Phosphorus Nutrition of Alfalfa

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Phosphorus Nutrition of Alfalfa. Phosphorus (P) Nutrition of Alfalfa. U.S. alfalfa hay yields keep increasing Nutrient uptake and removal Alfalfa root development General P nutrition P boosts hay yield, recovery, and quality P inputs: frequency and source
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Phosphorus Nutritionof Alfalfa Phosphorus (P) Nutritionof Alfalfa
  • U.S. alfalfa hay yields keep increasing
  • Nutrient uptake and removal
  • Alfalfa root development
  • General P nutrition
  • P boosts hay yield, recovery, and quality
  • P inputs: frequency and source
  • Requirement for balanced nutrition
  • Outline: Yield, ton/A U.S. Alfalfa Hay Yields…An Upward Trend Year Source: USDA-NASS Record Yield:Researchers at University of Arizona(Yuma) set record for alfalfa yieldin a year:24.1 tons/A alfalfa hay in10 cuttings
  • Optimal and uniform irrigation
  • Chopped hay removed immediately after cutting
  • N fertilizer regularly added – was it needed?
  • 460 lb P2O5/A added before planting
  • K management unknown
  • 1,440 lb K2O and 360 lb P2O5/A removed in hay
  • Ludwick, 2000; Arizona Alfalfa Nutrient Uptakeand Removal
  • Alfalfa has higher demandfor nutrients than most crops
  • Alfalfa Root Development
  • Most lateral roots are near the soil surface for the first year, but more deep lateral roots develop as the plant ages
  • Alfalfa has lower root density than many grasses and a deeper rooting zone
  • P and K application increase root growth, enabling roots to obtain moisture and nutrients from greater volume of soil
  • Available P Unavailable P Phosphorus in Soils
  • Total P in many soils (0 to 6 in.) ranges from 400 to 2,000 lb/A…but only a fraction of that is available for plant uptake each season
  • Lower Pconcentration Diffusion Plant root Higher Pconcentration The primary cause of low, short-term uptakeof P fertilizer:
  • The inability of P to move to absorbing roots
  • Temperature Effect on Nutrient Uptake Cool soil temperatures will:
  • slow nutrient release from soil organic matter
  • reduce diffusion of nutrients to the roots
  • hinder root absorption and translocation
  • Adequate P is essential for strong root systems Higher levels of nutrients are needed to support vigorous plant growth in cool soil conditions P Functions in Plants
  • Energy storage and transfer
  • Phosphate compounds are “energy currency”
  • (such as ADP and ATP)
  • Structural component of biochemicals
  • Seed formation
  • Calcium and magnesium phytate
  • Maintenance and transfer of genetic code
  • Root growth, rapid crop establishment
  • Early maturity, quicker recovery
  • Soil P, ppm Number of nodules Soil water holding capacity P Fertilization Increases Nodulation Azcon et al., 1988 Nodule dry weight, mg/plant P application, lb P2O5/A PFertilization Increases Nodule Growth Gates, 1974 0 0 1 1 2 2 6 6 P conc., mmol P conc., mmol P Improves Alfalfa Growth and Recovery Alfalfa regrows faster after cutting with adequate P Alfalfa develops more shoots after cutting with adequate P Li et al., 1998 P Response: Timing and Application Study
  • Six-year study initiated to evaluate effect of P timing and application method
  • Broadcast or banded P fertilizer
  • Frequency:
  • 100 lb P2O5/A every year
  • 200 lb P2O5/A every 2 years
  • 600 lb P2O5/A in a one-time preplant application
  • Total 6-year P rate was the same for all treatments: variables were timing and placement
  • Mullen et al., 2000; OK 30 Year 1 Year 6 20 Alfalfa yield response, % increase above check 10 0 100/yr 200/2 yr 600/6 yr 200/2 yr 600/6 yr Knifed-in 6 in. deep P application, lb P2O5/A and frequency Yield Response to P inYears One and Six Mullen et al., 2000; OK 7 Cumulative Yield Response 6.8 6 5.8 5 4.7 4 Total yield increase, ton/A 4.2 3 3.4 2 1 0 100 lbs/A/yr 200 lbs/A/2-yr 600 lbs/A/6-yr 200 lbs/A/2-yr 600 lbs/A/6-yr Knifed-in 6 in. deep P Application, lb P2O5/A and frequency Yield Response:Method and Timing Mullen et al., 2000; OK Broadcast application Average annual yield increase, lb/A P application, lb P2O5/A Increase in Alfalfa GrowthDue to P Fertilization(split over 5 years or one-time application) Mullen et al., 2000; OK Disc-band application Average annual yield increase, lb/A P application, lb P2O5/A Increase in Alfalfa GrowthDue to P Fertilization(split over 5 years or one-time application) Mullen et al., 2000; Alberta Broadcast application Average annual yield increase, lb/A Influence of P Application on Increasing Alfalfa Yield(one-time application or annual application) Mullen et al., 2000; Alberta Disc-band application Average annual yield increase, lb/A Influence of P Application on Increasing Alfalfa Yield(one-time application or annual application) Mullen et al., 2000; Alberta (STP=8 ppm,0-45-0) Total 3-year yield, ton P application rate, lb P2O5/A Alfalfa Response toAdded P Fertilizer
  • Yield response to added P most evident at first cutting
  • Soil P fertility was maintained by small annual applications or a large one-time application
  • James, 1995; Utah Established StandsOften Need Additional P
  • Soil testing and tissueanalysis can revealneed for fertilization.
