Phosphorus Nutrition of Alfalfa Phosphorus P Nutrition of

Phosphorus Nutrition of Alfalfa

Phosphorus (P) Nutrition of Alfalfa Outline: • 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

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 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 P 2 O 5 15 K 2 O 60 Ca 30 Mg 6 S 6 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

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 Available P Unavailable P

The primary cause of low, short-term uptake of P fertilizer: Higher P concentration Plant root ffu sio n Lower P concentration Di • 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

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

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

P Improves Alfalfa Growth and Recovery P conc. , mmol 0 1 2 6 Alfalfa regrows faster after cutting with adequate P P conc. , mmol 0 1 2 6 Li et al. , 1998 Alfalfa develops more shoots after cutting with adequate P

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 30 Alfalfa yield response, % increase above check Year 1 Year 6 20 100/yr 200/2 yr 600/6 yr Knifed-in 6 in. deep P application, lb P 2 O 5/A and frequency Mullen et al. , 2000; OK

Yield Response: Method and Timing Total yield increase, ton/A 7 Cumulative Yield Response 6. 8 6 5. 8 5 4. 7 4 3 4. 2 3. 4 2 1 0 100 lbs/A/yr 200 lbs/A/2 -yr 600 lbs/A/6 -yr Knifed-in 6 in. deep P Application, lb P 2 O 5/A and frequency Mullen et al. , 2000; OK

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

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

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

Total 3 -year yield, ton Alfalfa Response to Added P Fertilizer (STP=8 ppm, 0 -45 -0) P application rate, lb P 2 O 5/A • 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 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.

What P Source Is Superior for 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 P 2 O 5/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 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 fertilizer sources • Placement compared: – Surface banding or broadcast on established alfalfa stands No yield differences due to fertilizer placement Koenig, 2003; Utah

Effect of P Fertilizer on Soil P Concentrations • Failure to replace harvested nutrients will gradually deplete soil nutrient supply and reduce yields Soil Test P, ppm 14 12 (annual application, 115 lb P 2 O 5/acre) 10 8 Initial 1982 1983 1984 7 ppm critical value 6 4 2 0 Check MAP DAP Treatment Cihacek, 1993; NM APP

Preparing the Soil Before Planting Is Key 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. Low P Adequate P • Eliminate soil p. H problems - alfalfa does not thrive in acid soils

Alfalfa hay yield, ton/A/yr Balanced P and K Nutrition Is Essential for Optimal Yields 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 • 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 subsequentyear phosphate • Application can be made any time of the year-frequently during winter months to meet the highdemand 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

Cumulative alfalfa yield, g/pot Both P Fertilizer and Animal Manure Provide Nutrition for Alfalfa Goss & Stewart, 1979; Texas

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 30092 -2837 Phone: 770 -447 -0335; Fax 770 -448 -0439 Website: www. ipni. net Reference 06128