ISHS Acta Horticulturae 792: V International Symposium on Irrigation of Horticultural Crops
NEW TOOLS AND METHODOLOGIES FOR IN SITU MONITORING OF ROOT ZONE SALINITY AND LEACHING EFFICIENCY UNDER DRIP AND SPRINKLER IRRIGATION |
| Authors: | T.K. Biswas, G. Schrale, R. Stirzaker |
| Keywords: | soil water extractor, wetting front detector, leaching efficiency |
| Abstract:
The existing Water Allocation Plan for the River Murray Prescribed Water Course encourages Riverland growers to achieve a water use efficiency of at least 85%. Water use efficiency (WUE) has been defined as the volume of water used “consumptively” by the crop i.e., evapotranspiration divided by the total volume applied to the field. The increase in water use efficiency introduces the risk of salt build up in the root zone, due to insufficient leaching. Even though there is still a leaching fraction, salt build up has been observed, so it is unclear how efficiently salt is being leached from the profile. In order to assess the leaching efficiency i.e. how much of the existing salt is moved through the profile by a leaching event, a pilot study was conducted between December 2004 and February 2006 for drip and under-canopy sprinkler irrigation. A soil water extractor (SWE), which samples soil water by applying a suction of 60-70 kPa, was used to determine the salt concentration in the soil profile 24 hours after irrigation. Simultaneously, a FullStop wetting front detector (WFD), which automatically collects a soil water sample when the soil is wetter than 2 kPa suction, was used at the same depth to sample water that was moving through the profile during, or just after, irrigation or rain. This paper field tests a new method for assessing leaching efficiency from the salinities of the water samples collected by the SWE and FullStop WFD. The results from the measured depth of top 0.3 m soil layer indicated a difference in the leaching efficiency between the two irrigation types, with drip having an average value of 65% and under-canopy sprinklers 93%. Higher leaching efficiencies for the under-canopy sprinklers may be due to the lower application rate (per unit wetted area), which would mean water was infiltrating through small diameters pores. The study has demonstrated how simple soil water monitoring tools such as SWE and FullStop WFDs can be used together to estimate in-situ leaching efficiencies of irrigated land. The tools could show irrigators when to leach, and under which conditions salt is leached most efficiently. | |
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