Abstract: To establish a complex clean production model of seawater planting and raising in saline mudflat, it’s necessary to explore the conditions of cultivating economic crops under seawater irrigation. In this paper, a field plot experiment was conducted to study the coupling effects of seawater irrigation and nitrogen (urea N) fertilization on the yield, ion distribution, and total nitrogen content of grain amaranth in the coast of north Jiangsu Province. Under 20% seawater irrigation, the fresh mass and grain yield in treatment 120 kg N·hm^-2 increased significantly, compared with those in treatment 60 kg N·hm^-2, and the grain yield had no significant difference with that in treatment 180 kg N·hm^-2. Under 40% seawater irrigation, the grain yield in treatment 120 kg N·hm^-2 was the highest, but still significantly lower than that under 20% seawater irrigation and in treatment 120 kg N·hm^-2. Under freshwater irrigation, the grass yield was the highest in treatment 60 kg N·hm^-2, while the grain yield was the highest in treatment 180 kg N·hm^-2. Under 20% seawater irrigation and in treatment 120 kg N·hm^-2, the grain yield and grass yield were not significantly different from the highest values. With increasing N fertilization rate, the K⁺ content in stem and leaf increased, while the Na⁺ and Cl^- contents in root, stem, and leaf increased after an initial decrease. The K⁺/Na⁺ ratio in stem was increased with the increasing N fertilization up to 120 kg·hm^-2, but decreased when the N fertilization increased to 180 kg N·hm^-2. Under 20% seawater irrigation, the total N content in leaf was the highest in treatment 120 kg N·hm^-2; while under 40% seawater irrigation, nitrogen fertilization rate had less effect on the total N content in leaf. It was concluded that in the coastal beach of north Jiangsu, 20% seawater irrigation and 120 kg N·hm^-2 fertilization could significantly improve the salt tolerance of grain amaranth, and increase its economic yield.

Key words: Forage rye, Tillering dynamics, Accumulated temperature, Planting density, Equal design method