GRACEnet Site Characterization and Sampling Protocol

Purpose and scenarios

The purpose of GRACEnet (**G**reenhouse gas **R**eduction through
**A**gricultural **C**arbon **E**nhancement **net**work) is to develop
the ARS organization necessary for a coordinated multi-location research
program to address scientific and program issues related to agricultural
carbon sequestration, greenhouse gas emissions reduction and
environmental benefits related to these activities.

The multi-location research will focus on agricultural management
scenarios that can be implemented and monitored at each location. The
emphasis will be on management rather than crop or crop sequence due to
varied regional cropping practices. At each location, and in each
management scenario, measurements will be made that will quantify the
management practice with respect to soil carbon storage, greenhouse gas
emissions and changes in other soil properties. In general terms, but
not rigid mandates, the four scenarios are as follows:

1\. **Business as usual** - This scenario refers to management practices
typical of an area. Included will be the major crop(s), tillage
practice(s) and inputs used in the representative area. These as
business as usual systems should be economically viable or at least used
by the majority of producers that are able to continue in production
agriculture in that area of the country. The number of sub- treatments
(since there will be many variations on typical practices within most
areas) that a unit will study is up to each unit.

2\. **Maximum carbon sequestration** - This scenario refers to
management practices that will generate the most sequestered carbon.
This scenario was the subject of more debate than any other. The
discussion primarily revolved around whether this treatment should focus
on those practices that would be economically viable or whether they
need only be technically feasible. We thought it best at this time to
let a unit decide if it wants to pursue either 2a (Economically Viable)
or 2b (Technically Possible). Ideally data for both scenarios could be
obtained, if these are very dissimilar scenarios in your study area.

3\. **Optimize Greenhouse Gas Benefits** - This scenario refers to
changing management practices such that greenhouse gas production is
reduced or eliminated. This scenario will require the measurement of
N~2~O in most systems. Methane measurement will be especially important
in animal systems. The best way for us to initially accomplish both
methane and N~2~O measurements for animal systems will be to join with
the air quality (atmospheric emissions) activities planned in the Manure
and Byproduct Utilization National Program, which plans on measuring a
number of air quality and emissions parameters at animal feeding
operations (AFOs) for swine, dairy, beef and poultry. Developing the
capability and capacity to measure these trace gases, especially N~2~O
in crop, range and pasture lands is a top priority. Nitrous oxide and
methane data will be one of the distinguishing features of GRACEnet.

4\. **Optimize Environmental Benefits** -- This scenario refers to the
optimization of agricultural systems to sequester carbon, reduce trace
gas emissions and to increase other environmental benefits. Many units
are already researching treatments that are attempting to improve the
environmental friendliness of agricultural systems. If they are already
doing this, all that needs to be done is adding soil carbon and trace
gas measurements. In any case what comprises this scenario will be left
to the best judgement of each unit=s scientists.

The following guidelines for soil and plant sampling fields under the
management scenarios described above were developed by the GRACEnet
participants. These are only intended to be guidelines since soils,
crops and conditions are different in different areas of the country. We
emphasize consistent methods and detailed record keeping to ensure
proper QA/QC.

# **Site Characterization**

##  Site characterization should be conducted at the beginning of the study for each management scenario that will be included by the research unit. In addition, long-term climate data should be gathered and organized such that each location can easily search for locations with similar climates. Short-term climate data i.e. after scenarios begin should be organized by scenario with monthly climate summaries. The raw climate data should be archived in a spreadsheet format. 

## Landscape and soil profile attributes

Georeferenced location of experimental area

Soil survey map of experimental area

Field slope and aspect

Soil type and texture

Morphological soil profile description

## Climatic attributes 

## Air and soil temperature

Soil water content over time

## Precipitation

## Evaporation (or humidity and wind speed)

## Net radiation

##  Wind speed and direction

## Vegetation / Crop

Characteristics, planting date, row width

Rotation (s)

Phenological measurements

Biomass yield

Management history (current coupled with vegetation/crop)

Tillage practice with chronology and physical description

Cultivation during growing season

Surface residue status

Fertilization, date, type and rate

Amendments

# **Soil Sampling Guidelines**

## Assume spatial independence of soil properties and thus use a random sampling pattern. Record GPS coordinates of each sampling location and collect samples using a core method compositing a minimum of 8 cores per depth. If soil property variability is known the number of cores for compositing can be adjusted. As a rule of thumb biological soil properties have a spatial coefficient of variation (%CV) of \>50%, chemical properties 25 to 45% and physical properties 15 to 40% depending upon the scale of sampling.

