nutrient management in subtropical tree crops the avocado model

Nutrient Management in Subtropical Tree CropsThe avocado model

Avocado Fertilization

Tissue%Dry WtNew shoots36Leaves 40Fruit 33Small branches 38< 1 inSmall branches 551-2 inScion trunk 48Rootstock trunk41 Scaffolding roots37Small roots 35New roots4.6

Figure 1.

N Uptake (lbs N/a)

(128 lbs Fruit FW/tree)

Chart1

14.26335352425.81497797366.29955947141.179607095426.167400881120.216740088150.8810572687

9.06318832611.629955947110.375356253820.063749204617.444933920719.97444933926.7189647577

Roots

Trunk

Canopy Branches

Green Twigs

Leaves

New flushes

Fruit

Sheet1

OFFN Content (g per tree)SpringEarly SummerLate SummerFall

Tree Component1-AugNov-01Dec-01Jan-02Feb-02Mar-02Apr-02May-02Jun-02Jul-02Aug-02Sep-02Oct-02Nov-02Dec-02Avg DecJan -MarApr-JunJul-SepOct-Dec

Fine Roots941061291531-Aug1273.8624398064OFF1105131015141611

Small Roots (1")110838383Jan-021364.4869456207409Roots

Rootstock trunk7171107107Feb-02950.66666666673810.5242290749ON333295370391

Reproductive333295370391Mar-0212270.8401189827OFF339323398353

Trunk (scion)48484872487296727296967272487260Apr-021172.74

Wood >6"1681268412612612612616884168168168168126168126May-021553.56CB765.1780750978808

Scaffold Branches (wood 4-6")183122183183122183244244183305244244244183183183Jun-021751.44Sm Bran117.191435101200

Branches 2-4"287123123123123143.5164164123205205164205164205164Jul-021734.958

Small Branches (wood 1/2-2")127.1780750978239.2764369614105.50458715614520013514575100130125192210120252178.752293578Aug-021379.481Fruit Harvest

New shoots (green twigs, 6"1688412616884126126168126126168168210126126168CB729755

Scaffold Branches (wood 4-6")305122183244122122122244244244244305305183244264Sm Bran165.1314398063170

Branches 2-4"20582205205123164164164164205164246205164164205

Small Branches (wood 1/2-2")516817811292160768512518090100140170155137Dec-FebMar-MayJun- JulAug- Nov

New shoots (green twigs, 6"0.400.300.200.300.30.30.30.40.20.40.40.40.40.30.4

Scaffold Branches (wood 4-6")0.300.200.300.300.200.300.400.400.300.500.400.400.400.300.3

Branches 2-4"0.700.300.300.300.300.350.400.400.300.500.500.400.500.400.5

Small Branches (wood 1/2-2")0.500.700.400.500.500.500.500.500.500.500.500.600.700.500.6

New shoots (green twigs, 6"14-14320Canopy Branches93100.0825688073

OFFDry WeightScaffold Branches (wood 4-6")-2081-1561Green Twigs5138

Tree Component1-AugNov-01Dec-01Jan-02Feb-02Mar-02Apr-02May-02Jun-02Jul-02Aug-02Sep-02Oct-02Nov-02Dec-02Branches 2-4"-142107Leaves150122

Fine Roots12121212Small Branches (wood 1/2-2")-2146925New flushes4652.3065

Small Roots (6"424242424242424242424242424242

Scaffold Branches (wood 4-6")616161616161616161616161616161RootsTrunkCanopy BranchesGreen TwigsLeavesNew flushesFruit

Branches 2-4"414141414141414141414141414141ON712212361132

Small Branches (wood 1/2-2")253426294027291520262532302442OFF2362493013

New shoots (green twigs, 6"424242424242424242424242424242

Scaffold Branches (wood 4-6")616161616161616161616161616161

Branches 2-4"414141414141414141414141414141

Small Branches (wood 1/2-2")172336282340191725301820283422.2

New shoots (green twigs, 6"1608059118597684155.479.8134.4126130.2113.4130.2155.4107.1

Scaffold Branches (wood 4-6")21411614617111017798201.3164.7170.8237.991.5140.3219.6189.1167.75

