How Legacy Nutrients Affect Farm

Conservation Measures

Andrew SharpleyCrop, Soil,& Environmental

Sciences

Water to Worth 2015Advancing

Sustainability in Animal Agriculture

Seattle, WA

Today’s presentation

Dealing with a 10-ton gorilla

Legacy P & system response Soil

BMPs

Hydro-chemistry

Fluvial

Where do we go from here?

Soil

Hydro-chem

BMPs

System

Uptake & release of P by sediments affects waterbody response

Decline in soil P with crop

offtake is slow

Adoption of BMPs by farmers

is variable

BMPs can take time to decrease

P runoff

Soil processes

Hydro-chemical response

System response

BMP response

Wetlands trap & buffers can trap then recycle P

Legacy drivers

Time for ground water to reach stream can

vary from days to years

1988

1990

1992

1994

1996

1998

2000

2002

2004

2006

2008

2010

2012

0

100

200

300

400

500

Available soil P (Mehlich-3), mg/kg

Grazed pasture

Dairy manure added

75 kg P/ha/yrPasture cut

for hay

Crop response

Soil response

Land use

Location

Decline Time Decline

mg P/kg yearsmg P kg-1

yr-1

Pasture OK.260 - 190

15 4.7

Corn NC 100 – 20 16 4.7

Wheat Canada125 – 109

4 4.0

Soybean

IA 95 - 10 27 3.2

Soil response

BMPs can take time to effectively decrease P runoffPonds

trap P

BMP response

Time for buffer to become effective

Wetlands trap P

But are not infinite sinks

for P

Can eventually

release P

• 1.2 billion broilers produced annually in AR

• In 2003 Judge set 300 mg/kg Mehlich-3 P

threshold Litter rates went from 3 to 1.3

tons/acre/yr

• In 2014 Most of the litter exported out of

watershed 85% in Eucha-Spavinaw & 45% in Illinois

River Watershed

Judge reduced STP threshold to 150 mg/kg

BMP response

AR Water Resources Center, 2012

Diss. P Total P

2000 0.224 0.377

2003 0.148 0.244

2011 0.070 0.130

Mean annual concentration, mg/L

BMP response

Time for water body to biologically

respond to P input

Response to BMPs takes

time

Variable delivery time from source to

point of impact

Hydro-chemical response

36

48

15

Baseflow dissolved P, µg/L

27

Stormflow dissolved P,

µg/L

170

124

304

202

I mile

Fluvial effects

0

50

100

150

200

250

300

1990 1995 2000 2005 2010

Lake Pµg/L Recovery phase

Internal recycling of ‘legacy’ P (10-15 y)

Water quality target met

P inputreduced 60%

Water quality target

40 µg/L

Lake response

Loch Leven, Scotland;Linda May & Bryan Spears,

CEH

Lakes (c.5-30 yr)

Groundwater (<1 –

50 yr)

In-channel (<1 yr)

Riparian & floodplains

(<1 – 1000 yr)

Soils & hillslopes (c.5-30 yr)

Legacy P lag times

Maumee River

watershed

Sandusky River

watershed

MICHIGAN

Lake ErieLake Erie

OHIORichards et al., 2002

System response

Early 1980s, nonpoint source controls

1975 1980 1985 1990 19953

4

5

6

7

1975 1980 1985 1990 199515

20

25

30

35

40

Conservation measures reduced fertilizer P inputs

Maumee Sandusky

Fertilizer P, 103 tonnes P/yr

1975 1980 1985 1990 1995 2000 2005 20100.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14 Maumee River

1975 1980 1985 1990 1995 2000 2005 20100.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14 Sandusky River

Baker et al (2014) J. Great Lakes Research

P loss trendsMean total P mg/L

1975 1980 1985 1990 1995 2000 2005 20100.0

0.2

0.4

0.6

0.8

Maumee River

1975 1980 1985 1990 1995 2000 2005 20100.0

0.2

0.4

0.6

0.8

Sandusky River

Mean dissolved P, mg/L

Some of the drivers

Increased DP input & blooms result of…Same annual rainfall but more intense spring

rains Prior to 2008 – 12% of annual rains 2008 to 2011 – 30% of annual rains

Surface soil P buildup with no-till

Increased tile drainage of soils created more critical source areas

Solutions need to consider day-day farm management decisions

What can we do?

Conservation initiatives, metrics, & outcomes should account for & adapt to legacy impacts Legacies mask/delay water quality

improvements Some practices will transition from sinks to

sources of P – no-till soils & buffers

Model fluvial processing of P Move from delivery coefficients &

distance functions to process-based model

What can we do?

Legacy P will likely become a resource As costs of fertilizer production

increase Market forces & govt. intervention will

determine how quickly legacy P stores are tackled

What can we do?

Need better understanding of Spatial & temporal aspects of watershed

response to nutrient load reductions Scale at which responses may occur in a

more timely fashion

Local water quality & quantity benefits evident more quickly at a smaller scale

Important to demonstrate change & foster accountability & ultimately wider adoption of conservation practices

In conclusion

Thank youQuestions?