Forage Legume Nitrogen Fixation: Forage Legume Nitrogen Fixation Gerald R. Smith TAES Overton


Topics: Topics Advantages of Legumes Biological Nitrogen Fixation Management Summaries


Advantages of Legumes: Advantages of Legumes High quality forage Extend the grazing season comparison to warm season grasses common use is overseeding Capable of biological nitrogen fixation amount of N fixed depends on many factors Many annual legumes can be managed for reseeding


Biological Nitrogen Fixation: Biological Nitrogen Fixation Legume plants and Rhizobium bacteria team up to remove N from the air Nodules form on legume roots when this system is working


Legume + Rhizobium Team: Legume + Rhizobium Team Legume Plant forms a nodule in response to Rhizobium provides energy and protection for the bacteria in the nodule converts fixed N to organic N and produces high protein forage Rhizobium bacteria infects plant provides genetic information that allows N fixation uses the plant energy and nodule environment to accomplish N fixation


Biological Nitrogen Fixation Concerns: Biological Nitrogen Fixation Concerns Legume species must be matched with correct Rhizobium species or strain Fixed N is first available to the legume plant and through recycling available to other plants N fixation is regulated by the plant based on need. High soil N will reduce N fixation.


Biological Nitrogen Fixation Concerns: Biological Nitrogen Fixation Concerns Legume species must be matched with correct Rhizobium species or strain inoculation is the process of applying a commercial culture of Rhizobium to legume seed before planting. correct inoculant must be used for each forage legume. wrong Rhizobium + clover = no N fixation.


Clovers Groups Based on Response to Rhizobium Strain: Clovers Groups Based on Response to Rhizobium Strain 12 or more groups Group A: berseem, crimson, and persian Group B: ball, white, and red Group I: arrowleaf One general “clover” inoculant does NOT exist!!!!! Burton, J.C. 1985


Slide9: Burton, J. C. 1985


Slide10: What if I can’t find nodules or if my clover plants are small and light green??? 1. No inoculation 2. Wrong inoculum (Rhizobium strain) 3. Hot, dry conditions after planting 4. Very acid soils (pH less than 5.0)


Slide11: What about mixing inoculated clover seed with fertilizer and applying both at the same time?? 1. Not the best idea. 2. Would be fine if you need to add seed to and existing stand. Don’t bother with inoculum. 3. The inoculum cannot survive very long exposed to the chemical salts in the fertilizer.


Slide12: Preinoculated Seed?? 1. Generally refers to seed preinoculated and then coated with lime or an inert clay. Fungicides can also be added. 2. No problems after two years of trials at Overton. 3. Research in progress.


Inoculating Forage Legume Seed: Inoculating Forage Legume Seed Be sure to use the correct inoculant Follow package instructions Inoculants that include an adhesive are best Inoculation is very important the first time you establish a new forage legume Remember that the inoculant is carrying live bacteria. Protect from heat and sun.


Biological Nitrogen Fixation Concerns: Biological Nitrogen Fixation Concerns Fixed N is first available to the legume plant and through recycling available to other plants clover will not directly provide N for the ryegrass in a clover-ryegrass mixture clover will provide N through recycling to warm season grass pastures


Clover and Ryegrass Response to Nitrogen Fertilization: Clover and Ryegrass Response to Nitrogen Fertilization


Biological Nitrogen Fixation Concerns: Biological Nitrogen Fixation Concerns Nitrogen fixation is regulated by the plant, based on need. high soil N will reduce N fixation. fertilizer N applied to clover-ryegrass mixtures will cause rapid yield response in ryegrass will cause only moderate yield response in total mixture (clover + ryegrass)


Clover and Ryegrass Response to Nitrogen Fertilization: Clover and Ryegrass Response to Nitrogen Fertilization


Response of Clover-Ryegrass Mixture to Applied Nitrogen: Response of Clover-Ryegrass Mixture to Applied Nitrogen Lb N / acre Total Season Yield (lb dry forage / acre)


Slide19: Early (Feb 21) Forage Yield of Clover - Ryegrass Mixture 60 lb N/ac applied in early winter (Dec. or Jan.) gives highest efficiency on early forage yields of mixtures (Evers and Haby, 1995)


Biological Nitrogen Fixation Summary: Biological Nitrogen Fixation Summary Inoculate to match legume with Rhizobium Avoid nitrogen fertilization of pure stands of forage legumes Use reduced rates of N fertilizer on legume-grass mixtures Plan for efficient use of legume forage and recycled N


Slide21: Vegetation Areas of Texas Pineywoods Gulf Prairies and Marshes Post Oak Savannah Blackland Prairies South Texas Plains Cross Timbers and Prairies Edwards Plateau Trans-Pecos High Plains Rolling Plains


Pineywoods: Pineywoods Crimson Clover Ball Clover White Clover Hairy Vetch Rose Clover Arrowleaf Clover disease problems Red Clover no reseeding late production Alfalfa


Seasonal distribution of forage yield at Overton, TX. Six year averages.: Seasonal distribution of forage yield at Overton, TX. Six year averages.


Slide24: Yuchi Overton Experimental Arrowleaf Clover, May 25 2000, Rusk Co. TX


Slide25: Overton Experimental Yuchi May 25. 2000, Rusk Co. TX


Blacklands and Cross Timbers: Blacklands and Cross Timbers Medics Bur Clover Button Clover Hairy Vetch Sweetclover new breeding effort Rose Clover no wet soils Red Clover no reseeding Berseem Clover poor cold tolerance reseeding ?


Gulf Prairies and Marshes: Gulf Prairies and Marshes White Clover Berseem Clover reseeding ? Bur Clover Sub Clover


Slide28: La S-1 White Clover Ladino White Clover


Cost Comparisons: Cost Comparisons


Legume PasturePrinciples: Legume Pasture Principles Soil Test follow recommendations Select forage legume consider forage program objectives use best adapted forage legume for site soil drainage and type, potential cold damage Buy high quality seed and inoculum Inoculate


Legume PasturePrinciples -- page 2: Legume Pasture Principles -- page 2 Plan legume acreage needs carefully consider seed costs Prepare site Use best seeding method available Develop a plan for late spring growth graze hay ??? reseeding


Manage for Reseeding?: Manage for Reseeding? Can you afford to defer grazing do you have more forage than your cattle can use in the late spring? Can you accept a slow start on warm season grass Risk level (high risk = no reseeding) ball, white and rose = low arrowleaf = low if you allow seed to mature crimson = medium (high if summer is wet) red and berseem = high