cBeth Quantalog Densitometer and on a Joyce Loebel 
  
out on a Ma 
MK III CS recording microdensitometer. Acreage of individual 
fields was determined digitally by employing a special compu- 
ter programme designed by LANGE (1978). Analog image enhance- 
ment techniques including electronic density slicing and colour 
coding were used for relative damage level quantification and 
All the cropland area covered by the pho- 
educational purposes. 
tographs was mapped carefully on 1 : 5.000 cadastral maps. At 
each test site, 10 sugar beet fields showing nematode infesta- 
tions were selected. From these, soil samples were taken in 
order to determine soil water content, nutrients, and nematode 
For the latter, individual soil samples, consisting 
area to a depth 
occurence. 
of at least 25 subsamples collected in 2 x 5m 
of 25 cm, were mixed thoroughly, divided, and the aliquots 
were sent to different governmental and private laboratories 
for investigation. The purpose of this was to determine the 
accuracy of the different methods and investigators. The modus 
of collecting these samples is shown in Picture 1 (below). 
Nutrient and water determination samples were taken from the 
infestation centers and the turgid field parts. 
a 
pte "T M 
area 7 infested are\ turgid area 
"T T 
\ 
5m 
x : 
P4 
+ 2 3 4.5 /5,72'9- 9 10 plot no. 
  
see DO ., 
. 
a? 
— 07 
le 
  
  
  
  
  
  
  
  
  
  
  
  
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Picture l Soil sample collection modus 
Immediately after processing and official releasing of the 
aerial photographs, they were pre-interpreted and the results 
were compared to the actual situation in the fields. 
Spectral reflectance properties of the leaves of infested and 
non-infested plants as well as of petioles and soil were measur- 
éd in a Zeiss PMQ II laboratory spectrophotometer with an inte- 
grating sphere in the 500 - 950 nm wavelength interval at