Fertility Management

Irrigated Potato Production

Important Nutrients Primary macronutrients Nitrogen Phosphorus Potassium

Total potato plant N, P, and K Uptake Days After Emergence Nutrient Uptake (lb/ac)

Total Potato Plant N, P, and K Uptake Rates at Aberdeen Days After Emergence Nutrient Uptake Rates (lb/ac/day) (lb/ac/day) K N P

Early-Season Soil Nutrient Placement

Fertilizer Placement DryFertigation P, K N Foliar

Relative Nutrient Mobility in Soil Nitrogen – Mobile (nitrate>urea>ammonium) Potassium – moderately low mobility Phosphorus – low mobility

Nitrogen Necessary for protein and chlorophyll Used in large quantities by plants Quantity available fluctuates rapidly Shortage associated with marked yield loss Application important in all soils

Soil N Cycle LEACHING (NO3 - )

Nitrogen Deficiency Symptoms General chlorosis (pale green color) Younger leaves turn darker green, old leaves remain yellow Upward cupping of deficient leaflets when severe

Potato Variety Nitrogen Response Trials Aberdeen, 2005

Soil Analysis One composite sample per acres 0-12 inch sampling depth for potatoes Combine samples (zig-zag pattern) Random but accurate samples

Total N Recommendations for Russet Burbank Potatoes Potential Yield (cwt/acre) Soil NO 3 -N (0-12 in depth) ppm lb N/acre

Nitrogen Fertilizer Management Program Apply up to 25-60% of N prior to planting Apply remainder of N (40-75%) through the irrigation system during tuber development according to crop requirements Slow release or controlled release N fertilizers applied preplant can be used to reduce N leaching

Preplant N applications Nitrogen (partial application) 25-30% on sandy soils % on sandy loam soils % on silt loams Nitrogen fertilizers – urea, mono- ammonium phosphate, ammonium sulfate, ammonium polyphosphate

In-Season N Applications  Begin after tuber initiation and adjust according to tuber bulking rates and weekly petiole N concentrations  Cut-off 3 to 4 weeks before vine kill  Begin after tuber initiation and adjust according to tuber bulking rates and weekly petiole N concentrations  Cut-off 3 to 4 weeks before vine kill Target = Total Seasonal N Requirement - preplant + sidedress applications

Calculating In-Season N Application Rates Based on lb N/ac/day or week, which changes according to crop demand Once tuber bulking begins, weekly crop N requirements can be estimated based on relationships between tuber growth rate and plant N uptake Daily N uptake rates for different potato cultivars range from about 2 to 5 lb N/ac/day depending on the tuber-bulking rate Can be applied as dry or liquid N fertilizers

Calculating In-Season N Application Rates Russet Burbank requires about 3-4 lb N/ac/day (20-25 lb N/week) to prevent the loss of both N and dry matter from the tops and roots to the tubers during tuber bulking Assuming 75-80% plant N uptake efficiency for injected N fertilizer, about 30 lb N/ac would satisfy crop N requirements for a week Adjustments to projected rates to account for N mineralization should be based on weekly petiole nitrate tests

Total Yield Response to N for A TE and Russet Burbank at Aberdeen ID,

Tissue Analysis Petiole analysis the most common Sample 4 th petiole Sample under consistent conditions Dry the tissue immediately Private and public labs Base applications on sufficiency

A TE Petiole Nitrates, 2013

Recommended petiole and soil (0-18 inches) NO 3 -N concentrations for Russet Burbank potatoes during different growth stages Tuber Tuber Tuber Tuber Sample Vegetative Initiation Bulking Maturation NO 3 -N (ppm) Petiole ,000-25,000 15,000-20,000 10,000-15,000 Soil > < 15

From Rowe, 1993

Factors Affecting Petiole Nitrogen Concentrations Plant Factors: photosynthesis dry matter production N metabolism transpiration Soil Factors: temperaturemoisturemineralization NH 4 + /NO 3 - physical conditions : Root Factors: carbohydrate supply root health root length / depth

Critical Time Period – N builds up in (or is applied to) soil before plant uptake and may be lost Impact of Weather on Soil N Supply, Soil N Losses, and Crop N Demand Soil/ Plant N SpringSummerFall Potato N Uptake Soil mineral N, Normal year Soil mineral N, Wet spring Amount of N fertilizer needed… …In normal year …in year with wet spring

