Annual variations in the nitrogen-chlorophyll leaf reflectance of hackberry, honey mesquite and live oak in south Texas, were compared. In spring, leaf reflectance at the 0.55 m wavelength and nitrogen (N) concentration was high but leaf chlorophyll (chl) concentrations were low. In summer, leaf reflectance and N-concentration were low but lead chl concentrations were high. Linear correlations for both spring and summer of leaf reflectance with N and chl concentration or deviations from linear regression were not statistically significant

Escobar, D. E.

Everitt, J. H.

Gausman, H. W.

English

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AgRISTARS
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Early Warning and Crop
Condition Assessment
E82-1026 7
EW-U2-04251
JSC-17824
A Joint Program for
Agriculture and
Resources Inventory
Surveys Through
Aerospace
Remote Sensing
FEBRUARY 1982
LEAF REFLECTANCE-NITROGEN-CHLOROPHYLL RELATIONS AMONG
THREE SOUTH TEXAS WOODY RANGELAND PLANT SPECIES
H. W. GAUSMAN, J. H. EVERITT, AND D. E. ESCOBAR
(E82-1020) LEAF
REFLECTAPiCI -NITFidGEii-C.^LutuPhYL.L. bELATICNS
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U.S. DEPARTMENT OF AGRICULTURE
SOIL AND WATER CONSERVATION RESEARCH
SUBTROPICAL TEXAS AREA, SOUTHERN REGION
WESLACO, TEXAS
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Lyndon B. Johnson Space Center
Houston. Texas 77058
LEAF REFLECTANCE-NITROGEN-CHLOROPHYLL RELATIONS
AMONG THREE SOUTH TEXAS WOODY RANGELAND PLANT SPECIES
PRINCIPAL INVESTIGATORS
H. W. Gausman, H. H. Everitt, and D..E. Escobar
APPROVED BY
1 enn i s . oatwr' Fit , Manager
Early Warning/Crop Condition Assessment Project
AgRISTARS Program
Houston, Texas
February 1982
k'
Leaf Reflectance-Nitrogen
-Chlorophyll
 Relations Among
Three South Texas Woody Rangeland plant Species
Leaf reflectance within the 0.40- to 0.75-pm waveband is influenced primarl-
ly by chlorophyll (chi) pigments (2, 3,13). Reflectance can be used to: evaluate
turf color (3), estimate the nitrogen (N) status of sweet pepper leaves (14),
measure amounts of biomass or vegetation density (15, 16), and demonstrate
leaf spectral and color4nh wed Mm image differences among shrubs and woody
pmt species (5, 8, 9).
Leaf reflectance measurements have not been used to estimate the N or chi
status of rangeland plants. A pilot study (7) indicated that leaf N concentration
of six of seven rangeland species decreased as the season progressed from March
to June or October. Visible light reflectance at the 0.55-µm wavelength of five of
these species decreased as N concentration decreased; reflectance at this wave-
.+ngth is affected by chi concentration (13). In crop plants the leaf visible light
reflectance increased (decreased chi) and was inversely correlated with leaf N
concentration (2, 13). This difference between rangeland and crop plants may
have been caused by variation in leaf maturation or senescence (11), effects of
salinity on leaf chi concentration (6), or chi may have a different dependence on
leaf N content (14).
Our objective, therefore, was to make additional reflectance measurements to
further evaluate their possible use to predict leaf N concentrations of three high-
ly important south Texas rangeland woody plant species. The capability to
estimate leaf N concentration using reflectance measurements would be a quick
method of evaluating forage protein (N x 625) content, which is highly impor-
tant for livestock and wildlife production.
1
f^ .
MATERIALS AND METHODSi 
Three woody plant species common on south Texan rangelands, nomenclature
after Correll and Johnston (4), were used in this study: Hackberry (Cells laevi-
