Saline soils are of great concern globally. Selecting the Yellow River Delta as a model site, the influence of reclamation on soil salinity and saline soil quality was investigated. Soil quality index (SQI) was applied to statistically analyze 210 soil profile samples collected at seven depth layers in 30 sampling sites among native saline soils and three croplands (peanut, cotton, and wheat) in May 2020. After reclamation, the soil salt content (SSC) reduced from 4.52 g/kg to 1.44 g/kg after reclamation, with the degree of soil salinity reducing from severe to slight. The nitrate nitrogen (NO₃⁻-N) contents of peanut, cotton, and wheat croplands were 1.90, 2.02, and 4.29 times higher and the available phosphorus (AP) contents were 5.43, 3.57, and 8.77 mg/kg higher than that of the saline soils, respectively, while the soil ammonium nitrogen (NH₄⁺-N) and available potassium (AK) contents were decreased. The NO₃⁻-N, AN, and AP contents of the three croplands showed a significant surface aggregation at depth of 0–30 cm. SQI increased by 0.10, 0.09, and 0.02 after the reclamation with the enhancement effect of wheat and cotton was more pronounced. It was discovered that reclamation notably improved the soil quality as a result of crop growth and field management of fertilization and irrigation.

It is important to strengthen the studies on the response of soil respiration components to tillage practices and natural precipitation in cropland. Therefore, soil heterotrophic respiration (R_H) and autotrophic (R_A) respiration were monitored by a root exclusion method in the North China Plain (NCP). The tillage practices included no-tillage (NT) and conventional tillage (CT), and the study periods were the summer maize growth stages in 2018 and 2019. R_H, R_A, soil water content and temperature were measured continuously for 113 days by an automatic sampling and analysis system. The soil R_H values on bright days and rain-affected days were higher under NT in 2018 (14.22 and 15.06 g CO₂ m⁻² d⁻¹, respectively) than in 2019 (8.25 and 13.30 g CO₂ m⁻² d⁻¹, respectively). However, the R_A values on bright days and rain-affected days were lower under NT in 2018 (4.74 and 4.97 g CO₂ m⁻² d⁻¹, respectively) than in 2019 (5.67 and 6.93 g CO₂ m⁻² d⁻¹, respectively). Moreover, NT decreased R_H but increased R_A compared to CT in 2019. Compared to bright days, the largest increase in both R_H and R_A after rain pulses was under CT in 2019 (6.75 and 1.80 g CO₂ m⁻² d⁻¹, respectively). Soil water content and soil temperature were higher in 2018 than in 2019. Moreover, NT increased soil water content and decreased soil temperature on bright days compared to CT in 2019. Furthermore, soil temperature accounted for more variations in R_H on bright days and rain-affected days, but soil water content had a greater influence on R_A on bright days. However, after precipitation, higher soil water content decreased R_A under NT in 2018, while soil water content was positively related to R_A under CT in 2019. This study determined the differential response of R_H and R_A to tillage practices and natural precipitation pulses, and we confirmed that excessively dry soil increases soil carbon loss after rain events in the NCP.

The depth of shallow groundwater significantly influences crop growth and yield by altering the physicochemical properties of farmland soil profiles. Concurrently, shallow groundwater is subject to various changes, and it remains unclear how alterations in shallow groundwater depth within field soil impact soil physicochemical properties, crop yields, and the overall dynamics of groundwater transformations. To address these uncertainties, this study utilized a sample plot equipped with a volume lysimeter and implemented four distinct groundwater depths as treatment conditions: G0 (no groundwater depth), G1 (a groundwater depth of 40 cm), G2 (a groundwater depth of 70 cm), G3 (a groundwater depth of 110 cm), and G4 (a groundwater depth of 150 cm). This study was carried out on a weekly basis to monitor fluctuations in ion content in shallow groundwater and soil moisture after the summer maize harvest, and special attention was afforded to non-irrigation conditions. This study also scrutinized the distribution of salt and nutrients in soil profiles and assessed changes in summer maize yield. Very interesting findings were obtained by conducting the study. Firstly, the shallower the groundwater depth, the higher the water and salt content of the soil surface. Small, frequent rainfall events (precipitation ≤ 25 mm) facilitated the effective removal of salt from the soil surface. Despite increased rainfall contributing to salt ion dilution in groundwater, the risk of soil surface salinization increased at the surface level. Secondly, a linear relationship existed between groundwater depth and surface soil moisture and salt content. With every 10 cm increase in groundwater depth, the surface soil moisture and salt content decreased by 0.56% and 0.06 g/kg, respectively. Soil nutrients tended to accumulate in the surface layer, with nutrient content increasing with depth. However, C/N was not notably affected by groundwater depth. Thirdly, Na⁺ and K⁺ consistently dominated the soil surface. As soil salinity increased, the prevalence of Cl⁻ and SO₄²⁻ increased, with the rate of SO₄²⁻ increase surpassing that of chlorine. HCO₃⁻ altered by rainfall served as an indicator of soil alkalization characteristics, while Na⁺ and K⁺ in soil, along with Cl⁻ and SO₄²⁻ derived from groundwater, represented soil salt composition and salinization trends. Ultimately, under the conditions of this study, the most favorable groundwater depth for the growth of summer maize was determined to be 1.1 m. Analyzing the impact of different shallow groundwater depths on the physicochemical properties of farmland soil enhances our understanding of the mechanisms of interaction between groundwater and soil in agricultural ecosystems. This knowledge is instrumental in significantly improving the soil environment, thereby ensuring optimal crop yields.