Branches 2-4"13516017216412398107164200.9135.3172.2151.7143.5172.2155.8164

Small Branches (wood 1/2-2")17015015316018411610287222135.2102.5192213153.6294223.4908256881



Branches 2-4"13516017216412398107152185156180279131193246201

Small Branches (wood 1/2-2")1141002071551061726712412014495258193279200243



Branches 2-4"0.480.270.250.270.270.290.350.40.270.330.420.370.350.420.4




Branches 2-4"0.330.390.420.40.30.240.260.370.450.380.440.410.320.470.6




Branches 2-4"414141414141414141414141414141

Small Branches (wood 1/2-2")253426294027291520262532302442



Branches 2-4"414141414141414141414141414141

Small Branches (wood 1/2-2")172336282340191725301820283422.2

New shoots (green twigs,

Figure 3.

Fruit Dry Wt (g/fruit)

Chart1

85.572.480.37

281963

352366

412678

4527810

42261010

43.123271010

58341212

66451214

67461214

83481318

86561422

Total

Flesh

Peel

Seed

Aug 17,2001

Aug, 17, 01. Hrvest Data Nutrient concentrations in tree components of mature, on (A) and off (B) Hass avocado trees, measured in August 2001.

Tree 101Nutrient Concentration (percent)PPM

Tree ComponentNPKSMgCaNaNO3FeAlMnBCuZnMo

Fine Roots1.000.220.240.120.191.220.3644914042097664115536

Small Roots0.400.090.210.060.080.460.21147270697938216131

Scaffold Roots0.400.090.200.060.070.470.1612615097532321471

Rootstock0.200.080.100.020.020.090.22625540410121

Trunk0.300.040.270.050.070.570.0589411610175219

Scaffold Branches0.400.060.380.070.10.680.058602022751919428

Branches 2-4"0.500.190.670.040.170.60.021081812471319741

Small Branches0.500.170.330.050.170.780.14815943755527226106

New shoots0.800.391.210.090.330.930.053185453612351166

Leaves2.000.210.890.30.511.510.022771902035643757

Fruit2.600.222.080.40.080.070.0073624174445220

Seed.1.500.241.120.160.090.240.04219531523892066

Flesh2.600.222.080.400.080.07

Flesh2.300.392.250.200.180.180.0170802531612711450

Flesh2.900.362.730.410.130.160.013116254959533

Flesh3.100.282.310.330.090.050.0110472214549229

Flesh3.100.482.600.380.160.170.0226073451153944

Flesh Avg2.600.352.390.340.130.13

Peel1.200.241.770.160.120.160.02236251581031134

Peel0.900.090.730.100.150.220.0127221141369742

Peel0.900.090.770.080.140.230.0229119121267739

Peel1.300.261.890.320.140.110.0130221108751049

Peel1.200.231.480.270.120.230.0233821131177839

Peel Avg1.100.181.330.190.130.190

Tree 102

B.Nutrient Concentration (percent)

