Using Plants for Nitrogen

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Using Plants for Nitrogen

• Wilbur Frye
• Professor Emeritus U.K.
• Executive Director K.D.A.

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INTRODUCTION

• Throughout history of agriculture, N harvested
  was replaced by legumes, if at all
• N in animal wastes traced to legumes
• Value of green manures found in writings of
  Xenophon (434 to 355 B.C.)
• Colonial America knew value of green manure, but
  little practiced on farms
• -Used long-term pasture rotations
• -Applied animal manure for grain crops
• -Moved to virgin soil

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INTRODUCTION, contd

• World War I was dawn of synthetic N
• -Haber/Bosch process for synthetic ammonia
• N2 H2 ?? NH3
• air nat. gas ammonia
• World War II NH3 used to make explosives
• Ushered in era of cheap synthetic N fertilizers
• NH3 ? amm. nitrate, amm. sulfate, MAP, DAP,
• urea, UAN

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Farmers quit using

• Green manure crops
• Animal manures
• Crop rotations with legumes
• Natural N saltse.g., sodium nitrate

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ERA OF EXPENSIVE FERTILIZERS

• Are we there yet?
• How much farther?
• What can we do to ease the pain?

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USING PLANTS FOR NITROGEN

• Three questions to answer
• ? Is it practical?
• ? What are the benefits?
• ? Is it economical?

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Winter Legume Cover Crops

• Well adapted to Kentucky southern Indiana
• ? Hairy vetch best
• Cropping systems
• ? Continuous no-till corn
• ? Cornwheatsoybean rotation (2-year)
• ? Cornwheat rotation (2-year) (farther north)

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Is It Practical?

• TillageNo-till, conventional tillage, reduced
  tillage
• PlantingOverseed late Aug.early Sept. before
  harvest
• Drill after harvest
• Hope for snow during extreme cold
• Plant corn by mid-May directly into live cover
• SprayBurn-down weed control
• Cutter-rollerBurn-down weed control
• Possibilities of Roundup-Ready corn

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Above-ground Dry Matter Yield in Southeast
(tons/acre)
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Above-ground N Accumulation in Cover Crops
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Corn Yield--Lexington
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Liabilities of Legume Cover Crops

• Cost of seed and seeding
• Loss of economic production (left for mulch
  instead of harvested)
• Depleted soil water in dry spring weather
• ? May decrease stand
• ? Increase water stress in early season
• Cooler, wetter, no-till soil in normal spring
• ? More N loss, less N mineralization
• Volunteers in winter wheatfrom hard seeds

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Effect of Planting Method
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Effect of Planting Date on Corn Yield
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Effect of Kill Date (Waggner, 1987)
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Soil Water at Corn Planting

Depth, inches
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Returns Above Direct Expenses Based on 1981 and
1982 Prices
/ac.
N fertilizer, lb/ac.
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Re-establishing Legume and Grass Hay and Pasture

• Legume hayCornLegume hay
• Alfalfa, red clover, etc.
• Grass-legume hayCornHay
• Grass-legume pastureCornPasture

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First year responses of corn to fertilizer N
after 5 years of alfalfa
1997 Corn
yield (bu./acre)
Check
141 Spring N (75
lb/acre) 143
Second year responses of corn to fertilizer N
after 5 years of alfalfa
1998
Corn yield (bu./acre)
Check
126 Spring N
(150 lb/acre) 139

Lexington, KY, W.O. Thom
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of N Recovered from Labeled Alfalfa and Urea
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Biological Nitrogen Fixation in Forage Crop
Communities

N fixed
(lb./ac./yr.) Alfalfa
Lexington KY 189 Red clover
Lexington KY 138
White clover Lexington KY
114 White clover New
Zealand 603 Birdsfoot
trefoil Minnesota
52-103 Soybean Corn belt USA
13-136
Heichel (1985)
On B horizon with minimal soil N
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Economics of Renovating Pastures with Clover

• Increased revenues
• ? Weaning wt. ?40 lb.
• ? Conception ?10
• 81 more lb/cow 81
• Decreased expenses
• ? None considered0
• Positive effect 81

• Decreased revenues
• ? None considered0
• Increased expenses
• ? Renovation-25/ac./yr.
• ? 2 ac./cow-calf unit
• Neg. effect 2 x 2550
• Net effect 31/cow-calf/yr

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Benefits of Legume Cover Crops

• Biologically fixed N2 from air
• More efficient use of water
• ? Less runoff more infiltration
• ? Lower evaporation higher transpiration
• More effective erosion control
• Better weed control
• Increased soil organic N and C
• Increased soil productivity (rotation effect)
• Less overall leaching of N (released slowly)

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Potential Problems

• Low germination of cover crop in very dry
  falldrilling may help
• Winter killextreme cold w/o snow cover
• Decreased stand of summer cropdry weather before
  and after crop planting
• Hard seeds that last a year or more interfere
  with wheat in rotationmay need wheat herbicides

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USING PLANTS FOR NITROGEN

• ? Is it practical?
• ? What are the benefits?
• ? Is it economical?

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