N Fertilization in Colorado Raj Khosla Colorado State University May 19 th & 20 th Oklahoma State University Raj Khosla Colorado State University May 19 th & 20 th Oklahoma State University

Traditional practices of application of N fertilizer New precision nitrogen management

Corn N Fertilization: N rate (lb/A) = 35 + [1.2 x EY (bu/A)] N rate (lb/A) = 35 + [1.2 x EY (bu/A)] - [8 x avg. ppm NO 3 -N in soil*] - [8 x avg. ppm NO 3 -N in soil*] - [0.14 x EY (bu/A) x %OM] - [0.14 x EY (bu/A) x %OM] - other N credits (lb/A) - other N credits (lb/A) EY = expected yield %OM = percent organic matter * in the top 2 ft of soil. NO 3 Other credits: manure applications; legume crop, NO 3 in irrigation water, etc.

Legume Croplb N/Acre credit Alfalfa >60% stand (4-6 plants / sq ft.) % stand (3-4 plants / sq ft.) % stand (0-3 plants / sq ft.) 0-70 Dry beans25 Manurelb N/ton credit Beef10 5 (at 50%DM) Dairy15 3 (at 20% DM) Poultry25 20 (at 75% DM) N Credits: Dry basis---As is---

N Credits: NO 3 in irrigation water: N credit (lbs/A) = NO 3 -N (ppm) x 0.23* x water (inches) * an acre-inch of water contains 0.23 lbs on N for each ppm of NO 3 -N

Timing: Sprinkler irrigated: Starter band N; plus Side-dress at V6-V8 and additional N via fertigation and additional N via fertigation Furrow irrigated: Majority pre-plant apply N (heavy texture) Plus some side-dress (light 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

NO 3 -N in soil (ppm)Soil Organic matter 0-1 ft0-2 ft0-1% %>2.0% ---Fertilizer rate, lb N/A >15>18000 Dryland Wheat N Fertilization: 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]

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

I. Techniques of Identifying Management Zones & N Mgmt Bare soil imagery Topography Farmer’s experience Technique I. Technique I. Involves three data layers (SCMZ):

Technique II. Technique II. Involves six data layers (YBMZ): Bare soil imagery Topography Previous year’s yield map Soil O.M. Soil texture (sand/silt/clay%) Soil C.E.C. I. MZ Technique and N mgmt…

Soil E.C a. Technique III. Technique III. Involves only one data layers (ECMZ): I. MZ Technique and N mgmt…

Technique IV. 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 I. MZ Technique and N mgmt…

Step # 3 Take soil samples based on cluster sampling (2-4 cluster / strata) I. MZ Technique and N mgmt… Technique IV. Technique IV. Involves alternative soil sampling procedure to create management zones

Technique IV. Technique IV. Involves alternative soil sampling procedure to create management zones 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. Soil reaction (pH) Soil O.M. Soil Sand % Soil Silt% Soil Clay% Soil NO 3 I. MZ Technique and N mgmt…

Management Zones delineated for Site 1: Technique I Soil color based Technique II Soil color + yield + other soil prop. Technique III Soil E.C a. Technique IV Aerial imagery + Smart sampling + Spatial modeling I. MZ Technique and N mgmt…

Management Zones delineated for Site 2: Technique I Soil color based Technique II Soil color + yield + other soil prop. Technique III Soil E.C a. Technique IV Aerial imagery + Smart sampling + Spatial modeling I. MZ Technique and N mgmt…

Management Zones delineated for Site 3: Technique I Soil color based Technique II Soil color + yield + other soil prop. Technique III Soil E.C a. I. MZ Technique and N mgmt… Technique IV Aerial imagery + Smart sampling + Spatial modeling

Various Nitrogen Management Strategies are being tested: (i)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 Experimental Strips across management zones I. MZ Technique and N mgmt…

Nitrogen, Phosphorus and Potassium Removal Data I. MZ Technique and N mgmt…

a a b Nitrogen Uptake Range: 126 lbs/ac to 146 lbs/ac I. MZ Technique and N mgmt…

a ab b Phosphorus Uptake Range: 26 lbs/ac to 36 lbs/ac I. MZ Technique and N mgmt…

Potassium Uptake a a b Range: 40 lbs/ac to 50lbs/ac I. MZ Technique and N mgmt…

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. (R, G, B, and NIR) on one center pivot field.

F Blue (B) 450 to 520 nm F Green (G) 520 to 600 nm F Red (R) 630 to 690 nm F Near-Infrared (NIR) 760 to 900 nm II. Remote Sensing: Spectral Wavebands

V. Remote Sensing… Data is collected throughout the growing season from two view points 1) Top View 2) Inclined 75 o view Top View Inclined 75 o 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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