## The required depth increments for GRACEnet sampling are 0-5 and 5-10 cm. These depths will tend to show increases in soil carbon and thus would be considered a minimum data set. Preferred sampling depth increments are 0-5, 5-10, 10-20, 20-30, 30-60, 60-100 cm. If near-surface stratification is not present depth increments of 10 cm to 30 cm for the third and beyond samples are adequate. During soil sampling an assessment of surface residues should be made, the mass should be determined over a 0.25 m^2^ area.

### A suggested mass of soil of at least 500g should be collected from each depth for the initial i.e. time zero sampling. Future soil sample mass can be adjusted for the assessments being conducted. The timing and frequency of sampling will be system dependent.

Soil samples should be kept cool in the field and during transport.
Samples should be maintained at 4^0^C as much as possible during
processing. First sieve each soil sample through a 2 mm sieve and remove
a sample for gravimetric water content.

# 

# **Soil Assessments**

For the required and optional soil property measurements we will use
standard methods of analysis. There are several references listed at the
end of this document that can be consulted for proper procedures and
step-by-step instructions.

Required measurements

## Soil organic C (combustion)

## Soil inorganic C

## Particulate organic matter C 

## Soil bulk density

## Total N

## Extractable NH~4~-N and NO~3~-N

Extractable P and K

## Soil pH (water)

## Electrical conductivity

## Particle-size distribution (initial sampling)

Optional measurements

## Soluble organic C (required if there is drainage in the system)

## Microbial biomass C and N

## Water-stable aggregates

## Total C by mid/near infrared method (Jim Reeves)

Moisture release curve

# **Plant Sampling Guidelines**

## Above and belowground plant biomass should be assessed. Methods to collect plant biomass should be determined by individual researchers based on the vegetation / crop sampled. Timing and frequency will be system dependent.

# **Plant Assessments**

## *Aboveground biomass:*

Required

> Live and dead biomass on an oven-dry basis (60^0^C) (clipping from the
> soil surface if possible)
>
> Ashed biomass
>
> Harvest (grain) yield
>
> Total carbon and nitrogen

Optional

> Residue quality parameters (e.g., Lignin, soluble C, others?)
>
> Leaf-area index

## *Belowground biomass:*

Required

> Root biomass on an oven-dry basis (by depth)
>
> Ashed roots
>
> Total carbon and nitrogen

Optional

> Residue quality parameters (e.g., Lignin, soluble C, others?)

# **Organic amendments Assessments** 

## On sites where organic amendments are applied, the following assessments are suggested:

Total C and N

Extractable NH~4~-N and NO~3~-N

Extractable P and K

Soil pH

Suite of elements (contaminants with potential negative effects)

# **Sample Archiving**

## Sample archiving will be an essential component of GRACEnet. From the initial soil and plant sampling i.e. time zero a minimum of 50 g air-dried soil and 5 g oven dried plant material should be archived. At each subsequent sampling a minimum of 10 g of soil and 1 g of plant material should be archived. The samples should be kept in airtight containers i.e. sample vials in moderate climate conditions. If possible a field moist sample should be archived at 4^0^C.

### 

# **References**

## Carter, M.R. (ed.). 1999. Soil sampling and methods of analysis. Lewis Publ. Boca Raton, FL.

## Doran, J.W., and A.J. Jones (ed.). 1996. Methods for assessing soil quality. SSSA Spec. Publ. 49. SSSA, Madison, WI.

## Klute, A. (ed.). 1986. Methods of soil analysis. Part 1 -- Physical and mineralogical methods. 2nd ed. SSSA Book Series No. 5. SSSA and ASA, Madison, WI.

## Lal, R. (ed.). 2001. Assessment methods for soil carbon. Lewis Publ. Boca Raton, FL.

## Robertson et al. (ed.). 1999. Standard soil methods for long-term ecological research. Oxford Univ. Press. New York.

## Sparks, D.L. (ed.). 1996. Methods of soil analysis. Part 3 -- Chemical methods. SSSA Book Series No. 5. SSSA and ASA, Madison, WI. 

## Weaver et al. (ed.). 1994. Methods of soil analysis. Part 2 -- Microbiological and biochemical methods. SSSA Book Series No. 5. SSSA and ASA, Madison, WI.