1. Managing Nitrogen in Kansas Cropping Systems
Soil Fertility 101

2. Nitrogen is critical for crop production in Kansas
Plant available N is naturally deficient in most agricultural soils
Our primary crops utilize large amounts of N
Nitrogen cost is going out the roof
A major environmental issue in Kansas and the US is loss of nitrate N from agricultural soils

3. Nitrogen is critical for crop production in Kansas
Most Kansas soils contain 1,000’s of pounds of N per acre
Why isn’t all that N available to crops?
Will it become available?
How much N is normally available to crops?
Can we count on it?

4. Soil Organic Matter- the reservoir for storing N in soils
The vast majority of the N present in most soils is in SOM
Several “pools” or forms of organic materials are present in soils
Recently added plant and animal materials
Soil bio-mass
Partially decomposed organic materials
Recalcitrant decomposition products-true soil OM
What we refer to as SOM is all of the above!

5. How much SOM and N is normally present?
The soil organic matter content of most agricultural soils in Kansas ranges from 1-4%, with an average of 2.2%
Soil organic matter is roughly 5% N
So……
2,000,000 pounds X = 44,000 lbs SOM
44,000 lbs SOM/a X 0.05 = 2,200 lbs N/a

6. How does organic N become available to plants?
The process is called mineralization or ammonification, and is the breakdown of proteins and amino acids as a source of energy.
R-NH2 + H2O NH3 + R-OH + Energy
This is an aerobic biological process sensitive to temperature, and soil moisture. But mineralization occurs through fall and winter, when ever the soil is not frozen.

7. Transformation of inorganic N to organic N - immobilization
In the presence of plenty of carbon/energy, the process can be reversed. Inorganic N is utilized to produce protein to grow more “bugs” to use the carbon/energy.
Similar to what happens in a rumen when we add urea to balance a high energy/low protein ration.

8. The balance between immobilization and mineralization
The key driver of mineralization is the C:N ratio of the residue/plant material/animal waste being added to the soil
If the C:N ratio is < 25:1, net mineralization will likely occur, and N will be released
If the C:N ratio is >25:1, net immobilization will likely occur, and N will be tied up

9. Typical Carbon and Nitrogen Content of Organic Materials
Source
Microorganisms
Soil O.M.
Alfalfa
Soybean Residue
Rotted Manure
Green Rye
Cornstalks
Small grain straw
Grain Sorghum
Sawdust
% Carbon 50 52 40
--- --
% Nitrogen
6.2
5.0
3.0
--- --
0.7
0.5
0.1
C:N Ratio
8:1
10:1
13:1
15:1
<20:1
36:1
60:1
80:1
400:1

10. So what does all this mean?
Soil organic matter mineralizes at a rate of around 2% per year, primarily during March through December.
44,000 lbs OM X 0.05% N X 0.02% min = 44 pounds N/year.
Most of this would be available to summer crops
Most would be available to wheat in a wheat/fallow rotation
Only a portion would be available to DC wheat, since the preceding summer crop would use it

11. So what does it all mean?
The amount of N available from previous crop residue (Previous crop credit) will depend on the amount of residue and the C:N ratio
Little or no credit with wide C:N ratios
Significant credits with narrow C:N ratios
Also impacted by the amount of residue above and below ground (think alfalfa crowns and roots and the adjustment of alfalfa credit for stand)

12. General KSU N Recommendation for Corn
Nrec = [Yld x 1.6*] – 20 x %SOM – PCA – PNST – H2O – Manure
Previous Yield Goal
Crop %SOM = % Soil OM x 20 = 40
PCA = Previous Crop Adjustment
Corn Corn = 0, sorghum = 0
Wheat Wheat = 0, sunflower = 0
Sorghum soybean = 40, poor alfalfa = 50
Sunflower PNST = 24 in. N Soil Test = 30
Soybean in fallow systems add 20 lbs
Alfalfa H2O = Irrigation Water N = 0
Manure = 0
*1.6 is the estimated amount of N taken up by the whole plant, roots, stalk and ear.

