| Dear Joe (and all),
It appears that "general knowledge" in California is that drip increases salt concentrations. Further, by localizing water delivery, it doesn't lead to good root growth by trees and shrubs. Yet, in New Mexico, Arizona, Utah, and Nevada, all states in the US that are as if not more arid than California, drip is standard for all planting except lawns. I've been trying to understand the differences for some time and as I build my understanding, I'll share it with all of you (if you are interested).
In my experience here in Southern California (where our water is HARD) doesn't support salt concentration or limited root growth issues as they pertain to drip .
I am quite sure it has nothing to do with soil type - I have sand so there is never an issue about anaerobic soils. And the gardens I design have all types of soils. They all have been extremely successful with no obvious problems resulting from salt buildup or trees and shrubs that dont appear to thrive.
I've never observed any indication of salt concentrating around emitters in any garden.
Further, in a single garden bed, there are so many emitters overall, that as tree/shrub rootzones expand, they must certainly encounter drip emitters from neighboring plants. In my observation, they are never limited to just the emitters around their perimeters.
I just did a cursory search of the literature on-line and found several studies that state that drip does not promote salt buildup and may in fact, help prevent salt buildup:
Vineyards in Australia: http://www.irrigateway.net/publications/Soil_salinity_in_drip_irrigated_vineyards_of_the_MIA.pdf
Squash in the middle east "The advantages of subsurface drip irrigation were related to the relative decrease in salt accumulation in the root zone area where the plant roots were active and water content was relatively higher." (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T3X-4DPYMRV-2&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=961839155&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=a9b54d3b3516cdba137d8c70e6349334)
This study says that drip actually moves salt away from plant roots whereas furrow irrigation concentrates salt around the roots: http://www.uark.edu/depts/ifse/grapeprog/articles/fs4-4c.pdf
A study about irrigation methods and landscape from Texas A & M University (one of the main Ag universities in the US) says: "Poor quality irrigation water containing moderate amounts of salt often can be used more successfully with drip irrigation than with sprinkler or surface irrigation. Less total salt is added with drip irrigation since less water is applied. In addition, a uniformly high soil moisture level is maintained with drip irrigation, which keeps the salt concentration in the soil at a lower level." (http://aggie-horticulture.tamu.edu/extension/homelandscape/water/water.html)
This study from UC Davis and UC Riverside says: "One option for coping with the high soil salinity levels caused by saline, shallow groundwater conditions along the west side of the San Joaquin Valley is to convert from sprinkler or surface irrigation methods to drip irrigation....et soil salinity measurements showed considerable leaching around the drip lines" (http://vzj.geoscienceworld.org/cgi/content/abstract/7/2/810)
BTW, several of the studies that do show salt buildup with drip are studies of agricultural lands irrigated with saline water. That is not the case here (yet).
I did not do an exhaustive search but clearly there is much controversy over both these issues - enough that I would caution anyone against accepting either as "standard knowledge."
The best thing to do is to find a method that works best for you - drip, overhead, micro-mist, etc. Consider the availability of water in your area, the kinds of plants you have, the limitations put on you by your water agency, and the conditions in your own garden.
Nan
On Jul 19, 2009, at 12:26 PM, Joseph Seals wrote:
| Another factor in root rot development is an accumulation of salt in the soil. Much of California has hard water (it's INCREDIBLY HARD here and almost as hard in Southern California). Most root rot organisms thrive on higher salt levels. And, as a seque to my final point, salt levels in gardens have increased tremednously over the last couple of decades with the rising popularity of drip systems. Fourth, drip systems (not that you asked, Pamela) are an efficient way to use water (as engineers would testify) but not close to being the most effective way to water plants to encourage them to become more drought tolerant in our climates. Too many people have bought into the concept of Micro-Irrigation and there's too much money behind it so I don't suspect that it will be questioned too much nor too soon. But there are many inherent problems with it. I won't go into the cosmetic issues nor a host of minor issues but the four big issues are that drip systems don't water in a way that encourages a plant to have a wide and deep root system, drip systems leave a soil saturated for too long, drip systems concentrate salts and, fourth, drip systems don't push oxygen into a soil as do typical sprinkler and other, more "effective" systems. Micro-irrigation -- including "drip" -- was invented in Israel to make use of little available water that offered a low-pressure situation. It was created for row crops and some fruit trees. It was not designed for a drought-tolerant landscape. Joe
Joe Seals
Horticultural Consultant
Pismo Beach, California
Home/Office: 805-295-6039
Pamela Steele wrote: What are Mediterranean climate gardeners' views on the time of day to water plants. We need to water our new plants here in Spain for their first year over the dormancy period in our hot dry summer until they get their roots down. I was always led to believe the best time for these new plants to get most benefit was watering in the evening and so the ground would stay damp all night until morning. Lately, I have had some interesting discussions about watering in the evening and there are some theories that it is not as beneficial to the plants as early morning (7-8am) watering because in the evening the ground is still hot from the baking sun. Watering in the early morning when the ground is relatively cold is apparently more beneficial for the roots. Do you agree? I would love to hear your experience and advice. Best wishes Pamela |
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