Sandy Loam No nutrients Can We Build Soil Health Through

Introduction Methodology

Objective: To determine how plant litter quality impacts the transfer of plant residues to SOM fractions stabilized via organo-mineral association.

ResultsResults & Conclusions

Can We Build Soil Health Through Greater

Soil Organic Matter Stabilization?Carolina Cordova*, Dan Olk2, Johan Six3, Michael Castellano1,

1Iowa State University Dept. of Agronomy; 2USDA-ARS National Lab. for Agriculture and the Environment, Ames, IA ; 3Department of Environmental

Systems Science, ETH Zurich, Zurich, Switzerland

* Corresponding author: [email protected]

Reference

Fig. 2 Effect on the amount of Carbon accumulated from different

plant litter additions *. Fig. 3 Effect on the amount of Nitrogen accumulated from different plant

litter additions at the end of the incubation *.

High quality

(Low C:N)

Low quality

(High C:N)

Fig. 1 Plant litter quality rank.

(*) Just aboveground plant litter used, collected at maturity.

The experiment was conducted as a 180 day laboratory incubation in a fully factorial completely randomized design with

the following factors: two soil types (Sandy Loam and Silt Loam subsoils with low SOM), four plant litters (alfalfa, corn,

oats, soybean), and two nutrient inputs (with and without).

Samples were incubated for four 46-day cycles. At the beginning of each cycle, ground plant litter (8.70 g OC kg-1 soil)

was added to each sample. At the end of each cycle, any partially decomposed plant litter was removed by air blowing.

Table 1. Selected properties of sub-soils Clarion and Fayette before the incubation.

Measurements

CO2 flux was frequently measured to calculate cumulative C mineralization with linear interpolation and numerical

integration. Plant litter C transfer to stable SOC mineral fine fractions (<53 µm) was measured prior to and at the end of the incubation

by isotopic analysis (δ13 C natural abundance using a two-pool isotopic mixing model) as well as calculating the mass

transfer of C and N (i.e., the increase in soil C and N over the four, 46 day incubation cycles).

Soil organic matter (SOM) stabilization relies on the quality of plant litter inputs.

Plant litter quality (PLQ) may affect both nutrient availability and long-term SOM

stabilization through the transfer of C and N to soil fractions that are stabilized against

mineralization by organo-mineral association.

PLQ classifies plants according with their chemical composition. Plant litters with low C/N

ratios and low polyphenol concentrations are considered to high quality; as a result, they

are easily metabolized by soil microbes (Fig. 1).

Cotrufo, et al. (2013) proposed that high quality plant litters result in faster and greater

SOM stabilization via organo-mineral association because high quality litters yield more

microbial residues and microbial residues dominate SOM stabilized via organo-mineral

association.

Soil type, plant litter and nutrient addition

significantly affected the amount of C and N

stabilized via organo-mineral association.

Soil type played an important role in the SOC

stabilization of the accumulated C and N. The

Sandy Loam soil had higher C and N accumulation in the <53µm fraction than the silt

loam.

C mineralization (i.e., CO2-C production) was

greater for high quality than low quality plant

litters.

Our results are consistent with the concept that

high PLQ promotes greater transfer of organic

matter to soil fractions that are stabilized against

mineralization via organo-mineral association.

Cotrufo F., Wallenstein M., Boot C., Denef K., Paul D. (2013), The

microbial efficiency-matrix stabilization (MEMS) framework

integrates plant litter decomposition with SOM stabilization. Global

Change Biology. 19:988-995.

Plant Litter *C:N

ratio

Alfalfa 16.6

Oats 22.5

Corn 78.5

Soybean 88.9

Acknowledgements

This project was funded by USDA NIFA, SENESCYT and the William

T. Frankenberger Professorship of Soil Science.

Sub-Soil groupClay

(%)

pH

(1:1 H2O)

Total

Carbon

Total

Nitrogen

Total

Carbohydrates C:N

ratio

-------g kg-1 soil------

Sandy Loam (Clarion) 15.70 7.07 4.07 0.47 0.73 8.73

Silt Loam (Fayette) 31.50 5.12 2.87 0.40 0.67 7.29

Fig. 4 Carbon to Nitrogen ratio of material accumulated in the soil fine

fraction <53µm *.

Fig. 5 Cumulative amount of CO2-C produced *.

(*) Data are means and SE, n=4. Significant differences between the soils and treatments marked by different letters (p-value < 0.05).

Data are from mass transfer method. However, the δ13C and mass transfer methods were highly correlated (R = 0.98; y = x*1.12 + -1.04).

Variable p-value

Soil <.0001

Plant <.0001

Nutrients (Nut.) <.0001

Soil*Plant 0.0072

Soil* Nut. 0.1601

Plant * Nut. 0.0572

Soil *Plant*Nut. 0.1107

Plant litter

Corn Soybean Oat Alfalfa

g c

arb

on

kg

-1 s

oil

<5

3µ

m

0

2

4

6

8

10

12

14

16

Sandy Loam No nutrients

Sandy Loam with nutrients

Silt Loam no Nutrients

Silt Loam with Nutrients

Variable p-value

Soil <0.0001

Plant <.0001

Nutrients (Nut.) <0.0001

Soil*Plant <0.0001

Soil* Nut. 0.0247

Plant * Nut. 0.0104


Plant litter


g n

itro

gen

kg

-1 s

oil

<53

µm

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Sandy Loam no Nutrients

Sandy Loam with Nutrients



Variable p-value

Soil <.0001

Plant <.0001

Nutrients (Nut.) 0.0334

Soil*Plant <0.0001

Soil* Nut. <0.0001

Plant * Nut. 0.0022

Soil *Plant*Nut. <0.0001

Plant litter


C t

o N

ra

tio

0

5

10

15

20

25

30

35





Variable p-value

Soil <0.0001

Plant <0.0001

Nutrients (Nut.) 0.4935

Soil*Plant 0.1504

Soil* Nut. 0.2399

Plant * Nut. 0.8874


Plant litter


g C

O2

-Ca

rbo

n k

g-1

so

il

0

1

2

3

4





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Sandy Loam No nutrients Can We Build Soil Health Through