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How Management Practices Impact the Relative Proportion of Dissolved P

in Surface Runoff

Antonio MallarinoDepartment of Agronomy

Iowa State University

Extension and OutreachIOWA STATE UNIVERSITY

Phosphorus Lost from Fields

• Dissolved P in water (DRP, DTP, TRP) and particulate P (bound to soil particles)

• Particulate P and algae growth:- Slower but long-term impact- Iowa P Index: "70% of amount delivered to

Iowa mostly shallow lakes will be available for a long period of time"

• Dissolved P, large short-term impact- Mostly dissolved P in subsurface drainage- Variable proportion in surface runoff


Iowa P Index Three Components

Soil Erosion(Particulate P)

Water Runoff(Dissolved P)

Tile Drainage(Dissolved P)

Source Factors- soil P- application method,timing, and rate

Soil and water conservation practices


Tillage and P Application

• No-till reduces erosion (and corn yield)• No yield response to P placement in Iowa

even for no-till, other than starter• Incorporation/injection of manure is good

for N management and odor control• Injection/banding and incorporation by

tillage reduce runoff P loss if soil erosion and runoff are not increased

• The timing of operations and runoff events and P source are key issues


What Do we Say or Farmers Do?• No yield response to P placement or timing of

application in Iowa even for no-till• The spring is not a practical time to apply

fertilizer; wet soils, rain, little time; very little rainfall in the fall, low risk of surface runoff

• Most apply manure & P before corn of C-S; they need to empty pit or stockpiles

• We say don't till in the fall, apply manure-N in spring or as late as possible in the fall

• Most fertilizer P & solid manure are applied in the fall to soybean ground not incorporated


This Presentation

• Effects of P source, tillage, and time to a runoff event on P loss with surface runoff

• Studies conducted under natural or field simulated rainfall

• Runoff P fractions- Dissolved reactive P (DRP, filtered)- Total dissolved P (filtered, digestion or ICP)- Bioavailable P (FeO filter paper)- Total P

On-Farm Rainfall Simulations2000s National Runoff P Project Protocol

Short-Term EvaluationsP Source, Tillage, Time to Runoff


P Source, Immediate Runoff EventNo Incorporation, Broadcast 50 kg P/ha to Soybean Residue

Means of 21 Fields

Run

off P

Los

s (k

g ha

-1)

0.0

0.5

1.0

1.5

2.0

2.5

No P

BeefCattle

Manure

PoultryManure

LiquidSwine

Manure

FertilizerDissolved PTotal P

18% 29% 31%

49%

88%% Dissolved P of TP

Haq & Mallarino, ISU


Source, Short-Term Runoff TimingNo Incorporation, Broadcast 50 kg P/ha to Soybean Residue

Means of Six Fields

Dis

solv

ed R

unof

f P (k

g ha

-1)

0

1

2

3

4

Tota

l Run

off P

(kg

ha-1

)

0

1

2

3

4Fertilizer

No P

24 hours10 days10 days wet

24 hours10 days10 days wetFertilizer

LiquidSwineManure

PoultryManure

No P

81

8174

67

87

85

5266

32

80

1828

LiquidSwineManure

PoultryManure

% Dissolved P of TP

Haq, Allen, & Mallarino, ISU


Source, Runoff Timing, Incorporation

With/Without Incorporation, Broadcast 50 kg P/ha to Soybean ResidueMeans of Two Fields

Run

off P

Los

s (k

g ha

-1)

0

1

2

3

4

No P

PoultryManure

Fertilizer24-hr Event, Incorporated24-hr Event, Not Incorporated

LiquidSwine

Manure

10-day Event, Not Incorporated

No P

PoultryManure

FertilizerLiquidSwine

Manure

No P

PoultryManure

Fertilizer

LiquidSwine

Manure

21%57%

68%

52%

5% 20%

47%

52%

11%47%

69%63%

Dissolved PTotal P

Dissolved PTotal P

Dissolved PTotal P

DRP % of TP DRP % of TPDRP % of TP

Allen, Haq, & Mallarino, ISU


Tillage and Runoff Event Timing

• Let's add the P rate factor


Liquid Swine P Rate, Incorporation, Time

Allen and Mallarino, 2008

Dis

solv

ed P

(g h

a-1 )

0.0

0.1

0.2

0.3

0.4

0.5

0 10 20 30 40 50

Run

off T

otal

P (g

ha-

1 )

