Diagnosis of nitrogen nutrition of winter wheat and summer corn using images from digital camera equipped on unmanned aerial vehicle

The large number of population and scarce land resources require crop yield per unit area to be increased greatly to ensure the food supplies and food security in China. To meet this requirement, chemical fertilizer application is an important and simple measure. Consequently, the agricultural non-point pollution caused by chemical fertilizer is becoming more and more serious. Precision fertilization is one of the important technologies to control agricultural non-point source pollution, while soil nutrient testing and crop nutrition diagnosis are indispensable works of precision fertilization. With the increasing of agriculture scale management, it is urgent to develop fast, economic and nondestructive techniques of the nitrogen nutrition diagnosis of crops. In this study, in the light of related researches of diagnosis of nitrogen nutrition in winter wheat and summer corn using digital photographs, cost-effective unmanned aerial vehicle (UAV) system was introduced and digital camera mounted on its platform was used to obtain the canopy photographs of crops. To determine the appropriate aerial heights and sensitive color parameters of aerial photographs for the diagnosis of nitrogen nutrition of winter wheat and summer corn, the relationships between a variety of color parameters retrieved from the aerial photographs obtained at different heights and the status of nitrogen nutrition of winter wheat and summer corn measured in situ in 2015 were analyzed. It was indicated that VARI (visible atmospherically resistant index based on digital photography) and B/(R+G+B) were the most sensitive color parameters for the diagnosis of nitrogen nutrition in winter wheat and summer corn, respectively. For the winter wheat, 16 m was the suitable aerial height at jointing stage, and the diagnosis model was:stem sap nitrate concentration= 2.103 4e^18.874VARI. 50 m was the best aerial height for summer corn at big trumpet stage, and the diagnosis model was:vein nitrate concentration=1.526×10³²×B/(R+G+B)^50.445. The established diagnose models were verified at the same field in 2016. The results showed that the determination coefficients of relationship between predicted and observed nitrate nitrogen concentrations of stem sap of winter wheat and vein of summer corn were 0.80 and 0.85, respectively, with significant levels of P < 0.01. In 2017, the method was applied to the diagnosis of nitrogen nutrition of winter wheat and summer corn in Nanpi County, Hebei Province, and the prescription maps of top-dressing nitrogen fertilizer for winter wheat and summer corn were made. The nitrogen fertilization rates of winter wheat and summer corn given by the prescription maps were fitting well with the growth status of crops. As shown in this study, diagnosis of nitrogen nutrition of winter wheat and summer corn using photographs from digital camera equipped on UAV was a cost-effective way to achieve precision management of fertilization. Beyond the achievements of this study, there were still problems should be solved to enhance the practicability and applicability of this method.