Pecan Fertility ManagementNitrogen, Phosphorus, and Potassium

Dr. Jim WalworthUniversity of Arizona

Magnesium

Sulfur

Calcium

Nitrogen

Potassium

Phosphorus

Macronutrients Micronutrients

Manganese

Iron

Copper

Nickel

Zinc

the Metals

Molybdenum

Boron

Chlorine

the Others

Assessing Nutrient Status

¨ Visible Symptoms¤ Useful for diagnosing serious problems after the fact

¨ Leaflet Tissue Analysis¤ Tells you the actual nutrient status of the tree¤ Most closely related to tree performance¤ Not site-specific – the same standards can be used for all pecans

¨ Soil Analyses¤ May tell you WHY you have (or may get) a problem¤ Not as closely related to leaf nutrient concentrations or tree

performance¤ Very good for measuring salinity, pH, other soil properties¤ Interpretation and recommendations may be soil-specific

Standard pecan leaf sampling¤ Collect middle pair of leaflets on middle leaf of current year’s growth

in mid to late July¤ Collect 30 to 50 pairs of leaflets per sample¤ Leaves from fruiting or non-fruiting shoots?

Leaf nitrogen and potassium can be affected by the presence or absence of fruit

Fruit absent

Potassium

Leaf

K (%

)

Date

Fruit present

Influence of Fruit Development on Seasonal Elemental Concentrations and Distribution in Fruit and Leaves of Pecan

Diver et al., 2008

Fruit absent

Fruit present

Leaf

N (%

)

Date

Nitrogen

“Sufficient” pecan leaf nutrient levels

Arizona New Mexico

Oklahoma

Native & low input High input

Nitrogen 2.05 – 2.96 2.50 – 3.00 2.30 – 3.00 2.40 – 3.00

Phosphorus 0.10 – 0.16 0.14 – 0.19 0.12 – 0.30 0.14 – 0.30

Potassium 1.00 – 1.59 1.25 – 2.50 0.85 – 2.50 1.00 – 2.50

Root growth of pecans peaks in March to mid-April. Young roots are most effective for absorbing nutrients, so we expect best fertilizer response to occur in this timeframe.

March – Mid April

Dr. Astrid Volker

Nitrogen

Leaf Photosynthesis in Nitrogen-starved ‘Western’ Pecan is Lower on Fruiting Shoots than Non-fruiting Shoots during Kernel Fill

Heerema et al., 2014

Fruiting shoots

Non-fruiting shoots

Leaf nitrogen concentrations of at least 2.5% were required to maximize photosynthesis

Leaf nitrogen standards – how much N is enough?

Long-term Performance of Pecan Trees when Nitrogen Application is Based on Prescribed Threshold Concentrations in Leaf Tissue

• Sixteen year study on “Stuart” pecans

• 100 lb/ac of N (broadcast ammonium nitrate) was applied if leaf N was below the following thresholds (2.25, 2.50, 2.75, or 3.00%) or 200 lb/ac of N annually

• There was benefit from leaf N up to 2.75%

2.5

2.6

2.7

2.8

2.9

2.25 2.5 2.75 3.00 200

Leaf

N (%

)Worley, 1990

010203040506070

2.25 2.50 2.75 3.00 200Yi

eld

(kg/

tree

) B B

A AAB

0

0.2

0.4

0.6

0.8

1

1.2

2.25 2.5 2.75 3.00 200Fr

uit p

er te

rmin

al BAB

A A

B

6.5

7.0

7.5

8.0

8.5

2.25 2.5 2.75 3.00 200

Nut

wt (

g/nu

t)

A

AA

B

A

Tree establishment - response of pecan seedling to applied nitrogenDr. Astrid Volder

• Mohawk seedlings in sprinkler irrigated silt loam received 5 nitrogen treatments• 0, 52, 103, 206, 412 lb/ac • Broadcast (NH4)2SO4 split mid-May and mid-June• Results

• Root length was greatest in the 229 kg/ha N treatment• Root length and lifespan were reduced by higher N application rates • No effect of N application on leaf N, photosynthesis, trunk diameter growth

Nitrogen treatment

(lb/ac)

Leaf nitrogen (mg/kg)

2010 2011

0 1.96 2.05

52 2.12 2.04

103 2.00 2.20

206 1.99 2.06

412 2.02 2.01

0 N52 N103 N206 N412 N

Tree establishment - response of pecan seedling to applied nitrogen Walworth, Heerema, Sherman

• Newly planted (in 2015) Western and Wichita trees

• UAN32 fertigated in split applications: 15 to 95 lb/ac of N annually

• Measurements: leaf nitrogen, photosynthesis, trunk diameter

• Results to date• Leaf nitrogen concentrations not greatly affected by nitrogen application

