This study aimed to investigate the regulatory mechanisms of different interlayer materials on water infiltration, evaporation, and water-salt distribution in saline-alkali soil, providing a theoretical basis for amelioration of saline-alkali soil.

A typical saline-alkali soil from Wuyuan, Inner Mongolia, was selected for laboratory soil column simulation experiments. Four treatments were established: CK (no interlayer), JG (straw interlayer), SC (mixed sand layer), and JS (combined mixed sand and straw interlayer), and the effects of composite and single interlayers on soil water infiltration processes, evaporation processes and salt variation patterns were investigated.

When the wetting front moved to 40 cm, the interlayer treatment was 3.5%-10.6% longer than that under CK treatment, and 13.8%-55.2% longer than that under CK treatment when passing through the interlayer. The time of wetting front reaching the bottom of 100 cm under JG treatment was delayed by 780, 540, 120 min compared with CK, SC and JS treatment, respectively. After infiltration, the average soil water content under JG, SC and JS treatments in 0-40 cm soil layer was 22.9%, 18.7% and 21.9% higher than that under CK treatment, respectively. The soil salt content in the 0-40 cm soil layer was 18.6%-29.6% lower than that under CK treatment. The desalination rate under JS treatment in 40-70 cm soil layer was the highest, which was 49.4% lower than that under CK treatment. The salt content under each interlayer treatment in 70-100 cm soil layer was lower than that under CK treatment, and the decrease under JS treatment was the largest. During the continuous 45 d evaporation process, the interlayer significantly inhibited cumulative evaporation. The evaporation under CK treatment was 572 mm, and the evaporation under JG, SC and JS treatments decreased to 194, 235 and 205 mm, respectively, which was 66.1%, 58.9% and 64.2% lower than that under CK treatment, respectively. During the continuous evaporation process of 45 days, the water content of 0-100 cm profile of each treatment decreased with depth. In the 0-40 cm soil layer, the water content under CK treatment continued to decrease with the prolongation of evaporation time, and on the 15th, 30th and 45th days, the water content was 23.4%, 21.0% and 21.6%, respectively. The water content under JG, SC and JS treatments decreased by 14.6%-33.8%, 11.2%-17.0% and 14.9%-30.3% compared with CK treatment, respectively. The decrease of water content under JG and JS treatments was significantly greater than that under SC treatment. In the 45-60 cm soil layer, the water content under the interlayer treatment was higher than that under the CK treatment, and on the 15th day, the JG, SC and JS treatments increased by 4.8%, 3.7% and 5.4%, respectively. During the evaporation process, the salt content in the 0-100 cm profile of each treatment showed a 'low-high' distribution. In the 0-40 cm soil layer, the average soil salt content under JG, SC, and JS treatments was 35.0%-70.3%, 19.1%-51.4%, and 32.8%-62.7% lower than that under CK, respectively. In the 40-70 cm soil layer, the salt content of each treatment increased first and then decreased, and the JG, SC and JS treatments increased by 10.6%-14.4% compared with CK treatment. In the 70-100 cm soil layer, the average soil salt content under JG, SC and JS treatments was 8.4%-28.3% lower than that under CK treatment.

In summary, laying interlayers in saline-alkali soil could effectively regulate the distribution of water and salt. The effects of mixed sand layer and straw combined interlayer on inhibiting phreatic evaporation and salt return were better than that of single interlayer.

This study was conducted to explore the responses of saline-alkali soil respiration to straw interlayer and irrigation regime, and to clarify the relationships between soil respiration rate and soil temperature/water content in Hetao Irrigation District.

A randomized block design was set up in 2015 with three treatments: autumn and spring irrigation (I_SA), spring irrigation without autumn irrigation (I_S), and spring irrigation plus straw interlayer without autumn irrigation (SI_S). Soil respiration, soil temperature and moisture content were measured in 2017 and 2018, and the temperature sensitivity of soil respiration rate was also estimated.

(1) Soil temperature and soil moisture content in the 0-20 cm soil layer fluctuated obviously, while it was relatively stable in the 20-40 cm soil layer. SI_S increased the soil temperature in 0-40 cm soil depth and moisture content in 20-40 cm soil depth. (2) The soil respiration rate in 2017 was higher than that in 2018. It was the highest in the flowering stage, followed by budding stage, before spring irrigation, before sowing, and harvest stage. (3) The soil respiration rates of I_S and SI_S were significantly higher than I_SA at the flowering stage (P<0.05). Compared with I_SA, I_S and SI_S increased soil respiration rate by 0.12-0.44 and 0.06-0.42 μmol·m^-2·s^-1, respectively. Compared with the I_S, the soil respiration rate of SI_S decreased by 0.01-0.49 μmol·m^-2·s^-1. These results indicated that the soil respiration rate was increased without autumn irrigation, while it was decreased with straw interlayer. (4) The soil respiration rate positively correlated with soil temperature (P<0.01), while it had no significant correlation with soil moisture content. Soil temperature at the 0-20 and 20-40 cm soil layer explained 40.74%-53.84% and 39.27%-53.46% variation of soil respiration rate, respectively. (5) The temperature sensitivity of soil respiration (Q₁₀) varied within 1.68-1.98 for different treatments, and the Q₁₀ of the 20-40 cm soil depth was higher than that of the 0-20 cm soil depth. Compared with I_SA, I_S and SI_S reduced Q₁₀. However, SI_S increased Q₁₀ compared with I_S.

Overall, the straw interlayer increased the soil temperature in 0-40 cm soil depth and moisture content in 20-40 cm soil depth, reduced soil respiration rate, and increased the temperature sensitivity of soil respiration, which was used as an effective practice for water saving and emission reduction in the Hetao Irrigation District.