Tree ComponentNPKSMgCa

Fine Roots0.800.230.390.090.271.390.12613810201357683610535

Small Roots0.700.110.210.150.120.870.347274.001144.001929.0048.0036.008.0080.00

Scaffold Roots0.400.080.270.060.060.490.0992953294801719417

Rootstock0.200.040.120.020.020.070.19297141641029

Trunk0.200.040.120.020.020.060.21516910123916

Scaffold Branches0.400.060.310.060.060.640.11913357642123453

Branches 2-4"0.300.190.480.020.130.420.036118981151929437

Small Branches0.700.541.410.060.250.860.03311517923331381563

New shoots0.800.571.550.110.331.060.02762463525391462

Leaves2.100.261.150.390.541.710.02428821019210449986

Immature Fruit1.900.312.080.380.130.15

Seed.1.30.271.270.180.10.330.0233225856399026211

Flesh0.80.221.780.350.080.10.015176742427

Flesh1.70.41.950.190.120.180.01668830613541544

Flesh1.70.331.940.320.120.180.017061941048830

Flesh1.90.312.080.380.130.150.0158732646711133

Flesh1.60.351.830.290.140.170.01248229613671943

Flesh Avg1.540.321.920.310.1180.156

Peel0.900.101.250.120.150.310.022363191018621045

Peel0.700.070.420.060.120.150.0124251261040625

Peel0.800.090.770.100.110.310.0133181681656739

Peel0.900.211.720.090.140.220.012416.0017.007.008.0062.0011.0035.00

Peel0.800.151.190.090.10.20.0173261261148933

Peel Avg2.440.121.070.090.1240.238

Nov 8, 01

8-Nov-01


Tree ComponentNPKSMgCaNaNO3FeAlMnBCuZnMoCl %

Fine Roots

Small Roots

Scaffold Roots

Rootstock

Trunk ( >6" )0.300.050.310.070.070.54126.0050.0024.0014162190.96

Scaffold Branches0.200.030.190.030.030.25

Branches 0.5- 2"0.400.070.330.030.080.280.01158.0014.0013.007222250.776596.6

Branches 2-4"0.300.040.270.040.060.28197.0014.004.006141190.59

Scaffold Branches 4"- 6"0.200.030.160.020.030.190.007234.0013.0011.006111100.516305.7

