Potassium Nutrition of Alfalfa

1. Potassium Nutritionof Alfalfa

2. Potassium (K) Nutritionof Alfalfa Outline: • Plant development • Diagnosis • Yield and quality • Economics • Irrigation and record yields • Cation competition • Balanced nutrition

3. Alfalfa Production • In addition, Canada has 11 million acres yielding 1.4 ton/A • U.S. crop value $7 billion per year, 2000-2003 USDA-NASS; Statistics Canada

4. 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 • Nutrient applications increase root growth, enabling roots to obtain moisture and nutrients from greater volume of soil

5. Dryland Irrigated Alfalfa Root Morphology(Approximately 2 Months after Planting) • Dryland • Deeper penetration • Fewer but longer laterals • More secondary branches • Irrigated • Shallower • More but shorter laterals • Less secondary branches Weaver, 1926 (NE)

6. Irrigated Dryland Alfalfa Root Morphology(Approximately 3 Months after Planting) • Dryland • Root system is more profusely branched • Branches reached same depth as tap root • Shallower root system • Irrigated • Fewer branches • Greater rooting depth • Tap root is the dominant structure Weaver, 1926 (NE)

7. Dryland Irrigated Alfalfa Root MorphologyEnd of First year • Dryland • Greater number of branches in upper 1 ft. of soil • Maximum depth of 5 ft. • Roots oriented downward • Irrigated • Fewer branches in upper 1 ft. of soil • Maximum depth of over 6 ft. • Greater lateral extent of root system Weaver, 1926 (NE)

8. Dryland Irrigated Alfalfa Root MorphologyJuly 10, Second Year • Dryland • Depth of over 9 ft. • Roots oriented downward • Little lateral extension • Irrigated • Depth of nearly 10 ft. • Greater lateral extention Weaver, 1926 (NE)

9. Factors Restricting Root Growth Reduce NutrientUptake Disease damage Nutrient deficiencies Excess salt or sodium Poor nodulation Soil compaction Poor drainage Insect damage Low oxygen Temperature Acidity

10. Recovery of K fromVarious Soil Depths Recovery at the end of the growing season with K placed in the Spring at various depths in an established alfalfa stand Peterson and Smith, 1973

11. Diagnosis of Nutrient Deficiencies • Visual Observation • Soil Testing • Tissue Analysis

12. In K-deficient alfalfa, small white or yellowish spotsfirst appear around theouter edges of older leaves

13. K Deficiency in Alfalfa Severe K Deficiency Moderate K Deficiency

14. Typical K Concentrations(at optimum fertility) • Stems near top of plant contain themost K • Leaf K concentration is similar among upper and lower leaves • Roots contain less K • Forage containing 2.5% K removes 60 lb of K2O per ton of dry matter harvested Lanyon and Smith, 1985

15. Shoot K, % Growth Stage K Concentration Declineswith Maturity Barton and Reid, 1977 (WV)

16. Soil Testing andPlant Analysis • Soil Testing • Verify that K levels are being maintained • Soil pH 6.5 or higher for efficient N fixation • Plant Analysis • Usually sample the top 6 in. at harvest • Indication of adequate K fertility: • <2% indicates insufficient K for winter hardiness • Optimum yields usually contain around 2.5% K • Record yield of 10 tons/A (non-irrigated), K content of 3%

17. K Deficiency Hurts More Than Yield Adequate K Improves: • Plant persistence • Number of shoots per plant • Shoot yield Deficient K: • Reduces root starch storage • Reduces protein concentration in root • Results in poor survival and slowshoot growth Li et al., 1997 (IN)

18. K2O added, lb/A K Fertilization IncreasesNodule Activity Grewal and Williams, 2002 (Australia)

19. K2O added, lb/A K Fertilization ImprovesHay Quality Grewal and Williams, 2002 (Australia)

20. No K 100 lb K O/yr 2 100 80 Stand density (%) 60 40 20 0 1971 1972 1973 1974 1975 1976 1977 Year K Helps Reduce Winterkillin Alfalfa Plant counts taken in May as % of those previous September Bailey, 1983 (MB)

21. Alfalfa Responses to Kin Mixed Stands • Largest where soil K fertilitylevels are low • Increases over the lifeof the stand • Includes quality as wellas yield • Increased proportion oflegume to grass  more protein • Increases in irrigated production

22. Response to K IncreasesOver Life of Stand 4-yr total Most Economic Rate Hay yield, tons/A 1989 1992 1990 1991 Initial soil test Kwas 35 ppm (low) Fertilizer K2O, lb/A Klausner and Goyette, 1993 (NY)

23. Response to K IncreasesOver Life of Stand Rock Springs Landisville Yield, tons/A Most Economic Rate Alfalfa response to K at two sites Forage K, % Initial soil test K ranged from 130 to 170 ppm Fertilizer K2O, lb/A Beegle, 1992 (PA)

