ISHS Acta Horticulturae 537: III International Symposium on Irrigation of Horticultural Crops
SPECIFICITY OF SAP FLOW INDEX FOR MIST IRRIGATION CONTROL |
| Author: | N. Nadezhdina |
| Keywords: | Apple orchard, impulse-mist-sprinkling, automatic irrigation control system, physiological algorithm. |
| Abstract:
Measurements of sap flow using the "symmetrical" heated probe method were utilised for mist irrigation control regime in the apple orchards in the semi-arid region of southern Ukraine. The sensor was equipped with a linear heater placed equidistantly between two thermocouples, all inserted within hypodermic needles. Diurnal patterns of temperature differences recorded by the sensor (called sap flow index - SFI), were unusual (when compared to ordinary records of sap flow) with two typical peaks in cloudless days and depression between them. Relationship between SFI and heat pulse velocity was non-linear for the whole range, but linear and highly sensitive under very low sap flow rates. Due to such special features, SFI gave distinct signals for switching mist irrigation on and off based on the ratio of its predawn value (SFIp) to its midday value (SFId). The critical value of SFIp/SFId equal to or more than 1.0 indicated water stress in trees (resulting from a combination of the previous plant water deficit and current dehydration), under which the impulse-mist-sprinkling system was switched on. Long-term use has demonstrated high sensor reliability and adequate water stress determination over several growing seasons. | |
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