Hui Wang1,2*, Anders K. Mortensen1 and René Gislum1 Evaluating critical nitrogen dilution curve in grass seed production using images from unmanned aerial system Hui Wang1,2*, Anders K. Mortensen1 and René Gislum1 1University of Aarhus, Department of Agroecology, Slagelse, Denmark 2China Agricultural University, Forage Seed Laboratory, Beijing, PR China * Corresponding author: wanghui89@cau.edu.cn Figure 2. NDVI map of field experiments. Scale of NDVI is shown to the right. BACKGROUND Nitrogen (N) is important to achieve high seed yields, however N can at the same time have a negative impact on the surrounding environment. Scientists, companies and authorities are working to develop a method that is able to optimise the utilisation of N in agricultural crops. One method that is current being tested is the use of crop index to predict seed yield or the N-application rate necessary to achieve maximum seed. AIMS The overall aim is to test the possibility of using critical N dilution curve developed by Gislum and Boelt (2009) to define the optimum N application rate for grass seed production. The first step is to evaluate the possibility to replace time-consuming plant sampling and analysis of N status and biomass by using images from drone mounted camera. RESULTS AND DISCUSSION Different vegetation index maps were created using Pix4d and it was possible to cut out pixels from the sampling area (Figure 2 and 3). It was also clear that some of the experimental plots had sufficient or in-sufficient N concentrations as some dots were placed above or below the critical N dilution curve (Figure 4). The correlation coefficient between different vegetation indexes from the cutting area and the measured N concentration or shoot dry matter was however low (data not shown). One of the reasons could be the fact that plant cuts were taken late in the growing season where. We will continue this project and include more data, especially data in the earlier growth season. The eBee drone is 96 cm wide and the weight is 0.71 kg. It is made of EPP foam and has a carbon frame and parts. The propel is at the back and is driven by an 160W engine. The battery has a capacity of 11.1 V and 2150 mAh. The maximum air time is 45 minutes and the speed is 40 to 90 km per hour. The eBee can be controlled up to 3 km from the control unit and can cover up to 1000 ha. The linear landing precision is 5 meters but strongly dependent of wind speed. Figure 3. Green (a), red (b), red edge (c) and NIR (d) maps from field experiments. a b c d MATERIAL AND METHODS Grass samples (0.5*0.5 m) were regularly collected from plot experiments and analysed for biomass and total N (Figure 1). Images of the cutting area were acquired prior to sampling using an eBee drone equipped with a MultiSPEC 4C camera (capturing green, red, red edge and near-infrared wavelengths). Different vegetation indexes were calculated from pixels within the cutting area. All analysis were made using eMotion3, Pix4D and MatLab. N% DM kg N ha-1 NDVI Green Red Red edge NIR 8m 2.5m 0.5m Cutting area Figure1. Cutting area in one plot and indexes measured of cutting area. Figure 4. Critical N dilution curve together with N% and DM for the cuts. Gislum, R., & Boelt, B. (2009). Validity of accessible critical nitrogen dilution curves in perennial ryegrass for seed production. Field crops research, 111(1), 152-156.