gnfa Mild.), honey mesquite (ftsopb ShrA loss Ton. var.), and live oak
(Quercus ubginiana Mill.). Hackberry is a major spades on bottomland range
sites. Live oak is abundant on deep sands and grows in formations ranging from
dense, uniform stands to frequent thickets or motta in underbrush. Honey mes.
quite Is a dominant species throughout the area and grows on a -- witty of sites
(deep sands, sandy loam, day looms, heavy days).
Leaves of these species were collected once during spring (Macon) and once
during summer (July) to measure their spectral reflectance ana to determine
their dil and N concentrations. Leaves from each of 12 trees of each species
were collected from all portions of tree canopies for both spring and summer
measurements. Detached leaves were thoroughly mixed and endosed immediate-
ly In air-tight plastic bags and stored on ice to minimise dehydration during
transport to the laboratory.
At each collection, two leaves from each of the 12 trees of each plant species
were used to measure spectral reflectance. Total leaf chi and N concentrations
(10) were determined in duplicates for each of the 12 trees of each spades. The
means of these measurements and determinations were used to represent each
tree of each species.
Total diffuse reflectance of upper (adasial) surface of single leaves over the
0.4 to 0.7-Mm visible light waveband was measured with a Beckman Model
DR-2A spectrophotometer, equipped with a reflectance attachment. (Mention of
company name or trademark is for the readers' benefit and does not constitute
endorsement of a particular product by the USDA over others that may be com-
mercially available.) These data have been corrected for decay of the barium
sulfate standard to give absolute radiometric data (1). Reflectance data given In
this study are for the 0.55-ptn wavelength because it is most sensitive to a change
In leaf reflectance caused by a difference in pigment concentration (13).
The West (12) was used to test statistical differences between means of leaf N
and between leaf chi concentrations for spring and summer for each of the three
Plant species. Linear correlations of reflectance w4h leaf N and chi and N with
chi were calculated. Deviations from linear regression were lls o tested.
RESULTS AND DISCUSSION
Leaf Reflectance
The mean reflectance value for the Ilmey-green colored leaves of the three
woody plant species during spring was 16A%. Leaf reflectance among the plant
spades showed that hackberry (17.6%) and mesquite (17.00 were significantly
s
 higher than live oak (14.6%). In summer, the plant species leaves, which had be-
come darker green, absorbed more light, thus significantly (p - 0.01) reducing
the three species' mean reflectance value to about 8.1%-a reflectance decrease of
50.6% from spring to summer. In summer leaf reflectance of hackbarry (&0%)
and mesquite (7.196) were significantly lower than that of live oak (9.396).
ORIGINAL PAGE 13
OF POOR QUALITY
L*af N and Chi Concentrations
Table  I shows both spring and summer leaf N and chi concentrations of the
three woody plant species. Mesquite and hackbom had 94 and 37% higher N
concentration In the spring and 132 and 84% higher N concentration in the
summer, respectively, than did live oak. Leaf N concentrations of hackberry,
mesquite, and live oak decreased 34, 41, and '50% frrom gpring to summer,
respectively.
Table 1. The leaf nitrogr . ('', and total chlorophyll (chi) concentration of
the three woody ,nt species during the spring (March) and summer
(July) of 1979.
Nitrogen	 Chlorophyll
Species	 Spring Summer	 Diff. Summer Sprinf	 Diff.
..........96...........
	