24. Greatest response occurred in 5th year Added K, lb K2O/A Response to K IncreasesOver Life of Stand Berg et al., 2003 (IN)

25. Response increases after intensive management 1985 • Alfalfa response to K under intensive 5-cut management • Initial soil test K of 170 ppm in 1984, declined to 80 ppm in the unfertilized treatment by spring 1987 Most Economic Rate Yield, tons/A 1986 1985 Forage K, % 1986 Fertilizer K2O, lb/A Sheard et al., 1988 (ON)

26. Soil K Levels:Turn K Fertilizationinto Profit Example: Annual economic returnto K fertilizer use: Assuming $90 per ton of hay and K2O at $0.15 per pound (price ratio of 3 lb hayper lb of K2O)

27. Economics ofK Fertilization The most economic rate of K fertilization changes as the ratio of K prices to hay prices changes

28. Profitability:Short vs. Long-Term The yield increase in response to K application gets larger as the alfalfa stand ages

29. Recommended K rate Alfalfa stand density, plants/ft2 K2O application rate, lb/A K Fertilization According toSoil Test RecommendationMaintains Alfalfa Stands Burmester et al., 1991 (AL)

30. 3 2 Yield, tons/A 1 0 4.5 5 5.5 6 6.5 7 Soil pH Alfalfa Response to Soil pH Follet and Wilkinson, 1995

31. pH 6.1 pH 5.3 Yr3 pH 4.7 Yr 3 Alfalfa yield, ton/A Yr 3 Yr 2 Yr 2 Yr 2 Yr 1 Yr 1 Yr 1 Liming Acid Soil Improves Alfalfa Growth andNutrient Recovery Walworth and Sumner, 1990 (GA)

32. Alfalfa shoot composition Liming Acid Soil Improves Alfalfa Growth and NutrientRecovery Walworth and Sumner, 1990 (GA)

33. How Does this Changewith Irrigation?

34. 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

35. Cumulative Hay Yield, Tons 200 400 600 600 0 K2O rate, lb/A Optimum K Rate in Irrigated Alfalfa: An Example Best economic return Too much in one application Koenig, 2002 (UT)

36. Placement and Application Options • Establishment • Broadcast to build up soil test K before seeding • Banded starters should contain mostly P • Maintenance • Apply following harvest to replace removal • High rates: split over several cuts to avoid salt injury • To boost winter hardiness, apply before critical fall growth period (before last 6 weeks of growth) • When soil K levels are high, spring applications can lead to higher K levels than desired, and may be unnecessary

37. Spring Harvest, 2001 Fall Harvest, 2000 K applied, lb K2O/A K applied, lb K2O/A) K Impacts Fall Harvestmore than Spring • Yield response to K found in last harvest of 2000 • For first harvest of 2001, no response to K fertilization was observed • Reason:K can be released from soil minerals during winter and spring Volenec, 2002 (IN)

38. Manure Management • Manure supplies many nutrients • but usually not in the ratio requiredfor alfalfa! • Physical problems • compaction, crown damage,leaf burn, salinity • Nutritional problems • N can stimulate weeds • excessive K can cause cation • imbalance in dairy feed rations

39. Luxury Uptake of K forDairy Feed • K in alfalfa varies from<1.5% to >3% • Luxury uptake when soil Kis very high • K levels above 3% unnecessary • Liquid manure systems efficientlyrecycle K • High K forage: A concern fordry dairy cows • Leads to milk fever, retained placentas after calving • For the transition period (2 to 4 weeks before calving) forage with <2% K desired; dietary K should be <1.2% • Corn silage, grains, distillers grains are low K feeds • Anionic salts (chlorides or sulfates of NH4+, Mg, or Ca) can help correct the problem

40. Tissue Mg, % Magnesium Concentrations in Alfalfa K applied, lb K2O/A K Competes with Other Cations for Plant Uptake: Mg Burmester et al., 1991 (AL)

41. Calcium Concentrations in Alfalfa Tissue Ca, % K applied, lb K2O/A K Competes with Other Cations for Plant Uptake: Ca Burmester et al., 1991 (AL)

42. Sodium, ppm Sodium Concentrations in Alfalfa K applied, lb K2O/A K Fertilization ReducesUptake of Other SoilCations: NA James, 1988 (UT)

43. Alfalfa hay yield, ton/A/yr Balanced P and K Nutrition Is Essential for Optimal Yieldsand Stand Maintenance Berg et al., 2003 (IN)

44. Recommended K rate Yield, tons/A K applied, lb K2O/A Fertilization According to Soil Test Recommendations Burmester et al., 1991 (AL)

45. Summary –K Nutrition of Alfalfa • Alfalfa takes up and removeslarge amounts of K from the soil • Fertilization is essential for highyields, stand longevity,and winter hardiness • Fertilized to optimum, foragecontains 2 to 3% K • Application: pre-plant and following harvests • Apply recommended rates to avoid luxury uptake

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