  • P fertilizer does not movefar in soil:
  • Soil incorporationprior to planting is best
  • Top-dressed and irrigated P is suitablefor subsequent fertilization
  • P moves during freeze/thaw cycles, washes into soil cracks, and is taken up by shallow surface roots and crowns  and becomes available for plant uptake.
  • What P Source Is Superiorfor Alfalfa?
  • Three-year study with 24 cuttings:
  • 10-34-0 applied in irrigation water
  • 10-34-0 sprayed on soil surface
  • 11-52-0 granules broadcast applied
  • (0, 20,40, 60, 100 lb P2O5/A/yr for 3 years)
  • Positive hay yield response to P, but:
  • No differences in P sources or methodsof application in yield or tissueP concentration
  • Ottman et al., 2001; AZ P Source? Not a Significant Factor for Alfalfa Yields
  • Four P sources compared(2 liquid, 2 solid):
  • Yield response to P fertilization(11 to 27% increase) under irrigation No differences in P fertilizersources
  • Placement compared:
  • Surface banding or broadcast onestablished alfalfa stands No yield differences due tofertilizer placement
  • Koenig, 2003; Utah 14 (annual application, 115 lb P2O5/acre) 12 10 Initial 8 7 ppm critical value Soil Test P, ppm 1982 6 1983 4 1984 2 0 Check MAP DAP APP Treatment Effect of P Fertilizeron Soil P Concentrations
  • Failure to replace harvested nutrients will gradually deplete soil nutrient supply and reduce yields
  • Cihacek, 1993; NM Adequate P Low P Preparing the Soil Before Planting Is Key Prior to planting:
  • Incorporate P forestablishment of strongroot systems, promotingrapid recovery, andmaintaining healthy stands
  • Provide balanced nutrition:Adequate K, Ca, Mg, S, B, etc.
  • Eliminate soil pH problems - alfalfa does not thrive in acid soils
  • Alfalfa hay yield, ton/A/yr Balanced P and K NutritionIs Essential for OptimalYields and Stand Maintenance Berg et al., 2005; IN Proper Attention to All Nutrients Is Required for Healthy Plants and High Yield Levels Berg et al., 2005; IN General Guidelines for P Fertilization Plants
  • Use soil testing to guide P fertilization decisions and use local recommendations for best results
  • Incorporate adequate P into the top 2 to 6 in. of soil prior to planting to meet the first years of productionand nutrient removal in harvested hay
  • Use tissue analysis to determine need for subsequent-year phosphate
  • Application can be made any time of the year-- frequently during winter months to meet the high-demand period in the Spring
  • (avoiding application to snow-covered, frozen, or saturated fields with the potential risk of runoff)
  • Diagnosis of P Deficiencies Plants
  • Visual Observation:
  • Distinct P deficiencies are seldom observableon alfalfa – not an effective diagnostic method!
  • Soil Testing
  • Soil test prior to planting and regularly afterwards
  • Tissue Analysis
  • Best way to monitor plant performance andprevent hidden hunger and yield loss
  • Recommended tissue concentration:
  • 0.25 to 0.40% P in top third of plant
  • Both P Fertilizer and Animal Manure Provide Plants Nutrition for Alfalfa Cumulative alfalfa yield, g/pot Goss & Stewart, 1979; Texas Manure Management Plants
  • Manure supplies many nutrients –but not in the ratio required for crops
  • Physical problems –compaction, crown damage,leaf burn, salinity
  • Nutritional problems –N can stimulate weeds, extra Kcan cause cation imbalance for dairy feed rations
  • Excessive manure applicationmay buildup P concentrations to levelsof concern in water runoff
  • Summary- Plants P Nutrition of Alfalfa
  • Alfalfa roots grow best in nutrient-rich soil; Prepare the seedbed prior to planting and supplement in later years as needed
  • Adequate P promotes vigorous N2 fixation, shoot development, and faster regrowth after cutting
  • Uptake of P continues through the season and is harvested in large amounts. The P fertilizer source is not important
  • Placement near the seedling boosts establishment and stand longevity
  • Crop response to P is best predicted with a soil test and subsequent tissue testing
  • Nutrient management is an essential key to profitability and efficient use of other inputs
  • International Plant Nutrition Institute (IPNI) Plants 655 Engineering Drive, Suite 110Norcross, GA 30092-2837Phone: 770-447-0335; Fax 770-448-0439Website: www.ipni.net Reference 06128
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