Effects of biochar and conditioner on pioneer crops planted in coastal barren severe saline-alkali soil

Mechanisms that assist in reclaiming the coastal barren severe salt-affected soils in arid and semi-arid regions when treated with soil amendments have not been well characterized. Aiming at biological improvement, development, and utilization of barren severe saline-alkali soils, a field experiment was conducted to apply biochar and soil conditioner for pioneer crops planted in the coastal barren severe saline-alkali area of the North China Low Plain. Six treatments included single or combined application of two-level biochar rates (0 and 1.25 kg∙m⁻²) and three-level soil conditioner rates (0, 0.83, and 1.66 kg∙m⁻²) at the start of the experiment. Biochar significantly inhibited younger plant growth at the early stage of oil sunflower but had no marked impact on grown-up plants during the later stage, and grain quantity and yield. Meanwhile, biochar increased N and P contents in stems, leaves, and shells, the K content in stems, shells, and kernels of oil sunflowers, and promoted the transfer of K and Ca from leaves to kernels. However, biochar impeded Mg uptake and decreased the Mg content of stems and sunflower discs but had no significant effect on Na uptake by oil sunflowers. Soil conditioner significantly increased the growth of stems, leaves, and discs, and improved the grain yield. In addition, it promoted P transfer to the kernel. At an application rate of 1.66 kg∙m⁻², the soil conditioner promoted the transfer of N to the kernel preferentially and significantly improved the Ca content of stems, leaves, and discs, while increasing the Mg content of stems. Co-application of biochar and soil conditioner weakened the negative impact of biochar on plant growth, increasing uptake of N, P, K, and Ca, and facilitating transferring N, P, and K to the kernel, whereas reducing Na and Mg uptake for oil sunflower. Oil sunflowers, other than cotton, as a pioneer crop, are more suitable for planting in coastal barren, severely saline-alkali areas. The results from this preliminary study show that the co-application of biochar and soil conditioner provides an alternative method of waste recovery, converting straw resources into a value-added product, development, and bio-reclamation for coastal barren severely salt-affected soils, and the option of salt-tolerant pioneer crops that are adaptive to coastal areas.