Development of a Response Index for Corn

Development of a Response Index for Corn

Development of a Response Index for Corn

Robert Mullen

Ohio State University

Robert Mullen

Ohio State University

Response IndexResponse Index

• RI first proposed by Johnson and Raun, 2003 (inverse of sufficiency index)

• RI = Yield of N Rich / Yield of Check (0N)– Direct measure of N response

• RI first proposed by Johnson and Raun, 2003 (inverse of sufficiency index)

• RI = Yield of N Rich / Yield of Check (0N)– Direct measure of N response

Response IndexResponse Index

• Can we reliably predict the response to applied N during the growing season?

• Environmentally and economically important– Less N subject to denitrification, leaching, and

runoff– Produce more with less inputs

• Is the relationship stable at different stages of growth?

• Can we reliably predict the response to applied N during the growing season?

• Environmentally and economically important– Less N subject to denitrification, leaching, and

runoff– Produce more with less inputs

• Is the relationship stable at different stages of growth?

Response IndexResponse Index

• In-season estimates of RI were used to identify RI at harvest for winter wheat

• In-season estimates of RI were used to identify RI at harvest for winter wheat

y = 0.99x - 0.01

r2 = 0.65

0

0.5

1

1.5

2

2.5

3

3.5

4

0 1 2 3 4

RI-NDVI

RI-

Har

vest

y = 0.99x - 0.01

r2 = 0.65

0

0.5

1

1.5

2

2.5

3

3.5

4

0 1 2 3 4

RI-NDVI

RI-

Har

vest

Response IndexResponse Index

• Would RI for corn work as well?

• Can RI be identified at early stages of growth (< V8)?

• Would RI for corn work as well?

• Can RI be identified at early stages of growth (< V8)?

Response IndexResponse Index

• Varvel et al., 1997– Used SPAD meters to identify N response at

various stages of growth• V6 – R3

• Relationship has been established between GNDVI and SPAD meter reading (Shanahan et al., 2003)

• Varvel et al., 1997– Used SPAD meters to identify N response at

various stages of growth• V6 – R3

• Relationship has been established between GNDVI and SPAD meter reading (Shanahan et al., 2003)

Can RI work for corn?Can RI work for corn?

• Varvel data shows that pseudo-RI can be determined at various stages of growth– Very little data for some stages of growth– Lack of response at most locations (especially

where corn followed soybeans)

• Varvel data shows that pseudo-RI can be determined at various stages of growth– Very little data for some stages of growth– Lack of response at most locations (especially

where corn followed soybeans)

Can RI be estimated at early stages of growth?

Can RI be estimated at early stages of growth?

• Red NDVI determined significant difference between N rate at V4

• Red NDVI determined significant difference between N rate at V4

N rate RNDVI RNDVI

0 0.209 0.204

60 0.234 0.249

120 0.247 0.239

180 0.263 0.244

Linear P=0.0149 P=0.0319

Can RI be estimated at early stages of growth?

Can RI be estimated at early stages of growth?

• Green and red NDVI determined differences between treatments at V6

• Green and red NDVI determined differences between treatments at V6

N rate RNDVI GNDVI

0 0.531 0.437

60 0.654 0.530

120 0.664 0.546

180 0.678 0.540

Linear P=0.0001 P=0.0001

DiscussionDiscussion

• Practicality of N rich strip– Production scale agriculture without

sophisticated sensors– Answer N loss questions and helps make N

application decisions

• Practicality of N rich strip– Production scale agriculture without

sophisticated sensors– Answer N loss questions and helps make N

application decisions

DiscussionDiscussion

• The earlier, the better– Determination of RI early in the season would

be better• Lack of high-clearance application equipment• Increase in application window

• The earlier, the better– Determination of RI early in the season would

be better• Lack of high-clearance application equipment• Increase in application window

Conclusions?Conclusions?

• Continue research to identify relationship between RI-NDVI and RI-Harvest for corn.

• “Calibrate” RI at various growth stages with N application rates if yield cannot be predicted accurately (this will be difficult).

• Encourage use of N rich strips in production fields to answer simple N application questions.

• Continue research to identify relationship between RI-NDVI and RI-Harvest for corn.

• “Calibrate” RI at various growth stages with N application rates if yield cannot be predicted accurately (this will be difficult).

• Encourage use of N rich strips in production fields to answer simple N application questions.

Questions?Questions?