Soil salinity distribution based on remote sensing and its effect on crop growth in Hetao Irrigation District

Abstract: Soil salinity analysis on a regional scale is of great significance for protecting agriculture production and maintaining eco-environmental health in arid and semi-arid irrigated areas. In this study, we explored the soil salinity distribution and its effect on crop growth in Hetal Irrigation Dsitrict based on field investigation and remote sensing inversion. The Hetao Irrigation District (Hetao) in Inner Mongolia Autonomous Region suffered long-term soil salinization problem. Field sampling experiments and investigations related to soil salinity, crop growth and yields were carried out at 281 different sampling points across the whole area during April to August in 2015. Spatial-temporal soil salinity characteristics were systematically analyzed as well as the corresponding impacts on crops. The remote sensing inversed soil salinity model had the accuracy of the determination coefficient of 0.75 (P<0.01) and the root mean square error of 0.10% at the validation process. The relationships between soil salinity and crops and groundwater depth were investigated. The results showed that the surface soil (0-10 cm) and the root zone soil (0-100 cm) had the mean of soil salinity 0.12%-0.20% and the mean of soil salinity was all below 0.40%. The salinity could be lower than 0.10% in some regions. The uncultivated land was mainly sever salinized. The soil salinity of the uncultivated land averaged 1.15% at 0-10 cm and 1.60% at 0-100 cm. The soil salinity had a good relationship with the total amount of irrigated water, the conditions of drainage system, and the groundwater depth. Mild salinization with the soil salinity less than 0.20% for all the investigated soil was founded when the depth of groundwater depth was about 2.0 m. Remotely sensed map of soil salinity distribution for surface soil was derived based on the Landsat OLI data with a 30 m resolution and showed that the spatial distribution of soil salinity based on remote sensing was consistent with the sample analysis, and the correlation coefficient was 0.87. Over 14% of the land with its salinization exceeded the level of heavy salinized soil in Hetao Irrigation District, and about 86% of the total area was nonsalinized or mildly salinized soil. Crops such as corn, wheat, fruits and vegetables were planted in the area with low salinity while sunflower was widely planted in the area with severe salinized soil or saline soil, and the leaf area index decreased with the increasing of soil salinity. Based on the investigation results, the corn field was classified into high level (yield>12 000 kg/hm2) and low level (yield <12 000 kg/hm2) and the sunflower field was high (yield>3 000 kg/hm2) and low level (yield<3 000 kg/hm2). The high yield level had relatively lower soil salinity than the field with low yield. So it is very important to minimize the salinity of root zone for sunflowers at the stage of filling period, especially for the lower reach of the Hetao. In addition, the strong spatial variability of salinization was clearly presented by the map of soil salinity. Overall, this paper can provide very useful information for salinization control and guidelines for agricultural production and soil-water management in Hetao.