station, Special Report 1015 80-93

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. 2000. Onion storage decomposition unaffected by late season irrigation reduction.  HortTechnology. 10:176-178.

Shock,C.C. 1999.  Irrigation management that produces value for growers and environmental stewardship. Irrigation Association 1999 Proceedings of the International Irrigation Show, p: 101-108

Shock, C.C., R.J. David, C.A. Shock, and C.A. Kimberling. 1999. Innovative,automatic, low-cost reading of Watermark soil moisture sensors. Irrigation Association 1999 Proceedings of the International Irrigation Show, p: 147-152

Feibert, E. B. G., C. C. Shock and L. D. Saunders. 1998. Nitrogen fertilizer requirements of potatoes using carefully scheduled sprinkler irrigation.  HortSci. 32:262-265.

Shock, C. C., J. Barnum, and M. Seddigh. 1998. 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., E. B. G. Feibert, and L. D. Saunders. 1998. Onion yield and quality affected by soil water potential as irrigation threshold.  HortSci. 33:188-191.

Shock, C. C., E. B. G. Feibert, and L. D. Saunders. 1998. Potato yield and quality response to deficit irrigation.  HortSci. 33:655-659.

Shock, C.C. 1998. Instrumentos para determinação da humidade do solo.  Simpósio de Energia, Automação e Instrumação. XXVII Congresso Brasileiro de Engenharia Agricola, Poços de Caldas, MG, Brasil. pp 137-149.

Shock, C. C. , E. B. G. Feibert, and M. Saunders. 1998. SDI irrigation scheduling for profit and environmental protection. Irrigation Association. Proceedings of the International Irrigation Show pp. 33-39. San Diego, CA.

Shock, C. C., E. B. G. Feibert, and L. D. Saunders. 1997. Irrigation and onions; automating the process could produce higher quality results. Resource, ASAE, October. pp 13-14.

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

Mitchell, A. R. and C. C. Shock. 1996. A Watermark data logging system for ET measurement. ASAE. Proceedings of the International Conference on Evapotranspiration and Irrigation Scheduling pp. 468-473. San Antonio, TX.

Shock, C. C., E. B. G. Feibert, and L. D. Saunders. 1996. Precision irrigation scheduling with granular matrix sensors. ASAE. Proceedings of the International Conference on Evapotranspiration and Irrigation Scheduling pp. 1105-1108. San Antonio, TX.

Thomson, Youmos, and Wood. 1996. Evaluation of Calibration Equations and Application Methods for the Watermark Granular Matrix Soil Moisture Sensor. Applied Engineering In Agriculture. 12:99-103.

Stieber, T. D., and C. C. Shock. 1995. Placement of soil moisture sensors in sprinkler irrigated potatoes. Am Potato J. 72:533-543.

DeOreo And Lander, 1994. Automated Irrigation Scheduling Using Soil Moisture Sensors. Paper no. 94-2119 ASAE, St. Joseph, MI.

Shock, C. C. and J. M. Barnum. 1994. Integration of granular matrix sensors for soil water monitoring into AgriMet and HydroMet. OSU, Malheur Experiment Station Special Report. 936:169-186.

Eldredge, E. P., C. C. Shock and T. D. Stieber. 1993. Calibration of Granular Matrix Sensors for Irrigation Management. Agron J 85:1228-1232.

Hawkins, A. J. 1993.  Electrical sensor for sensing moisture in soils. U.S. Patent 5,179,347. Date issued: 12 January.

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

Eldredge, E. P., C. C. Shock and T. D. Stieber. 1992. Plot sprinklers for irrigation research. Am Potato J 84:1081-1084.

Warrick, A. W. 1990. Nature and Dynamics of Soil Water (In) Irrigation of Agricultural crops. Eds. B.A. Stewart and D.R. Nielsen. Madison, WI. pp. 69-73.

Pogue, W. R. 1990. Watermark Soil Moisture Sensor - an update. ASAE paper No. 90-2582.

Thomson and Armstrong. 1987. Calibration of the Watermark Model 200 Soil Moisture Sensor. Applied Engineering in Agriculture 3:186-189.

Larson, G. F. 1985. Electrical sensor for measuring moisture in landscape and agricultural soils. U.S. Patent 4 531 087. Date issued: 23 July.

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Last updated  Tuesday June 19, 2007 .