Published in Conference Proceeding from IA Technical Conference, November 1, 2003.
The Irrigation Training and Research Center (ITRC) of Cal Poly State University, San Luis Obispo, CA, hypothesized that there is salinity accumulation in the root zone of tree crops that have been irrigated with drip or micro-spray irrigation systems, located in arid and semi-arid regions. Therefore, a study was conducted by ITRC during the summer of 2002 to examine the long-term impact of drip and micro irrigation on salinity accumulation in orchards, focusing on the salinity concentration pattern across a soil profile. The project also provided information to support recommendations on the most effective and efficient leaching techniques.
During the study, two rows of soil cores were collected in ten orchards that had been irrigated with drip or micro-sprayers. Eight of the ten fields were located in the semi-arid climate of the west side of the San Joaquin Valley, CA; the other two were located in Coachella Valley, CA. Fields were selected that had a known irrigation history, without a high water table. Soil samples were collected to a depth of 2.4 m and then tested for ECe. Graphs of soil salinity concentrations for soil profiles 2.4 m deep across two tree rows were developed from these data.
Key points from the salinity accumulation study include:
- In drip-irrigated orchards, there is a significant amount of salt accumulation on the edges of the wetted areas along tree rows.
- Deep percolation with drip still leaves substantial amounts of salt in the soil.
- Orchards with micro irrigation systems accumulate salt in the middle of the tree rows, which is on the edges of the wetted patterns.
- Soil texture affects salt accumulation to a certain extent. There was more salt accumulation in heavier soils compared to sandy soils.
The results from the study suggest that salinity accumulation is a serious concern when an orchard that has been irrigated with drip/micro is removed and a new crop is planted. Many of the fields studied had salinity concentrations on the edges of wetted areas that could be detrimental to a new crop if the salts were not leached prior to planting.
The findings of this study prompted ITRC to conduct a reclamation leaching study. The reclamation leaching study was completed to quantify the leaching water required to remove salts from the effective root zone of trees. This experiment tested a new reclamation leaching technique – multiple lines of low-flow drip tape used to apply water to the area of salinity accumulation along a tree row. The reduction in salinity with a given depth of deep percolation is predictable. The new leaching procedure uses about 1/3 – ½ of the volume of water normally needed for reclamation irrigation.
Bioresource and Agricultural Engineering
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