Using In-Season Nitrogen Management and Wheat Cultivars to Improve Nitrogen Use Efficiency

The development of more efficient N management strategies and more N-efficient plants is crucial to achieving maximum grain yield with minimum N fertilizer inputs. An on-farm study was conducted during 3 yr (one site per year) with six N levels and two soft wheat (Triticum aestivum L.) cultivars: an N-efficient cultivar (KN) and a major commercial cultivar (LM). The goal was to evaluate the potential to improve grain yield and N use efficiency (NUE) and to determine the optimal N management strategy for the two cultivars in the North China Plain. Optimal N fertilizer rates (ONR) were determined for an in-season N management strategy by estimating soil NO3-N content in the root zone from a target N value at two wheat growth periods. Compared with farmers' practices, the ONR reduced N fertilizer by 68%, from 369 to 117 kg N ha(-1), without any yield losses while decreasing N losses from 123 to 30 kg N ha(-1) across all wheat cultivars and years. Grain yield with ONR treatment increased from 5.5 to 6.4 Mg ha(-1) and improved agronomic N efficiency from 12 to 16 kg kg(-1), N partial factor productivity from 50 to 61 kg kg(-1), and physiological N efficiency from 21 to 37 kg kg(-1) for KN compared with LM. More efficient N use, low N demand, and high growth and N uptake postanthesis contributed to high grain yields and high NUE for KN. Changes in N management may not be necessary during early growth for all wheat cultivars, but more N must be available at later growth stages to achieve maximum grain yield for KN, given its high growth and N uptake postanthesis.