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Managing Nitrogen in Kansas Cropping Systems

Managing Nitrogen in Kansas Cropping Systems

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Managing Nitrogen in Kansas Cropping Systems

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  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 0.022 = 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 --- -- -- 40 40 40 40 % Nitrogen 6.2 5.0 3.0 --- -- -- 0.7 0.5 0.5 0.1 C:N Ratio 8:1 10:1 13:1 15:1 <20:1 36:1 60:1 80:1 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 100 140 180 %SOM = % Soil OM x 20 = 40 PCA = Previous Crop Adjustment Corn 90 154 218 Corn = 0, sorghum = 0 Wheat 90 154 218 Wheat = 0, sunflower = 0 Sorghum 90 154 218 soybean = 40, poor alfalfa = 50 Sunflower 90 154 218 PNST = 24 in. N Soil Test = 30 Soybean 50 114 178 in fallow systems add 20 lbs Alfalfa 40 104 168 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 80 100 120 140 160 ________________________________________ Corn 58 90 122 154 186 Wheat 58 90 122 154 186 Soybeans 30* 50 82 114 146 Alfalfa 30* 30* 62 94 126 Fallow 30* 70 102 134 166 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 140 220 ___________________dryland___________irrigated______ defaults observed* default observed* Wheat 154 102 282 208 Soybeans 114 62 242 160 Savings @ $0.50 $25 $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 30 50 70 %SOM = % Soil OM x 10 = 20 PCA = Previous Crop Adjustment Corn 22 70 118 Corn = 0, sorghum = -30 Wheat 22 70 118 Wheat = 0, sunflower = -30 Sorghum 52 100 148 soybean = 0, fair alfalfa =+20 Sunflower 22 100 148 Fallow = +20** Soybean 22 70 118 PNST = 24 in. N Soil Test = 30 Alfalfa 2 50 98 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

  19. 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 0 91 98 0.32 --- --- --- 40 S 106 115 0.36 38% 17 38% 70 S+sd 124 133 0.38 47% 18 60% 100 S+sd 135 149 0.42 44% 16 37% 130 S+sd 156 164 0.40 50% 15 70% 160 S+sd 161 172 0.46 44% 8 17% 190 S+sd 177 177 0.43 45% 5 53% 220 S+sd 160 154 0.43 31% - 23 --- 200 pp 173 162 0.41 41% --- ---

  20. 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!

  21. Example: Corn following wheat • N Rate = (ygx1.6) – 20xSOM - PNST- PCA = (160x1.6) – 20x2.5 – 30 – 0 = 256 – 50 – 30 = 176 N Rate = 176 @ 50% NUE would provide 88 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!!!!!!!!

  22. 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

  23. 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

  24. General Approach

  25. 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.

  26. Winter Wheat N Rate Calculator

  27. Winter Wheat Yield Prediction 2006-2008

  28. Winter Wheat Nitrogen Sensor Calculator Performance 2006-2009

  29. K-State Sorghum N Rate Calculator

  30. Grain sorghum yield relationship used to estimate yield potential of the field.

  31. Comparison of Sensor Based N Rec’s to Soil Test Based Rec’s, 2006-2008

  32. 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

  33. 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

  34. 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

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

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

  37. Dealing with denitrification

  38. 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

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

  40. Flooding and N efficiency N Source Weeks after Applying 2 4 7 -----percent yield ---- NH3 98 100 87 UAN 100 79 72 120 pounds N applied sidedress 4” water applied

  41. Response to Time of Application, Controlled Release Fertilizers and Nitrification Inhibitors in No-till Corn, Manhattan 2009 Treatment Yield, bu/a No N 120 February urea on surface 159 February ESN on surface 179 Urea V-2 191 Urea V-2+ Agrotain + DCD 201 Urea/ESN blend 201 Weber and Mengel

  42. 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

  43. 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)

  44. 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

  45. Placement of N in no-till corn Mengel, Nelson and Huber, 1982

  46. Response to UAN Placement in No-till Corn, Manhattan 2008 & 2009 Treatment Yield, bu/a No N 91f UAN on surface 132e UAN surface banded 142de UAN coulter banded 156bc UAN surface banded + SU 157bc Urea/ESN blend 169a Weber and Mengel

  47. Response to Surface Applied N in No-till Corn, Manhattan 2008 & 2009 Treatment Yield, bu/a No N 91f UAN on surface 132e Urea on surface 149cd Urea + Agrotain 163ab Urea + SU 168a Urea/ESN blend 169a Weber and Mengel

  48. 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

  49. Building an efficient system for high residue no-till corn in a poorly drained soil “System” Yield 150 UAN on surface 120 150 UAN knifed in 162 50 surface+100 SD 164 50 PP knifed in + 172 100 SD Knifed in