In-Season N Management:Minnesota Perspective

2010 Nitrogen Algorithm WorkshopAug. 3 and 4th Stillwater, OK

Jeff Vetsch and Gyles RandallUniv. of Minnesota

Southern Research and Outreach Center

Research questions (answers)• Performance of mid- to late-season N

applications for corn in MN

• Sensor response vs crop response in corn after soybean and corn after corn

• Sulfur deficient corn vs N deficient corn: Can sensors delineate?

• Wet fields in Northern Corn Belt: Sensor based supplemental N recommendations.

Corn yield responses to mid to late sidedress NTotal Sidedress Corn yield Precip 3-wk

Site Rot. N rate Timing PP Split After SDlb N/A bu./ac. Inches

04-1 CC 120 avg. V8 181 181 6.104-1 CC 120 avg. V12 181 179 3.405-1 CS 105 avg. V9 151 152 1.705-1 CS 105 avg. V12 151 150 2.705-2 CC 160 V6 174 188 3.905-3 CC 120 avg. V10 167 158 4.606-1 CS 90 V7 197V2 195 1.106-1 CS 90 V12 197V2 184 3.706-2 CC 100 avg. V7 195 186 0.706-3 CS 90 avg. V6 213 208 0.906-4 CS 90 V6 191 172 - - -06-5 CS 90 V6 195 186 - - -07-1 CS 90 V7 181V2 176 2.407-1 CS 90 V12 181V2 128 2.007-2 CC 100 avg. V8 155 159 2.407-3 CC 120 avg. V6 184 189 3.107-3 CS 90 avg. V6 214 215 3.1

Corn yield responses to mid to late sidedress NTotal Sidedress Corn yield Precip 3-wk

Site Rot. N rate Timing PP Split After SDlb N/A bu./ac. Inches

08-1 CS 90 V7 168V2 161 1.408-1 CS 90 V12 168V2 150 5.508-2 CC 120 avg. V6 216 213 0.908-2 CS 90 avg. V6 230 229 0.909-1 CC 120 avg. V6 192 186 2.309-1 CS 90 avg. V6 204 202 2.3

1 of 23 sites gave a positive yield response to sidedress N at V6

8 of 23 sites gave a negative yield response (averaged 16 bu./ac.)

14 of 23 sites had no response - similar yields

Summary: Performance of mid-season N applications in Minnesota

• In 35% of comparisons split application of N yielded less than a single application.

• Because of the risk of a yield penalty with mid-season N applications on dry land corn, Univ. of Minnesota recommends all sidedress N be applied no later than V6.

Corn yield response to sidedress UAN applicationRelative

Grain N NUE Chloro.V2 SD Timing Yield Silage Fert. N VT-R1 V7 V9

bu/A lb N/A bu/lb N % NDVI NDVI

0 0 V2 111 72 70.9 0.620 0.75490 0 V2 182 130 0.79 93.9 0.664 0.806

180 0 V2 201 166 0.50 98.7 0.674 0.81430 60 V2+V7 183 134 0.80 92.9 0.660 0.80215 75 V2+V7 172 126 0.67 91.9 0.640 0.77815 75 V2+V12 154 108 0.48 83.0 0.649 0.778

LSD: 0.10: 8 7 1.6 0.019 0.013

N rate and timing GreenSeeker

- lb N/A -

2006-08 avg., corn after soybean at Waseca

Summary: Split N applications of UAN• No differences in NDVI at V7 and V9 were

found among the 90 and 180 lb/A N applied at V2 and 30+60 lb/A (V2+V7) treatments.

• Very small differences in NDVI were found between the zero N control and 180 lb N/A, this would make algorithm calibration difficult.

• Appling a small amount of starter N (15 lb N/A) at V2 and then delaying N application to V7 or V12 decreased yield, N uptake and NUE, compared with 90 lb N/A at V2 and 30+60 lb N/A at V2+V7.

