ITRC Report November 1, 2003, pages 1-65.
A soil salinity accumulation study was conducted by ITRC during the summer of 2002 to examine the long-term impact of drip and micro irrigation on salinity build-up in orchards, focusing on the salinity concentration pattern across a soil profile. This study assessed the current level of salinity accumulation in orchards irrigated with drip/micro systems and provided information to support recommendations on the most effective and efficient leaching techniques.
There is a concern that soil salinity accumulation in orchards, which comprise large acreages in the Central Valley of California, will eventually require reclamation leaching. Not only would this consume large quantities of water, burt salts leached from crop root zones could also pollute drains, waterways, and aquifers resulting in serious water quality complications.
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 2.4m deep across two tree rows were developed from these data.
Key points from the salinity accumulation study include:
- In drip-irrigation orchards, there is a significant amount of salt accumulation on the edges of the wetted areas along tree rows.
- We found that 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.
- Some of the salt applied through irrigation water is being leached from the root zone.
- Soil texture affects salt accumulation to a certain extent. There is 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 finding 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.
Bioresource and Agricultural Engineering
© 2003 ITRC
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