The Development and Utilization of Saline–Alkali Land in Western Jilin Province Promoted the Sequestration of Organic Carbon Fractions in Soil Aggregates

Soil samples from T (0~20 cm) and S (20~40 cm) layers of four saline–alkali rice fields (R5, R15, R20, and R35) with different reclamation years were selected to study the distribution of soil aggregates and the contents of readily oxidizable organic carbon (ROC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), potentially mineralizable carbon (PMC), and soil organic carbon (SOC). The effects of large macroaggregate (>2 mm, LMA), small macroaggregate (0.25 to 2 mm, SMA), and microaggregate (<0.25 mm, MA) particle size, soil layer, and soil physicochemical properties on SOC fractions were also analyzed. The results showed that the LMA size in saline–alkali paddy fields were easily decomposed and was unstable due to the influence of the external environment. With the increase in reclamation years, the proportion of LMA in the S layer decreased gradually. The ROC, DOC, MBC and TOC contents of aggregates in the T and S layers gradually increased with the increase in reclamation years, and SOC fractions contents of aggregates in different grain sizes were SMA > LMA > MA. An effective way to increase carbon sink and improve the ecological environment in western Jilin Province is to change the soil environment by planting rice in saline–alkali land.

A Study on the Durability of Dispersive Soils Improved by Alum in Western Jilin Province of China

Dispersive soil, which has the characteristics of low erosion resistance and high dispersibility in water, is the main reason for the channel slope failure that happened in the planning area of the Western Alkaline Treatment project in Jilin Province. Therefore, the study focused on the improvement of dispersive soil. In this research, pinhole test and crumb test were conducted on the soil under varying percentages of alum (1%, 1.5%, 2%, 2.5%, and 3%). Results indicated that alum can reduce the dispersivity of soil distinctly, and the optimal content of alum was 2.5%. This research also investigated the durability of 2.5%-alum-improved dispersive soil for dispersibility under the condition of freeze-thaw cycle. The soil samples with 2.5% alum content were subjected to pinhole test, crumb test, double hydrometer test, and percentage of exchangeable sodium ion test under the different number of freeze-thaw cycles. The results showed that the 2.5%-alum-improved soil was unaffected by the number of freeze-thaw cycles, which illustrated that alum can be used to improve soil dispersivity in engineering practice.

Electrical Conductivity Inversion Method of Saline Soil based on Sentinel-2 MSI data

Electrical conductivity (EC) is not only an important index to evaluate the degree of soil salinization, but also an essential basis for judging whether saline soil can be improved and assess the effect of improvement efforts. Satellite remote sensing provides much information for large scale EC inversion of saline soil, which enables the possibility for evaluating the degree and distribution of soil salinization. Taking the salinized region of western Jilin Province as the study area, 328 salinized soil samples were collected, and the EC was measured in June 2019. The construction of the optimal spectral parameters was based on the correlation between the conductivity and the spectral reflectivity of Sentinel-2 MSI data; after satisfying the normal distribution for the Box-Cox transformation of EC, the inversion model of EC was established by using linear regression model, support vector machine (SVM), regression tree (RT), Gaussian process regression (GPR), and ensemble tree (ET). The verification results of the model on the validation set showed that the performance of GPR was optimal (R2 = 0.66, RMSE = 0.48 mS/cm, MAE=0.52 mS/cm), which increased R2 by 29.04% compared with the traditional linear regression model. Finally, according to the GPR model, the EC results of pixel-level resolution (10 m × 10 m) of saline soil in western Jilin Province were inversed, which provided a scientific basis for the study of the distribution characteristics and improvement scheme of saline soil.

Cu and Na contents regulate N uptake of Leymus chinensis growing in soda saline-alkali soil

Leymus chinensis (L. chinensis) is the dominant plant in the eastern margins of the Eurasian temperate grasslands. It is a very robust species, exhibiting good saline-alkali resistance and stabilizing soil. In this study, 67 soil samples and L. chinensis were collected in western Jilin province, China. The contents of N, P, K, S, Mn, Fe, Zn, Cu and Na were measured, revealing that the growth of L. chinensis was mainly restricted by N based on the stoichiometric N: P ratios of plant. Furthermore, path analysis indicated that N was significantly correlated with K, S, Cu, and Zn. Imbalances in the homeostasis of these four elements may thus constrain N. The homeostasis index of Cu (HCu) in sites with 100%-70% of vegetation cover was only 0.79, it was classified as a sensitive element. However, K, S and Zn, whose concentrations in L. chinensis were significantly related to those of N, exhibited no homeostatic characteristics. These results suggest that when seeking to treat saline-alkali stress, it is important to add fertilizers containing K, S, and Zn to avoid growth limitation. Na+, an ion associated with high soil alkalinity, exhibited weak homeostasis in L. chinensis even in sites with only 40%-10% of vegetation cover. When soil Na exceeded 16000 mg/kg, the homeostasis mechanism of L. chinensis appeared to be overwhelmed, resulting in rapid and probably harmful accumulation of Na. Proper control of N content can alleviate the toxicity of Na stress in L. chinensis and enhance its Na tolerance. Together, these results suggest that combined fertilization with N, K, S, Zn and Cu should be applied to improve grasslands growth. The results of this study can provide a reference basis for sustainable grassland management.