Objective To solve the problems of poor soil structure and low nutrient content in some tobacco fields in Guangdong Province, the study was carried out to explore the effects of different amounts of seaweed residue on the physicochemical properties of tobacco planting soil and tobacco growth.

Method Through pot experiments, five treatments were set: CK: no fertilization; S1: conventional fertilization, without seaweed residue application; S2: conventional fertilization, applying seaweed residue accounting for 1% of soil weight; S3: conventional fertilization, applying seaweed residue accounting for 2.5% of soil weight; S4: conventional fertilization, applying seaweed residue accounting for 5% of soil weight.

Result The application of seaweed residue accounting for 5% of soil weight was beneficial to increase the proportion of 0.25-1 mm soil aggregates. The application of seaweed residue accounting for 2.5%-5% of soil weight was beneficial to improve soil pH value, increase the soil nutrition contents and the soil enzymatic activity. Compared with S1 treatment, the alkali-hydrolyzable nitrogen, available phosphorus, available potassium, exchangeable calcium, exchangeable magnesium and organic matter of soil increased 12.22%, 20.15%, 9.51%, 34.08%, 68.08% and 10.39% respectively, and the activities of sucrase, urease, phosphatase and catalase were significantly improved 30 days and 60 days after the application of seaweed residue. In addition, the application of 2.5%-5% seaweed residue was beneficial to promote tobacco growth, increase plant height, stem diameter and leaf number, and improve tobacco yield. Compared with S1, the fresh weight of upper leaves under treatments S2, S3 and S4 increased by 13.26%, 21.27% and 17.43%, respectively. The total fresh weight of S3 treatment was the largest, which was 12.48% higher than that of S1 treatment.

Conclusion The application of a certain amount of seaweed residue according to the weight ratio of soil was beneficial to improve the aggregate structure of tobacco planting red soil, increase the soil enzymatic activity, enhance the soil nutrient content, promote the growth of tobacco plants and increase the yield of tobacco leaves. The effect of application rate of seaweed residue accounting for 2.5% of soil weight was better.