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Nitrogen in Pasture Soils
Brian ArnallFeb 5. Tishomingo
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Nitrogen in the Plant
• Part of– Amino Acids: Building blocks of proteins– Enzymes: responsible for all biological process– Nucleic Acids– Chlorophyll
• Needed for Carbohydrate use• Increases root growth
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Liebig's Law of the Minimum
• Growth is controlled not by the total of resources available, but by the scarcest resource. – Only by increasing the amount of the limiting nutrient (the one most scarce in relation to "need") was the growth of a plant or crop improved.
Justus von Liebig1803 ‐ 1873Justus von Liebig1803 ‐ 1873
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Bray’s Nutrient Mobility Concept
Root SystemSorption Zone
Root SurfaceSorption Zone
Nutrient limitation expressed as a % of potential yield, or “sufficiency”, and independentof the environment
Nutrient limitation directlyrelated to yield potential, and dependent on the environment
Mobile Nutrients Immobile Nutrients
Plants respond to the totalamount of mobile nutrientspresent
Plants respond to the concentration of immobilenutrients present
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N‐Cycle
• OM• 2 OMProcesses
• 2 N Processes
• 3 Sinks• 4 losses• 5 additions
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Organic Matter
• Central point of the Nitrogen Cycle• In an acre furrow slice 1000 lbs N per 1% OM• A continuous flow of N into and out of OM.
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N rate recommendation
• Nitrogen Recommendation =
Yield Goal N rate – Residual N• 35‐60 lbs N per ton• Residual N is
– 0‐6” (Top‐soil) Soil Test NO3 – 6‐18” (Sub‐soil) Soil Test NO3– NO3 from irrigation– Cover Crop Credits.
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N rates
Forage 1 ton yield 3 ton yieldBermudagrass 50 150Cool Season 60 180Old World 35 110Love grass 35 110
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4 R’s
1. Right Source2. Right Place3. Right Rate4. Right Time
IPNI: International Plant Nutrition Institute
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Nitrogen Sources
• Urea 46‐0‐0– Most available, cheapest / lb N– Worst for rain fed forage
• UAN 28‐0‐0– Most expensive, Applicators limited– Better for pre green up or post harvest
• Ammonium Nitrate 34‐0‐0– More Expensive, Limited Availability– The BEST Nitrogen Source for Forage
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Urea vs AN
• Urea– Goes to NH3 then NH4.– Needs ½ inch of rain/ irrigation or worked in.– Warmth, Wind, Humidity increases loss
• Ammonium Nitrate– Unless Soil pH is High >7.0 No loss– Can be applied any time any day.
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This year?
• What does your pasture look like?• Species, growth period• Spotty rains• Grazing pressure
• Did you lose any Stand?
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Management Approach• For severely‐damaged pastures, recovery is the only
option.– May require 1 year or longer for full recovery.
• For moderately‐damaged pastures, focus on recovery early and production late.– May require 2 to 3 months of growth to fully recover.
• For slightly‐damaged pastures, manage as usual focusing on maximum production potential.– Should recover in 2 months or less.
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What are the primary factors that control forage production?
• Some we can controlFertilityStocking rate
• Some we have no controlWaterGrowing season
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Approach for Post‐drought Pasture Management
• Water management (moisture conservation/use)• Manage similar to recent/new plantings• Reduce competition
– Livestock– Plant
• Management focus (order of importance)– Weed control– Fertility– Grazing deferment
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Top Three Pasture Management Practices for Drought Recovery
1. Arrange for aggressive weed control measures.• Mob graze grassy weeds.• Chemical control for broadleaf weeds.
2. Plan on fertilization.• Base on soil test.• Focus primarily on phosphorus (root growth).
3. Prepare for grazing deferment.• Don’t graze too early!• Allow time for adequate root growth.
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Thank you !!!
Brian Arnall373 Ag Hall405‐744‐[email protected] available @ www.npk.okstate.eduTwitter: @OSU_NPKYouTube Channel: OSUNPK
www.extensionnews.okstate.edu
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Old World Bluestem with Slight Damage
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Weeping lovegrass Pasture with Moderate Damage
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Old World Bluestem Pasture with Moderate Damage
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Old World Bluestem Pasture with Severe Damage