Potato Yield Response to N Fertilizer Following Fall or Spring Plowing of Alfalfa, Aberdeen 2002 Nitrogen Rate (lbs N/acre) Yield (cwt/acre) Spring plow Fall plow Potato Rotation Study Rexburg, ID

Russet Burbank potato yields as influenced by N rates after alfalfa, wheat, or maize averaged across 2004 and 2005 seasons

Phosphorus Second most critical nutrient Essential for energy transfer Critical for root growth Generally low in soil availability Rapidly tied up by soil Management is long-term Application important in all soils

From Rowe, 1993

Total Potato N, P, and K Uptake Days After Emergence Nutrient Uptake (lb/ac)

Phosphorus and Dry Matter Accumulation Days After Emergence Accumulation/maximum Accumulation/maximum dry matter P

Soil P Buffering Capacity Depletion of solution P brings absorbed P into solution to maintain equilibrium Rate of establishing new equilibrium depends on rate of desorption from absorbed forms and rate of diffusion (i.e., the withdrawal rate is proportional to the size of the bank)

Phosphorus Precipitation on CaCO 3 P adsorbed to CaCO 3 surfaces forming ion clusters Clusters allow for nucleation of Ca-P crystals Common in calcareous soils of Southern Idaho

Calcite equilibrated for 10 days Calcite equilibrated for 10 days 0 ppm P 10 ppm P 25 ppm P 50 ppm P 100 ppm P 500 ppm P

Ammonium Phosphates Reaction pH

P Fertilizer Granule CaHPO4 4 H2OH2O adsorption precipitation Ca 2+ H 3 PO 4

Recovery of Fertilizer P Plants recover 5 to 20% Remainder reacts with soil components Residual fertilizer P builds up soil P to increase future availability

Phosphorus Fertilizer Program Adequate P concentration in bulk soil to maintain optimal P concentration Starter bands to enhance early season P availability Maintenance / building of soil P levels

Preplant Phosphorus Options  Ammonium Phosphates - liquid and dry  Avail  Humic Acids  Controlled Release P In-Season P Sources – APP ( ) and phosphoric acid

Broadcast Band

Preplant P Fertilizer Recommendations for Russet Burbank Potatoes Apply an additional 40 to 80 lb of P 2 O 5 /acre as a starter at planting for soil test P levels below 30 ppm. Add 25 lb P 2 O 5 /acre as a starter for additional 100 cwt/acre above 400 cwt/acre. Soil Test P (0-12 inch depth ) ppm Percent Free Lime lb P 2 O 5 /acre

Dry Matter Balance (total / tubers) (total / tubers) Average P in leaves (%) Y = 0.76X – 0.7 r 2 = 0.67 (0.22) Westermann and Kleinkopf, % P = sufficiency level

Phosphorus Fertigation Maintain petiole P concentration above 0.22% through tuber bulking 30 to 40 lb P/A in late July can increase total P uptake 4 to 5 lb/ac Typically use APP ( ) or Phosphoric acid

Potassium Used in large quantities by plants Important in translocation of nutrients Easily leached in sandy soils Some soils naturally low Application important in all soils

Total Potato N, P, and K Uptake Days After Emergence Nutrient Uptake (lb/ac)

Forms of Potassium in Soil Mineral5, ,000 ppm Non-exchangeable ppm Exchangeable ppm Solution1-10 ppm

K Absorption by Plants  Primarily by diffusion and mass flow  Related to K intensity (solution K)  Diffusion : % of K uptake  Mass Flow : % of K uptake  K quantity (Q) = exchangeable K

Relationship between STKC and K Diffusion STKC, ppm K Diffusion ppm / day > y = x – 0.30 r 2 = 0.64 >

Relationship between STKC and slow-release K from soil extracts Relationship between STKC and slow-release K from soil extracts STKC, ppm Slow Release K, ppm / day Slow Release K, ppm / day > 175

Soil K Recommendations Critical STKC for potatoes = 175 ppm About 4.6 lb K 2 O/ac required to raise STKC 1 ppm per 1 foot of soil (without fixation) Estimated K fixation 5% at 150 ppm STKC and 27% at 25 ppm STKC

Potassium fertilizer recommendations ppm lb K 2 O/ac (0-12 1nch) Soil Test K Yield Goal (cwt/ac)

Potassium Fertilization Guidelines Probability of a K response: loamy sand > sandy loam > loam > silt loam Slight advantage for K 2 SO 4 over KCl > 200 lb K 2 O/A) for: specific gravities No. 1’s