Small Branches0.700.180.570.060.20.820.001208.0046.0018.0012273400.91

New shoots0.800.421.060.150.3310.008182.0061.0022.0016426610.750.1

Leaves2.100.150.660.450.441.921159.00227.00112.0075355340.64

Fruit

Seed.0.80.191.060.120.080.0413592649156150.730.1

Seed.0.80.21.040.110.070.02132226242060.660.1

Seed.0.80.20.990.120.060.0814952658165150.591250.6

Seed.0.70.211.020.130.080.0913002321217719

Seed.0.90.21.060.120.080.061422249136140.560.1

Seed Avg0.800.201.030.120.070.06

Flesh1.600.251.820.240.090.061.008278.0022.001.006.00104.008.0036.000.533950.9

Flesh1.600.231.890.210.070.041.008359.0022.004.00103.008.0035.000.45589.7

Flesh1.400.211.440.190.100.091.008377.0026.006.0088.006.0025.000.433319.3

Flesh1.400.221.500.220.100.081.007940.0025.006.0088.007.0027.000.590.11

Flesh1.900.221.660.240.110.081.008782.0031.006.0098.007.0032.000.343346.70

Flesh Avg1.580.231.660.220.090.07

Peel1.200.241.530.100.070.071.00659.0026.005.006.0065.006.0023.000.543899

Peel1.300.251.700.090.070.04867.0027.005.004.0073.007.0025.0010

Peel1.000.191.150.050.080.121.00424.0022.004.006.0052.005.0015.0003359

Peel1.100.221.350.100.080.111.00606.0023.007.007.0060.006.0020.000.392761.10

Peel1.300.241.660.100.090.121.00513.0026.006.007.0070.006.0023.000.4801108.500

Peel Avg1.180.231.480.090.080.09

Tree 2

B.Nutrient Concentration (percent)PPM

Tree ComponentNPKSMgCaNO3FeAlMnBCuZn

Fine Roots

Small Roots

Scaffold Roots

Rootstock

Trunk0.200.020.030.020.010.080.0193.0036.0044.00369100.156293.2

Scaffold Branches 4- 6 "0.200.030.190.030.030.250.00683.0042.008.0081010.46

Branches 2-4"0.200.030.180.030.040.22192.0010.003.007810.19

Small Branches 0.5" to 2"0.300.120.440.050.160.690.002180.0043.0021.00131820.47

New shoots0.600.320.740.140.341.140.007145.0055.0022.0018304530.41

Leaves1.700.150.610.480.542.28643.00281.00142.0011228430.78

Fruit

Seed.0.70.160.860.10.050.0813161710173130.80.1

Seed.0.60.170.860.110.050.060.0065342611320512.221697.8

Seed.0.90.180.950.150.050.0819692319344180.96550

Seed.0.80.160.970.120.050.061241215115181.030.1

Seed.0.140.830.050.0714932210114181.16368.2

Seed Avg0.750.160.890.120.050.07

Flesh1.40.211.450.190.120.141842158844260.4

Flesh1.40.191.430.180.10.110.0026401247864270.547499.5

Flesh1.60.191.340.220.110.1217106247934260.57457.53

Flesh1.50.211.730.220.080.080.0027971198735270.512735.7

Flesh1.20.171.340.210.10.19613177596250.492720.4

Flesh Avg1.420.191.460.200.100.10

Peel0.900.140.940.070.070.131.00429.0017.002.008.0041.003.0014.000.436445.10

Peel1.000.181.150.070.070.12342.0019.001.008.0050.004.0017.000.557059.10

Peel1.100.151.120.080.080.14416.0018.002.007.0057.004.0015.000.50197.00

Peel1.000.181.280.070.070.10730.0020.003.008.0044.005.0026.000.594434

Peel0.900.181.180.070.080.121.00596.0019.002.008.0038.005.0015.000.586412

Peel Avg0.980.171.130.070.070.12

Dec 13, 01

December 13, '01Harvest Data

Tree 6 OFFNutrient Concentration (percent)PPM

Tree ComponentNSPKMgCaNaNO3FeAlMnBCuZn

Fine Roots

Small Roots

Scaffold Roots

Rootstock

Trunk0.200.030.050.120.030.250.014157077710237

Wood >6"0.200.010.050.20.070.490.015430271919218

Scaffold Branches (wood 4-6")0.300.040.030.110.020.140.0141121458111

Branches 2-4"0.300.060.050.250.060.350.0133715141016220

Small Branches (wood 1/2-2")0.400.050.210.510.180.630.0287435361727530

New shoots (green twigs, 6"


Branches 2-4"0.500.030.050.40.10.760.00541385422337


New shoots (green twigs, 1")

Rootstock trunk0.300.040.040.290.030.140.0155910310714136110.51

Reproductive

Trunk (scion)0.300.040.030.190.040.170.036159322619114270.31

Wood >6"0.30.040.040.380.070.580.005227312342176271.45


Branches 2-4"0.400.040.050.470.080.41118301642207211.1


New shoots (green twigs, 2"0.200.050.030.140.020.080.10614155315470.10.175

Small scaffold roots (1/2-1")0.300.070.060.190.050.320.1130921838616216140.870.116

large scaffolding roots 1-2"0.300.060.060.20.040.30.0916919737012236110.92

Scaffold Roots (>1")

