Nutrient Management gIn Brassica Crops

Richard SmithUC Cooperative Extension, Monterey County

Nitrogen Management of Leafy VegetablesLeafy Vegetables

• Nitrogen management ofNitrogen management of vegetables in the coastal production districts is underproduction districts is under greater scrutiny

• Growers will need to report N usage to the Central Coast gRegional Water Quality Control Board in 2014Board in 2014

Nitrogen Management of Leafy VegetablesLeafy Vegetables

• As a result, growers are lookingAs a result, growers are looking for tools to improve nitrogen use efficiencyefficiency

Nitrogen Management of Leafy VegetablesLeafy Vegetables

• An important tool in nitrogenAn important tool in nitrogen management is to account for residual N mineralized from priorresidual N mineralized from prior crop residues

Nitrogen Management of Leafy VegetablesLeafy Vegetables

• Another way of improvingAnother way of improving nitrogen use efficiency is to capture nitrate that may havecapture nitrate that may have moved to deeper in the soil profile

d b i it b k t th fand bring it back to the surface for another opportunity to use it

Nitrogen Management of Leafy VegetablesLeafy Vegetables

• Crops like sugar beets and small grains, when they were viable g , ycrops in the Salinas Valley, were capable of retrieving nitrogencapable of retrieving nitrogen from deeper in the soil profileC d thi b t• Cover crops can do this but we are limited in their use

Nitrogen Management of Leafy VegetablesLeafy Vegetables

• In recent studies funded by the Fertilizer Research and Education Program (CDFA), we observed that cole crops can scavengethat cole crops can scavenge nitrate

Nitrogen Uptake by Broccoli, Cauliflower and Cabbage

Nitrogen Dynamics in ColeNitrogen Dynamics in Cole Crops – Summer ProductionCrops  Summer Production

Crop Dry BiomassLbs/A

Percent Nitrogen

Percent Potassium

Potassium UptakeLbs/A

PhosphorusUptakeLbs/ALbs/A Lbs/A Lbs/A

Broccoli 8,585 4.0 4.2 360 44Cauliflower 6 930 4 1 4 3 299 45Cauliflower 6,930 4.1 4.3 299 45Cabbage 11,564 3.0 3.2 361 42

Nitrogen Dynamics in ColeNitrogen Dynamics in Cole Crops – Summer ProductionCrops  Summer Production

Crop Harvest Leaves Stalks Roots Residue ProductN/A N/A N/A N/A N/A

Broccoli 99 198 41 11 23899 198 41 11 238Cauliflower 61 204 20 10 224C bb 164 9Cabbage 188 164 ‐‐‐ 9 163

Nitrogen Dynamics in ColeNitrogen Dynamics in Cole Crops – Summer ProductionCrops  Summer Production

Crop Fertilizer Crop Uptake ScavengedCrop Fertilizerapplied

Crop Uptake Scavenged from soil

Broccoli 181 337 155C liflCauliflower 260 285 21Cabbage 215 337 97g 215 337 97

Nitrogen Uptake CurveSummer Broccoli

Summer broccoli400

500

ssssssssssssssss

b/ac

re)

300

400

y = 5.72x - 157.9R2 = 0.89

ssssssssssssssss

N (l

b

200

100

Days after germination water

0 20 40 60 80 1000

Nitrogen Dynamics in ColeNitrogen Dynamics in Cole Crops – Winter ProductionCrops  Winter Production

Crop Dry Biomass

Percent Nitrogen

Percent Potassium

Potassium Uptake

PhosphorusUptake

Broccoli 5,539 4.5 3.3 194 32Cauliflower 6 490 4 2 3 7 236 36Cauliflower 6,490 4.2 3.7 236 36

Nitrogen Dynamics in ColeNitrogen Dynamics in Cole Crops – Winter ProductionCrops  Winter Production

Crop Harvest Leaves Stalks Roots ResidueCrop HarvestProductN/A N/A N/A N/A

Residue 

N/A

Broccoli 94 128 29 8 156Broccoli 94 128 29 8 156

Cauliflower 70 160 14 9 175

Nitrogen Dynamics in ColeNitrogen Dynamics in Cole Crops – Winter ProductionCrops  Winter Production

Crop Fertilizerapplied

Crop Uptake

Scavenged from soilapplied

N/AUptakeN/A

from soilN/A

Broccoli 272 249 23+Broccoli 272 249 23+Cauliflower 351 273 78+

Nitrogen Uptake CurveWinter Broccoli

400

Winter broccoli300

ssssssssssssssss

b/ac

re)

200

y = 2.62x - 153.8R2 = 0.71

N (l

b

100

0

Days after germination water

0 20 40 60 80 100 120 140 160

Nitrogen Uptake by Broccoli, Cauliflower and Cabbage

• Where is the extra nitrogen coming from inWhere is the extra nitrogen coming from in the summer‐grown broccoli?

