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 Requirement for balanced nutrition Outline:

U.S. Alfalfa Hay Yields … An Upward Trend Year Source: USDA-NASS Yield, ton/A

Record Yield: Researchers at University of Arizona (Yuma) set record for alfalfa yield in a year: 24.1 tons/A alfalfa hay in 10 cuttings Optimal and uniform irrigation Chopped hay removed immediately after cutting N fertilizer regularly added – was it needed? 460 lb P 2 O 5 /A added before planting K management unknown 1,440 lb K 2 O and 360 lb P 2 O 5 /A removed in hay Ludwick, 2000; Arizona

Alfalfa Nutrient Uptake and Removal Alfalfa has higher demand for nutrients than most crops Nutrient Amount Removed lb/ton P2O5P2O5 15 K2OK2O60 Ca30 Mg6 S6 N (through fixation)60

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

The primary cause of low, short-term uptake of P fertilizer: The inability of P to move to absorbing roots Plant root Higher P concentration Lower P concentration Diffusion

Adequate P is essential for strong root systems Higher levels of nutrients are needed to support vigorous plant growth in cool soil conditions 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

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

P Fertilization Increases Nodulation Azcon et al., 1988 Soil P, ppm Number of nodules Soil water holding capacity

P Fertilization Increases Nodule Growth Gates, 1974 P application, lb P 2 O 5 /A Nodule dry weight, mg/plant

P Improves Alfalfa Growth and Recovery Li et al., 1998 Alfalfa regrows faster after cutting with adequate P P conc., mmol Alfalfa develops more shoots after cutting with adequate P P conc., mmol

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 P 2 O 5 /A every year –200 lb P 2 O 5 /A every 2 years –600 lb P 2 O 5 /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

Yield Response to P in Years One and Six Knifed-in 6 in. deep P application, lb P 2 O 5 /A and frequency /yr200/2 yr600/6 yr200/2 yr600/6 yr Year 1Year 6 Alfalfa yield response, % increase above check Mullen et al., 2000; OK

Yield Response: Method and Timing P Application, lb P 2 O 5 /A and frequency Knifed-in 6 in. deep Cumulative Yield Response lbs/A/yr200 lbs/A/2-yr600 lbs/A/6-yr200 lbs/A/2-yr600 lbs/A/6-yr Total yield increase, ton/A Mullen et al., 2000; OK

Increase in Alfalfa Growth Due to P Fertilization (split over 5 years or one-time application) Broadcast application Average annual yield increase, lb/A P application, lb P 2 O 5 /A Mullen et al., 2000; OK

Increase in Alfalfa Growth Due to P Fertilization (split over 5 years or one-time application) P application, lb P 2 O 5 /A Disc-band application Average annual yield increase, lb/A Mullen et al., 2000; Alberta

Influence of P Application on Increasing Alfalfa Yield (one-time application or annual application) Broadcast application Average annual yield increase, lb/A Mullen et al., 2000; Alberta

Influence of P Application on Increasing Alfalfa Yield (one-time application or annual application) Disc-band application Average annual yield increase, lb/A Mullen et al., 2000; Alberta

James, 1995; Utah 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 Alfalfa Response to Added P Fertilizer P application rate, lb P 2 O 5 /A (STP=8 ppm, ) Total 3-year yield, ton

Established Stands Often Need Additional P Soil testing and tissue analysis can reveal need for fertilization. P fertilizer does not move far in soil: –Soil incorporation prior to planting is best –Top-dressed and irrigated P is suitable for 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.

Ottman et al., 2001; AZ What P Source Is Superior for Alfalfa? Three-year study with 24 cuttings: – applied in irrigation water – sprayed on soil surface – 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 methods of application in yield or tissue P concentration

Koenig, 2003; Utah 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 fertilizer sources Placement compared: –Surface banding or broadcast on established alfalfa stands No yield differences due to fertilizer placement

Cihacek, 1993; NM CheckMAPDAPAPP Treatment Soil Test P, ppm Initial (annual application, 115 lb P 2 O 5 /acre) 7 ppm critical value Effect of P Fertilizer on Soil P Concentrations Failure to replace harvested nutrients will gradually deplete soil nutrient supply and reduce yields

Prior to planting: Incorporate P for establishment of strong root systems, promoting rapid recovery, and maintaining healthy stands Provide balanced nutrition: Adequate K, Ca, Mg, S, B, etc. Eliminate soil pH problems - alfalfa does not thrive in acid soils Low P Adequate P Preparing the Soil Before Planting Is Key

Alfalfa hay yield, ton/A/yr Berg et al., 2005; IN Balanced P and K Nutrition Is Essential for Optimal Yields and Stand Maintenance

Proper Attention to All Nutrients Is Required for Healthy Plants and High Yield Levels Berg et al., 2005; IN

General Guidelines for P Fertilization 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 production and 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 Visual Observation: –Distinct P deficiencies are seldom observable on alfalfa – not an effective diagnostic method! Soil Testing –Soil test prior to planting and regularly afterwards Tissue Analysis –Best way to monitor plant performance and prevent 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 Nutrition for Alfalfa Goss & Stewart, 1979; Texas Cumulative alfalfa yield, g/pot

Manure Management 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 K can cause cation imbalance for dairy feed rations Excessive manure application may buildup P concentrations to levels of concern in water runoff

Summary- 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 N 2 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) 655 Engineering Drive, Suite 110 Norcross, GA Phone: ; Fax Website: Reference 06128