spectral reflectance-based nitrogen management for subsurface drip irrigated cotton raj yabaji,...
TRANSCRIPT
Spectral Reflectance-based Nitrogen Management for Subsurface Drip
Irrigated Cotton
Raj Yabaji, Kevin Bronson, Cary Green, Eduardo Segarra, and Adi Malapati
Texas A & M Univ. – Texas Agric. Exp. Stn, and Texas Tech Univ, Lubbock, TX
Introduction
• The Southern High Plains of Texas average 3000-4000 ft in elevation, 18 in. rainfall/yr and 80 in. open pan evaporation/yr.
• The densest concentration of cotton production in the world is here. 3 to 4 million ac of cotton are planted each yr. Cotton is mono-cropped.
• Half of the cotton acreage is dryland, half is irrigated from the declining Ogallala aquifer. % 70 of the irrigation is center pivot, 25 % is furrow-irrigated, & 5 % is subsurface drip.
In-season sensing of N status for Cotton
Nitrogen management for subsurface drip irrigated cotton
Objectives
• Test spectral reflectance as an N management guide for SDI cotton
• Refine the window of N fertilizer injection in SDI cotton
• Compare 32-0-0 with 28-0-05S as N fertilizer sources in SDI cotton
• Measure denitrification in SDI cotton as affected by N management
Materials & Methods
Station 1
Station 2
Station 3
Station 4
Station 5
Station 6
Station 7
Station 8
Station 9
Station 10
Station 11
Station 12
Station 13
Station 14
Station 15
Station 16
GS 28MB 32MB 32EB 28EB 32EB GS 32MB Zero 28MB 28EB 28EB 28MB GS 32EB 32MB
Rep 1 Rep 1 Rep 1 Rep 1 Rep 1 Rep 2 Rep 2 Rep2 Rep 2 Rep 2 Rep 2 Rep3 Rep 3 Rep 3 Rep 3 Rep 3
101 105 109 113 117 201 205 209 001 213 217 301 305 309 313 317
102 106 110 114 118 202 206 210 002 214 218 302 306 310 314 318
103 107 111 115 119 203 207 211 003 215 219 303 307 311 315 319
104 108 112 116 120 204 208 212 004 216 220 304 308 312 316 320
Plot plan
600 ft
8, 40-in rows
Treatments • 32-0-0 or 28-0-0 5S injected early bloom to mid bloom (5 weeks)
• 32-0-0 or 28-0-0 5S injected early bloom to peak bloom (8 weeks)
• Zero-N (1 plot/station/rep)
• Reflectance-based mgt: 0.5 X N early to peak bloom, N injection rate adjusted upwards by 100 % when
• GVI (Green vegetative index)reflectance/GVI soil test < 0.95 or statistical significance.
• Amount of N fertilizer = 150 lb N/ac (for 2.5 bale/ac) – 0-24 in soil test NO3-N – irrigation water NO3
Nitrogen requirements for high-yielding cotton
Yield goal Nitrogen requirement1
bales/ac lb N/ac
1.5 90
2.0 120
2.5 150
3.0 180
3.5 210
1Nitrogen fertilizer plus 0-24 inch NO3-N
Cropscan MSR 16
• Passive sensor (natural light)
• 16 wavebands (up & down)
• 48 inches above canopy• Within 2 hrs solar noon• Percent reflectance =
Refltd irrad @ λ /
Incoming irrad @ λ
Vegetative indices (Bausch and Duke, 1996)
• Green vegetative index = R820/R550
• Red vegetative index = R820/R650
R = percent reflectance at λ (nm)
Results
Green vegetative index for SDI cotton Lubbock, 2005
**
0
1
2
3
4
5
6
7
8
9
10
165 175 185 195 205 215 225
Julian Days
GV
I
Soil test based
Reflectance-based
Zero-N
Green vegetative index for SDI cotton Lubbock, 2006
0
1
2
3
4
5
6
7
8
9
165 175 185 195 205 215 225
Julian Days
GV
I
Soil test based
