Optimization of Topdressing for Winter Wheat by Accurate Growth Monitoring and Improved Production Estimation

Topdressing accounts for approximately 40% of the total nitrogen (N) application of winter wheat on the Huang-Huai-Hai Plain in China. However, N use efficiency of topdressing is low due to the inadaptable topdressing method used by local farmers. To improve the N use efficiency of winter wheat, an optimization method for topdressing (T_HP) is proposed that uses unmanned aerial vehicle (UAV)-based remote sensing to accurately acquire the growth status and an improved model for growth potential estimation and optimization of N fertilizer amount for topdressing (NFT). The method was validated and compared with three other methods by a field experiment: the conventional local farmer’s method (T_LF), a nitrogen fertilization optimization algorithm (NFOA) proposed by Raun and Lukina (T_RL) and a simplification introduced by Li and Zhang (T_LZ). It shows that when insufficient basal fertilizer was provided, the proposed method provided as much NFT as the T_LF method, i.e., 25.05% or 11.88% more than the T_RL and T_LZ methods and increased the yields by 4.62% or 2.27%, respectively; and when sufficient basal fertilizer was provided, the T_HP method followed the T_RL and T_LZ methods to reduce NFT but maintained as much yield as the T_LF method with a decrease of NFT by 4.20%. The results prove that T_HP could enhance crop production under insufficient N preceding conditions by prescribing more fertilizer and increase nitrogen use efficiency (NUE) by lowering the fertilizer amount when enough basal fertilizer is provided.