Enhancing Sorghum Yield and Profitability through Sensor Based N

Management

Dave Mengel and Drew Tucker

Department of Agronomy

K-State

Situation: Risk

• Sorghum is the summer crop of choice where it is too dry to produce dryland corn.

• Yields vary widely from year to year due to weather, especially rainfall and temperature.– Using county level yield records, farmers

produce <50 bu/a sorghum 30% of the time in central Kansas and 40% of the time in western Kansas

Situation: N Management

• N fertilizer costs are significant, $20-40/a or more, depending on rate and source. This represents 10 to 20% of gross revenues.

• Optimum N rates vary from year to year.– Need varies due to changes in yield– Carryover varies dramatically from field to field– In-season N loss can be significant at times.– People refuse to use the profile N soil test

Long-term N Response Study Hutchinson KS

• Wheat-sorghum-soybean rotation. No-till– Sorghum yields averaged 72 bu/acre ‘91-’05– Range: 10-142

• <50, 3 years• 51-75, 5 years• 76-100, 4 years• >100, 3 years

Long-term N Response Study, Hutchinson KS

• Mean optimum N rate, 50 lbs N/acre– Range: 0-100

• 0, 4 years, 10 to 75 bu/a• 25, 2 years, 47 to 63 bu/a• 50, 3 years, 76 to 97 bu/a• 75, 2 years, 94 to 107 bu/a• 100, 4 years, 50 to 142 bu/a• 125, 0 years

The Big Question

• Can a N management strategy be developed to: – Reduce economic risk in bad years?– Take advantage of the potential of good years?– Fine-tune N needs in high yielding irrigated crops?– Reduce environmental risk in sensitive

environments?– Enhance profitability in the long run?

Our Approach

• Apply a base level of N to carry the crop through the first 40-50 days. 20 to 30 lbs/a

• Evaluate the crop at 35-45 days– If yield potential is low, soil moisture is limited

and outlook bleak……. punt– If moisture reserves and weather outlook are

good……., use sensor technology to estimate yield potential, and add appropriate N

The Devils in the Detail

• How good is your weather crystal ball?

• How early can we accurately estimate yield potential in sorghum?

• How early can we pick up differences in N levels between “normal” and “reference” strips?

• How late can N be applied and still be utilized and/or get a response?

More Details

• How do we need to apply late N?– And not damage the crop– And get the best response

• How much N must be put down early to maximize yield potential in good years?

• Can sensors be used to do this on the go?

Procedures 2006

• Locations: Manhattan, Belleville, Tribune, Hutch/Partridge

• No-till planted, surface plus profile N ST• Normal practices for weeds, bugs, fert etc• N treatments: 0 to 150 lbs N; pre, post/sd or

both.• Measure: leaf, stover and grain N, yield and

various sensor measurements using Greenseeker, Crop Circle and SPAD meter

Tribune

Belleville

Hutch

Manhattan

INSEY vs. Grain Sorghum Yield in 2006

y = 4.9019e156.22x

R2 = 0.5869

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

180.0

200.0

0 0.005 0.01 0.015 0.02 0.025 0.03

INSEY (NDVI/Days After Planting)

Yie

ld B

u/A

c

NDVI/GDD's vs. Grain Sorghum Yield in 2006

y = 4.4102e3804.4x

R2 = 0.6562

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

180.0

200.0

0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012

NDVI/GDD's

Yie

ld B

u/A

c

NDVI vs. Grain Sorghum Yield in 2006

y = 0.8018e7.177x

R2 = 0.7745

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

180.0

200.0

0.3 0.4 0.5 0.6 0.7 0.8 0.9

NDVI at GS-3 (30-40 days post-plant)

Yie

ld B

u/A

c

Sufficiency Index vs. Relative Grain Sorghum Yield in 2006

y = 2.1715x - 126.64

R2 = 0.8695

0

20

40

60

80

100

120

0 20 40 60 80 100 120

Sufficiency Index

Rel

ativ

e Y

ield

%

Sufficiency Index vs. Change in Yield from Additional N in 2006

y = -1.4183x + 149.01

R2 = 0.7681

-10

0

10

20

30

40

50

60

70

50 60 70 80 90 100 110

Sufficiency Index

Yie

ld B

u/A

c

-20

-10

0

10

20

30

40

50

60

70

80

0.8 1 1.2 1.4 1.6 1.8

Relationship of Response Index and ∆ Yield in Sorghum in 2006

Response Index, NDVI reference/ NDVI unfertilized

∆G

rain

Yie

ld B

u/A

c∆Yld = 101.05 RI -91.95

R2= .73

Effect of time and method of N application on sorghum yield, 2006

0

20

40

60

80

100

120

Check 40 day SB 30 day SB 40 day Inject 30 day Inject

2007 Work

• Continuing work on sorghum, wheat and corn at multiple locations

• Plan on providing sensor based N rate calculators for wheat and sorghum this fall on our ST website (sorghum, developed by Drew and Bill Raun, is currently on the OSU/NUE site)

• Starting preliminary work on cotton and canola

GS-3 NDVI .60, check plot GS-3 NDVI .65, reference plot

GS-3 N Rec. 45 lbs/Ac

Questions?