**Roles of Nitrogen Deep Placement on Grain Yield, Nitrogen Use E**ffi**ciency, and Antioxidant Enzyme Activities in Mechanical Pot-Seedling Transplanting Rice**

**Lin Li 1,2, Zheng Zhang 1,2, Hua Tian 1,2, Zhaowen Mo 1,2, Umair Ashraf 1,3, Meiyang Duan 1,2, Zaiman Wang 4, Shuli Wang 1,2, Xiangru Tang 1,2,\* and Shenggang Pan 1,2,\***


Received: 2 August 2020; Accepted: 21 August 2020; Published: 25 August 2020

**Abstract:** Mechanical pot-seedling transplanting (PST) is an efficient transplanting method and deep nitrogen fertilization has the advantage of increasing nitrogen use efficiency. However, little information is available about the effect of PST when coupled with mechanized deep nitrogen (N) fertilization on grain yield, nitrogen use efficiency, and antioxidant enzyme activities in rice. A two-year field experiment was performed to evaluate the effect of PST coupled with deep N fertilization in both early seasons (March–July) of 2018 and 2019. All seedlings were transplanted by PST and three treatments were designed as follows. There was a mechanized deep placement of all fertilizer (MAF), broadcasting fertilizer (BF), no fertilizer (N0). MAF significantly increased grain yield by 52.7%. Total nitrogen accumulation (TNA) was enhanced by 27.7%, nitrogen partial factor productivity (NPFP) was enhanced by 51.4%. nitrogen recovery efficiency (NRE) by 123.7%, and nitrogen agronomic efficiency (NAE) was enhanced by 104.3%, compared with BF treatment. Moreover, MAF significantly improved peroxidase (POD), catalase (CAT), and notably reduced the malonic dialdehyde (MDA) content for both rice cultivars, compared to BF. Hence, the result shows that mechanical pot-seedling transplanting coupled with nitrogen deep placement is an efficient method with the increase of grain yield and nitrogen use efficiency in rice cultivation in South China.

**Keywords:** deep N fertilization; peroxidase activity; catalase activity; rice cultivation
