Abstract: Straw returning is an effective way to maintain and improve soil quality. To explore the effects of straw returning by wet harrow in autumn on soil enzyme activity, soil nutrient content and rice yield in southern Liaoning rice region, an experiment following randomized block design was conducted in Panjin City, Liaoning Province. There were two factors with two levels of each factor, namely, no straw returning (S₀), total straw returning (S₁), panicle fertilizer reduction of 16 kg·hm^-2 (N₁) and conventional panicle fertilizer dosage of 32 kg·hm^-2 (N₂). The results showed that straw returning to the fields by wet harrow in autumn significantly increased the activities of β glucosidase, urease and FDA hydrolase in the soil, and significantly decreased the activities of invertase. The activity of alkaline phosphatase was significantly decreased at tillering stage and heading stage by straw returning, but increased by 6.2%-13.5% at maturity stage compared with S₀N₂. Polyphenol oxidase activity was significantly decreased at tillering stage, but increased by 20.8%-26.7% and 22.3%-28.7% at heading and maturity stages compared with S₀N₂, respectively. Soil available potassium, organic carbon and total nitrogen contents at different growth stages of rice were significantly increased by returning straw with wet harrow in autumn, while soil nitrate content and soil pH at tillering stage and mature stage were significantly decreased by straw returning with wet harrow in autumn. The soil ammonium content at tillering stage of rice was significantly increased by 42.2%-41.0%, compared with that of S₀N₂. There was no significant difference in soil nitrate nitrogen, available phosphorus, available potassium and organic carbon contents between S₁N₁ and S₁N₂. Soil polyphenol oxidase activity was significantly positively correlated with soil organic carbon content, while alkaline phosphatase activity was significantly positively correlated with soil available phosphorus content. The activities of soil urease, FDA hydrolase and β glucosidase were significantly positively correlated with soil available potassium and total nitrogen contents. Soil invertase activity was significantly negatively correlated with soil ammonium nitrogen, nitrate nitrogen, available potassium, organic carbon and total nitrogen contents. There was no significant difference in rice yield among different treatments. In summary, straw returning to the fields by wet harrow combined with reduced application of panicle ferti-lizer in autumn can stabilize yield and maintain soil nutrient balance, promote soil nutrient supply and transformation, which has guiding significance for straw returning treatment in rice area of southern Liaoning.

Key words: returning by wet harrow in autumn, rice, straw, soil enzyme activity, soil nutrient.