Effect of crop rotation on corn response to preplant vs split N: NDVI, yield and NUE.

NDVI Grain NUE NDVI Grain NUEPreplant V6 V8 Yield Fert. N V7-8 Yield Fert. N

lb N/A lb N/A NDVI bu/A bu/lb N NDVI bu/A bu/lb N

0 0 0.76 167 0.64 8660/80 0 0.79 208 0.68 0.74 174 1.10

120/160 0 0.80 223 0.47 0.76 216 0.8130/40 90/120 0.78 224 0.48 0.73 214 0.80

RI: 1.06 1.34 1.18 2.51

Corn after soybean Corn after cornN rate (CSC/SCC)

2007-09 avg., Port Byron sil, SE MN

Observations: Effect of crop rotation

• Corn following soybean– Response index (RI) = 1.06 for NDVI at V8;

RI = 1.34 for grain yield.

• Corn after corn– RI = 1.18 for NDVI at V7-8; RI = 2.51 for

grain yield (very responsive site).

The effect of sulfur on early growth of corn and relative leaf chlorophyll content at R1 at Waseca.

V7 (June 21, 2010) R1 Relative

Sulfur rate Plant height DM Yield Leaf chloro.

lb/A inch ton/A %

0 32.5 0.260 90.8

5.8 34.6 0.305 96.1

11.5 34.8 0.306 98.8

Funding provided by AFREC & FFF

Sulfur responses in corn documented on medium and fine textured soil in MN.

• Corn fertilized with S was 7% taller, had 17% more dry matter, and was a darker green color than the untreated control.

• Implications for in-season sensing for N:– Sensors unlikely to delineate between N & S – Sulfur deficient corn frequently shows symptoms

of N deficiency as well, especially later in the season.

– Sulfur responses are more common in corn after corn with high residue (reduced tillage).

Nafziger recommends applying nitrogen to corn in low, wet areas only after the water is gone and plants start to green up, which indicates they are getting some oxygen. If plants are stunted and far behind the rest of the field, applying nitrogen may not help."I don't recall seeing severely stunted, deficient plants standing in saturated soils come back to produce much yield," he said. "That's not proof it can't happen, but the deck is stacked against these plants. Applying more inputs may be a demonstration of more hope than is justified."

“Realize that the areas showing nitrogen deficiency have also lost some yield potential, so a full-rate application is likely not the best alternative, simply because the plant won't be able to use all that nitrogen to make yield. The sooner you apply nitrogen, the better response you are likely to see.”

“… areas needing a rescue nitrogen application are most often patchy, so targeted applications rather than even applications across the field are key to minimizing cost and potential nitrogen loss to the environment and to increasing return on investment.”

“Aerial photographs can be converted into variable nitrogen rate maps to guide a variable rate applicator.”

Fabián G. Fernández

Appropriate Strategy?

NDVI

Ap

plicati

on

Rate

“Starve the Rich”

NDVI

Ap

plicati

on

Rate RI =1.5

RI = 2.0

Multiple Factors + N Limiting Yield

NDVI

Ap

plicati

on

Rate

Compromise Strategy

Ap

plicati

on

Rate

NDVI

“Feed the Rich”

Raun et al., 2007

Are sensor based algorithms designed for these extreme conditions (rescue N

applications) and are they effective?• No reference strip in most fields

– What does one use for a reference?

• What if much of field has reached NDVI saturation? Red-edge?– Can sensors delineate between sufficient

and deficient areas of fields near NDVI saturation? Mid-row sensing?

Questions Jeffrey Vetschjvetsch@umn.edu

http://sroc.cfans.umn.edu/http://sroc.cfans.umn.edu/People/Staff/JeffreyVetsch/

index.htm

507-837-5654

Univ. of Minnesota

Southern Research and Outreach Center

Starter NATS Only No Starter or S Broadcast S, no N

Photo courtesy of Dan Kaiser, 2009