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Using Plants for Nitrogen

Using Plants for Nitrogen. Wilbur Frye Professor Emeritus U.K. Executive Director K.D.A. INTRODUCTION. Throughout history of agriculture, N harvested was replaced by legumes, if at all N in animal wastes traced to legumes

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Using Plants for Nitrogen

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  1. Using Plants for Nitrogen Wilbur Frye Professor Emeritus U.K. Executive Director K.D.A.

  2. 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

  3. INTRODUCTION, cont’d • 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

  4. Farmers quit using: • Green manure crops • Animal manures • Crop rotations with legumes • Natural N salts—e.g., sodium nitrate

  5. ERA OF EXPENSIVE FERTILIZERS • Are we there yet? • How much farther? • What can we do to ease the pain?

  6. USING PLANTS FOR NITROGEN Three questions to answer: ● Is it practical? ● What are the benefits? ● Is it economical?

  7. Winter Legume Cover Crops • Well adapted to Kentucky & southern Indiana ▪ Hairy vetch best • Cropping systems ▪ Continuous no-till corn ▪ Corn—wheat—soybean rotation (2-year) ▪ Corn—wheat rotation (2-year) (farther north)

  8. Is It Practical? • Tillage—No-till, conventional tillage, reduced tillage • Planting—Overseed late Aug.–early Sept. before harvest —Drill after harvest • Hope for snow during extreme cold • Plant corn by mid-May directly into live cover • Spray—Burn-down + weed control • Cutter-roller—Burn-down + weed control • Possibilities of Roundup-Ready corn

  9. Above-ground Dry Matter Yield in Southeast (tons/acre)

  10. Above-ground N Accumulation in Cover Crops

  11. Corn Yield--Lexington

  12. 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 wheat—from hard seeds

  13. Effect of Planting Method

  14. Effect of Planting Date on % Corn Yield

  15. Effect of Kill Date (Waggner, 1987)

  16. Soil Water at Corn Planting % Depth, inches

  17. Returns Above Direct Expenses Based on 1981 and 1982 Prices $/ac. N fertilizer, lb/ac.

  18. Re-establishing Legume and Grass Hay and Pasture • Legume hay—Corn—Legume hay Alfalfa, red clover, etc. • Grass-legume hay—Corn—Hay • Grass-legume pasture—Corn—Pasture

  19. 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

  20. % of N Recovered from Labeled Alfalfa and Urea

  21. 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 * On B horizon with minimal soil N Heichel (1985)

  22. Increased revenues ▪ Weaning wt. ▲40 lb. ▪ Conception ▲10% 81 more lb/cow = $81 Decreased expenses ▪ None considered=$0 Positive effect: $81 Decreased revenues ▪ None considered=$0 Increased expenses ▪ Renovation-$25/ac./yr. ▪ 2 ac./cow-calf unit Neg. effect: 2 x $25=$50 Net effect: $31/cow-calf/yr Economics of Renovating Pastures with Clover

  23. 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)

  24. Potential Problems • Low germination of cover crop in very dry fall—drilling may help • Winter kill—extreme cold w/o snow cover • Decreased stand of summer crop—dry weather before and after crop planting • Hard seeds that last a year or more interfere with wheat in rotation—may need wheat herbicides

  25. USING PLANTS FOR NITROGEN ● Is it practical? ● What are the benefits? ● Is it economical?

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