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Establishing methods for scientific and rational use of brackish water resources is the key to farmland irrigation in the Yellow River Delta region of China. In this study, we conducted laboratory simulation experiments with soil columns and monitored the changes in water infiltration and salt distribution under eight irrigation treatments, including four intervals (0, 30, 60, and 90 min between irrigations) and two sequences (brackish-brackish-fresh water and brackish-fresh-brackish water). The results showed that the duration of water infiltration into the soil was higher under intermittent irrigation than continuous irrigation, with the highest value recorded at the 90-min irrigation interval. There was no significant difference in the mean soil water content between the brackish-brackish-fresh water (28.01–29.71%) and brackish-fresh-brackish water (28.85–29.98%) irrigation treatments. However, the mean soil desalination rate of the brackish-brackish-fresh irrigation treatment (42.51–46.83%) was higher than that of the brackish-fresh-brackish irrigation treatment (39.48–46.47%), and a much higher soil desalination rate was observed at the 90-min irrigation interval, compared with the other intervals. In conclusion, brackish-brackish-fresh water irrigation at longer time intervals (e.g., 90 min between irrigations) is conducive to reduce soil salt content in the surface soil in the study region.

During field application of biochar, the bulk density of tilled soil initially decreases and then increases over time, until reaching the initial level of compacted soil. This study evaluated the optimal biochar particle size for promotion of water infiltration and retention in a saline soil with various bulk densities after application. Corn straw biochar, pyrolyzed at 450 °C for 0.5 h, was prepared in different particle sizes (S1 ≤ 0.25 mm, S2 = 0.25–1 mm, and S3 = 1–2 mm) and separately mixed into the 0–30 cm soil layer at two rates (R1 = 10 g kg−1 and R2 = 100 g kg−1), with tilled (D1 = 1.1–1.43 g cm−3) and compacted (D2 = 1.45 g cm−3) bulk densities. Five models were applied to simulate water infiltration into biochar-amended soils. Compared with the non-biochar control, the S1 treatment increased cumulative water infiltration by 41% (bulk density = 1.26 g cm−3) to 11% (bulk density = 1.45 g cm−3). However, the effect of the S3 treatment on cumulative water infiltration shifted from positive (+19.3%) to negative (–22.4%) with increasing bulk density. The S2 treatment resulted in the highest water retention at the tilled bulk density, whereas a significant increase (12.7%) in water retention was observed in the S1 treatment at the compacted bulk density. The Kostiakov–Lewis, Kostiakov, and United States Department of Agriculture – Natural Resources Conservation Service models performed better than the Philip and Horton models to describe the relationship between cumulative water infiltration and infiltration time, except for the D2R2S1 treatment. This study provides evidence for amelioration of saline soil by straw biochar in the Yellow River Delta.