Soil Fertility Management Under Tight Crop Production Margins. John Sawyer Antonio Mallarino Department of Agronomy Iowa State University

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1 Soil Fertility Management Under Tight Crop Production Margins John Sawyer Antonio Mallarino Department of Agronomy Iowa State University

2 Nitrogen Application Almost Always Needed To Increase Corn Yields Sawyer and Barker, 2015 Yield Increase From N application (Long Term) SC 68% and CC 171%

3 Diminishing Return to Nitrogen Application 0.10 price ratio, CNRC database

4 Net Return Determines MRTN Rate and Most Profitable N Rate Range (CNRC - SC Main Region) $0.40/lb N:$4.00/bu 204 research trials

5 Corn Price Effect on Net Return and Nitrogen Cost (CNRC - SC Main Iowa Region)

6 Corn Nitrogen Rate Calculator (CNRC)

7 Corn Nitrogen Rate Calculator (CNRC)

8 High Corn Yields Do Not Mean High Optimum (Needed) Nitrogen Rates High Yield Environments in Iowa (> 220 bu/acre) Mean Mean Yield Rotation No. EONR at EONR at Max. lb N/acre bu/acre SC CC EONR at 0.10 N:Corn price ratio. Through J. Sawyer and D. Barker. ISU Agronomy Extension.

9 Nitrogen Is Needed for Corn Production A Challenge with Tight Margins Need N fertilization for profitable production Match rates to crop rotation Over-application reduces profits and increases water quality nitrate-n risk Corn and N prices influence optimal rate Return from N investment (and return to pay for other production costs) decreases considerably with low corn prices Consider low end of profitable N rate range

10 Phosphorus (P) and Potassium (K) For P and K soils often have adequate levels Naturally high levels Previously applied fertilizer, manure, lime Should not simply cut applications or reduce rates Use soil sampling/testing to make decisions PM 1688 Revised October 2013

11 Soil Sampling Get a good representation of variation across fields Can decide on site-specific (VR) applications or whole field application Will help with tough decisions on where and when to change rates (reduce if possible) Soil type/map unit, Zone, or Grid sampling Consider sampling every two years instead of standard four years for P and K

12 Soil-Test P and Yield Response 100 Relative Grain Yield (%) CORN SOYBEAN 40 VL L Op H VH Interpretation Classes VL L Op H VH Interpretation Classes Bray-1 Soil-Test P (ppm) Bray-1 Soil-Test P (ppm) Mallarino, ISU

13 Soil-Test K and Yield Response Dry Test Moist Test Relative Crop Yield (%) Dry Test Moist Test VL L Opt H VH Classes VL L Opt H VH Classes Dry Soil-Test K (ppm) Corn Soybean Relative Crop Yield (%) Moist Soil-Test K (ppm) Corn Soybean Mallarino, ISU, 2013

14 Soil-Test P Levels, Prices and Economic Return Net Returns from P ($/acre) $7.00/bu corn $16.00/bu soyb $0.45/lb P 2 O 5 $5.00/bu corn $12.00/bu soyb $0.45/lb P 2 O 5 $3.00/bu corn $8.00/bu soyb $0.45/lb P 2 O 5 VL L O H VH VL L O H VH VL L O H VH Soil-Test P (ppm) Soil-Test P (ppm) Soil-Test P (ppm) Removal-based rates were applied for the High and Very High categories although is not recommended.

15 Soil-Test K Levels, Prices and Economic Return New Test with Moist Soil Samples (direct moist or slurry) Net Returns from K ($/acre) $7.00/bu corn $16.00/bu soyb $0.35/lb K 2 O $5.00/bu corn $12.00/bu soyb $0.35/lb K 2 O $3.00/bu corn $8.00/bu soyb $0.55/lb $0.35/lb K 2 O -100 VL L O H VH VL L O H VH VL L O H VH Moist Soil-Test K (ppm) Moist Soil-Test K (ppm) Moist Soil-Test K (ppm) Removal-based rates were applied for the High and Very High categories although is not recommended.

16 Rate Example from Publication PM 1688 Dry or Moist Sample Handling Very Low Low Optimum High Very High Bray-1 or Mehlich Mehlich-3 ICP Olsen Crop Corn Soybean Corn-Soybean (50) 0 * For Optimum assumes 180 bu corn and 55 bu soybean Soil Test P Categories ppm Fertilizer Recommendations* P 2 O 5 /acre Needed & provides slow build up Maintain based on removal No need & doesn't pay Response Frequency (%): <1

17 P and K Management with Tight Margins Don't reduce P or K application rates in lowtesting soils, even in rented fields And, do not try to build up soil tests faster Don t fertilize high-testing soils, especially with variable rate application Maybe apply just a starter rate Optional or reduced rate with Optimum tests Strong justification for soil sampling and use of variable rate application

18 Sulfur and Micronutrient Management with Tight Margins Sulfur Alfalfa high response frequency 47% time yield response in corn (110 trials) Less yield response in soybean Coarse textured, sideslope landscape, eroded, low organic matter soils; no-tillage, reduced-tillage, high crop residue, alfalfa prior crop, no manure application, no S applied in fertilizers or irrigation Micronutrients (B, Cu, Mn, Zn) Only one positive yield increase with 105 siteyears of recent research (and a few yield decreases) - foliar or soil application

19 Nutrient Management Resources CROP 3073 Nitrogen use in Iowa corn production Corn N Rate Calculator PM 1688 A general guide for crop nutrient and limestone recommendations in Iowa PM 287 Take a good sample to help make good decisions Soil Fertility Web Site