Implications Of These C Loss Pathways For Management

An important aspect of relating management practices to carbon sequestration is quantifying the pathways of C loss from soil as well as measuring the increase in C storage and the net amount of C stored. The above review showed great variability in the amounts of sediment and C transported within a management treatment. Nevertheless, there was no

Table 18.5 Flow-Weighted Averagea Monthly Total Organic Carbon Concentrations in Subsurface Flow

Minimum Maximum Mean Standard Deviation Coefficient of (mg/L) (mg/L) (mg/L) (mg/L) Variation (%)

Corn/Soybean-Rye Rotations

Minimum Maximum Mean Standard Deviation Coefficient of (mg/L) (mg/L) (mg/L) (mg/L) Variation (%)

Corn/Soybean-Rye Rotations

Y102 ABC

0.5

4.5

1.B

0.S

51

Y103 ABCD

0.7

3.2

1.4

0.4

31

All lysimeters

0.5

4.5

1.5

0.B

42

Rotationally Grazed Pastures

B Area

1.0

3.2

1.7

0.5

30

D-E Area

1.0

3.5

2.3

0.5

24

All watersheds

1.0

3.5

2.0

0.B

31

a Average for 10 years.

Notes: SD = Standard Deviation; CV = Coefficient of Variation.

Source: From Owens, L.B., R.W. Malone, D.L. Hothem, G.C. Starr, and R. Lal.

2002a. Soil Tillage Res., 67:65-73. With permission.

a Average for 10 years.

Notes: SD = Standard Deviation; CV = Coefficient of Variation.

Source: From Owens, L.B., R.W. Malone, D.L. Hothem, G.C. Starr, and R. Lal.

2002a. Soil Tillage Res., 67:65-73. With permission.

significance with C concentration on sediments, except with no till, among the different tillage management practices or between corn and soybeans (Table 18.2). Thus, greater C losses occurred with greater sediment losses, i.e., sediment and C losses were greater with disk than with no-till (Table 18.3). This means that land management should be selected for soil loss reduction and not for reduction of C concentration on sediment. Reducing soil loss reduces C loss.

Carbon concentrations are much lower in subsurface flow than on sediments (Tables 18.2 and 18.4), and they did not differ greatly among the management practices studied. Likewise, C losses via subsurface flow are considerably less than via sediment (Tables 18.3 and 18.4). Average annual C losses via sediment were 1.4 to 4.8 and 1.7 to 13 times the average annual C losses via subsurface flow for corn and soybeans, respectively. These small losses of C in subsurface flow indicate that there are more important pathways of C loss to be addressed by management practices. Thus, reduction of C loss via subsurface flow should not be a major consideration when selecting land use practices for C sequestration.

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