practical ways to improve water qualitycemonterey.ucdavis.edu/files/85410.pdf · practical ways to...

Practical ways to improve water quality

Salinas/Castroville area ditches, creeks and sloughsAverage of 2005-07 monthly sampling of 11 sites

W t lit M t E d 2005 2007Water quality parameter

Measurement unit

Exceedance threshold

2005-2007 monthly average

NO3-N PPM > 10 25PO4-P PPM > 0.5 0.63Algae % survival > 110 228

Turbidity NTU > 50 587Water toxicity % survival < 80 27ySediment toxicity % survival < 80 24

Source of nutrients ?Source of nutrients ?FertilizerWell water

What soluble nutrient load does vegetable field runoff carry ?

In 13 Salinas Valley trials …

PPMNO3-N PO4-PNO3-N PO4-P

Low 1 0.1High 48 2 1High 48 2.1Mean 12 0.7

How about drain tile effluent ?How about drain tile effluent ?

2002-04 drain tile sampling in the Salinas Valley

Why is drain tile effluent so high in NO3-N?all NO3-N is in the soil solution

Relationship of soil NO3-N to soil solution NO3-N :

Soil NO3-N NO3-N in soil solution (PPM)(PPM) Sandy loam Clay( ) y y

10 50 30

In 13 Salinas Valley field trials runoff turbidity rangedfrom 200 - 4,600 NTU

Bottom line :Any water escaping from a vegetable field is likely to exceed

t lit t d d f ll t twater quality standards for one or more pollutants

What can be done ?Treat the water to remove pollutantsReduce the application of materials that can move in waterReduce the volume of water that leaves the field

Water treatment :

Consistently reduce sediment lossMinimally effective for soluble nutrientsMay conflict with microbial food safety practices

Water treatment :

PAMPAM

Water treatment :

PAM

Highly effective for sediment removalRelatively inexpensive, can be automatedInconsistently effective at reducing soluble nutrients

Most practical solution is to limitthe volume of runoff or leachate …

… and drip irrigation is the ideal tool

Crop water use can be predicted by canopy size and ETo :

80

100

over

40

60

80

t can

opy

coor

lettu

ce

0

20

1 2 3 4 5 6 7 8 9 10

Perc

ent fo

1 2 3 4 5 6 7 8 9 10

Weeks after planting

Irrigation requirementIrrigation requirement can be predicted by canopy size and ETo :

100120

To

406080

rcen

t of E

Tfo

r let

tuce

020

1 2 3 4 5 6 7 8 9 10

Per f

Efficient seasonal drip irrigation volume ≈ 80 – 120 % of ETo

Weeks after planting

250ied

Drip irrigation management varies greatly among growers :

150

200

250

ETo a

ppli

rip

50

100

150

easo

nal E

with

dr

Ideal zone

0

50

1 2 3 4 5 6 7 8 9 10 11 12 13 14% o

f se

Commercial field

Drip-irrigated lettuce fields in the Salinas Valley

250lied

Consequences of excessive irrigation :

150

200

ETo a

ppl

drip

50

100

50

easo

nal E

with

d

Ideal zone

0

50

1 2 3 4 5 6 7 8 9 10 11 12 13 14% o

f se

Commercial field

Assume early summer conditions northern Salinas Valley locationAssume early summer conditions, northern Salinas Valley location,sandy loam soil :

If field 5 applied 5 inches of water with drip, h fi ld 14 li d 10 i hthen field 14 applied 10 inches

If soil is 10 PPM NO3-N, field 14 lost > 50 lb N/acre in leaching !

Long irrigation intervals ruin drip irrigation efficiency :

In drip-irrigated celery fields …

8

10ys

io

ns

4

6

rage

day

n irr

igat

2

4

Ave

rbe

twee

n

01 2 3 4 5 6 7 8 9

Field

Long irrigation intervals lead toheavy individual applications :heavy individual applications :

1.5

2

ches

ion

Light soilHeavy soil

0 5

1

erag

e in

cer

irrig

at

Maximum for efficient irrigation

0

0.5

1 2 3 4 5 6 7 8 9

Ave pe efficient irrigation

1 2 3 4 5 6 7 8 9

Field

Above this maximum range the leaching fraction becomes significant !

What constitutes efficient fertigation ?

