Use of aerial imagery to detect N response in corn following alfalfa

FR 5262Matt Yost 

Stephen Palka

http://www.rothamsted.ac.uk

Alfalfa provides N to following crops

~100 lb N ac-1 yr-1

2% N

~200 lb N ac-1 yr-1

http://www1.umn.edu/news

Alfalfa provides Nitrogen to corn for 2 years

State1st-year N credit†

2nd-year N credit†

-------- lb N ac-1 --------IA 170 140IL 100 30IN 140 ---KS 120 ---MI 140 ---MN 150 75MO 100 ---ND 150 75NE 150 ---OH 140 ---SD 150 75WI 150 50

42 on-farm alfalfa-corn N rate trials (2009-2012)K

Regrowth, tillage time

No-till

Manure

Predictors

Stover removal, predictors

1st-year corn31 site-years

2nd-year corn11 site-years

More trials needed: Can yield differences be detected with NDVI?

0

20

40

60

80

100

Economicoptimum

N rate(lb N/acre)

1st year corn - ROHE

Fall applied manure

4 fertilizer N rates

Corn 2011

2nd year corn – MARPE

Aerial imagery: - 1m spatial resolution- 4 bands (RGB, NIR)- collected Aug. 2011

Create shapefiles of plots in ArcMap:GPS points (10-70 cm accuracy)Projected to NAD 83 UTM Zone 15N

Change image band order:Originally IR R G B, changed to B G R IR in ArcMap

Calculate vegetation Indices:Create AOI for plotsUse signature editor to average pixel values for plots.

Methods

ROHE MARPE

Aerial images

Shapefiles of plots with -1.5 ft buffer

NDVI - MARPE

NDVI - ROHE

Methods of NDVI calculation

NDVI related to corn grain yield

Other indices were not better – IR/RED

Other indices were not better - TNDVI

Highest correlation – Silage yield vs. IR/Red

Can NDVI be used to detect corn yield differences?

Main effect P values (P > F)Grain yield Silage yield NDVI

Manure 0.484 0.164 0.326

N 0.003 0.025 0.042

Manure*N 0.515 0.339 0.952

Regrowth 0.177 - 0.656

N 0.021 - 0.018Regrowth*N 0.234 - 0.835

YES!

Are the slopes of yield and NDVI related? - ROHE

Are the slopes of yield and NDVI related? - MARPE

Conclusions

• Farmers could use aerial imagery to determine whether N fertilizer treatments affected corn yield.

• This would make it easy for farmers to conduct their own research.

• More fields and correlations are needed to validate this conclusion.

Future work: More fields, larger plots, Tassel cap transformations, online tools