Soil salinity variations and cotton growth under long-term mulched drip irrigation in saline-alkali land of arid oasis

The sustainable development and utilization of saline-alkali land are closely related to holding fast the minimum cultivated land area of China. The change of soil salt in cotton field under long-term mulched drip irrigation (MDI) is connected with the development of the national cotton industry. From 2015 to 2019, five cotton fields with different applying years of MDI, which were reclaimed in 2004, 2008, 2010, 2012 and 2015 respectively and were saline-alkali wasteland before, were monitored continuously in the Manas River irrigation area of Xinjiang. By means of continuous location monitoring and spatial–temporal variability (For example, the monitoring data of cotton fields under MDI in 2004, 2008, 2010, 2012 and 2015, and in the year of 2015 were counted as 12, 8, 6, 4 and 1 years, respectively), the spatial–temporal variations of soil salt and ions in cotton field with 1-16a MDI technology were presented. The cotton growth characteristics and its main influencing factors were also analyzed in the study. The results showed that saline-alkali cotton field experienced changed from intensive saline soil to moderate saline soil and finally to non-saline soil under long-term MDI. The change of soil salt and the response of cotton growth to soil salt were divided into three typical stages. Firstly, soil desalinated rapidly in 1-4a MDI cotton field, which the annual average desalination rate was 24.93% in 0–100 cm soil layer (root zone). Additionally, the survival rate of cotton rocketed from 1.48% to 42.04%, and yield increased sharply from 72.43 kg ha−1 to 3075.90 kg ha−1. Soil desalination was lower in 5-11a MDI cotton field, which the annual average desalination rate was 10.92% at the root zone. The annual survival rate and yield of cotton increased by 6.26% and 5.18%, respectively. After 12a MDI, the soil salt in cotton field tended to be generally constant, which the average salt content in root zone was less than 2.49 g kg−1. The survival rate of cotton was stable above 90.39%, and the yield per unit area exceeded 5401.32 kg ha−1. Ions, sodium absorption ratio and Cl− and SO42− equivalent ratio (CSER) in cotton soil also decreased with the extension of MDI. Salt composition changed year by year, but the type of intensive saline soil had always been chloride-sulphate solonchak (0.2 < CSER < 1). In practice, with a higher irrigation quota and ideal irrigation water quality, the soil salt environment of saline-alkali soil MDI cotton field had developed in favor of cotton growth in an oasis irrigation area. However, this management practice caused between 124.21–143.61 mm of water resources waste. Therefore, we should further enhanced the consciousness of water-saving and implemented quota management in practice.

On the importance of monsoon rainstorm impact period in soil salinization

Long-term soil salt accumulation could lead to salinization. Aimed to prevent soil salinization, we investigated soil salt dynamics, its interface with the groundwater table, rainfalls duration and the impact periods when salt is mostly accumulated. Total soil salt accumulation and dynamic distribution were monitored in the 0–80 cm layer in alluvial farmland from 2018 to 2020. We found soil salt contents increased by 0.15 g kg–1 and 0.07 g kg–1 in the 0–40 and 40–80 cm soil layers, respectively, which indicated that soil salinization occurred. We defined the rainstorm impact period (RIP) as period when soil salt dynamic distribution was affected by rainstorm event. The salinity time-trend during RIP was sequentially characterized by a first salt leaching, followed by a rapid and then slow salt accumulation, which took the first 4 days, from day 4 to 10, and then beyond, respectively. In the first leaching stage, salt migration content was determined by rainfall (P < 0.05) which could leach 41.5% of salt on average in the whole soil layer. In the rapid accumulation stage, lots of salt accumulated due to high evapotranspiration and shallow groundwater table. In the slow accumulation stage, salt accumulation rate was inhibited by deeper groundwater table. In addition, the total accumulated soil salt in the whole soil layer increased by 0.14 g kg–1 in the RIPs, which comprised only 14.5% of the overall study period, but the value accounted for 63.6% of the salt accumulation, thereby indicating that RIPs were the main periods when salt accumulated during the soil salinization process. Our results provided insights into soil salt dynamic distribution during RIPs, thereby facilitating the effective prevention and control of soil salinization.

