Presentation on theme: "Using Plants for Nitrogen Wilbur Frye Professor Emeritus U.K. Executive Director K.D.A."— Presentation transcript:
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 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
INTRODUCTION, cont’d World War I was dawn of synthetic N ─Haber/Bosch process for synthetic ammonia N 2 + H 2 →→ NH 3 air nat. gas ammonia World War II NH 3 used to make explosives Ushered in era of cheap synthetic N fertilizers NH 3 → amm. nitrate, amm. sulfate, MAP, DAP, urea, UAN
Farmers quit using: Green manure crops Animal manures Crop rotations with legumes Natural N salts—e.g., sodium nitrate
ERA OF EXPENSIVE FERTILIZERS Are we there yet? How much farther? What can we do to ease the pain?
USING PLANTS FOR NITROGEN Three questions to answer: ● Is it practical? ● What are the benefits? ● Is it economical?
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)
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
Above-ground N Accumulation in Cover Crops N, lb./acre% fixation KentuckyHairy vetch15384 C. clover5636 Bigflo. Vetch7558 Rye25--- AlabamaHairy vetch11979 C. clover11979 Rye25--- GeorgiaHairy vetch13775 C. clover15278 Rye34---
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
Returns Above Direct Expenses Based on 1981 and 1982 Prices $/ac. N fertilizer, lb/ac.
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
First year responses of corn to fertilizer N after 5 years of alfalfa Check 141 Spring N (75 lb/acre) 143 1997 Corn yield (bu./acre) 1998 Corn yield (bu./acre) Second year responses of corn to fertilizer N after 5 years of alfalfa Check 126 Spring N (150 lb/acre) 139 Lexington, KY, W.O. Thom
% of N Recovered from Labeled Alfalfa and Urea N added In tops 1 st crop In soil > 1 st crop Lost > 1 st crop In tops 2 nd crop Sourcelb./acre % % % % Alfalfa 86 16 67 17 5 Alfalfa 35 18 67 15 4 Urea 45 46 33 21 3
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
Economics of Renovating Pastures with Clover 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
Benefits of Legume Cover Crops Biologically fixed N 2 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)
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
USING PLANTS FOR NITROGEN ● Is it practical? ● What are the benefits? ● Is it economical?
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