Effects of different sand-cover thicknesses on crops in bare saline-alkali land in the Songnen Plain

The salinization of the Songnen Plain seriously restricts the sustainable development of farming and animal husbandry. Sand-covering and planting crops on the sand layer are effective methods to utilize salinized land. To study the effects of different sand-cover thicknesses on different crops, maize, sunflower, barley, and alfalfa were planted on bare saline-alkaline land with sand-cover thicknesses of 10, 20, 30, and 40 cm in the Songneng Plain. All four crops grew normally in the first year after sand-covering but grew weakly at the settlement stage. In the second year, all four crops grew powerfully. Sand-cover of over 20 cm significantly promoted maize growth. Maize yield was 4 298 kg·ha⁻¹ with sand-cover of 40 cm, which was 2.5 times higher than that with sand-cover of 10 cm (P < 0.05). The hay yield and total root biomass of alfalfa were the highest with sand-cover of 30 cm, and reached 8 597 and 3 367 kg·ha⁻¹, respectively; these were 3.36 and 1.28 times higher than those with sand-cover of 10 cm (both P < 0.05). The yields of sunflower and barley were highest with sand-cover of 40 cm; these were 33.4% and 269.5% higher than those with sand-cover of 10 cm, respectively. However, there were no significant differences among sand-cover thicknesses of 20 cm, 30 cm, and 40 cm. Therefore, maize should be planted with sand-cover of more than 20 cm, alfalfa with sand-cover of 30 cm, and sunflower and barley with sand-cover of 40 cm. The results show that these crops can be grown successfully by sand-covering in saline-alkali land.