iring crop residue cover 
Line-transect methods 
lethods use a system of 
: residue is determined 
the intercept is read at 
on the length of the line 
100 feet long and have 
itandard technique used 
stigated. For example, 
pots on the surface for 
; a line, it must be used 
stereographic pairs of 
ographs. An important 
or multispectral video 
and residue classes on 
es between classes (soil 
1 time, however video 
h experience, Morrison 
! minutes per image as 
ise primarily when the 
l somewhat subjective 
residue cover that are 
residues with soil using 
ice during degradation. 
idgment present in the 
¡ristics. Unfortunately, 
getation (Bauer, 1975) 
he near infrared (Aase 
ils are often spectrally 
tre, iron oxide content, 
1980). Furthermore, 
particular wavelength 
t al. 1993; McMurtrey 
It or nearly impossible 
>ils is possible using a 
dmum first derivative 
m. McMurtrey et al. 
itered at 440 nm when 
be fluorescence in the 
in, and NADPH. The 
ually contribute more 
soils. 
i there d am, soybean, 
is was a broad band 
d low intensity broad 
band emissions over the 400-690 nm region for excitations of 300-600 nm. The range of relative fluorescence 
intensities (RFI) for the crop residues was much greater than the RFI observed for the soils. Moisture quenched the 
fluorescence, but the relative difference between crop residues and soils remained fairly constant regardless of 
moisture status. In general, older crop residues had lower minimum and lower maximum RFI values than recently- 
harvested residues. As the crop residues decompose, their RFI values approach the RFI of the soil. Greater than 
90% of the crop residues less than 2 years old could be discriminated from 35 of the 40 dry soils and 39 of the 40 
wet soils using fluorescence. They concluded that fluorescence techniques are less ambiguous and better suited for 
discriminating crop residues and soils than reflectance methods. Furthermore, if properly implemented, fluorescence 
techniques can be used to quantify crop residue cover in the field. 
Table 1. Relative fluorescence intensity (RFI) of representative wet and dry soils. (After Daughtry et al., 1993). 
SOIL 
SERIES 
LOCATION 
RFIdry 
RFI wet 
SOIL 
SERIES 
LOCATION 
RFI Puy 
RFIwpe 
Academy 
California 
10.5 
5.7 
Granada 
Mississippi 
9.5 
5.0 
Amarillo 
Texas 
12.0 
5.7 
Hersh 
Nebraska 
21.4 
8.5 
Barnes 
Minnesota 
10.1 
5.4 
Palouse 
Washington 
6.1 
3.9 
Caribou 
Maine 
12.4 
5.5 
Tifton 
Georgia 
21.5 
7.0 
Codorus 
Maryland 
17.7 
7.1 
Wilhams 
North Dakota 
8.1 
5.3 
Gaston 
N. Carolina 
5.9 
4.2 
Zahl 
Montana 
8.3 
5.5 
Table 2. Relative fluorescence intensity (RFI) of recently-harvested and weathered crop residues. (After Daughtry 
et al., 1993). 
CROP 
AGE 
NO. 
MIN. 
MAX 
MEAN 
Com 
1 week 
70 
42.9 
239.4 
97.7 
2 months 
170 
23.6 
124.8 
58.1 
8 months 
140 
13.6 
167.5 
52.9 
Sorghum 
1 year 
150 
26.5 
259.6 
101.4 
3 years 
180 
14.0 
202.2 
64.0 
Soybean 
1 week 
120 
15.4 
149.5 
76.8 
1 year 
70 
17.1 
77.2 
48.0 
Wheat 
1 week 
70 
20.2 
56.1 
38.9 
3 months 
70 
16.0 
52.0 
34.2 
Wheat 
2 months 
250 
22.6 
119.6 
63.1 
1 year 
120 
17.3 
72.8 
40.1 
2 years 
150 
11.2 
51.6 
25.8 
All Residues 
1560 
11.2 
259.6 
59.6