Assessing Soil Health in Missouri Agricultural Soils

Kristen Veum Robert KremerKeith Goyne

Soil Health Workshop. Bradford Extension and Research Center. Oct. 8, 2013

• Why? Most important consideration.• When?

• Time of year (seasonal, management activities)

• Across years (trends)• Where?

• Management Practice Comparisons & Reference Soil Comparisons (fence row, uncultivated soil)

• Landscape Position / Landforms / Soil types

• Rhizosphere, Depth differences• How?

• Soil sampling and handling/storage protocols

Soil Sampling ConsiderationsWhen, Where, How, & Why

Biological properties can change rapidly (dynamic):

• Spatially• Depth – generally decline with

depth• Landscape (rhizosphere, hillslope)

• Temporally• Season• Crop and other management

activities• Climate differences (i.e., drought

years)• Short-term and long-term trends

Biological Soil Properties

• Goal: Translating soil properties into a soil quality or soil health score.

• How?• Measure important soil properties (i.e., soil health

indicators) • Assign a score based on relationships with soil

functions (water infiltration, crop productivity, etc…).• General Categories: More is Better, Less is Better,

Optimal Value• The scores are combined into one final number.

• Each existing soil health index uses a unique set of soil properties and a unique way of scoring soil health. Some are quantitative, some are very subjective. Many are region-specific.

What is a soil quality/health index?

• Soil Management and Assessment Framework (SMAF) soil quality index

• Cornell Soil Health Test (CSHT)• Assessing Agronomic and Environmental

Performance of Management Practices in Long-Term Agroecosystem Experiments (AEPAT)

• Soil Conditioning Index (SCI)• Biological Quality of Soil (QBS)• CCME Soil Quality Index (SoQI)• Forest Soil Quality Index (FSQI)

Soil Quality/Health Indices

• Scores based on data linking soil indicators to soil functions, such as crop productivity, water infiltration, and environmental protection.

• Based on site-specific characteristics that account for important factors such as crop, climate, soil texture, mineralogy, etc.

• 13 indicators representing 4 soil function groups:• Physical – aggregate stability, bulk density, water filled

pore space, available water capacity• Chemical – electrical conductivity, pH• Nutrient – P, K, Na adsorption ratio• Biological – SOC, microbial biomass-C, β-glucosidase,

mineralizable N

The Soil Management Assessment Framework (SMAF) soil quality index

SMAF Example: Centralia Plots (2008) 5 Cropping Systems (since 1991):• Minimum Till Corn – No Till Soybean (MTC-NTS)• No Till Corn – No Till Soybean (NTC-NTS)• Integrated Crop Mgt - Wheat (cover) - Corn

(cover) – Soybean (ICM-WCS) • Switchgrass formerly intensively cropped (SG)• Cool-season grass & legume (CRP)3 Landscape Positions:• Summit, Backslope, and Toeslope

SMAF Example: Centralia Plots

6 SMAF Indicators Selected (of 13)**You do not need to measure all possible indicators in order to use an index• Soil Organic Carbon• Extractable Phosphorus• Extractable Potassium• Water pH• Bulk Density• Water Stable Aggregates

Centralia SMAF Scores byLandscape Position

Clear landscape position differences in SMAF scores

• Measure of organic matter

• Source of many important nutrients

• Affects cation exchange capacity, water holding capacity, soil aggregation, etc.

• Considered a ‘keystone’ soil health property

Soil Organic Carbon (SOC)

Soil Organic Carbon: Cropping SystemsMeasured Values and SMAF scores

Clear effects of croppingsystem in SOC data andSMAF SOC scores.

CRP has highest SOC and SOC score. The switchgrass still reflects the degradation from previous intensive management

Soil Organic Carbon: Landscape PositionsMeasured Values and SMAF scores

Clear effects of landscapeposition in SOC data andSMAF SOC scores

The increased clay contentof the backslope changes soiltexture and affectsthe SMAF score

• measures the function of the microbial community

• reflects the quantity and quality of available substrates

• different enzymes represent decomposition and cycling of different nutrients• phosphatase – phosphorus• nitrogenase – fix nitrogen• dehydrogenase – overall microbial

activity• β-glucosidase – breakdown of cellulose,

etc.

Microbial Enzyme Activity

β-Glucosidase: Cellulose degradationMeasured Values and SMAF scores

Clear effects of cropping system from disturbance

The “more is better” concept translates greater enzyme activity into higher SMAF scores

CRP>Cover>No-till>= SWG>MinTill

• Reflects soil structure and resistance to erosion, slaking, etc.

• Tends to be stronger with increased clay and organic matter

• Extremely important for water infiltration, aeration, etc.

Water Stable Aggregates

Water Stable Aggregates:Measured Values and SMAF scores

Clear effects of cropping system in aggregate stability.

Trend relates to soil disturbance

SMAF scores all fairly high. This is due to the way SMAF scores aggregate stability.

Water Stable Aggregates:Measured Values and SMAF scores

Clear effects of landscape position in aggregate stability.Clay and organic matter are important in soil aggregation. The scores reflect the SMAF algorithm…..

Bulk Density• Increases with

compaction from traffic -- can increase with no-till compared to conventional tillage

• Increased bulk density is associated with reduced aeration and water infiltration

Bulk DensityMeasured Values and SMAF scores

The “less is better” concept translates greater bulk densityinto lower SMAF scores.

Switchgrass has the highest bulk density due to previous intensive cropping practices

Overall SMAF Scores by Cropping System

• Is a subset of total N• Sometimes called the ‘active

N fraction’• Supplies N for crop growth

Mineralizable Nitrogen

Mineralizable Nitrogen: By DepthMeasured Values and SMAF scores

Centralia (2010 data):Surface 0-10 inches Subsurface 10-20 inches

Depth differences for raw data and SMAF scores. Illustrates the decline in biological properties with depth.

Consider how perennial vegetation differs from annual cropping systems…

Does the SMAF Work?Sanborn Field Example

Veum et al. 2013 (Biogeochemistry)

• Each soil health indicator tells us something important about the soil

• A soil may perform some functions well but not others

• Together, the soil health indicators tell a more comprehensive story about the soil

• Necessary to make more informed management decisions.

Why can’t we just measure one variable for soil health?

Many Important Variables not currently in the SMAF or other soil health indices• Active C

• Cornell Soil Health Test

• Phospholipid Fatty Acids (PLFA)• tomorrow’s talk

• Other microbial enzymes

• Need more biological variables in soil health indices

Selected SMAF References

• Stott, D.E., C.A. Cambardella, R. Wolf, M.D. Tomer, and D.L. Karlen. 2011. A soil quality assessment within the Iowa River South Fork Watershed. Soil Science Society of America Journal 75:2271-2282. doi:10.2136/sssaj2010.0440.

• Stott, D.E., S.S. Andrews, M.A. Liebig, B.J. Wienhold, and D.L. Karlen. 2010. Evaluation of β-glucosidase activity as a soil quality indicator for the Soil Management Assessment Framework (SMAF). Soil Science Society of America Journal 74:107-119. doi:10.2136/sssaj2009.0029.

• Karlen, D.L., G.E. Varvel, J.M.F. Johnson, J.M. Baker, S.L. Osborne, J.M. Novak, P.R. Adler, G.W. Roth, and S.J. Birrell. 2011. Monitoring soil quality to assess the sustainability of harvesting corn stover. Agronomy Journal 103:288. doi:10.2134/agronj2010.0160s.