13. Nitrogen fertilizer recommendations for corn following different crops
Previous crop Yield Goal, bu/a
________________________________________
Corn
Wheat
Soybeans 30*
Alfalfa 30* 30*
Fallow 30*
2% soil organic matter, no profile nitrate test

14. A recommendation based on default values is not accurate!!!!
Soil organic matter mineralization
Default value is 2% SOM x 20 lbs N/a/% =40
Values found range from <1 to >5, average is 2.2% SOM

15. A recommendation based on default values is not accurate!!!!
24 inch profile soil N test
Default value is 30 pounds per acre
Spring 2007 Survey of Kansas fields going to corn or sorghum found values ranging from 21 to 416 lbs nitrate N, with average of 98 lb N per acre

16. For an accurate recommendation, figure out how much N is really available
Yield Goal, bu/a
Previous crop
___________________dryland___________irrigated______
defaults observed* default observed*
Wheat
Soybeans
$ $ $40
* 98 lbs N in profile, 1.2 % SOM, 5 ppm N in H20

17. General KSU N Rec’s for Wheat
Nrec = [Yld x 2.4] – PNST – %SOM – PCA– H2O – Manure
additional adjustments for tillage and grazing
Previous Yield Goal
Crop %SOM = % Soil OM x 10 = 20
PCA = Previous Crop Adjustment
Corn Corn = 0, sorghum = -30
Wheat Wheat = 0, sunflower = -30
Sorghum soybean = 0, fair alfalfa =+20
Sunflower Fallow = +20**
Soybean PNST = 24 in. N Soil Test = 30
Alfalfa H2O = ppm N x 0.226/inch
Manure = 0
No-till = - 20
Grazing = - 40/100 lbs gain
*2.4 is a coefficient, it does not represent pounds of N or pounds of fertilizer

18. Managing N Fertilizers

20. N response to dryland corn: Manhattan, 2006
N Rate N Uptake Grain Yield Harvest Percent N Increment Increment
lbs/a lbs/a bu/a Index Recovery Response Recovery
40 S % %
70 S+sd % %
100 S+sd % %
130 S+sd % %
160 S+sd % %
190 S+sd % %
220 S+sd %
200 pp %

21. N Rates as a function of NUE
KSU N Rates are based on an assumed NUE of 50%
If you can consistently attain 10% higher NUE, rates can/should be reduced!
But, if you have soils prone to high N loss or use practices which result in lower NUE, rates should be increased!

22. Example: Corn following wheat
N Rate = (ygx1.6) – 20xSOM - PNST- PCA
= (160x1.6) – 20x2.5 – 30 – 0
= 256 – 50 – 30 = 176
N Rate = 50% NUE would provide pounds additional N
(176 x 0.5 =88)
N needed at 60% NUE to give 88 lbs N
= 88/0.6 =147!!!
N needed at 40% NUE to give 88 lbs N
= 88/0.4 = 220!!!!!!!!

23. The first step in managing N is figuring out how much is present
Soil Organic Matter Test
%SOM X 20 lbs/a
Profile N test at the right time!
Prior to planting wheat, test in August/September
Prior to planting corn/sorghum, test in March/April
Sampling later will confuse residual nitrate with SOM and Previous crop credits
Test irrigation water
Test manure

24. An alternative first step: using sensor technology to measure the N contributed by soil
Sensor technology has developed rapidly
Both handheld and on the go sensors are available
These systems are designed to make in-season additions of N to crops
KSU has current sensor based recommendation systems for wheat, sorghum and corn
OSU has excellent sensor based recommendation systems also

25. General Approach

26. Our General Approach to Algorithms and Rate Calculators
Our approach to developing rate calculators is based on: An in-field reference strip; calculated response index (RI); relationship of RI at sensing to RI at harvest; expected N uptake; and NUE.
Yield potential is estimated by sensor from reference strip.
Yield response to additional N is based on the expected RI at harvest based on RI at sensing and yield potential of reference.
Additional N need to optimize yield is estimated from N uptake data across a range of yield levels,
Estimated NUE is used to covert N uptake need to fertilizer N need. Base is 50%, but can be adjusted up or down based on soils, climate or management practice.

27. Winter Wheat N Rate Calculator

28. Winter Wheat Yield Prediction 2006-2008
INSEY is NDVI/DAP where the average temp is greater than 40 degrees F. This is the min. temperature for wheat growth. 28

29. Winter Wheat Nitrogen Sensor Calculator Performance 2006-2009
Johnson 2009 was abnormally dry after N application, which resulted in lower NUE, and in Partridge heavy weed pressure induced a higher N response than what was expected. 29

30. K-State Sorghum N Rate Calculator

31. Grain sorghum yield relationship used to estimate yield potential of the field.
DAP is days from planting to sensing when average temperature is greater than 63 degrees F which is the min. temperature for seed germination. 31

32. Comparison of Sensor Based N Rec’s to Soil Test Based Rec’s, 2006-2008
This is the new summary table when using the table listed in the previous slide and using efficiency factors of .4 for below 60, .5 if it was between , .55 if it was between , and .60 for , and .65 for above. One important thing to remember is if we get within 10 pounds one way or the other is we are really only trading dollars once you get that close due to the nature of the N responsiveness curve. In years where the price of grain is low compared to the price of fertilizer, we want to be 10 pounds on the negative side, and vice versa. A yield goal of 120 was used at Manhattan, and 80 at all other sites. 32

