Managing Nitrogen in Kansas Cropping Systems Soil Fertility 101

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

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?

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!

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

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.

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.

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

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

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

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)

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.

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

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

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

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

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

Managing N Fertilizers

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% --- ---

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!

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!!!!!!!!

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

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

General Approach

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.

Winter Wheat N Rate Calculator

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

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

K-State Sorghum N Rate Calculator

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

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 60-100, .55 if it was between 100-120, and .60 for 120-140, 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

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

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

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

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

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

Dealing with denitrification

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

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

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

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

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

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)

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

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

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

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

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

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

Questions?

Sidedressing on Sands Wet “Normal” Year Year 120 N PP 108 137 120 N SD 121 139 160 N PP 120 146 160 N SD 121 141

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

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