30

202530

upta

ke/ w

eek)

51015

ettu

ce N

lb

/ ac

re

90 - 120 lb N/acreat harvest

01 2 3 4 5 6 7 8 9 10

W k ft l ti

Le (l

Weeks after planting

202530

ptak

ew

eek)

101520

tuce

N u

p/ a

cre

/ w90 - 120 lb N/acre

at harvest

05

1 2 3 4 5 6 7 8 9 10

Lett

(lb

Weeks after planting

40

20

30

N u

ptak

ere

/ w

eek)

180 - 220 lb N/acre

0

10

20

Cel

ery

N (l

b / a

cr 180 220 lb N/acreat harvest

01 2 3 4 5 6 7 8 9 10 11 12

Weeks after transplanting

2007 lettuce fertigation trials :

FieldFieldFieldLettuce Lettuce Lettuce

typetypetypeSoil NOSoil NOSoil NO333---N at startN at startN at startof fertigation (PPM)of fertigation (PPM)of fertigation (PPM)g ( )g ( )g ( )

111 headheadhead 202020222 headheadhead 272727333 romaineromaineromaine 212121

2007 lettuce fertigation trials :

Reference evapotranspiration Drip irrigation Field (ETo , inches) applied (inches)

1 6.2 4.92 6 5 4 72 6.5 4.73 2.4 2.8

6080

gatio

ncr

e)

field 1

12 f

02040

25 30 35 40 45 50 55 60 65

N fe

rtig

(lb/

ac 127 lb N fertigated

25 30 35 40 45 50 55 60 65

Days after planting

153 lb N fertigated406080

gatio

ncr

e)

field 2

153 lb N fertigated

02040

25 30 35 40 45 50 55 60 65

N fe

rtig

(lb/

ac

67 lb N f ti t d

25 30 35 40 45 50 55 60 65

Days after planting

60

80

atio

nre

)

field 3

67 lb N fertigated

0

20

40

N fe

rtig

a (l

b/ac

r

25 30 35 40 45 50 55 60 65Days after planting

80n field 1

Reduced N treatment created by eliminating some N fertigation :

0204060

N fe

rtig

atio

n (l

b/ac

re) field 1

x x0

25 30 35 40 45 50 55 60 65

Days after planting

N

80n field 2

0204060

N fe

rtig

atio

(lb/

acre

) field 2

xx

025 30 35 40 45 50 55 60 65

Days after planting

N

80

n field 3

20

40

60

N fe

rtig

atio

(lb/

acre

)

x0

25 30 35 40 45 50 55 60 65Days after planting

Results :

lb N / acreMean

plant wtCrop N uptake

Field Treatment total fertigated (lb) (lb / acre)Field Treatment total fertigated (lb) (lb / acre)1 Grower 169 127 2.29 98

Reduced N 92 50 2.31 91

Results :

lb N / acreMean

plant wtCrop N uptake

Field Treatment total fertigated (lb) (lb / acre)Field Treatment total fertigated (lb) (lb / acre)1 Grower 169 127 2.29 98

Reduced N 92 50 2.31 91

2 Grower 171 153 2.16 103Reduced N 64 46 2 27 101Reduced N 64 46 2.27 101

Results :

lb N / acreMean

plant wtCrop N uptake

Field Treatment total fertigated (lb) (lb / acre)Field Treatment total fertigated (lb) (lb / acre)1 Grower 169 127 2.29 98

Reduced N 92 50 2.31 91

2 Grower 171 153 2.16 103Reduced N 64 46 2 27 101Reduced N 64 46 2.27 101

3 Grower 115 67 1.92 102Reduced N 67 19 1.81 87

Conclusion :given careful irrigation, a modest level of N fertigation is sufficient

What will efficient fertilization do to water quality ?Reduced N application limits potential N lossReduced N application limits potential N loss

What will efficient irrigation do to water quality ?N concentration of runoff or leachate might increase but

concentration x volume = load

N concentration of runoff or leachate might increase, butenvironmental load will decrease substantially

What will efficient irrigation do to water quality ?N concentration of runoff or leachate might increase but

concentration x volume = load

N concentration of runoff or leachate might increase, butenvironmental load will decrease substantially

Example : lettuce field 14 – 230% of ET appliedExample : lettuce field 14 230% of ETo applied50 PPM soil solution NO3-N in 5 inches of leaching = 57 lb N/acre

Example 2: lettuce field 5 – 110% of ETo applied100 PPM soil solution NO3-N in 0.5 inches of water loss = 11 lb N/acre3

Putting it together:Minimize and/or treat sprinkler irrigation during crop establishmentDrip irrigate based on ET, with irrigation frequent enough to be efficient Fertigate modestl timing N application to meet crop ptakeFertigate modestly, timing N application to meet crop uptake

What about winter ?Leave as little NO3-N in the profile as possible after fall cropLeave as little NO3 N in the profile as possible after fall cropEmploy winter cover where practical