Rootstock trunk0.300.060.040.160.040.240.0952027286165310.67

Reproductive

Trunk (scion)0.200.040.030.140.030.190.117419156115110.17

Wood >6"0.30.060.050.310.050.420.033221511175170.6

Scaffold Branches (wood 4-6")0.300.050.060.360.070.50.0054436142011180.87

Branches 2-4"0.400.050.090.420.10.540.0044134192210210.67

Small Branches (wood 1/2-2")0.500.070.170.640.180.80.009416150222812350.71

New shoots (green twigs, 6"0.40.10.070.40.070.730.01948413415229221.2447.41

Trunk (scion)0.30.10.090.30.10.40.027163.034.029.010.019.07.029.00.947.51

Fruit

Peel 11.10.10.171.40.120.110.021210281310707250.740.10247.1

Peel 21.10.10.211.50.120.090.01624526118838300.648.03

Peel 31

Peel Avg1.10.110.221.700.120.140.019159392611848240.7847.61

Flesh 11.70.390.282.410.110.050.0115498241510112271.120.25549.32

Flesh 22.10.40.332.730.10.050.0125627243512813321.310.01948.25

Flesh 31.40.320.262.20.10.060.016380211510010251.20.15446.24

Flesh Avg

Seed 10.80.150.271.320.120.060.0122582558248180.8742.65

Seed 210.170.321.590.120.050.0132252545289210.842.09

Seed 30.60.140.271.260.090.050.0153172059169190.7743.87

Seed Avg

Tree 38 ON

Tree ComponentNSPKMgCaNaNO3FeAlMnBCuZnMoCl %C %

New flushes

Reproductive

Canopy Leaves2.50.50.231.10.521.590.0121961401052005075310.82646.67

Green twigs10.20.531.40.41.110.027767659954917820.870.21944.75

Small Branches (wood 1/2-2")0.70.10.260.90.230.930.016129069783317652.3946.1

Branches 2-4"0.40.10.090.60.090.470.015437512011312.5346.76

Scaffold Branches (wood 4-6")0.40.10.080.60.090.680.0115039482410393.4447.07

Wood >6"0.30.10.060.40.060.450.013342436157261.8647.66

Trunk (scion)0.30.10.080.40.10.50.03928.038.032.035.018.07.057.01.948.21

Fruit

Peel 110.10.181.50.120.10.015291413719250.610.13947.59

Peel 210.10.141.60.10.070.01531129519280.490.01447.65

Peel 31.10.10.191.90.090.050.02491361577410310.6447.63

Peel Avg

Flesh 12.20.390.352.810.10.050.0145118265710816311.570.18446.37

Flesh 22.40.420.343.150.10.040.015606730169218401.670.01945.82

Flesh 32.40.40.282.170.070.020.021603330559917412.230.03745.63

Flesh Avg

Seed 10.90.170.331.570.120.050.00822224482110200.6642.3

Seed 210.160.291.580.160.050.01447305102712211.1142.22

Seed 310.160.241.480.130.020.011142245249160.8642.43

Seed Avg

149.52

188.16

31.36

24.924.9886621315

lbs

3.814.2672220521.336

1.131.265622056.328

2.783.1136220515.568

6.116.8432220534.216

3842.5622050

10000 kg/ha

11200

150

30047.3

181.818181818216.5

63.8

Mar 6, 03

March 6th, 2003


Tree ComponentNPKSMgCaNaNO3FeAlMnBCuZnMoCl %

Reproductive2.70.461.510.250.340.980.121471991651007022651.171

Leaves1.900.200.730.330.661.990.008240.0090.0066.00200366410.680.68

New shoot green twigs0.700.380.740.090.431.160.01993.0063.0034.0044427680.550.241

Branches(wood) 0.5- 2"0.600.160.510.040.190.690.0187.0053.0042.0028287430.641

Branches (wood) 2-4"0.300.050.280.080.060.310.0081.0020.0010.0015153150.581

Branches (wood) 4"- 6"0.300.040.250.070.050.40.0318.0023.0016.0017153170.981

Wood >6"0.200.030.130.090.030.160.1152.0013.008.00910280.321

Scion Trunk0.200.020.090.070.020.080.10472.0012.006.0068260.121

Rootstock Trunk0.30.040.210.120.030.170.08410465739133120.291

large Roots >2"0.30.060.250.050.050.240.02218616325720194150.770.755

large Roots 1- 2 "0.40.060.220.060.060.320.04617422234019215201.310.75

Roots 0.5- 1"0.40.070.290.070.070.360.05417132651225256291.760.115

Roots < 0.5"0.600.080.280.090.110.640.161288.00645.00997.004337101152.921.062

Very Fines Roots1.400.180.430.170.251.540.38381.00593.00885.005669239037.171.173

Fruit

NOT FOR N 15 .Seed 10.700.201.260.110.10.050.0062581636267190.551

NOT FOR N 15 Seed 20.500.170.770.070.090.060.0061741327145140.760.281

NOT FOR N 15 Seed 30.700.211.030.080.10.070.0052991628245150.671

Seed Avg0.630.191.020.090.100.060.01243.6715.002.337.0021.335.6716.000.660.76

from fruit 6 & 8

composite seed Fruit 6&80.700.221.100.110.100.080.01120.0019.003.007.0021.008.0020.000.641.00

NOT FOR N 15 Flesh 11.300.292.460.380.100.0449762048910260.421

NOT FOR N 15 Flesh 20.800.211.680.180.080.052990126795170.211

NOT FOR N 15 Flesh 31.000.272.270.250.100.052644198747220.321

Flesh Avg1.030.262.140.270.090.050.003536.6717.000.006.0080.677.3321.670.321.00

composite flesh Fruit 6&81.100.282.250.230.100.052868.0024.006.00102.007.0022.000.2901.000

NOT FOR N 15 Peel 11.300.171.550.090.220.200.013124221517769450.431

NOT FOR N 15 Peel 21.000.111.370.070.160.170.010139251415556250.3103.47

NOT FOR N 15 Peel 31.100.131.580.080.160.160.009175221117567280.42.23

Peel Avg1.130.141.500.080.180.180.01146.0023.0013.3316.3362.337.3332.670.372.18

composite peel Fruit 6&81.200.131.430.090.180.160.12146.0029.0017.0016.0077.008.0037.000.300.56

Tree 4

Tree Component

Reproductive2.80.51.580.260.310.810.013349115112365934801.371.00.

