Irrigation with freezing saline water for 6 years alters salt ion distribution within soil aggregates
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It is well known that irrigation with saline water is increasingly popular for reclaiming saline-alkali soil and for increasing crop productivity in some countries and regions. Saline irrigation results in the changes of salt distribution patterns and soil aggregation. The purpose of this study was to investigate the alteration of salt ions distribution within different soil aggregate fractions after irrigation with freezing saline water.
Materials and methods
In a field experiment after irrigation with freezing saline water for 6 years, soil samples (0–10-, 10–20-, and 20–30-cm depths) were collected from three treatments: freezing saline water irrigation with plastic film mulching (IM), freezing saline irrigation without plastic film mulching (IO), and no saline irrigation and no mulching (CK). The bulk soils were separated into five size classes (i.e., 5–8, 2–5, 1–2, 0.25–1, and < 0.25 mm) by the dry-sieving method. Then, the salinity and ion (i.e., Ca2+, Mg2+, K+, Na+, HCO3−, SO42−, and Cl−) concentrations within each aggregate size class were determined.
Results and discussion
Total soil salinity significantly decreased under IM and IO relative to CK in the 0–30-cm layer. The macro-aggregate fractions (> 2 mm) dominated the aggregate size distribution (approximately 60%) for IM, whereas the < 2.0-mm fraction represented the largest fraction for CK (accounting for 60%). And the average mean weight diameter (MWD) of aggregates was increased under IM and IO compared with CK in the 0–30-cm soil layer. Across the aggregate size fractions, with the exception of HCO3−, the total salt content and ionic contents followed the general order of CK > IO > IM. The IM treatment significantly increased the ratios of Ca2+, K+, HCO3−, and SO42− compared with the corresponding fractions under CK. The low Mg2+ contents and relative ratios, the high Ca2+ relative ratios, and low Mg2+/Ca2+ ratios within the macro- and medium-aggregates were associated with soil aggregation. And the decrease in the Na+ concentration reduced the negative effects on soil aggregation.
After long-time irrigation with freezing saline water, soil aggregation is improved along with the alteration of salt ions distribution in the upper soil layers. It offers a potential opportunity for reclaiming saline soil in the coastal regions where saline groundwater is the sole water resource.
KeywordsSaline water irrigation Saline soil Soil aggregates Soil salinity
This study was supported by the National Natural Science Foundation of China (41271241), the Natural Science Foundation of Hebei Province of China (D2017503016), and the National Key Research and Development Program of China (2016YFC0501303).
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