Reflectance-based
Zero-N
**
*
*
Nitrogen fertilizer injections Lubbock, 2005
0
10
20
30
40
50
60
70
80
90
100
165 175 185 195 205 215 225
Julian Days
Cu
mu
lativ
e N
Fe
rtili
zer
( lb
ac-1
)
Soil test-based to peak bloom
Reflectance-based
Soil test-based to early bloom
Nitrogen fertilizer injections Lubbock, 2006
0
20
40
60
80
100
120
165 175 185 195 205 215 225
Julian Days
Cu
mu
lativ
e N
Fe
rtili
zer
( lb
ac-1
)
Soil test-based to peak bloom
Reflectance-based
Soil test based to early bloom
Spring soil nitrate, N fertilizer amounts injected, well water nitrate, and total N supply, Lubbock, TX, 2005
N source N timing Spring
soil NO3
1
Starter N fertilizer
N fertilizer injected
Well water-NO3
Total N supply
--------------------------------- lb N/ac -------------------------------
28-0-0-5 Early bloom2 8 22 90 20 140
28-0-0-5 Peak bloom3 7 22 90 20 139
32-0-0 Early bloom2 8 22 90 20 140
32-0-0 Peak bloom3 8 22 90 20 140
32-0-0 Reflectance-based3
7 22 65 20 115
Zero-N N/A 7 22 0 20 49
Spring soil nitrate, N fertilizer amounts injected, well water nitrate, and total N supply, Lubbock, TX, 2006
N source N timing Spring
soil NO3
1
Starter N fertilizer
N fertilizer injected
Well water-NO3
Total N supply
--------------------------------- lb N/ac -------------------------------
28-0-0-5 Early bloom2 35 0 100 28 163
28-0-0-5 Peak bloom3 30 0 100 28 158
32-0-0 Early bloom2 35 0 100 28 158
32-0-0 Peak bloom3 27 0 100 28 155
32-0-0 Reflectance-based3
24 0 85 28 137
Zero-N N/A 16 0 0 28 44
Correlations of Green vegetative index (GVI), chlorophyll meter (SPAD) readings, leaf N, biomass and lint yield,
SDI cotton Lubbock 2005-6 GVI-early bloom SPAD-early bloom GVI-mid bloom SPAD-mid bloom
2005
Leaf N-early bloom 0.45 - -
Biomass-early bloom 0.37 0.44 - -
Leaf N-mid bloom - - 0.70 0.25
Biomass-mid bloom - - 0.31
Lint yield 0.36
2006
Leaf N-early bloom 0.70 0.59 - -
Biomass-early bloom 0.58 0.44 - -
Leaf N-mid bloom - - 0.85 0.54
Biomass-mid bloom - - 0.47 0.51
Lint yield 0.53 0.28 0.58 0.33
Leaf N SPAD NDVI_cropscan NDVI_greenskr 550nm
Biomass -0.33 -0.21 0.48 0.58
Leaf N 0.37 -0.28 -0.46 -0.47
SPAD -0.32 -0.38 -0.26
NDVI_crops 0.75 -0.20
NDVI_grnsk 0.20
Cropscn_550
Correlations with chlorophyll meter (SPAD) and spectral reflectance at early bloom Lamesa, 2003
Means: Biomass – 704 kg/ha, Leaf N – 3.9%, NDVI_cropscn – 0.43, NDVI_grnskr – 0.52
Leaf N SPAD NDVI_cropscan NDVI_greenskr 550nm
Biomass 0.30 0.34 -0.29
Leaf N 0.53 0.52 0.43
SPAD -0.30
NDVI_crops 0.47 -0.31
NDVI_grnsk
Cropscn_550
Correlations with chlorophyll meter (SPAD) and spectral reflectance at early bloom Lamesa, 2004
Means: Biomass – 1954 kg/ha, Leaf N – 3.7%, NDVI_cropscn – 0.73, NDVI_grnskr – 0.86
0.21
-0.32
N source N timing N
fertilizer injected
Green veg. index
Chlor. meter
Leaf N Biomass
% lb/ac
28-0-0-5S Early bloom1 90 8.7 a 42.8 a 3.5 b 4548 a
28-0-0-5S Peak bloom2 90 8.5 a 41.5 ab 3.6 ab 5810 a
32-0-0 Early bloom1 90 8.5 a 42.6 a 3.5 b 6204 a
32-0-0 Peak bloom2 90 8.8 a 41.0 b 3.7 a 6609 a
32-0-0 Reflectance-
based2 65 8.0 b 40.4 b 3.3 c 5695 a
Zero-N N/A 0 6.4 c 38.9 c 2.9 d 5786 a 1 Injected from 20 June to 22 July 2 Injected from 20 June to 12 Aug
