Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 Page 13 Page 14 Page 15 Page 16 Page 17 Page 18 Page 19 Page 20 Page 21 Page 22 Page 23 Page 24 Page 25 Page 26 Page 27 Page 28 Page 29 Page 30 Page 31 Page 32 Page 33 Page 34 Page 35 Page 36 Page 37 Page 38 Page 39 Page 40 Page 41 Page 4210 IREC Farmers' Newsletter No. 196 — Summer 2016 shown in Table 1. Basal fertiliser was applied 23 September 2015 and top-dressed urea was applied 10 December 2015. The treatments were replicated three or four times, with each replicate consisting of 3–9 beds of either 100 or 250 metres length. Spectral reflectance of the crop was measured in all the plots at 62, 83, 97, 118, 154, 160 and 169 days after sowing (DAS) using a Micasense Rededge camera (www.micasense.com) installed on a DJI Inspire 1 drone (Figure 1). The camera captured images corresponding to the spectral reflectance in the blue, green, red, red-edge and near infrared bands. All the images for each measurement day were uploaded to the Micasense Atlas Imagery & Analytics for Precision Agriculture service, where they were stitched together to produce a whole map of the site. Above-ground biomass was measured at first flower and plant nitrogen concentration (N%) was determined. Crop nitrogen uptake (N uptake) was then calculated. At maturity, two metres of plants in three adjacent rows per replicate were hand-picked. Seed-cotton was weighed and ginned to determine lint and seed yield. Three vegetation indexes were calculated from the multi-spectral images and their relationship with the in-field measurements was explored. These were: 1.  normalised difference vegetation index [NDVI = (NIR – R) / (NIR + R)], sensitive to variations in biomass and nitrogen status in some crops, e.g. wheat 2. normalised different red-edge index [NDRE = (NIR – RE) / (NIR + RE)], calculated using data from the red-edge region of the light spectrum, which has been reported in many studies as sensitive to the leaf chlorophyll content (see for instance Figure 2) 3.  canopy chlorophyll content index (CCCI = NDRE/NDVI), which is the NDRE index normalised by biomass. Correlation with plant nitrogen The spectral measurements showed small differences between treatments early in the season when plants from the lowest nitrogen rates were likely able to draw on nitrogen reserves in the soil. Differences between treatments, however, became more evident later in the season when the nutrient requirements of plants increased during boll formation. Figure 3, for example, shows the evolution of the NDRE index at the site from 97 to 160 days after sowing. possibility of acquiring images at a very high resolution (