33. The second step is determining the potential for N loss
N can be lost through several mechanisms
Runoff
Leaching
Denitrification
Volatilization
Immobilization
Most involve water and are impacted by soil properties and temperature

34. The third step is assessing the “tools” available to you
These include:
N timing-fall,spring, preplant,sidedress,fertigation
Placement-broadcast, knifed, dribble banded
Sources, AA, urea, UAN,
Specialty fertilizers, ESN
Additives, Agrotain
Sensors

35. Nitrogen loss mechanisms
Leaching: downward movement of nitrate N
Generally involves sandy, highly permeable soils
Of particular concern in areas of shallow, unprotected aquifers
The longer the time before uptake adds to the risk, by allowing N to convert to nitrate, and by increasing risk of leaching event
Irrigation can increase risk
Nitrate or quickly nitrate sources add to risk

36. Tools to deal with leaching
Traditional tool used to handle leaching
in sandy soils is delayed application or sidedressing

37. Other options Slow release fertilizers: IBDU, Urea formaldehyde
Coated urea
Sulfur coated
Polymer coated, ESN

38. Dealing with denitrification

39. Nitrogen loss mechanisms
Denitrification: gaseous loss of N from nitrate
A problem with nitrate, not ammonium
Generally involves heavier, less permeable soils
Time before use adds to the risk
Irrigation can increase risk
Nitrate or quickly nitrate sources add to risk
Warm temperatures greatly increase risk

40. Tools to deal with denitrification
Timing- sidedressing and fertigation
Nitrification Inhibitors
Slow Release Products

41. Flooding and N efficiency
N Source Weeks after Applying
-----percent yield ---- NH
UAN
120 pounds N applied sidedress
4” water applied

42. Response to Time of Application, Controlled Release Fertilizers and Nitrification Inhibitors in No-till Corn, Manhattan 2009
Treatment Yield, bu/a
No N
February urea on surface 159
February ESN on surface 179
Urea V
Urea V-2+ Agrotain + DCD 201
Urea/ESN blend 201
Weber and Mengel

43. Nitrogen loss mechanisms
Volatilization: gaseous loss of ammonia from surface applied urea
Requires presence of free ammonia at or very near the soil surface
Higher pH increases risk by favoring NH3 vs NH4
Evaporation of water is the driving force
Drying of wet soils-warm and windy
Generally associated with no-till or managed grass

44. Nitrogen loss mechanisms
Immobilization: utilization of N by biomass
Generally involves the presence of high C:N residue or manure
Placing fertilizer away from C reduces risk
Giving material time to partially decompose and reduce C:N ratio can help
Banding N can help by reducing N/C contact
Issue at times in no-till and when using poultry litter (sawdust, wood shavings, corn cobs etc)

45. Tools to deal with volatilization and immobilization
Placement of N below the residue
Urease Inhibitors
Agrotain
Controlled release N products
ESN
Use non-volatile sources
AN or AS

46. Placement of N in no-till corn
N Source
Placement
Yield
Bu/a
Earleaf N%
Ammonia
Knifed
139
3.06
UAN
135
2.85
Bdcst
118
2.48
Urea
123
2.45
Mengel, Nelson and Huber, 1982

47. Response to UAN Placement in No-till Corn, Manhattan 2008 & 2009
Treatment Yield, bu/a
No N f
UAN on surface 132e
UAN surface banded 142de
UAN coulter banded 156bc
UAN surface banded + SU 157bc
Urea/ESN blend 169a
Weber and Mengel

48. Response to Surface Applied N in No-till Corn, Manhattan 2008 & 2009
Treatment Yield, bu/a
No N f
UAN on surface 132e
Urea on surface 149cd
Urea + Agrotain 163ab
Urea + SU a
Urea/ESN blend 169a
Weber and Mengel

49. Build an efficient system
There is no one magic tool that will guarantee high NUE
Try to find the right rate
Apply the N in the most efficient manner possible

50. Building an efficient system for high residue no-till corn in a poorly drained soil
“System” Yield
150 UAN on surface
150 UAN knifed in
50 surface+100 SD
50 PP knifed in
100 SD Knifed in

51. Questions?

53. Sidedressing on Sands Wet “Normal” Year Year 120 N PP 108 137
120 N SD
160 N PP
160 N SD

54. Corn Yield as affected by Method of UAN Application
Scandia, 5-year average

55. Credits people don’t consider
24 inch profile soil test
Default value is 30 pounds per acre
92 samples from Kansas fall of 2006 found values ranging from 12 to >400, with average of 92 lb N per acre
Formula:
PNST = ppm N x sample depth in inches x 0.3
(14 x24 x 0.3) = 101