• Trunk growth incrementally increased by 60 lb/ac of nitrogen, 2.3%N

1.90

2.00

2.10

2.20

2.30

2.40

2.50

15 31 47 63 79 95

Leaf

nitr

ogen

(%)

Annual nitrogen application (lb/ac)

Mean leaf nitrogen (2015 - 2018)

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

15 31 47 63 79 95

Trun

k di

amet

er g

row

th (i

nche

s)

Annual nitrogen application (lb/ac)

Growth in trunk diameter (2015 - 2018)

Nitrogen application rate did not affect stem or root growth except the highest nitrogen application rate (768 lb/ac) reduced both stem and root growth

Effect of Nitrogen Fertigation on First-year Pecan Seedling Growth

Conner 2007

0, 77, 192, 384, or 768 lb/ac of N applied in 10 bi-weekly applications of calcium nitrate

0 77 192 384 768Total N applied (lb/ac)

• Ammonium nitrate applied in split applications • 0 , 18, 36, or 54 lb/ac of N, split between March and June or March, May, and June

Herrera and Duarte, 2000

18 36 54Nitrogen Treatments (lb/ac)

Trun

k di

amet

er in

crea

se (c

m)

Transplants:

Nitrogen rates and time of application effect on growth and nut production of mature transplanted pecan trees

• Results• Application of any N increased trunk and branch

diameter, but there were no differences between rates or timing

• Nitrogen did not affect leaf N, clusters per branch, or nuts per cluster

• 3rd year yield responded to ≥ 36 lb/ac of nitrogen

0 18 36 54Nitrogen Treatments (lb/ac)

Yiel

d (k

g/tr

ee)

b b

aab

Mature trees:Response of Pecan to Nitrogen Rate and Nitrogen Application Time

• Seven year study on Mohawk• Nitrogen application rate was 67 or 135 lb/ac

• Single application: 1st week of March, or • Split application: 60% 1st week of March and 40% 1st week of June • Additional 0 or 45 lb/ac in October if the fruit load was heavy

• Results• Leaf N was not well-related to N application rate or timing• October N did not affect or reduced percentage of fruiting shoots the following year

Smith et al., 2004

2

2.1

2.2

2.3

2.4

2.5

2.6

2.7

1996 1997 1998 1999 2000 2001 2002 2003

Leaf

nitr

ogen

(%)

Leaf nitrogen

75 single

75 spli t

150 single

150 split

Effect of Nitrogen Rates on Mature Western Pecan Trees

• Flood irrigated Western• Annual N application 106, 212, 318 lb/ac broadcast in 6 monthly

applications of broadcast ammonium nitrate followed by irrigation

• Results• No differences in yield or quality, fruiting shoots, or fruits per cluster• Leaf N was not affected by N application

Nunez-Moreno et al., 2018

Leaf nitrogen (%)N application

(lb/ac) 2005 2006 2007 2008 average

106 2.90 3.13 2.89 2.81 2.93

212 2.93 3.17 2.93 2.85 2.97

318 2.93 3.17 2.92 2.83 2.96

Influence of Nitrogen Application Time on Nitrogen Absorption, Partitioning, and Yield of Pecan

Acuna-Maldonado et al., 2003

• 112 lb/ac broadcast 15N labeled ammonium nitrate in March or split 75% in March & 25% in October

• Results• Most N was absorbed between bud break and the end of shoot expansion• Small roots were the largest site of N storage• N applications had no effect on yield, little on N absorption

Phosphorus and Potassium

Phosphorus response of newly planted Wichita and Western pecans

Walworth, Heerema, Sherman

• Phosphoric acid injected via drip• Trees planted and fertilizer applications started in 2014 • 0, 50, 100, or 150 lb P/ac split among May – July irrigations

0

10

20

30

40

50

60

70

80

90

0 50 100 150

Annu

al In

crea

se in

Tru

nk D

iam

eter

(mm

)

Phosphorus Application Rate (lb P/ac)

Trunk Diameter Growth - Western

2017-2018

2016-2017

2015-2016

2014-2015

0

10

20

30

40

50

60

70

80

90

0 50 100 150

Annu

al In

crea

se in

Tru

nk D

iam

eter

(mm

)

Phosphorus Application Rate (lb P/ac)

Trunk Diameter Growth - Wichita

2017-2018

2016-2017

2015-2016

2014-2015

Applied P (lb/ac P) 2014 2015 2016 2017 2018 Average

0 0.129 0.112 0.119 0.112 0.118 0.118

50 0.136 0.120 0.125 0.115 0.126 0.124

100 0.124 0.122 0.129 0.116 0.130 0.124

150 0.144 0.121 0.127 0.110 0.128 0.126

Effect of P fertilizer on leaf P (%)