Leaves2.20.270.950.510.591.410.013373978262389530.710.53

New shoot green twigs0.90.531.240.130.451.010.0212477357204718930.810.16

Branches(wood) 0.5- 2"0.50.20.560.060.160.510.009145413311247411.201.00

Branches (wood) 2-4"0.300.080.310.090.070.280.005108.0021.0010.007174200.761

Branches (wood) 4"- 6"0.300.060.270.070.050.260.00676.0018.0012.006143170.811

Wood >6"0.300.040.240.070.040.260.027103.0016.0011.006133230.731

Scion Trunk0.300.040.200.090.030.180.039131.0012.007.004112230.391

Rootstock Trunk0.300.030.170.010.020.060.046173.008.005.0028280.181

large Roots >2"0.300.060.240.040.040.160.012122.0098.00158.00420380.681

large Roots 1- 2 "0.30.060.230.050.040.210.02131132217919390.831

Roots 0.5- 1"0.40.090.290.050.070.340.05223230350418276201.831

Roots < 0.5"0.60.10.320.090.130.680.19330669311403440111763.630.677

Very Fines Roots1.30.20.40.190.241.210.45540797916213956234256.790.582

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Seed 2E

Seed 3E

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Flesh 2RD

Flesh 3U

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Peel 2

Peel 3

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Jun 12, 03

Fruit N content (mg/fruit)

Figure 4. Nitrogen content of Hass avocado fruit.

Each point is the mean between 5 and 12 fruit, with standard error bars.

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Fruit K content (mg/fruit)

Figure 5. Potassium content of Hass avocado fruit.

Each point is the mean between 5 and 12 fruit, with standard error bars.

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Table 1. Mineral balance (g per tree) of 20-year-old Hass avocado in California.LeavesProportion removed& twigsBranchesTrunkRootsFruitTotalby fruit (%)N559 65734293191173411.0P118 12913 85 53 39913.3K373 61056251377166522.6Ca575109395317 62086 0.3Mg183 47112 61 16 742 2.2S101 12014 65 45 34513.2Al1.1 4.40.732.70.0 39 0.1B1.8 3.60.4 1.71.4 915.9Fe3.4 6.40.922.00.3 33 1.1Mn3.0 3.60.3 1.30.1 8 1.1Na9.823.99.285.81.8 131 1.4Zn2.1 3.90.8 7.60.5 15 3.3In a 10,000 pound crop this translates into 30 # N and 50# K

So how do you manage these nutrients?

Every year is going to be somewhat different, according to yield.

Over application can lead to too much vegetative growth and contamination.

Too little can result in lower yields.

Start with the fall leaf analysis.Are you within the recommended range?

Look at crop load, is it higher or lower than last year.

If higher bump up N from last year by 20%, if lower drop it by 20%. K does not leach and does not need to be changed as long as within range.

Avocado NutritionAvocado is unique in that it is very efficient in recycling nutrients from the leaf mulch Generally, nitrogen should be applied every yearOccasionally Zinc should be appliedPhosphorous? Potassium? (maybe)Iron in calcareous soils

Citrus is similar

How much to apply?N and K should be based on leaf analysis in later summer, fall.

NOT soil analysis

Because of high pH soils north of San Diego, not a good idea to apply Ca and K nitrate, which raise pH. Stick with ammonium based materials. Organics have slight acidifying effect, as well.

Organics cost at least 10 X more than synthetics. And in coastal California release N in about 2 months. Warm soils.

