Short communicationInfiltration of melting saline ice water in soil columns: Consequences on soil moisture and salt content
Introduction
Soil salinization is a major constraint for crop production in semi-arid and arid areas. Usually soil salinization is determined by the interaction of climate and groundwater. In the monsoon climatic regions, soil salt and water content vary seasonally because of the changes in evaporation, rainfall and temperature (Shi et al., 1986, Wang, 1993). Spring season is the salinization period because of high evaporation and low rainfall, summer season is the desalination period due to high rainfall, autumn season is the re-aggregation period due to reduced rainfall and increased evaporation, and winter season is the latent period due to the low temperature and evaporation. Additionally, saline soil areas usually have a shallow groundwater table with saline groundwater. The technologies often used for saline soil reclamation include draining out groundwater through pumping and canals, and leaching soil salts using rainfall and freshwater irrigation which is accompanied with the replacement of saline groundwater by rainwater or freshwater (Shi et al., 1986, Wang, 1993). Because of freshwater shortage, however, these technologies have limited applicability in the monsoon regions.
Irrigation with saline groundwater that contains adequate dissolved divalent cations such as Ca2+ is one way to leach and reclaim sodic and saline-sodic soils (Qadir et al., 2001). One major problem with this method is the inadequate amount of divalent cations, particularly Ca2+, in the water that usually requires the application of gypsum. Other limitations of this technique are the difficulties in collection and conveyance of saline water and collection and disposition of drainage water (Qadir et al., 2001), and the need for excessive freshwater to leach the desorbed Na+ from the root zone. Water desalination by natural freezing has been used for a long time (Fournier et al., 1974). Shi et al. (2002) tried to get low salinity (and even fresh) water from the Bohai sea ice through natural freezing in winter and thawing in spring. They considered this method might provide a solution to the water shortage problem of that area. Due to the high cost and technical difficulties, however, it is difficult to utilize desalinized water directly to agriculture by natural freezing.
Based on the above studies, we hypothesize that saline soils may be improved by irrigation with water from melting saline ice. In the monsoon regions with cold winter (e.g., northern China), saline groundwater is used for irrigation in winter, which will be frozen to ice. The saline ice melts gradually in spring. Since meltwater at initial thawing stages contains more salts, infiltration of late-melted freshwater would wash out the deposited salts and create a desalinized soil surface layer. Therefore, the objective of this experiment was to investigate the changes in soil salt and water contents under infiltration of saline ice meltwater and elucidate the possible mechanisms of soil desalination by freezing saline water irrigation.
Section snippets
Materials and methods
A saline soil sample was taken from the coastal area of Haixing County of Hebei Province, China. Soil analysis indicated that the soil was a fine clay and its salt content was 4.8% (Table 1). The soil sample was air-dried (with water content of 0.02 g g−1), ground, sieved on a 2-mm sieve, and then packed into PVC cylinders (diameter: 16 cm; height: 100 cm). In order to take soil samples, pre-drilled holes were provided along the wall of PVC cylinders in a 5-cm interval. The holes were blocked with
Results and discussion
The soil water content and infiltration depth increased with the increase in applied ice volume, and there were interactions between salinity level and volume of applied water (Fig. 1). For the low volume treatment (1800 ml), the four salinity levels showed similar soil water content (0.27–0.28 g g−1) in the 0–10 cm soil layer. With further increase in soil depth, however, soil water content was higher in the saline ice treatments than in the salt-free ice treatment. For the medium (2700 ml) and
Conclusions and remarks
The objective of this work was to investigate the changes in soil water and salt contents under infiltration of saline ice meltwater. Soil water content increased with ice application volume. Comparing the different treatments, water content was higher in the salt-free ice treatment than in saline ice treatments in the top soil layers, but the trend was reversed in deeper soil layers. For both saline ice and salt-free ice treatments, salt content in the top soil layers was reduced, and the
Acknowledgements
The authors truly appreciate the time that Dr. Tusheng Ren and the anonymous reviewers spent on helping to clarify the confusion and improve the paper. This work was partly supported by the national 863 project (no. 2006AA1002067), the innovation project of the Chinese Academy of Sciences, and the key research project of Hebei Province (no. 06220111D). The authors express their gratitude to Dr. Mohan Chandra Saxena for revising the manuscript.
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