Yield Estimation and Quality Evaluation of Sweet Potato Using Spectral ReflectanceSATO Muneharu, ISHIGURO Etsuji, ISHIKAWA Daitaro, and SEKIOKA Shin-ichi

Faculty of Agriculture, Kagoshima University, Japan

0

100

200

300

400

500

600

150 170 190 210 230 250 270 290DOY

Num

ber

of le

aves

A-1 A-2 A-3 A-4 A-5 A-6 A-7 A-8

190～230day：y = 0.0055x + 0.2690 r = 0.80

230～302day：y = 0.0024x + 1.8176 r = 0.53

0

0.5

1

1.5

2

2.5

3

3.5

200 250 300 350 400 450 500 550 600Number of leaves

Tot

al le

af a

rea

(m2) y = 27.4580exp(1.5023x)

r = 0.83

0

500

1000

1500

2000

2500

3000

3500

1 1.5 2 2.5 3 3.5Total leaf area (m2)

Yie

ld (g

WB

)

0102030405060708090

100

400 500 600 700 800 900 1000

Wavelength (nm)

Ref

lect

ance

(%

)

152 155 159 164 169 176 180 190 194197 201 204 214 223 238 252 260 265273 279 287

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

400 500 600 700 800 900 1000

Wevelength (nm)

Val

ue

152 155 159 164 169 176 180 190 194 197

201 204 214 223 238 252 265 273 279 287

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

400 600 800 1000

Wevelength (nm)

Val

ue

152 155 159 164 169 176 180 190194 197 201 204 214 223 238 252260 265 273 279 287

y = 4.7099exp(-2.1523x)

ｒ = 0.80

1.2

1.7

2.2

2.7

3.2

0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6

ND520,710 ValueTo

tal l

eaf a

rea

(m2 )

y = 13770.exp(-7.8352x)r = 0.74

0

500

1000

1500

2000

2500

3000

3500

0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6ND520,710 Value

Yile

d (g

WB)

y = 3.2488x - 0.1412 r = 0.85

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

0.73 0.78 0.83 0.88

ND770,660 Value

N-co

ntents

(%)

y = 0.5825x + 0.1720 r = 0.75

0.2

0.22

0.24

0.26

0.28

0.3

0.32

0.34

0.1 0.15 0.2 0.25

ND550,660 Value

P-co

nten

ts (%

)

y = 1.3774x + 1.5869r = 0.71

2.3

2.5

2.7

2.9

0.6 0.65 0.7 0.75 0.8 0.85ND740,660 Value

K-con

tents (

%)

Fig.1 Changes of the number of leaves of sweet potato. Fig.2. Relationship between the total leaf area and the number of leaves. Fig.3 Relationship between the total leaf area and the yield.

Fig.4 Changes of spectral reflectance on the leaves of sweet potato.

Fig.5 First differential curves on spectral reflectance.

Fig.6 Secondary differential curves on spectral reflectance.

Fig.7. Relationship between the yield and ND520,710 index Fig.8. Relationship between the total leaf area and ND520,710 index

Fig.9 Relationship between the nitrogen content in leaf and ND770,660.

Fig.10 Relationship between the phosphorus content in leaf and ND550,660.

Fig.11 Relationship between the potassium content in leaf and ND740,660.

The total leaf areas, the numbers of leaves, the nitrogen contents of leaves, and the root yields of sweet potato plants were observed periodically throughout their cultivation period. And before digging up them, the spectral properties of their canopies were measured with a handheld spectroradiometer. Then the relationships among these traits were analyzed.Some of the NDVI models we had tried showed the close relation with total leaf area, the amount of yield, and the nitrogen content of leaves as well. This result opens up the way for the practical use of the spectral reflectance data in crop production.

Question: Can we estimate yield & quality of sweet potato before harvest remotely?Answer: Yes. Observe spectral reflectance signatures and use our model!

NIVI Model: ND520,710 = (R520 － R710) /(R520+R710)