855 
scence from in 
This volume. 
irborne measu- 
rs. Geo Journal, 
MEASUREMENT OF THE FLUORESCENCE OF CROP RESIDUES: 
A Tool for Controlling Soil Erosion 
meral oil spills 
C.S.T. Daughtry', J.E. McMurtrey III 1 , E.W. Chappelle 2 , and W.J. Hunter 3 
'USDA ARS Remote Sensing Research Lab, 
ts at sea with 
in press. 
Building 7 BARC-West, 10300 Baltimore Ave 
Belts vii le, MD 20705-2350 USA 
using airborne 
2 NASA Goddard Space Flight Center 
Greenbelt, MD 20771 USA 
copic detection 
l chlorophyll a 
3 USDA ARS Soil-Plant-Nutrient Research Lab 
Fort Collins, CO 80522 USA 
nd mapping of 
Appl. Opt., 22: 
ents: evidence 
Remote Sens. 
ABSTRACT 
Management of crop residues, the portion of a crop left in the field after harvest, is an important conservation 
admixtures by 
r SSSR (USSR), 
practice for minimizing soil erosion and for improving water quality. Quantification of crop residue cover is required 
to evaluate the effectiveness of conservation tillage practices. Current methods for quantifying percent crop residue 
cover are tedious and somewhat subjective. There is a need for new methods to quantify residue cover that are rapid, 
accurate, and objective. We found the fluorescence of crop residue to be a broad band phenomenon with emission 
of subsurface 
maxima at 420-495 nm for excitations of 350-420 nm. Soils had low intensity broad band emissions over the 400- 
690 nm region for excitations of 300-600 nm. The range of relative fluorescence intensities for the crop residues 
n by dye laser 
Engineering in 
.Y., USA: IEEE 
was much greater than the fluorescence observed for the soils. As the crop residues decompose, their blue 
fluorescence values approach the fluorescence of the soil. We conclude 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, not only crop residue cover, but also 
photosynthetic efficiency in the field. 
lutions: oil in 
KEY WORDS: Blue fluorescence, Soil, Litter, Remote Sensing 
ensing of the 
i, ESA SP-312, 
1 - INTRODUCTION 
nonitoring sea 
n press. 
; laser remote 
ht and in the 
1.1. Soil Erosion. 
Agricultural statistics (U.S.D.A., 1991 ) indicate that there is an average of 8.51 Mg/ha of sheet and rill water 
erosion on U.S. cropland soils per year. The rate of soil erosion can be significantly decreased by allowing 
unharvested dead plant material (crop residue) to remain on the soil surface. As little as 30% coverage of residue 
material across the soil surface can reduce soil erosion to 10% of its non-covered state. Over one-third of the tilled 
dopment of a 
ices in Remote 
U.S. cropland or 49.8 million hectares is classified as highly erodible land. Farmers with highly erodible croplands 
are required to implement approved control practices that will reduce soil erosion by December 31, 1994. Residue 
management is an effective management practice for reducing soil erosion and more than 66 % of the nearly 1.3 
million conservation compliance plans include management of crop residue as the primary technique for reducing 
T., Braun A., 
time pollution 
suits. EARSeL 
soil erosion. In order to comply with their plans, farmers must ensure that their highly erodible soils have an 
adequate amount of residue cover. An added benefit of conservation practices is that as the movement of eroded 
soil into streams and rivers is reduced, the concomitant movement of nutrients and pesticides adsorbed to soil 
Particles is also reduced. The overall result is less soil erosion and improved water quality. 
1-2 Residue Cover Measurement Techniques. 
Quantification of crop residue cover is required to evaluate the effectiveness of conservation tillage practices. 
Bonham (1989) reviewed the various methods of measuring terrestrial vegetation cover and grouped them into nine