Chapter 40 - Monitoring of spatiotemporal changes of soil salinity and alkalinity in eastern and central parts of Iran

Abstract

Soil salinity and alkalinity are major soil limitations of agriculture and land degradation in arid and semiarid regions. Salinity is a dynamic phenomenon that varies continuously over time and space. Therefore, this chapter investigates the processes of Spatio-temporal changes in soil salinity and alkalinity in eastern (site 1, during the period 2004–18) and central (site 2, during the period 1986–2030) parts of Iran using statistical analysis and digital soil mapping (DSM) methods, respectively. Surface soil samples (0–30cm) were collected at 160 locations from five geomorphic surfaces under different cultivation conditions in both 2004 and 2018 at site 1. There was a significant increase in the EC, Caex, Mgex, Naex, and SAR of all landforms (except dune field) over 14years, about twofold at site 1. The finding of soil alkalinity maps at site 2 shows an increasing trend of changes from east to west, consistent with the trend of changes in the most important environmental parameters (i.e., groundwater parameters, distance from the road and urban construction) identified using the random forest (RF) model. Based on 10-fold cross-validation, the RF model predicted soil alkalinity with an R2 value of 0.762016. To predict the soil alkalinity maps of site 2 in 1986, 1999, 2010, and 2030, the relationships between soil and environmental data from 2016 were used. Overall, the results of this study revealed that during long-term cultivation, the size of the areas with high (12–16dSm−1) and very high (16–32dSm−1) salinity and alkalinity classes were increased in the studied regions, especially in pistachio cultivation during irrigation with inadequate water and playa margin lands. The trends of soil salinity and alkalinity changes in these regions show an increase or decrease in different locations, which is consistent with natural and human activities.