Improvements in Grain Yield and Nitrogen Use Efficiency of Summer Maize by Optimizing Tillage Practice and Nitrogen Application Rate

CORE IDEAS: Compared with no tillage and subsoiling, deep vertical rotary tillage significantly increased grain yield of densely planted summer maize. Compared with no tillage, subsoiling and deep vertical rotary tillage significantly increased N use efficiency of densely planted summer maize. The T × N interaction showed that the grain yield of T3–N225 was the highest; however, T3–N150 or T2–N225 has better N use efficiency In light of the economic benefits, the optimal cultivation practice was deep vertical rotary tillage with N rate of 225 kg ha–¹. Long periods of single tillage practice combined with excessive nitrogen (N) application are major factors restricting high yield and high efficiency production in the North China Plain. Field experiments were conducted by using a split‐plot design. Main plots included three different tillage practices: no tillage (T1), subsoiling tillage (T2), and deep vertical rotary tillage (T3). Subplots consisted of four different N application rates (N300: 300 kg ha⁻¹; N225: 225 kg ha⁻¹; N150: 150 kg ha⁻¹; N0: 0 kg ha⁻¹) with a plant density of 90,000 plants ha⁻¹. Under the same N rate, T3 increased grain yield by 19.1 and 13.4% compared with that of T1 and T2. Under the same tillage practice, grain yield decreased with the reduced N rate, but the difference between N225 and N300 was not significant in most cases. Nitrogen agronomic efficiency (AEN), N recovery efficiency (REN), and partial factor productivity of applied N (PFPN) of T3 and T2 were higher than that of T1. Compared with T1, T2 increased AEN, REN, and PFPN by 6.5, 139.2, 6.1%, respectively, and T3 increased AEN, REN, and PFPN by 36.2, 82.1, and 20.1%, respectively. Levels of AEN, REN, and PFPN reduced with increasing N application rate in 2016, but N225 has the highest AEN and REN in 2017. The T × N interaction showed that the grain yield of T3–N225 was the highest; however, T3–N150 (2016) and T2–N225 (2017) had the highest AEN and REN. In light of the economic benefit, the optimal management strategy was 225 kg N ha⁻¹ paired with deep vertical rotary tillage.