N Fertilization in Colorado

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N Fertilization in Colorado
Raj Khosla Colorado State University May 19th
20th Oklahoma State University
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• Traditional practices of application of N
  fertilizer
• New precision nitrogen management

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Corn N Fertilization
Other credits manure applications legume crop,
NO3 in irrigation water, etc.
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N Credits
Legume Crop lb N/Acre credit
Alfalfa gt60 stand (4-6 plants / sq ft.) 100-140
30-60 stand (3-4 plants / sq ft.) 70-100
0-30 stand (0-3 plants / sq ft.) 0-70
Dry beans 25
Manure lb N/ton credit
Beef 10 5 (at 50DM)
Dairy 15 3 (at 20 DM)
Poultry 25 20 (at 75 DM)
Dry basis ---As is---
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N Credits
NO3 in irrigation water N credit (lbs/A) NO3-N
(ppm) x 0.23 x water (inches) an acre-inch of
water contains 0.23 lbs on N for each ppm of
NO3-N
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Timing
Sprinkler irrigated Starter band N plus
Side-dress at V6-V8 and additional N
via fertigation Furrow irrigated Majority
pre-plant apply N (heavy texture) Plus
some side-dress (light texture) With manure
application, they typically apply in Fall/Spring
plus side-dress N
Many farmers do not credit for manure, use it
for disposal purposes
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Dryland Wheat N Fertilization
NO3-N in soil (ppm) NO3-N in soil (ppm) Soil Organic matter Soil Organic matter Soil Organic matter
0-1 ft 0-2 ft 0-1 1.1-2.0 gt2.0
---Fertilizer rate, lb N/A--- ---Fertilizer rate, lb N/A--- ---Fertilizer rate, lb N/A---
0-3 0-5 75 75 75
4-6 6-9 75 70 50
7-9 10-12 75 45 25
10-12 13-15 50 20 0
13-15 15-18 25 0 0
gt15 gt18 0 0 0
Above table is for yield of 50 bu/A. To adjust N
rate for expected yields, add or subtract 25 lb
N/Ac for each 10 bu/A difference. Max N rate is
75lb N/A for dryland winter wheat
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New precision Nitrogen management strategies

• Management zones based N management
• Evaluating 4 different techniques
• Classifying fields into low, medium, and high
  productivity areas
• Real-time remote sensing based N management

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I. Techniques of Identifying Management Zones N
Mgmt
Technique I. Involves three data layers (SCMZ)
Bare soil imagery Topography Farmers experience
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I. MZ Technique and N mgmt
Technique II. Involves six data layers (YBMZ)
Bare soil imagery Topography Previous years
yield map Soil O.M. Soil texture
(sand/silt/clay) Soil C.E.C.
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I. MZ Technique and N mgmt
Technique III. Involves only one data layers
(ECMZ)
Soil E.Ca.
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I. MZ Technique and N mgmt
Technique IV. Involves alternative soil sampling
procedure to create management zones (SSMZ)
Step 1. Acquire bare soil imagery
Step 2. Differentiate spectral
variations/ strata using spatial statistical
techniques
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I. MZ Technique and N mgmt
Technique IV. Involves alternative soil sampling
procedure to create management zones
Step 3 Take soil samples based on cluster
sampling (2-4 cluster / strata)
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I. MZ Technique and N mgmt
Technique IV. Involves alternative soil sampling
procedure to create management zones
Soil reaction (pH) Soil O.M. Soil Sand Soil
Silt Soil Clay Soil NO3
Step 4. (a) Use spatial modeling to predict
measured soil properties, and
(b) based on predicted soil properties for the
entire field, management zones are delineated.
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I. MZ Technique and N mgmt
Management Zones delineated for Site 1
Technique IV Aerial imagery Smart sampling
Spatial modeling
Technique I Soil color based
Technique II Soil color yield other soil prop.
Technique III Soil E.Ca.
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I. MZ Technique and N mgmt
Management Zones delineated for Site 2
Technique IV Aerial imagery Smart sampling
Spatial modeling
Technique I Soil color based
Technique II Soil color yield other soil prop.
Technique III Soil E.Ca.
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I. MZ Technique and N mgmt
Management Zones delineated for Site 3
Technique IV Aerial imagery Smart sampling
Spatial modeling
Technique II Soil color yield other soil prop.
Technique I Soil color based
Technique III Soil E.Ca.
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Experimental Strips across management zones
I. MZ Technique and N mgmt

• Various Nitrogen Management
• Strategies are being tested
• Traditional uniform N strategy
• (ii) Grid soil sample based variable N mgmt.
  strategy
• (iii) Constant yield goal based variable N mgmt.
  strategy
• (iv) Variable yield goal based variable N mgmt.
  strategy

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I. MZ Technique and N mgmt
Nitrogen, Phosphorus and Potassium Removal Data
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I. MZ Technique and N mgmt
Nitrogen Uptake
a
a
b
Range 126 lbs/ac to 146 lbs/ac
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I. MZ Technique and N mgmt
Phosphorus Uptake
a
ab
b
Range 26 lbs/ac to 36 lbs/ac
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I. MZ Technique and N mgmt
Potassium Uptake
a
a
b
Range 40 lbs/ac to 50lbs/ac
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II. Remote Sensing
Remote-sensing for in-season nitrogen management

• High Clearance tractor
• Mounted with GPS unit 25 feet high radiometer
• Measuring canopy reflectance on four spectral
  wavebands
• (R, G, B, and NIR) on one center pivot
  field.

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II. Remote Sensing
Spectral Wavebands

• Blue (B) 450 to 520
  nm
• Green (G) 520 to 600 nm
• Red (R) 630 to 690
  nm
• Near-Infrared (NIR) 760 to 900 nm

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Top View
V. Remote Sensing
Data is collected throughout the growing season
from two view points 1) Top View 2) Inclined
75o view
Inclined 75o view
When areas within the field measure an NRI ?
0.95, the farmer is advised to fertigate an
appropriate amount of N as soon as possible
NRI Nitrogen Reflectance Index (Bausch and Duke
2001)
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Thank you