Effect of Periodic Winter Irrigation on Salt Distribution Characteristics and Cotton Yield in Drip Irrigation under Plastic Film in Xinjiang

Winter irrigation is an effective means of salt leaching, but the long-term effect on salinity is unclear. In 2008–2019, three different soil types of farmlands were selected as the study area by drip irrigation under film mulch combined with periodic winter irrigation in the non-growth period. The salinity of 0–150 cm as well as the survival rate and yield of cotton in the non-growth and growth periods were monitored, respectively. The mass fraction of soil salt decreased rapidly under winter irrigation, and then, the salt content in each observation layer increased with years of cultivation. After 10 years of application, the soil salt content basically stabilized at a low level. In 2008, the salinity of the 0–150 cm observation layer of loamy clay, loam, and sandy loam varied within 6–60, 10–65, and 4–22 g·kg−1; after four winter irrigations in 2019, corresponding values dropped below 5.74, 3, and 4.76 g·kg−1, respectively. The salinity returns rate of the different observation layers all exceeded 40%. The desalination rate of the different soils after four winter irrigations all exceeded 63.52%. Cotton survival rate and yield in different soils were directly proportional to each other. After the second winter irrigation, the survival rates on the different soils all exceeded 60%. The results of this study can provide technical support for the sustainable development of different types of soil, farmers’ income increase, and salinization land improvement.

Characteristics of soil salt crust formed by mixing calcium chloride with sodium sulfate and the possibility of inhibiting wind-sand flow

Soil salt crust can change the structure of aeolian soil and improve its resistance to wind erosion. Four ions (Na+, Ca2+, Cl−, and SO42−) with high contents in aeolian soil were selected for a salt crust experiment. The experiment set a variety of gradients of soil salt contents and salt mixing ratios of Na2SO4 and CaCl2. The physical properties of the salt crust were tested, and the wind erosion resistance of the salt crust was discussed. The results showed that the soil salt contents and salt mixing ratio influenced the resistance of the salt crust, especially in terms of its compressive strength and toughness. The former affected the compressive strength of the salt crust by changing the amount of cemented soil salt. The latter affected the kinds of crystals by changing the ion ratio, thus changing the structure of the salt crust and affecting its wind erosion resistance. The wind erosion resistance of the salt crust is complicated by the interaction between the soil salt content and salt mixing ratio. A multilayer crust can be formed in mixed salt, which has a strong wind erosion resistance. This result provides new findings on flowing sand soil and a new method for the treatment of flowing sand soil.

Suaeda salsa/Zea mays L. intercropping in saline soil on plant growth and rhizospheric physiological processes

Background and aims Halophytes possess the capacity to uptake high levels of salt through physiological processes and their root architecture. Here, we investigated whether halophyte/non-halophyte intercropping in saline soil decreases the soil salt content and contains root-dialogue. Methods Field and pot experiments were conducted to determine the plant biomasses and salt and nutrient distributions in three suaeda (Suaeda salsa) / maize (Zea mays L.) intercropping systems. The three treatments were set up by non-barrier, nylon barrier and plastic barrier between plant roots. Results The biomass of the non-barrier-treated maize was significantly lower than that of the nylon barrier-treated maize, whereas the suaeda root biomass showed a limited increase. The soil salt content negatively affected the non-barrier group’s roots compared with those in the nylon and plastic barrier-treated groups, and it was also higher on the maize side of the nylon-barrier treatment. There were higher available nitrogen and phosphorus contents in the soil of the non-barrier- and nylon barrier-treated groups compared with the plastic barrier-treated group. In addition, the pH was lower, and the available potassium content was higher, which suggested that rhizospheric processes occurred between the two species. Conclusions The suaeda/maize intercropping would decrease the soil salt content, and they also revealed potential rhizospheric effects though the role of root, which provides an effective way for the improvement of saline-alkali land.