Sugarbeet canopy type and accumulation of plant nitrogen as delineated by aerial photography and global positioning systems.
Moraghan, J.T.
Communications in soil science and plant analysis 1998, Vol. 29, No 19-20, pp. 2953-2959.
1998
บทคัดย่อ
Considerable within-field variation in the N content and appearance of sugarbeet (Beta vulgaris L.) leaf canopies is found often at root harvest. Since this heterogeneity can affect subsequent soil N mineralization, a study was initiated to determine if the within-field variation could be identified and located by aerial photography and a global positioning system (GPS). An aerial color photograph was taken of a commercial sugarbeet field prior to harvest. Three reflectance patterns associated with different degrees of canopy greenness ("green" [G], "yel1ow-green" [YG] and "yellow" [Y]) were identified readily. Four areas, each approximately 0.8 ha in size, with these three canopy types were selected. The canopy subsites were located by use of a GPS unit. The G, YG, and Y canopy types contained 277, 138, and 85 kg N ha-1, respectively, in sugarbeet tops. The corresponding leaf N concentrations were 30.6, 20.1, and 15.8 g kg-1, respectively. Postharvest soil NO3-N levels in the upper 120 cm of soil were 57, 14, and 10 kg ha-1 for the G, YG, and Y canopy sites, respectively. Nitrate-N in sugarbeet tops returned to the soils was at least partly responsible for the higher soil at the G subsites. In contrast to dry matter yield, recoverable sugar yield was significantly less for roots associated with the G-canopy type than for roots associated with the YG-and Y-canopy sites. Aerial photography and GPS technology can increase precision of soil testing for NO3-N after a sugarbeet crop, help to identify areas of increased soil N mineralization for a subsequent crop, and decrease subsequent N fertilizer use if a variable rate N-fertilizer applicator is used.