Elevated Sodium in Irrigation Water and Crop Injury
Elevated sodium and elevated chloride levels are being
observed more frequently in private water supplies in rural areas. In some
cases the water is being derived from large limestone aquifers and in other
cases the water is being derived from shale formations which have been the site
of historic oil and natural gas drilling. In other cases, the wellheads are
sited in karst areas which are frequently promulgated with sinkholes and caves that
can act as conduit for surface contaminants like road salt to contaminate the
aquifer.
Most greenhouse operators do not request that their
irrigation water be tested for chloride and/or sodium. One new operator
purchased a farm that had four sources of water on the property (spring, well, pond,
and stream). At first the grower ignored the extension agent’s recommendation
to test the quality of the well water before initiating production. After observing
cropping issues (as observed in the photo of the Altenanthera spp.) the grower
opted to test his well water for “everything”. The tests revealed that the EC
of the well water was 2.37 m/S with chloride levels at 523 mg/l and sodium
levels at 226 mg/l. While the EC level was high and had to be accounted for,
the grower had two bigger problems to worry about. The upper limits for chloride
and sodium in irrigation water are both 30 mg/l (as per the PSU laboratory) and
the levels of both were extremely elevated.
Subsequent testing and evaluation of the grower’s pond and spring
revealed that both of these water supplies also contained elevated levels of
chloride and sodium which would render them “unusable” from an irrigation
perspective. The use of a series of cisterns to collect rainwater to dilute the
well water was considered impractical and the cost to treat the water through a
reverse osmosis system was too high for the volume of water needed. As a
result, the grower opted to connect to the public water supply rather than pump
water with variable water quality from his stream which was located almost a half mile away.
In conclusion, please remember to annually evaluate the
quality of your irrigation water even if the water source has been used safely
for years. Poor quality water may impact your fertigation programs while
reducing crop quality and crop yield (vegetables).
Thomas Ford
Commercial Horticulture Educator, Penn State ExtensionTom has worked for over 40 years with Cooperative Extension in Maryland, North Carolina, and Pennsylvania. During his career he has worked intensively with vegetable and fruit growers, greenhouse and nursery operators, landscape and turf professionals and area farmers with their production and pest management issues.
Tom is a native of Central Maryland and resides with his wife, Laura and their four sons in Duncansville, PA. Tom has a B.S. degree in Ornamental Horticulture from the University of Maryland and a MBA from Frostburg State University in Frostburg, MD. Tom currently serves as a Commercial Horticulture Educator with Penn State Extension and is housed in the Cambria County Extension Office in Ebensburg, PA.