• Is broccoli is acting like a cover crop in that it• Is broccoli is acting like a cover crop in that it is bringing up nitrate from deeper in the root zone?zone?

Rooting Depth and Nitrate at the End of the Growing Season 

Spinach Root Distribution

9

6

7

8

4

5

roots/in

2

1

2

3

0

0‐4 4‐8 8‐12 12‐16 16‐20 20‐24

Depth (in)

Nitrate Distribution in Spinach Bedst H tat Harvest

20

25

15

N (m

g/kg soil)

5

10

NO3‐N

0

0‐4 4‐8 8‐12 12‐16 16‐20 20‐24

Depth (in)

Root Density of Lettuceat Various Soil Depths

Bed Width (inches)

5 10 15 20 25Plant Line Plant Line

Drip lineDrip line

5 10 15 20 25

5 0102030

Root N

umes

)

10

304050 60 70

mber / 100 cm

2D

epth

(inc

he

15

D

20

25

Soil Nitrate Distribution in Lettuce

Nitrate-N (ppm)Bed width (inches)

10 20 30 40 50

5

Plant row Plant rowDrip tapeNitrate‐N (ppm)

5

10

0 2 4 6 8 10

ches

)

10

15

012 14 16 18 20 22

Dep

th (i

nc 15

20

22 24 26

20

2525

End of Crop Nitrate DynamicsEnd of Crop Nitrate Dynamics

• Nitrate can accumulates at the bottom edgeNitrate can accumulates at the bottom edge of the root zone of lettuce and spinach

• Nitrogen from crop residues is also disced• Nitrogen from crop residues is also disced into the soil, enriching the upper soil layers with nitratewith nitrate

Measurements of nitrate in soil at various depths in the root zone

following a prior crop and over thefollowing a prior crop and over the crop cycle of broccoli 

Nitrogen in the Top Three Feet of Soil over the Broccoli Crop CycleSoil over the Broccoli Crop Cycle

One Field 

90Third foot

60

70

80

90

ppm

First foot

Second foot

20

30

40

50

NO

3-N

p

0

10

preplantearly growthearly growth

late growth harvest

Growth Stage of Broccoli

Residual Soil Nitrogen Utilized by the Broccoli Cropthe Broccoli Crop 

One FieldDepth Lbs N/A

1st 58 

2nd 70

3rd 263rd 26

Total 154

90Third foot

60

70

80

90

First foot

Second foot

ppm

20

30

40

50

NO

3-N

p

0

10

preplantearly growthearly growth

late growth harvest

Growth Stage of Broccoli

Evaluation of Nitrate in the 1st & 2ndFoot of Soil (5 fields)

4550 First foot

SecondDepth Lbs N/A

1st 40

202530354045 Seco d

foot 1st 40 

2nd 24

Total 64

05

101520

BaselineEarly growth

Mid‐growthLate growth

Harvest

Growth Stage of Broccoli

Broccoli Rooting DepthBroccoli Rooting Depth

45

50

34.1”

35

40

5

25

30

-inc

hes

15

20

Dep

th

5

10

0

0.1 0.2 0.3 0.4 0.4 0.5 0.6 0.7 0.8

Portion of the Growth Cycle

Early Mid Late Harvest

Cauliflower Rooting DepthCauliflower Rooting Depth60

5034.1”

30

40

-inc

hes

20

30

Dep

th

10

00.1 0.3 0.4 0.5 0.7 0.8

Portion of the Growth Cycle

90 Day Old Cauliflower Roots90 Day Old Cauliflower Roots

Cabbage Rooting DepthCabbage Rooting Depth50

35

40

45

30.9”

25

30

35

-inc

hes

15

20

5

Dep

th

5

10

0

0.1 0.3 0.4 0.6 0.8Portion of the Growth Cycle

RecommendationsRecommendations• Measure the levels of residual nitrate in the 

d f l i h h l f lsecond foot early in the growth cycle of cole crops

• Given that broccoli is taking up nitrogen from the top two feet, this information will give you a better sense of what nitrogen resources are available for that crop

• Careful water management will be necessary to maintain the nitrate in the top two feet pbefore the broccoli roots reach there

RecommendationsRecommendations• All of the cole crops leave sizeable quantities 

f i i h i idof nitrate in their crop residue • This nitrate will rapidly mineralize nitrate for subsequent crop use

• Again, careful irrigation will better assure g , gthat this nitrogen is available for subsequent crops that are shallower rootedp