EVALUATION OF PERCOLATION AND EVALUATION OF PERCOLATION AND NITROGEN LEACHING FROM A SWEET NITROGEN LEACHING FROM A SWEET

PEPPER PEPPER CROP GROWN ON AN OXISOL SOIL IN CROP GROWN ON AN OXISOL SOIL IN

NORTHWEST PUERTO RICONORTHWEST PUERTO RICO

Eric Harmsen, Eric Harmsen, Joel Colon, Joel Colon,

Carmen Lis Arcelay and Dionel Carmen Lis Arcelay and Dionel CadizCadiz

Agricultural and Biosystems Engineering Department University of Puerto Rico – Mayagüez Campus

This Material Is Based on Research Supported byUSDA/CSREES Grant No. CBAG-82 in

Tropical/ Subtropical Agriculture Research

BACKGROUNDBACKGROUND

NNitrate leaching through the soil profile can itrate leaching through the soil profile can result in a significant loss of fertilizer N, and result in a significant loss of fertilizer N, and may be a source groundwater contamination.may be a source groundwater contamination.

Highly weathered soils may exhibit Highly weathered soils may exhibit substantial anion exchange capacity (AEC), substantial anion exchange capacity (AEC), which retards the movement of anions such which retards the movement of anions such as NOas NO33

-- through the profile. through the profile.

However, AEC decreases as soil pH increases However, AEC decreases as soil pH increases by agronomic practices such as liming.by agronomic practices such as liming.

OBJECTIVEOBJECTIVE

To evaluate the effects of liming and To evaluate the effects of liming and fertigation on the leaching of fertigation on the leaching of nitrogen through a highly weathered nitrogen through a highly weathered tropical soiltropical soil

Study Area – NW Puerto Study Area – NW Puerto RicoRico

Field StudyField Study 2002 and 2003 at the UPR Experiment Station at Isabela, PR, 2002 and 2003 at the UPR Experiment Station at Isabela, PR,

using sweet peppers (using sweet peppers (Capsicum annuumCapsicum annuum, “Biscayne”) as the , “Biscayne”) as the test crop.test crop.

2 lime levels (Lime or No lime); 2 fertigation frequencies 2 lime levels (Lime or No lime); 2 fertigation frequencies (Weekly or Bi-weekly).(Weekly or Bi-weekly).

Soil samples collected every two weeks at 20 cm increments, Soil samples collected every two weeks at 20 cm increments, down to 80 cm.down to 80 cm.

Analyzed for NHAnalyzed for NH44++ and NO and NO33

-- concentrations by steam distillation concentrations by steam distillation (Mulvaney, 1996). (Mulvaney, 1996).

Road USDA TARS Facility

F1 F2

NL-F2L-F1

L-F1L-F2

L-F2

NL-F1

NL-F1 L-F1

NL-F2

NL-F1

L-F2

L-F2

NL-F1

NL-F2

L-F1NL-F2

North

Block 2

Block 1

Block 4

Block 3

@

@

Experimental LayoutExperimental Layout

Estimating Nitrogen LeachingEstimating Nitrogen Leaching

LLNO3NO3 = 0.01 ρ = 0.01 ρbb NO NO33 PERC / PERC / θθvolvol

LLNH4NH4 = 0.01 = 0.01 ρρbb NH NH44 PERC PERC / θθvolvol

Water BalanceWater Balance

Perc = (R-RO)+Irr-ETPerc = (R-RO)+Irr-ETcc + + SS

Perc = Perc = Deep percolationDeep percolation(R –RO) = (R –RO) = Rainfall – RunoffRainfall – RunoffIrr Irr = = Irrigation based on ETIrrigation based on ETpanpan

ETETc c = = Evapotranspiration based on Evapotranspiration based on

Penman-Monteith method.Penman-Monteith method.

S = S = Change in stored waterChange in stored water

IRR = ETIRR = ETpan pan = K= Kcc K Kpp E Epanpan

IRR = ETIRR = ETpan pan = =

Evapotranspiration Evapotranspiration based on panbased on pan

KKcc = = Crop coefficientCrop coefficient

KKpp = = Pan coefficientPan coefficient

EEpan pan = = Pan evaporationPan evaporation

ETETc c = K= Kcc ET EToo

ETETc c = = Evapotranspiration Evapotranspiration

based on Penman-based on Penman- Monteith method.Monteith method.

KKcc = = Calibrated crop coefficientCalibrated crop coefficient

ETETo o = = Reference Reference

evapotranspiration evapotranspiration

Calibration of the Water Balance Calibration of the Water Balance Equation Equation

• Calibration variables: (RO/R) Calibration variables: (RO/R)

• Calibration target: average soil Calibration target: average soil

moisture contentmoisture content

RESULTSRESULTS

Depth % Sand1 % Silt1 % Clay1

Soil Classification

Bulk Density Porosity

0-20 cm 35.10 19.35 45.55silty clay

1.36 0.49

20-40 cm 28.72 1.85 69.43

clay1.36 0.49

40-60 cm 22.50 5.00 72.50

clay1.31 0.51

60-80 cm 20.00 5.80 74.20

clay1.29 0.51

Depth

Hydraulic Conductivity

(cm/day)

In-Situ Field

Capacity Year 1

Site

In-Situ Field

Capacity Year 2 Site

Moisture Content at 0.33 bar Pressure

Moisture Content at

15 bar Pressure

Available Water

Holding Capacity (AWHC)

0-20 cm 1210.06 0.33 0.44 0.44 0.39 0.05

20-40 cm 316.99 0.33 0.37 0.37 0.27 0.10

40-60 cm 70.10 0.37 0.36 0.36 0.31 0.05

60-80 cm 12.19 0.37 0.38 0.38 0.3 0.08

Properties of the Coto ClayProperties of the Coto Clay

0.00

2.00

4.00

6.00

8.00

1/28/2003 2/27/2003 3/29/2003 4/28/2003 5/28/2003

Date

ET

(m

m/d

ay

)

ETo

Eto (long-term avg.)

