24. The Reclamation Effects Should Be Considered for Saline Soil Criteria in Soil Classification System

It is well known that most saline soils have salt accumulation at the soil surface and the root zone due to the capillary movement of saline groundwater and subsequent evaporation. The criteria for classifying soil as saline taxa are different in different soil classification systems. In Chinese Soil Taxonomy (CST), soils that have a salic horizon starting within 30 cm from the soil surface are named as Orthic Halosols. In the World Reference Base for the Soil Resources (WRB), soils that have a salic horizon starting within 50 cm from the soil surface are named as Solonchaks. In the US Soil Taxonomy (ST), soils that have a salic horizon starting within 100 cm from the soil surface are named as Salids. In China, a large area of saline soils was reclaimed for crop production. This chapter describes some soil profiles that were classified into saline taxa in CST, WRB, and ST before they are reclaimed, to see if these soils, after a long history of irrigation, are still classified into saline taxa in the three soil classification systems. The results showed that the salts were leached into certain depth, the salic horizons were observed at different depth from the surface, many profiles could not be classified as Orthic Halosols as identified earlier, some of them could not be classified as Solonchaks, and few of them even could not be classified as Salids. With a long irrigation history, the depth of salic horizon is related to the amount of irrigation water and irrigation models. When more water was used for irrigation each time, the salts were found at deeper layers. Relatively the surface irrigation leached the salts deeper than the drip irrigation. According to the present study, we suggest that the criteria of ST should be taken in order to keep the reclaimed saline soils in the saline taxa, i.e., soil classification should not be changed by irrigation. We also suggest that more soil survey should be taken for discovering how much water was used in normal irrigation models and how deep the salts were leached under such normal irrigation models. Through analyzing large amount of data, especially those data coming from reclaimed saline soils, the depth and index for salic horizon should be redefined to keep the reclaimed saline soils in the saline taxa of soil classification systems. In this chapter, we examined the criteria of saline soil classification and made some suggestions by citing other scholar’s research results published in the scientific literature.