0.0

0.2

0.4

0.6

0.8

Not Incorporated

Incorporated

Liquid Swine Manure P Rate (kg P ha-1)0 10 20 30 40 50

24-hour Event15-day Event

24-hour Event 15-day Event

5

6 7

1632

56

62

1

Not Incorporated

Incorporated1

4 612

1 9 93

Not Incorporated

IncorporatedNot Incorporated

Incorporated

ns

6-mo Event

Not Incorporated

Incorporated

0 10 20 30 40 50

ns

15-day Event24-hour Event

6-mo Event

Not Incorporated

Incorporated


Poultry Manure Rate and Incorporation

Kaiser, Mallarino, Haq, 2009

Poultry Manure at 0, 56, or 102 kg P/ha, Averages Across Eight FieldsRunoff 24-48 hours After Application

Total P

0

1

2

3

4Dissolved Reactive P

Run

off P

Los

s (k

g P

ha-1

)

0

1

2

3

4

Incorporated

Not Incoporated

ControlLow ManureHigh Manure

ControlLow ManureHigh Manure

Incorporated

Not Incoporated

7% 17% 31%19%

49%

59%

% DRP of TP


Tillage and Runoff Event Timing

• Let's add amendments for poultry manure application


Alum or Gypsum, Tillage, Time to Runoff

Haq and Mallarino, 2013

Fall Surface Application, 50 kg P/ha, 3 years different sites

DRP % of TP10% 40% 39% 6% 13% 14% 21% 28% 30%

DRP % of TP DRP % of TP

Run

off P

Los

s (k

g ha

-1)

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

ManureManure+ GypsumManure

+ Alum

Manure

Manure+ Gypsum

Manure+ Alum

Manure+ Gypsum

Manure

Manure+ Alum

24 hours Event Tillage24 hours Event No-Till 10 Days Event No-TillDissolved PTotal P

Dissolved PTotal P

Dissolved PTotal P


Major Results Summary• Short-term dissolved and total P loss was

Fertilizer > Liquid manure > Solid manure- Larger differences without incorporation - % dissolved P of TP: Same overall ranking but

smaller & less consistent differences- % dissolved P increased with the P rate- Manure soluble P not a good index

• A runoff delay greatly reduced the large total P loss with fertilizer & liquid manure- No clear effect on % dissolved P of total P- With no-till it was as effective at reducing

dissolved and total P loss as tillage


The NW Iowa Runoff P StudyCorn-Soybean Rotations

Tillage, Fertilizer, Liquid Swine ManureSix Years


Site and Management Practices

• Sac series (Oxyaquic Hapludoll), slope 3.3%, optimum STP (16-20 mg kg-1, 15 cm)

• Plots 30x6 m, 6 years study• Corn-soybean rotations• Tillage: No-till or chisel-plow/disk tillage• P: 2-year rate before corn (112 kg P/ha)

- Fertilizer P always broadcast- Liquid swine manure P always injected

• The most commonly used practices in Iowa for fertilizer or liquid manure


Soil Loss

Soil

Loss

(kg

ha-1

)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5 Tillage

No-Till

Fert

Swine

Fert Swine


Corn-Soybean Rotation Averages


Runoff P and % Dissolved P of Total PD

RP

Loss

(kg

P ha

-1)

0

1

2

3

4

Total P

21

57

19

57

% of TP

Tillage

No-Till

Tota

l P L

oss

(kg

P h

a-1)

0

1

2

3

4Tillage

No-TillFert

SwineFert

Swine

FertSwine


Corn-Soybean Rotation Averages


Placement and Cover Crop for No-TillR

unof

f P L

oss

(kg

ha-1

)

0.0

0.5

1.0

1.5

2.0

2.5

3.02X Broad P

to corn 1X Band Peach crop

No P, Rye

DRP

TP

DRP

TP

DRP

TP

Optimum STP

VH STP

Natural Rainfall, Corn-Soybean Rotation, Fertilizer P, 2-Year Avgs



Major Results Summary

• No-tillage reduced soil loss by 70%• Highest total P loss for broadcast fertilizer

with tillage, lowest and no differences for broadcast fertilizer with no-till or injected manure with or without tillage

• Twice more dissolved P loss with no-till, and no differences between P sources

• Confirmed value of cover crop to reduce P soil and P loss- Reduced % dissolved P of total P- Not much in ongoing dedicated study


Overall Thoughts

• No-till drastically reduces soil P loss and often also total P loss

• But sometimes increased dissolved P loss- Mainly with runoff events shortly after applying

broadcast P fertilizer or liquid manure- A runoff delay drastically reduces P loss

• Surface apply fertilizer or liquid manure in periods of low probability of runoff- In the fall as early as possible after harvest- Seems to be as good as incorporation by

tillage

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