# Presentation: 379425

## Soil carbon changes underbioenergy plantations

**Bioenergy Feedstock Development Programs**
**Oak Ridge National Laboratory**
**Curt Jawdy**
**November 7, 2001**

## Research Questions

**How does soil organic matter (SOM) change after conversion from agricultural to bioenergy crop production?**
**How will changes in SOM levels affect soil and site quality?**
**Which bioenergy crops best contribute to soil quality?**
**Which management practices can contribute to soil quality at bioenergy plantations?**

## Ecological role of SOM

**Aggregation**
**slows erosion**
**Soil conditioner**
**Water holding capacity**
**Permeability**
**Bulk density/penetration resistance**
**Soil organism food and function**
**Nutrient reserve**
**Leaching protection**
**Carbon sink**
**Largest terrestrial pool**

## Effects of SOM depletion on environment

**Decreased yields**
**Increased erosion**
**50%-90% savings for NT vs. CT**
**Increased leaching**
**Increased fertilizer use**

## Soil carbon equilibrium

**Affected by many factors**
**amount and type of biomass input**
**soil microbial community**
**moisture regime**
**oxygen supply**
**temperature**
**soil texture**
**supply of other nutrients**
**SOM declines 20-40% after conversion to cropland**
**Where will bioenergy be?**

**Notes:**
Figure from:

Lucas, R.E. and M.L. Vitosh.  1978.  Soil Organic Matter Dynamics.  Michigan State University Ag Experiment Station.  Report #358

## Hypothesis: bioenergy plantations increase C

**Affected by many factors**
**amount and type of biomass input**
**soil microbial community**
**moisture regime**
**oxygen supply**
**temperature**
**soil texture**
**supply of other nutrients**

**Biomass**
**has degradation resistant litter**
**provides good soil microbial habitat**
**has high water holding capacity**
**protects from oxidation**
**cools soil by shading/water**
**promotes aggregation**
**tight nutrient budget**

## Experimental Design

**Established 1995 on Decatur silt loam**
**Two reps of **
**sweetgum w/c**
**sweetgum n/c**
**no-till corn**
**switchgrass**
**corn**
**Trees planted on 1.5 m x 3 m spacing**
**Fertilized**
**Weed control**

## Measured variables

**Soil**
**carbon/nitrogen (1995, 1999, 2000, 2001)**
**extractable nutrients by Mehlich I (1995, 1999, 2000, 2001)****	**
**bulk density (1999, 2000, 2001)**
**carbon fractionation (2001)**
**soil enzymes (2001)**
**Percolation and Runoff**
**runoff volume (constant except 1 year)**
**nutrients (constant except 1 year)**
**Tree biomass (yearly)**
**nutrients (2001)**
**Root biomass (1999)**
**Litter biomass (2001)**
**nutrients (2001)**

## Slide 9

## Site Photograph

**Site Photograph**

## Soil sampling

**1995**
**5, 15, 30, 45, 60, 75, 90, 120 cm depths**
**Five random samples per plot**
**1999/2000**
**10, 20, 30, 40, 50, 60 cm depths**
**15 samples per plot (3 distances from tree, 5 slope positions)**
**2001**
**same depths as 1995**
**15 samples per plot (3 random from 5 slope positions)**

## Soil analysis

**1995 samples TVA sent to UGA for analysis**
**1999/2000 samples**
**cores cut into 10 cm segments and horizons determined**
**dried at 60C**
**segments weighed and b.d. calculated**
**broken and root/rocks over 10M removed and weighed**
**ground to 150M**
**analyzed using Loss on Ignition method**

## Slide 13

## Slide 14

## Slide 15

## Slide 16

## Relevant carbon changes

**Overall carbon content increased by 4-6 Mg/ha under bioenergy and no-till crops after five years**
**Most change occurs in upper horizon**
**Equilibrium not yet reached**

## Further research on site

**Biomass and nutrient inventory**
**what would be the overall effect if harvested next week?**
**Soil enzyme study**
**Soil carbon fractionation**
**Fate of nitrogen fertilizer**
**Effects of cover crop type on **
**soil carbon**
**aboveground productivity (AL A&M)**