Additional Questions, Resources, and Moving Forward Science questions raised in the development of a science assessment

Effect of Conservation Tillage Systems on Dissolved Phosphorus

Gregory McIsaacUniversity of Illinois

&Agricultural Watershed Institute

To what extent does conservation tillage contribute bioavailable P to surface waters?

• Highly variable in time and space depending on: – Fertilizer quantity, placement and timing – Soil characteristics and hydrology

Outline

• Surface P dynamics• Relationships between soil P and runoff P• plot studies– Natural rainfall – Simulated rainfall (sprinklers)

• Influence of surface runoff pathways

Dissolved P concentration in runoff or drainage versus soil test P at surface

(Sharpley et al. 2003)

Higher leaching below30 cm of dissolved P from manurebroadcast on no-till compared to incorporatedmanure

(Kleinman et al. 2009)

Stratification of soil test P in No-till (NT) vs Chisel Plow (CP)with (+) and without (-) manure history (Andraski et al. 2003)

Manure history and long-term tillage effects on Bray P1–extractable soil P levels at three depth increments (0–2, 2–5, and 5–15 cm) at Lancaster, Wisconsin, 2000.

Dissolved P load from No-till and Chisel Plowed 0.8 m2 plotsas a function of soil test P (Andraski et al. 2003)

Relationships between Bray P1–extractable soil P level (0–2 cm) and dissolved P loads in long-term chisel plow and no-till systems at Lancaster, Wisconsin, 2000. P loads were lowerfrom No-till because of reduced runoff, rainfall was applied at 75 mm/hr for one hour.

Runoff from No-till and Chisel Plow as a function of soil residue coversimulated rainfall event on 0.8m2 plots, 6th year of no-till

(Andraski et al. 2003)

Runoff from no-till (2nd & 3rd year) compared to other tillage systems, Tama silt loam soil

McIsaac et al. (1991)

R² = 0.7452

0

5

10

15

20

25

30

35

40

0 20 40 60 80 100

Runofffrom

65 mmrainfall (mm)

Residue cover (%)

no-till (short term)

tilled treatments

Soluble P loss in runoff from 65 mm of simulated rainfall

0

50

100

150

200

250

0 20 40 60 80 100

Soluble P lossfrom

65 mmrainfall (g P/ha)

Residue cover (%)

no-till (short term)

tilled treatments

(Data from McIsaac et al 1987)

(McIsaac et al. 1995)

Estimated fraction of surface applied P fertilizer available to runoff and leaching

(Vadas et al. 2008)

Infiltration rates measured on long-term no-till (> 6 years) and conventional tilled sites

17 years 6 years 6 yearsSilt loam sandy loam silty clay loam

0

10

20

30

40

50

60

70

80

90

100

site 15 c site 7 Site 11

final infiltration

rate (mm/hr)

Conv.

No-till

(Adapted from Savabi et al. 2008)

To till or not to till? • Where no-till reduces runoff substantially,

dissolved P loads in runoff may be low despite high concentrations

• P fertilizer and manure on the surface can be vulnerable to runoff when and where no-till does not reduce runoff significantly, such as– Coarser textured soils– Soils with high water table– Restricting subsurface layers– Frozen soils

Deep banding of P fertilizer reduced soil P at surface in 3 years77 kg P per hectare applied

(Fernandez and Shaefer 2011)

No-till Broadcast P

Strip-till Broadcast P

Strip-till Deep banded P

†Indicate significant differences at P < 0.1;

In row 19 cm 38 cm 57 cm--------Distance from crop row-------

P soil survey 2007 & 2008

Soil sampled sites in regions with high, medium and low soil P supplying power

598 corn fields samplednear end of growing season

(Fernandez et al., in press)

Surface to Subsurface Ratio for 547 Fields in Illinois

POrganic matter

Soil depth (mg kg-1) (%)0-8cm 64 a 3.5 a8-18cm 40 b 3.1 bRatio of Avg. values 1.6 1.1Avg. of site ratios 2.4 1.2

Fernandez et al. (in press)

Spatial distribution of Soil P0 to 18 cm (0 – 7 inches)

High P Supplying Power Soils

40 80 120 160 200

Bra

y P

1 S

oil

Ph

osp

ho

rus

(mg

kg

-1)

0

100

200

300

400

500

600

7% (14 fields) Below Cl

20% (40 fields) Maintenance (15-30 mg kg-1)

73% (148 fields) Above No Appl.Point

Medium P Supplying Power Soils

Number of Fields40 80 120 160

16% (26 fields) Below CL

24% (41 fields) Maintenance(20-33 mg kg-1)

60% (101 fields) Above No Appl. Point

Low P Supplying Power Soils

40 80 120 160

34% (60 fields) Below Cl

23% (41 fields) Maintenance(23-35 mg kg-1)

43% (76 fields) Above No Appl. Point

Fernandez et al. (in press)

Standard natural rainfall soil erosion plots uniform slopes, which minimize sediment deposition

http://www.cesperieni.ro/page3.html

Rainfall simulators increasingly used to study runoff and erosion processes

http://www.ars.usda.gov/Research/docs.htm?docid=18093

high intensity rainfall, water chemistry can influence results… useful for comparing different systems and investigating processes but do not fully capture seasonal variations

http://www.ars.usda.gov/is/graphics/photos/oct01/k9572-1.htm

Small plots do not generate rill erosion, or represent full hillslope hydrologyResults may be influenced by location on hill slope

Fig. 5.3

Summary

P fertilizer applied to the soil surface is highly vulnerable toloss in runoff during the first few weeks following application

Stratification of P at the soil surface contributes to high DRP concentrations in surface runoff.

Conservation tillage reduces runoff at some locations (some times) and this may mitigate against high DRP losses to runoff (although could contribute to subsurface losses)

Subsurface placement of P fertilizer, such as in deep banding in Strip Till, reduces stratification of P at the soil surface and probably reduces DRP concentrations in runoff.

Plot studies need to be interpreted with a recognition that plots do not fully capture seasonal or spatial variations in hill slope hydrology or P dynamics.

Thank you!

No-till (years 1 and 2) vs. Chisel Plow on the contour, Tama Soil

0

2

4

6

8

10

12

14

16

18

fall spring

Runoff from

47 mm rainfall (mm)

no-till

chisel

(Daverede et al. 2003)