ETpan

Evapotranspiration – 2003 SeasonEvapotranspiration – 2003 Season

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

3/27 4/11 4/26 5/11 5/26 6/10 6/25 7/10Date

Mo

istu

re C

on

ten

t (V

ol)

Estimated

Field Capacity

Measured

Measured Min

Measured Max 0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

1/28 2/17 3/9 3/29 4/18 5/8 5/28

Date

Mo

istu

re C

on

ten

t (V

ol)

Calibrated Soil Moisture ContentCalibrated Soil Moisture ContentRO/R = 0.25RO/R = 0.25

2002 2003

0

10

20

30

40

50

3/27/2002 4/16/2002 5/6/2002 5/26/2002 6/15/2002 7/5/2002Date

PE

RC

(m

m)

0

10

20

30

40

50

1/30/2003 3/1/2003 3/31/2003 4/30/2003 5/30/2003Date

PE

RC

(m

m)

Estimated PercolationEstimated Percolation

2002 2003

0.00

5.00

10.00

15.00

20.00

3/27 4/16 5/6 5/26 6/15 7/5Date

Nit

ria

te C

on

ce

ntr

ati

on

(m

g/k

g) LF1

LF2

NLF1

NLF2

Soil Nitrate Concentration at 60-80 cm DepthSoil Nitrate Concentration at 60-80 cm Depth20022002

Nitrate, ammonium and nitrate plus ammonium (Total) Nitrate, ammonium and nitrate plus ammonium (Total) leached during Year 1 and 2 for the four experimental treatmentsleached during Year 1 and 2 for the four experimental treatments

  2002 2003

  Units LF1 LF2 NLF1 NLF2 LF1 LF2 NLF1 NLF2

NO3 kg/ha 36 50 47 42 34 32 34 24

NH4 kg/ha 10 13 21 11 2 3 2 3

Total kg/ha 46 63 67 54 36 35 36 27

Total % 21 28 30 24 16 16 16 12

0%

10%

20%

30%

40%

LF1 LF2 NLF1 NLF2Treatment

Le

ac

he

d N

Re

lati

ve

to

N A

pp

lied

(%

) 2002

2003

Percent of Nitrogen Leached Percent of Nitrogen Leached Relative to AppliedRelative to Applied

How much N was leached How much N was leached during the flooding events?during the flooding events?

The estimated amount of nitrogen lost The estimated amount of nitrogen lost (average of all treatments) on April 6, (average of all treatments) on April 6, 2002 and April 10, 2003 was 19.6 kg/ha 2002 and April 10, 2003 was 19.6 kg/ha and 20.1 kg/ha, respectively. and 20.1 kg/ha, respectively.

For years 1 and 2 this represented 34% For years 1 and 2 this represented 34% and 60% of the total N lost by leaching and 60% of the total N lost by leaching during the two seasons, respectively. during the two seasons, respectively.

-3.00

-2.50

-2.00

-1.50

-1.00

-0.50

0.00

0.50

1.00

29 41 54 66 79 91 104 116 129 142

Julian Date

Dar

cy V

elo

city

(cm

/day

)The method used in this study may The method used in this study may

underestimate nitrogen losses, because the underestimate nitrogen losses, because the contribution of unsaturated flow contribution of unsaturated flow

to the percolation was not consideredto the percolation was not considered

2003

ConclusionsConclusions

• No clear difference in nitrogen leaching No clear difference in nitrogen leaching was observed for the lime and no-lime was observed for the lime and no-lime treatments. treatments.

• No clear difference in nitrogen leaching No clear difference in nitrogen leaching was observed between the fertigation was observed between the fertigation treatments.treatments.

• The average percent of nitrogen (nitrate The average percent of nitrogen (nitrate plus ammonium) leached during the 1st plus ammonium) leached during the 1st and 2nd season, relative to the amounts and 2nd season, relative to the amounts applied, were 26% and 15%, respectively. applied, were 26% and 15%, respectively.

Conclusions cont.Conclusions cont.

• Leaching events were associated with large Leaching events were associated with large rainstorms, suggesting that leaching of N would rainstorms, suggesting that leaching of N would have occurred regardless of the irrigation have occurred regardless of the irrigation scheduling method used.scheduling method used.

• During the first and second seasons, During the first and second seasons, respectively, 34% and 60% of the total N lost by respectively, 34% and 60% of the total N lost by leaching occurred during a single day (April 6 in leaching occurred during a single day (April 6 in 2002 and April 10 in 2003) when flooding was 2002 and April 10 in 2003) when flooding was observed in the study areas. observed in the study areas.

• The N leaching results from this study may be The N leaching results from this study may be underestimated because the contribution of underestimated because the contribution of percolation from unsaturated flow was not percolation from unsaturated flow was not considered.considered.

Future WorkFuture Work

• Estimate N leaching rates using the Darcy Estimate N leaching rates using the Darcy velocity results, estimated from the tensiometers.velocity results, estimated from the tensiometers.

• Calibrate and validate a numerical model Calibrate and validate a numerical model (HYDRUS-2D) to simulate water and nitrogen (HYDRUS-2D) to simulate water and nitrogen movement.movement.

• Use the numerical model to develop best Use the numerical model to develop best management practices in terms of maximizing N management practices in terms of maximizing N uptake and minimizing N leaching.uptake and minimizing N leaching.