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Title: EVALUATION OF ENVIROSCAN CAPACITANCE PROBES FOR MONITORING SOIL MOISTURE IN CENTER PIVOT IRRIGATED POTATOES

Author
item Alva, Ashok
item Collins, Harold
item FRAISSE, C - WSU-IAREC, PROSSER, WA
item Boydston, Rick

Submitted to: Journal of Applied Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2002
Publication Date: 6/1/2003
Citation: ALVA, A.K., COLLINS, H.P., FRAISSE, C., BOYDSTON, R.A. EVALUATION OF ENVIROSCAN CAPACITANCE PROBES FOR MONITORING SOIL MOISTURE IN CENTER PIVOT IRRIGATED POTATOES. JOURNAL OF APPLIED IRRIGATION SCIENCE, 38:93-110. 2003.

Interpretive Summary: Real-time continuous monitoring of soil moisture content is important for optimal scheduling of irrigation to minimize crop water stress as well as excessive leaching of water below the rooting depth. Capacitance probes were used to monitor the soil moisture content in a sandy soil with potato production under a center pivot irrigation system. The cumulative evapotranspiration (ET) during the duration of the study was 600 mm which was very close to the cumulative irrigation, i.e. 596 mm. Soil moisture monitoring below the depth of rooting indicated minimal leaching of water to this depth. This study demonstrated that irrigation scheduling based on continuous monitoring of soil moisture content facilitated optimal irrigation management.

Technical Abstract: Careful irrigation scheduling is the key to providing adequate water to minimize potential leaching losses below the rootzone, while supplying adequate water to minimize negative effects of water stress. Capacitance probes were used for real-time continuous monitoring of soil moisture content at various depths in the surface 120 cm of soil under potato production in a Quincy fine sand. The soil moisture content measusred by capacitance probes showed a good correlation with soil moisture content measured using destructive soil sampling at various depths. The cumulative ET for this duration of the study was 600 mm, while the cumulative irrigation was 596 mm. Most of the irrigatin was scheduled to replenish 100% ET. The depth integrated soil moisture contents in the top 60 cm depth soil, i.e. rooting depth for potatoes, corresponding to field capacity soil moisture content, 1/3 depletion of the available soil moisture content, and at wilting point were referred to as "Full Point", "Refill Point", and "Driest Point", respectively. Considering the rooting zone of the top 60 cm depth soil, the depth integrated soil moisture content in this depth was generally maintained within the range of Full Point and Refill Point. The depth integrated soil moisture content in the 60 to 120 cm depth soil (below the rootzone) stayed above the Refill Point during most of June and July. this indicates that there was some leaching of water below the rootzone depsite careful irrigation scheduling to replenish the ET at each irrigation event. This study demonstrated that continual monitoring of soil moisture content within and below the rootzone of potato is important to optimize the irrigation scheduling to minimize leaching losses below the rootzone.