Phosphorus Nutrition of Alfalfa

1. Phosphorus Nutritionof Alfalfa

2. 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:

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

4. 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

5. Alfalfa Nutrient Uptakeand Removal • Alfalfa has higher demandfor nutrients than most crops

6. 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

7. 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

8. 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

9. 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

10. 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

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

12. Nodule dry weight, mg/plant P application, lb P2O5/A PFertilization Increases Nodule Growth Gates, 1974

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. (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

22. 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.

23. 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

24. 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

25. 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

26. 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

27. Alfalfa hay yield, ton/A/yr Balanced P and K NutritionIs Essential for OptimalYields and Stand Maintenance Berg et al., 2005; IN

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

29. 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 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)

30. Diagnosis of P Deficiencies • 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

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

32. 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 Kcan cause cation imbalance for dairy feed rations • Excessive manure applicationmay buildup P concentrations to levelsof concern in water runoff

33. 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 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

34. International Plant Nutrition Institute (IPNI)655 Engineering Drive, Suite 110Norcross, GA 30092-2837Phone: 770-447-0335; Fax 770-448-0439Website: www.ipni.net Reference 06128