Mid-bloom biomass, green vegetative index, chlorophyll meter readings as affected by N management, Lubbock, TX, 2005
Mid-bloom biomass, green vegetative index, chlorophyll meter readings as affected by N management, Lubbock, TX, 2006
N source N timing N
fertilizer injected
Green veg. index
Chlor. Meter
Leaf N Biomass
% lb/ac
28-0-0-5 Early
bloom1 100 7.8 a 48.2 a 3.36 a 5823 a
28-0-0-5 Peak
bloom2 100 7.5 b 48.1 a 3.58 a 5705 a
32-0-0 Early
bloom1 100 7.6 ab 49.4 a 3.40 a 6261 a
32-0-0 Peak
bloom2 100 7.7 ab 49.4 a 3.60 a 5902 a
32-0-0 Reflectance-
based2 85 7.0 c 47.9 a 3.49 a 5430 a
Zero-N N/A 0 5.0 d 39.9 b 2.61 b 3056 b
N source N timing N
fertilizer injected
Total N uptake
Recovery efficiency
Biomass Seed yield
Lint yield
------- lb N/ac ------ % ------------- lb/ac ---------------
28-0-0-5S Early bloom1
90 - -
- 2611 a 1865 a
28-0-0-5S Peak bloom2
90 - -
- 2598 a 1829 a
32-0-0 Early bloom1
90 - -
- 2629 a 1879 a
32-0-0 Peak bloom2
90 160 a 63 a 9647 a 2549 a 1812 a
32-0-0 Reflectance-based2
65 143 a 62 a 9164 a 2511 a 1817 a
Zero-N N/A 0 103 b - 8047 b 2072 b 1620 b 1 Injected from 20 June to 22 July 2 Injected from 20 June to 12 Aug
First open boll biomass, N uptake, seed and lint yields as affected by N management, Lubbock, TX, 2005
First open boll biomass, N uptake, seed and lint yields as affected by N management, Lubbock, TX, 2006
N source N timing N
fertilizer injected
Total N uptake
Recovery efficiency
Biomass Seed yield
Lint yield
------- lb N/ac ------ % ------------- lb/ac ---------------
28-0-0-5 Early bloom1
100 - - - 2002 a 1430 a
28-0-0-5 Peak bloom2
100 - - - 2094 a 1496 a
32-0-0 Early bloom1
100 117 a 71 a 8450 a 2038 a 1456 a
32-0-0 Peak bloom2
100 120 a 75 a 8636 a 2038 a 1456 a
32-0-0 Reflectance-based2
85 107 a 71 a 8048 a 1970 a 1407 a
Zero-N N/A 0 46 b - 4285 b 1324 b 1034 b 1 Injected from 12 June to 17 July 2 Injected from 12 June to 7 Aug
Year Irrigation Lint yield Recovery effcy-diff
Recovery effcy-15N
N application details
lb/ac --------- % ---------
2001 Sub drip 1230 60 31 3 injections of 30 lb/N/ac
2001 LEPA 1321 42 37 3 injections of 30 lb/N/ac
2002 LEPA 1227 40 - 3 injections of 30 lb/N/ac
2005 Sub drip 1678 63 - 30 injections in 8 wks
2006 Sub drip 1407 71 - 31 injections in 8 wks
2006 Furrow 1220 20 - Side-dress at 1st square
Recovery efficiency of 90 lb fertilizer-N/ac in cotton plants
Summary• Green vegetative index related to leaf N and
biomass, and responded to N fertilizer treatments. GVI reflected net N mineralization in zero-N plot.
• We tested spectral reflectance-based N management, i.e. initial N injections of ½ X of soil test recommendations, and adjusting upwards as GVI falls significantly below soil test management for 2 ½ bale/ac yield goal.
• Spectral-reflectance N injection saved 28 and 15 % N compared to soil test-based management for 2005 and 2006, respectively.
Summary cont.
• Recovery efficiency of N fertilizer injected daily in subsurface drip irrigated cotton is high, i.e. 62-75 %
• Denitrification from N fertilizer injections in SDI cotton was not detectable.