.......... MVg..........
Hackberry 3.93 2.61 1.32*	 2.91 1.78	 1.13*
Live Oak 2.87 1.42 1.45*	 1.73 1.01	 0.72*
besquite 5.57 3.29 2.28*	 2.28 0.90	 1.38*
Mean 4.12 2.44 2.31 1.23
* Significant at the 1% probability level.
Leal chi concentration was highest for hackberry in both spring and summer.
Hackberry leaves had 68 and 28% higher leaf chi concentrations than did live
oak and mesquite in summer, respectively; whereas, in spring, leaf chi concen•
trations were 76 and 9896 higher, respectively. From spring to summer, leaf chi
concentrations of hackberry, mesquite, and live oak increased 63, 71, and 15390,
respectively.
Leaf Reflectance vs N and Chi Concentrations
Linear correlations of reflectance with N and chi, and N with chi were not
statistically significant (p - 0.05) for the three species in the spring, except for
hackberry which had a 0.38 coefficient of determination for the correlation of
reflectance with N. The other coefficients of determination were below 0.19. In
summer, no correlations were statistically significant (p - 0.05) for any of the
three woody plant species. The eoeffleients of determination were all below
0.31. The deviations from linear regression were not statistically significant.
The relationship between leaf reflectance and leaf N and chi concentratlons,
however, showed that the leaf reflectance was positively related to leaf N con-
centmdon and inversely related to leaf chi concentration. For example, during
Spring leaf reflectances and N concentrations were high but leaf chi
ORIGiNAL PAGE 13
OF POOR QUALITY
concentrations were low; whereas, In summer reflectance and N concentra-
tions wen low but chi concentrations were high. Thew findings substantiated
results from our previous pilot study (7} since woody specles' leaf N concentra-
tions do not agree with crop plant results where reflectance was inversely cor-
related with leaf N concentration (14). However, according to our results, leaf
spectral reflectance messurements cannot be used to predict leaf N concentm.
tion for woody plant species.
ACKNOWLEDGEMENT
We thank Armando Ssldana for assisting with chemical analyses and R. R.
Rodrigues for helping with spectrophotometric measurements.
LITERATURE CITU',D
1. Allen, W. A., and A. J. Richardson. 1971. Calibration of a laboratory spec-
trometer for specular light by means of stacked glass plates. Rev. Sci. lnstr.
42:1813.1817.
2. Benedict, H. W., and R. Swidler. 1961. Nondestructive method for estimat-
ing chlorophyll content of leaves. Science. 133:2015-2016.
3. Birth, G. S., and G. R. McVey. 1968. Measuring the color of growing turf
with a reflectance spectrophotometer. Agron. J. 60:640-643.
4. Correll, D. S., and M. C. Johnson. 1970. Manual of the vascular plants of
Texas. Texas Research Foundation, Renner, TX. 1881 p..
5. Driscoll, R. S., and ML D. Coleman. 1974. Color for shrubs. Photogramm.
Eng. 40:451.459.
6. Gausman, H. W., W. A. Allen, R. Cardenas, and R. L. Brown. 1970. Color
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concentration and reflectance of seven woody plant species. J. Rio Grande
Valley Hort. Soc. 33:101-104.
A. H. Gerbermann, and R. L. Bowen. 1977.
Canopy wifectance-atructure-film image relations among three south Texas
rangeland plants. J. Range Manage. 30:449-450.
9. , and D. E. Escobar. 1976.
Iwaf spectral characteristics of nine woody plant species from Texas range.
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noses, Tullahoma. 5:333.349.
10. Horwitz, W. (ad.). 1965. Official Methods of Analysis, Ed. 10, Assoc. Offlc.
Agric. Chemists, Washington, D.C. 957 p.
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13. Thom, J. R., and H. W. Gausman. 1977. Leaf reflectance vs. leaf chloro.
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14. , and G. F. Oerther. 1972. Estimating nitrogen content of
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4
15. Tucker, C. J., L. D. Miller, and R. L. Pearson. 1973. Measurements of the
combined effect of green biomes, chlorophyll, and leaf water on canopy
spectroreflectance of the shortgrass prairie. Remote Sensing Earth Resources.
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16. Wiegand, C. L., H. W. Gausman, J. A. Cuellar, A. H. Gerbermann, and A. J.
Richardson. 1974. Vegetation density deduced from ERTS-1 MSS response.
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ing Ofce., Washington, D.G. p. 93-116.


Leaf reflectance-nitrogen-chlorophyll relations among three south Texas woody rangeland plant species

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