• Tree growth improved slightly by 50 (Western) or 100 (Wichita) lb/ac P

• Leaf P not well-related to P application• Leaf P increased slightly by addition of P

Response of pecan to annual soil band applications of P and K

• Phosphorus and potassium deficient 10 year old Pawnee in an acidic soil received annual treatments: control, banded phosphorus (DAP), potassium (KCl), P & K

• Results• P increased leaf P, alleviated foliar symptoms, improved flowering, produced darker

kernels• K increased leaf K and percentage of #1 kernels, but did not alleviate leaf symptoms

0.09 0.09 0.090.08

0.11

0.140.12

0.11

0.000.020.040.060.080.100.120.140.16

Yr 1 Yr 2 Yr 3 Yr 4

Leaf

P (%

)

No P P

0.78 0.730.81 0.860.82 0.79

1.07 1.11

0.00

0.20

0.40

0.60

0.80

1.00

1.20

Yr 1 Yr 2 Yr 3 Yr 4

Leaf

K (%

)

No K K

Smith and Cheary, 2013

Effect of K fertilizer on leaf K (%)Effect of P fertilizer on leaf P (%)

Growth of One-Year-Old Pecan Seedlings in Sand Culture to Various Levels of Potassium

• Pecan seedlings were watered with nutrient solutions with• 0, 60, 120, 240, 615, 990, 1365, 1740 ppm K

• Results after 4 months• K distribution: leaf > root > stem• Reduced growth when leaf K < 1.00%

Upson and Sparks, 1969

0.0

1.0

2.0

3.0

4.0

5.0

0 500 1000 1500 2000

Tiss

ue K

(%)

Nutrient solution concentration (ppm K)

Leaf K Root K Stem K

Leaf potassium (%)

Dry

Wei

ght (

gram

s)

Total plant

Leaves

Stems

Roots

Long-term Performance of Pecan Trees when Potassium Application is Based on Prescribed Threshold Concentrations in Leaf Tissue

• 19 year study on Stuart trees in Tifton loamy sand received 85 lb/ac K as broadcast KCl applied if leaf K was below threshold values • 0.25, 0.50, 0.75, or 1.00%

• Treatments did not consistently affect leaf K, nut yield or quality

0

10

20

30

40

50

60

70

80

0.25 0.50 0.75 1.00

Yiel

d (k

g/tr

ee)

00.10.20.30.40.50.60.70.80.9

11.1

0.25 0.50 0.75 1.00

Leaf

K (%

)

Worley, 1987

Foliar potassium sprays on adult pecan trees

• Multiple foliar sprays of K2SO4 or KNO3 at 2 wk intervals

• Results• Did not consistently increase leaf K• Nut size, kernel %, and yield generally did not respond to sprays

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

May 1984 July 1984 May 1985 July 1985

Leaf

K (%

)

Date sprays were initiated

0

1

3

5

Number of sprays

Smith et al., 1987

Influence of Elevating Tree Potassium on Fruit Drop and Yield of Pecan

• KCl was banded over drip emitters

• Results• Increase leaf K, kernel K, retention during early-midsummer drop, in-shell yield,

kernel percentage

• 1.25% minimum to reduce fruit drop

Wood et al., 2010

Nitrogen summary

• Optimum minimum leaf N• 2.30 to 2.75%

• Young trees & transplants• Minimum N requirement, little to no benefit from

fertilizing in 1st two or three years

• N fertilization• Varying rates and timing often have little effect on leaf N• Maximum N uptake from bud-break to end of shoot

expansion

Phosphorus summary

• Optimum minimum leaf P• 0.12%

• Young trees• Application of 50 – 100 lb/ac P increased growth relative

to no P

• P fertilization• Varying rates and timing often have little effect on leaf P• Fertilizing low P (~0.09%) trees can increase leaf P and

alleviate deficiency symptoms

Potassium summary

• Optimum minimum leaf K• 1.00% to maximize vegetative growth• 1.25% may be needed to minimize fruit drop

• K fertilization• Varying rates and timing often have little effect on leaf K• Even when foliar or soil K applications increase leaf K,

may not improve growth or yield

Conclusions• Fertilize according to leaf analysis results• Optimum minimum nutrient concentrations

• Pecans respond slowly, sometimes not at all, to N-P-K fertilizers in the season of application. Return bloom can be affected by nutrient deficiencies. • Pecan leaf N-P-K levels are not strongly related to amount of

fertilizer applied

Nitrogen Phosphorus Potassium2.30 to 2.75% 0.12% 1.00 – 1.25%

Conclusions

• Monitor tree nutrient status annually• Be patient• Pecan tree nutrient management is a long-term process• It may take several years to see changes in tree nutrient

status

https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1789-2019.pdf

Or search for: az1789 zinc