Early Season Rainfall for Quantifying Risk in Nitrogen Management

70th Annual Soil and Water Conservation Society Conference

July 27, 2015Peter Kyveryga, Analytics, Iowa Soybean Association

Pat Reeg and Tristan Mueller, On-Farm Network®, Iowa Soybean Association

Chris Anderson, Agronomy, Iowa State University

Nitrogen Management and Rainfall

A recent surge of commercial predictive N tools raise many questions related to:

• Impact of rainfall on nitrogen (N) loss and corn N status.

• Differences between application timing, rates, forms, methods in different cropping systems.

Spring and Summer Rainfall in Iowa

Chris Anderson, Agronomy, Iowa State Univ.

May-June Rainfall in 2015

Iowa Environmenatl Mesonet

Risk Assessment Paradigm

1. Agronomic risk of over or under N applications.

2. A need for a large number of trials (e.g. N Rate Calculator, Iowa State University) to estimate probabilities.

3. Addressing diverse management N practices in Iowa.

Adaptive Process to Quantify Risk

• Collecting feedback about N status : “Annual N Check-Up”.

• Estimating “When, Where and at What risk a given corn field would have Deficient or Excessive N status”.

Feedback about Late-Season Corn N Status

3424 corn fieldsfrom 2006 to 2014

Late-Season Aerial Imagery

Corn Stalk Nitrate Test

Des Moines Lobe and North West Iowa Plains

1800 fields2006 to 2014

N Rates Resulting in Optimal Corn N Status

Estimating Risk of Deficient or Excessive N Status

Defi

cien

t Excessive

Sufficient

Deficient Timing and N formsTotal N RatePrevious CropRainfall Year Interaction of several factors

=f{

Sufficient &Below

Excessive =f{

Probability of N Deficiency in Central Iowa

Normal rainfall range

Corn after SoybeanN rate=150 lb N/acre

Central and NW Iowa

Corn after CornN rate=180 lb N/acre

Fall AA

Spring AA

Fall SM

SD N and Spring UAN

May through June Rainfall (in) May through June Rainfall (in)

Northeast Iowa

685 fieldsfrom 2006 to 2014

Probability of N Deficiency in Northeast Iowa

Corn after SoybeanN rate=150 lb N/acre

North East Iowa

Corn after CornN rate=180 lb N/acre

May through June Rainfall (in) May through June Rainfall (in)

North East Iowa

Why Higher Risk for Corn after Soybean?

1. Greater NO3 loss in wet years due to rapid decomposition of soybean residues.

2. Greater tile flow under soybean.

3. A lower frequency of manure applications.

4. Unreliable estimates of soybean N credits.

Probability of Excessive N Status in North East

Corn after SoybeanMay-June Rainfall = 10 in

Corn after Corn May-June Rainfall = 10 in

Northeast IowaNortheast Iowa

Risk Category Interpretations

Probability Descriptive category

0 - 0.25 Very Low

0.25 - 0.50 Low

0.51 - 0.60 Moderate

0.61 - 0.80 High

0.81 – 1.0 Very High

No Concern

Risk Matrix of Deficient N Status: Des Moines Lobe

N Rate (lb/acre)

May-June Rainfall (in)5 11 16

Spring AA130 0.19 0.40 0.60150 0.16 0.35 0.56160 0.15 0.33 0.53

Spring UAN130 0.39 0.64 0.81150 0.35 0.59 0.77160 0.32 0.57 0.74

SD UAN/AA130 0.36 0.61 0.79150 0.33 0.57 0.76160 0.31 0.55 0.74

Corn afterSoybean

Developing Nitrogen Risk Calculator

1. Phase 1: 110 National Weather Service Cooperative Observer Stations in Iowa.

2. Phase 2: 4-km radar rainfall from the Iowa Environmental Mesonet.

3. To conduct “What-if-Scenario Analyses”, 4R Management education and risk assessment .

Acknowledgements

To hundreds of farmers and agronomists in Iowa

USDA Natural Resource Conservation Service

Integrated Farm Livestock Management Project

Iowa soybean checkoff

Many private and public partners