Spatial distribution of soil water and salt in a slightly salinized farmland

It is important to study the mechanisms associated with the spatial distribution of soil water and salt to control soil salinization and promote the sustainable development of farmland. In this study, six plots in gully farmland in the loess hilly region with different spatial locations were selected to determine the spatial distributions of soil water and salt and their correlation using the multifractal method. A grid method (15 m  15 m, 3,600 m2) was applied in the 0–20 and 20–40 cm soil layers where each sampling site was located at the center point coordinates. The results showed that the spatial variability of the soil water and salt were 1.41 and 1.73 times higher, respectively, in the upstream farmland than the downstream farmland. The uneven runoff and sediment distributions from gullies in the upstream farmland increased the spatial variability of the soil water and salt. In addition, the vulnerability of upstream farmland to waterlogging caused further in their spatial variability due to narrow landform features. Analysis using the joint multifractal method showed that the spatial variability of the soil water and salt was strongly correlated (P < 0.05) because of the coupling between soil water and salt. In addition, the spatial variability of the soil water and salt was strongly correlated in the 0−20 and 20−40 cm layers because of the spatial autocorrelations of the soil properties (P < 0.05), thereby indicating that the spatial distributions of soil water and salt in the whole soil layer could be represented by those in the 0−20 cm layer. Thus, we recommend using the 0−20 soil layer to sample the distributions of the soil water and salt. Our results provide a theoretical basis for studying the interactive mechanisms associated with the distributions of soil water and salt, and for optimizing the sampling method in the study area.

The effects of soil freeze–thaw processes on water and salt migrations in the western Songnen Plain, China

Seasonally freeze-thaw (FT) processes affect soil salinisation in cold and arid regions. Therefore, understanding the mechanisms behind soil salinisation during winter and spring is crucial for management strategies effectively alleviating this. This study aimed to explore the soil FT characteristics and their influences on soil water and salt migrations to clarify the underlying mechanism of the springtime soil salinisation in the western Songnen Plain, China. The spatiotemporal distributions of soil water and salt, frozen depths and soil temperatures were examined at depths of 0–200 cm in three typical landscapes (farmland, Leymus chinensis (Trin.) Tzvel (LT) grassland and alkali-spot (AS) land) from October 2015 to June 2016. Results indicated that the strongest freezing process occurred in AS land, which was characterised by the deepest frost depth (165 cm) and highest freezing rate (3.58 cm/d), followed by LT grassland, and then farmland. The freeze-induced upward redistribution and enrichment of soil water and salt caused the rise and expansion of the soil salification layer, which was the main source of explosive accumulations of surface salt in springtime. Therefore, the FT processes contributed to the surface soil salinisation and alkalisation. Landscapes also affected soil water and salt migrations during FT processes, with the trend being AS land > LT grassland > farmland.

Understanding the Role of Shallow Groundwater in Improving Field Water Productivity in Arid Areas

Soil water and salt transport in soil profiles and capillary rise from shallow groundwater are significant seasonal responses that help determine irrigation schedules and agricultural development in arid areas. In this study the Agricultural Water Productivity Model for Shallow Groundwater (AWPM-SG) was modified by adding a soil salinity simulation to precisely describe the soil water and salt cycle, calculating capillary fluxes from shallow groundwater using readily available data, and simulating the effect of soil salinity on crop growth. The model combines an analytical solution of upward flux from groundwater using the Environmental Policy Integrated Climate (EPIC) crop growth model. The modified AWPM-SG was calibrated and validated with a maize field experiment run in 2016 in which predicted soil moisture, soil salinity, groundwater depth, and leaf area index were in agreement with the observations. To investigate the response of the model, various scenarios with varying groundwater depth and groundwater salinity were run. The inhibition of groundwater salinity on crop yield was slightly less than that on crop water use, while the water consumption of maize with a groundwater depth of 1 m is 3% less than that of 2 m, and the yield of maize with groundwater depth of 1 m is only 1% less than that of 2 m, under the groundwater salinity of 2.0 g/L. At the same groundwater depth, the higher the salinity, the greater the corn water productivity, and the smaller the corn irrigation water productivity. Consequently, using modified AWPM-SG in irrigation scheduling will be beneficial to save more water in areas with shallow groundwater.

Soil water and salt distribution characteristics with sand pipe

Purpose Hydraulic conductivity is very low in saline-sodic soil, which decreases water infiltration. For saline-sodic soil, increasing infiltration water has a special meaning. Increasing infiltration water not only increases the water in the soil profile but also decreases the salinity of the soil, thus making it suitable for growing crops. This study aims to examine the effect of sand pipes on soil water and salt distribution through laboratory tests with different depths and diameters of sand pipes. Design/methodology/approach The soil water and salt distribution responses to different sand pipe depths and diameters was investigated. Treatments included sand pipes with diameters of 4 cm, 5cm, 6 cm and the same depth of 4 cm; with depths of 2cm, 6 cm and the same diameter of 5 cm, and a control with no sand pipe (with the diameter of 0 cm and the depth of 0 cm). Findings The results suggested that the amount of cumulative infiltration water and transport distance of the wetting front could be increased by increasing the depth and diameter of sand pipes. The soil water content in the soil profile decreased under all treatments except for the control, whereas the value of EC increased with increasing distance from the film hole center. Positive relationships were also found among the sand pipe depth, diameter and the zone of low salt content. Furthermore, salt leaching depth increased with sand pipe depth and diameter. Overall, the treatments with and without sand pipes exhibited obvious differences. Originality/value The correlation analysis proved that increasing the infiltration area through sand pipes positively affected the amount of infiltration water, wetting scope and salt leaching depth.