Supplement to Diagnosis and Management of Salinity Problems in Irrigated Pecan Production: Salt Leaching
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Date
2010-07
Authors
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Publisher
Texas Water Resources Institute
Abstract
In the publication prepared in 2006 with
the above title (TWRI. TR-287), we described
ways to diagnose salt problems which affect
irrigated production of pecans. We also discussed
the concepts of minimizing soil salinization, and
ways to lower soil salinity. However, the
materials presented were general and introductory
in nature. This article is to supplement the
previous publication with technical details, and
practices of salt leaching during the routine
irrigation as well as salt leaching irrigation for
restoration.
The aim of salt leaching is to keep soil
salinity of the root zone below the level that trees
can tolerate. The threshold salinity of irrigated
pecans is in the range of 2 to 3 dS m-1 when
measured in the soil saturation extract (Fig. 1),
which is an official method of measuring soil
salinity (Miyamoto et al., 1986). In the areas rich
in gypsum, trees may tolerate higher levels of soil
salinity, probably by 1 or 2 dS m-1. Calcium and
sulfate ions are less harmful to pecan trees than
sodium and chloride ions (Miyamoto et al.,
1985).
There are basically two ways to approach
the task of salt leaching. The first approach is to
maintain leaching following each irrigation so as
to keep soil salinity in check. The first half of
this article is devoted for describing ways to
minimize soil salinization through this approach.
The second approach is to let salts accumulate in
portions of the orchards, then to flush salts out
during the dormant period. This approach takes
the reality into account; soil salinity levels vary
widely even in a small orchard, and that it is more
convenient to carry out leaching during the
dormant period. Once a part of the orchard
begins to be salinized, (meaning that soil salinity
exceeds the threshold salinity level), growers
need to carry out salt leaching irrigation for
restoration. When dealing with restoration, the
causes of salinization have to be identified prior
to deciding the methods of salt leaching. This
Fig. 1 Trunk cross-section as affected by salinity or
Na concentrations in the soil saturation extract
(Miyamoto, 1986).
subject is discussed in the second part of this
article.