Potassium Nutrition of Alfalfa

Potassium (K) Nutrition of Alfalfa Outline: 1.Plant development 2.Diagnosis 3.Yield and quality 4.Economics 5.Irrigation and record yields 6.Cation competition 7.Balanced nutrition

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

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

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) Dryland Irrigated

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 Dryland Irrigated Weaver, 1926 (NE)

Alfalfa Root Morphology End 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 Dryland Irrigated Weaver, 1926 (NE)

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

Factors Restricting Root Growth Reduce Nutrient Uptake Disease damage Insect damage TemperatureAcidity Low oxygen Poor drainage Excess salt or sodium Nutrient deficiencies Poor nodulation Soil compaction

Recovery of K from Various Soil Depths Depth of placement, in.Recovery, % of applied Surface 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

Diagnosis of Nutrient Deficiencies Visual Observation Soil Testing Tissue Analysis

In K-deficient alfalfa, small white or yellowish spots first appear around the outer edges of older leaves

K Deficiency in Alfalfa Moderate K Deficiency Severe K Deficiency

Typical K Concentrations (at optimum fertility) Stems near top of plant contain the most K Leaf K concentration is similar among upper and lower leaves Roots contain less K Forage containing 2.5% K removes 60 lb of K 2 O per ton of dry matter harvested Plant part and growth stage K, % on dry matter basis Stems: near ground level 2% Stems: near topup to 6% Leaves: % Roots:1.1% Forage harvested at early bloom: 1.8% to 2.5% Top 6 in. at bud to early bloom: 2.0% to 3.5% Lanyon and Smith, 1985

K Concentration Declines with Maturity Barton and Reid, 1977 (WV) Growth Stage Shoot K, %

Soil Testing and Plant 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%

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 slow shoot growth Li et al., 1997 (IN)

K 2 O added, lb/A Grewal and Williams, 2002 (Australia) K Fertilization Increases Nodule Activity

K 2 O added, lb/A K Fertilization Improves Hay Quality Grewal and Williams, 2002 (Australia)

Plant counts taken in May as % of those previous September Bailey, 1983 (MB) K Helps Reduce Winterkill in Alfalfa Stand density (%) 100 lb K 2 O/yrNo K Year

Alfalfa Responses to K in Mixed Stands Largest where soil K fertility levels are low Increases over the life of the stand Includes quality as well as yield –Increased proportion of legume to grass  more protein Increases in irrigated production

Hay yield, tons/A Fertilizer K 2 O, lb/A Initial soil test K was 35 ppm (low) 4-yr total Most Economic Rate Klausner and Goyette, 1993 (NY) Response to K Increases Over Life of Stand

Rock SpringsLandisville Yield, tons/A Forage K, % Fertilizer K 2 O, lb/A Alfalfa response to K at two sites Most Economic Rate Beegle, 1992 (PA) Initial soil test K ranged from 130 to 170 ppm Response to K Increases Over Life of Stand

Berg et al., 2003 (IN) Added K, lb K 2 O/A Greatest response occurred in 5th year Response to K Increases Over Life of Stand

Yield, tons/A Fertilizer K 2 O, lb/A Forage K, % Most Economic Rate Sheard et al., 1988 (ON) Response increases after intensive management 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

Soil K Levels: Turn K Fertilization into Profit Example: Annual economic return to K fertilizer use: Assuming $90 per ton of hay and K 2 O at $0.15 per pound (price ratio of 3 lb hay per lb of K 2 O) Soil test K category Yield response K 2 O rateNet return tons/Alb/A$/A Very low Low High

Economics of K Fertilization The most economic rate of K fertilization changes as the ratio of K prices to hay prices changes Soil Test K Price Ratio Category2345 Most economic rate of K 2 O (lb/A) Very low Low High

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

Burmester et al., 1991 (AL) K 2 O application rate, lb/A Alfalfa stand density, plants/ft 2 K Fertilization According to Soil Test Recommendation Maintains Alfalfa Stands Recommended K rate

Follet and Wilkinson, Soil pH Yield, tons/A Alfalfa Response to Soil pH

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

Liming Acid Soil Improves Alfalfa Growth and Nutrient Recovery Walworth and Sumner, 1990 (GA) Alfalfa shoot composition

How Does this Change with Irrigation?

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

Cumulative Hay Yield, Tons K 2 O rate, lb/A Optimum K Rate in Irrigated Alfalfa: An Example Koenig, 2002 (UT) Best economic return Too much in one application

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

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) K Impacts Fall Harvest more than Spring Fall Harvest, 2000 K applied, lb K 2 O/A) Spring Harvest, 2001 K applied, lb K 2 O/A

Manure Management Manure supplies many nutrients –but usually not in the ratio required for 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

Luxury Uptake of K for Dairy Feed K in alfalfa varies from 3% –Luxury uptake when soil K is very high –K levels above 3% unnecessary –Liquid manure systems efficiently recycle K High K forage: A concern for dry 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 NH 4 +, Mg, or Ca) can help correct the problem

Burmester et al., 1991 (AL) K applied, lb K 2 O/A Tissue Mg, % Magnesium Concentrations in Alfalfa K Competes with Other Cations for Plant Uptake: Mg

K applied, lb K 2 O/A Tissue Ca, % Calcium Concentrations in Alfalfa K Competes with Other Cations for Plant Uptake: Ca Burmester et al., 1991 (AL)

K Fertilization Reduces Uptake of Other Soil Cations: NA James, 1988 (UT) Sodium Concentrations in Alfalfa K applied, lb K 2 O/A Sodium, ppm

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

Recommended K rate Yield, tons/A K applied, lb K 2 O/A Fertilization According to Soil Test Recommendations Burmester et al., 1991 (AL)

Summary – K Nutrition of Alfalfa Alfalfa takes up and removes large amounts of K from the soil Fertilization is essential for high yields, stand longevity, and winter hardiness Fertilized to optimum, forage contains 2 to 3% K Application: pre-plant and following harvests Apply recommended rates to avoid luxury uptake

International Plant Nutrition Institute (IPNI) 655 Engineering Drive, Suite 110 Norcross, GA Phone: ; Fax Website: Reference 06128