Potassium Fertilization Guidelines Banded K not as effective as broadcast K K in starter band should be < 50 lb K 2 O/ac (salt effect) Avoid high (>300 lb K 2 O/ac) spring applications yield reductions observed with spring applications of lb K 2 O/ac higher rates should be split fall/spring

Potassium Fertilization Guidelines Preplant K more effective than applying most of the K in-season (fertigation) Fertigation - no consistent difference between K sources (KCl, K 2 SO 4, KTS) Avoid large (>50 lb K 2 O/A) single fertigation applications

Potassium Fertilization Guidelines Use petiole testing to determine K fertigation requirements Maintain > ppm K in fourth petiole Cut off K fertigation 30 days before vine kill to avoid reducing specific gravity

N and P Fertilizer Effects on Specific Gravity of Russet Burbank Potatoes, Aberdeen (1985) N Applied (lb N/acre) P Applied (lb P 2 O 5 /acre)

Potassium Deficiency Symptoms Symptoms appear on young, full-sized leaves Leaflets become rugose (crinkled) Leaves take on a scorched appearance with black pigmentation and necrotic (dead tissue) edges

Potassium Deficiency Symptoms

Secondary Macronutrients Sulfur Calcium Magnesium

Sulfur Important as a component of proteins Often naturally available Many sources Fertilizer by-product Water supply Organic matter Some soils inadequate Ideally, 15 ppm or greater

Sulfur Deficiency Symptoms General chlorosis Similar to nitrogen deficiency except young leaves remain yellow over time Leaflet yellowing is uniform and general >0.20% S in petiole - sufficient

Sulfur deficiency Symptoms

Calcium Important for cell wall integrity Abundant in arid soils Ideally, 300 ppm or greater Passive uptake - moderate solubility Poor transport under cool conditions Foliar applications not transported to tubers Application necessary in acid soils for pH adjustment

Calcium Deficiency Symptoms Symptoms appear on youngest leaves first Leaflets cup upward Brown spotting on leaflets Leaflets eventually dry up and become brown if symptoms are severe >0.60% Ca in petiole - sufficient

Calcium Deficiency Symptoms

Magnesium Component of chlorophyll Derived from native rocks Some soils deficient Ideally, 100 ppm or greater Application commonly necessary in acidic soils

Magnesium Deficiency Symptoms Symptoms appear first on young mature leaves General chlorosis with veins remaining green Leaflets near growing point remain green Interveinal necrosis causes scorched look >0.30% Mg in petiole - sufficient

Mg Deficiency Symptoms

Micronutrients Boron Copper Iron Manganese Molybdenum Zinc

Micronutrients Essential as activators and for enzyme systems Availability affected by pH Boron naturally low in some soils Copper often deficient in muck soils Iron, manganese, and zinc unavailable in alkaline soils

Iron Deficiency Symptoms Growing point and young leaves become yellow or in extreme cases, white Usually not accompanied by necrosis Veins and leaflet ends remain green > 50 ppm Fe in petiole – sufficient > 4 ppm Fe in soil - sufficient

Iron Deficiency Symptoms

Manganese Deficiency Symptoms General yellowing of plant Leaves cup upward Brown spotting occurs on leaflets, especially along larger veins and mid-ribs > 40 ppm Mn in petiole – sufficient > 6-8 ppm Mn in soil - sufficient

Manganese Deficiency Symptoms

Zinc Deficiency Symptoms Little leaf occurs, showing as small, narrow, chlorotic leaflets Leaflets cup upward Tip-burn on leaflets Lower leaves bleach and fall from plant > 20 ppm Zn in petiole – sufficient > 1.5 ppm Zn in soil - sufficient

Zinc Deficiency Symptoms

Fertility Management Plan Prior to and at planting Soil analysis Preplant fertilizer applications Nitrogen (partial application) 25-30% on sandy soils % on sandy loam soils % on silt loams Phosphorus (broadcast and banded) Potassium (broadcast) Micronutrients, as needed

Fertility Management Plan During early tuber bulking Continue petiole testing Continue seasonal applications of N Correct deficiencies of P, K and micros Fertigation for P ( lbs P/ac) and K (<50 lbs K/ac) Foliar applications for Zn, Mn, and Fe

Fertility Management Plan During late tuber bulking Complete seasonal N applications Finish by late July – early August