Impact of alternate irrigation with reclaimed water and saline water according to sunflower growth period on plant and grain development

Abstract

To address the issue of freshwater scarcity for agricultural irrigation in arid and semi-arid regions, saline water and reclaimed water have great potential as alternative irrigation water. Therefore, a three-year field study was conducted in the Yinbei Irrigation District of Ningxia, China, to investigate the effects of alternate drip irrigation using freshwater (F), saline water (S) and reclaimed water (R) on sunflower growth. The study established six alternate drip irrigation schedules (SSR, SRS, RSS, SRR, RSR, RRS) and three continuous drip irrigation modes (FFF, SSS, RRR) based on the key sunflower growth stages: emergence-budding, budding-flowering, and flowering-maturity. The results revealed that during the emergence-budding stage and budding-flowering stage, saline water irrigation favored the allocation of dry matter to the roots, whereas reclaimed water irrigation was more effective in allocating dry matter to the leaves and faceplate, and significantly promoted nitrogen and phosphorus accumulation in sunflower plants. Furthermore, reclaimed water irrigation dramatically increased the crude protein content (12.6 %-15.4 %), unsaturated fatty acid content, and saturated fatty acid content in sunflower grains. During the flowering-maturity stage, reclaimed water irrigation was more conducive to dry matter accumulation in the plant, biomass allocation to the faceplate and grains, and resulted in an increase in sunflower grain yield by 2.1 %-5.0 %. Additionally, reclaimed water irrigation during the flowering-maturity stage significantly promoted radial development of the sunflower faceplate and markedly increased the linoleic acid and palmitic acid contents in the kernels, compared to saline water irrigation. The optimal irrigation schedule for sunflower cultivation in arid and semi-arid agricultural areas of China was suggested to be alternate irrigation with saline water during the emergence-budding stage and reclaimed water during the budding-flowering stage and flowering-maturity stage.