FertilizersN-P-K ratio is the grade and is required to be on all bags of fertilizer21-7-14 means that in 100 lbs of fertilizer you will get 21 lbs on N, 7 lbs of phosphate (P2O5) and 14 lbs of potash (K2O)

New Growers Quick Guide - Nitrogen0.5-1.0 actual pounds of nitrogen required per tree, per yearUsually divided into 8 or 9 applications to be injected into the irrigation systemOr, use this suggested hand application3 lbs triple 15 in early March/April0.5 lbs urea in June0.5 lbs urea in September

When to fertilize? An ExperimentExperiment conducted: control treatment was fertilized at 25 lbs N per acre in each time period (late January, mid April, mid June, mid July, late August and late October)An extra 25 lbs per acre was applied in January, or February or April or June or NovemberApril gave increased yield of 31% over control, and November gave increased yield of 39% over control (4 years of data)

New Quick Growers Guide IronIf interveinal yellowing of leaf, most commonly is iron deficiency, caused by high pH or waterlogging. Gradually acidify soil, review irrigation program. Start iron chelates in the meantime

New Growers Quick Guide - ZincYellow mottling between the veins of the leaves, small leaves, short internodes, rounded fruit, apply zinc sulfateHand, 3-5 lbs zinc sulfate per tree, every 3-5 yearsIrrigation with liquid zinc, 1-2 gallons per acre

New Growers Quick Guide Potassium

Leaf tip and marginal burn, starting on mature leaves, small brownish spotsSmall fruit, shriveled seedsSlow growthThin twigs, diebackConfused with chloride tip-burn which is much more common

Salt/Chloride Tip-BurnNot a nutrient deficiencyCaused by:Saline water (from wells, ponds or reclaimed water)Poorly leached soils that accumulate saltsUnder-irrigationToo much manureCombinations of above

Application MethodsLiquid application of fertilizers is best due to ease of application and reduction in labor costs. Hand application to soil - Many small groves still do not have fertilizer injection, Many growers still like to use triple 15 to get P and K, this is not water solubleFoliar, not suitable for Nitrogen or other materials due to thick waxy leaf surface in avocado, but very effective in citrus

Injection EquipmentBackflow prevention deviceInjectorTank that will not corrodeDifferential pressure tanks, or batch tanksVenturi devicePositive displacement pump, gas, electric or water powered

Nutrient Availability and UptakeThe atmosphere contains 78% N2 gasSome soil organisms and root nodules on legumes convert N2 to NO2Lightning also converts N2 to NO2Fertilizer companies use natural gas to convert N2 to NH3 (under high temperature and pressure). Prices going upOrganic manures are slowly converted to NH4 and NO3 for plant uptake

Nutrient Availability and UptakeAmmonium to nitrate takes 1-2 weeks at 75FAmmonium to nitrate takes 12 weeks or more at 50FAmmonium to nitrate is optimum at pH between 5.5 and 7.8Under anaerobic conditions, nitrate is lost from the soil as nitrous oxide, nitric oxide and N2 gases

Nutrient Availability and UptakeMost of N is taken up as nitrate (NO3-Some may be taken up as ammonium (NH4+)Nitrate is highly mobile in soil and moves to the roots quickly (and is leached out readily)Ammonium binds to soil particles and is converted to nitrate by bacteriaVery poor uptake when soils are cold, and as as nitrate readily leaches

Nutrient Availability and UptakePhosphorus (P)Most P in soil is tied up chemically, less than 1% may be available for uptake into plant. Mycorrhizal fungi help uptakeP taken up as phosphate ions: H2PO4-, HPO4--, or PO4Note: phosphorous acid is a phosphonate, not readily used as a nutrient- Rare documentation of supplemetal P in CA trees

Nutrient Availability and UptakePotassium (K)Taken up as K+ ions and remains in ionic form in the plant90-98% of K occurs in primary materials and is unavailable to the plants1-10% is trapped in expanding lattice clays and is slowly available1-2 % is in soil solution and readily availableDoes not readily leachMost fruit trees require 2x as much K as N

Nutrient InteractionsExcess K+ may compete with Mg and Ca uptakeExcess P interferes with Zn uptakeExcess Fe can induce Mn deficiencyIncreasing K fertilization can reduce B in the leaf analysisUSE LEAF ANALYSIS

SUMMARYNitrogen applications are typically 1 lb of N per tree per year as an acid-based source, and best applied in spring early fall AVOID winter applicationsPhosphorus is rarely called forPotassium as hand or helicopter applied can go on anytime as K2SO4Zinc and Iron as sulfate or chelate go on in the warm months

nutrient management in subtropical tree crops the avocado model

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