1. Gyles Randall Univ. of Minnesota 2007 NUE Workshop Monmouth, IL
Optical Sensing to Determine N Needs of Rainfed Corn in the Northern CornBelt: The Future
Gyles Randall
Univ. of Minnesota
2007 NUE Workshop
Monmouth, IL

2. Our Experience at Waseca
Number of field studies where NDVI measurements were made on N rate studies for corn.
Previous Crop
Year
Soybean
Corn 7 5
2007 4

3. General Findings NUE: not consistently improved with split N
Grain yield: preplant N generally > split N
for both CC & C-Sb
especially when split has a low rate of preplant N or SD N is applied after V8
NUE: not consistently improved with split N
NDVI: For CC, V6-V12 distinguished among N rates w/V7-V11 best.
For C-Sb, V7-V11 sometimes distinguished between 0-lb vs greater N rates.
delta NDVI is small, does not distinguish between 30 & 150 lb N rates.

4. Support Data 2005, Cont. Corn, N rate = 160 lb/A Appl. Time Corn
Preplant
V10
Yield
ANR
lb N/A
bu/A %
160
185 62 40
120
166 60
(NDVI at V8, V10, & V12 related to grain yield)

5. Support Data 2006, C-Sb, N rate = 90 lb/A Application Time Grain V2 V7
Yield
lb N/A
bu/A 90 --
197 30 60
200 15 75
190
184

6. Support Data 2006, Cont. Corn Appl. Time Corn PP V8 Total Yield ANR
lb N/A
bu/A %
120
206 63 20
100
181 44 40 80
198 67
160
216 68
190 45

7. Soil Properties Soils frozen over winter
Higher OM soils (>3%)
Soils frozen over winter
greater supply of mineralized N early in season
In IA, MN, and WI, 70 to 80% of total N taken up by corn after soybean is from the soil.

8. Effect of Rainfall on Soil Moisture
2007, May-July rainfall = 9.9” or 2.8” below normal
Depth
July 16
Aug. 1
feet
inches avail. water in 0-5’ profile
0-5
6.0
5.2
0-2
0.7
0.4
2-3
1.5
0.8
3-5
3.9
4.0
FMC = 11.05” available water in 0-5’

9. Factors Affecting Adoption of Optical Sensing for N Rate Guidance
Little interest among dealers, farmers, and consultants
fall and preplant application
workload (post-herbicides, insecticides & fungicides)
extra level of management
risk
cost (equipment, labor, time)
absence of research documenting the rewards/returns

10. What is the Future? - Dismal - Futile
- Jury is still out
- Dismal
- Futile
Are there options to the approach we have been taking?

11. Research Opportunities
Apply swine manure at a rate that meets the P requirement and then supplement w/N at V10+ based on simultaneous NDVI measurements and N-rich strips
will NDVI differences be
(1) predominantly related to N status
(2) sufficiently robust to differentiate application rates
will these “later” N applications be efficient
acceptance is likely to be scale-dependent
system needs extra management
Higher altitude hyperspectral imaging