Between-Bed %SOM and pH. 9. %SOM. 12. pH. 10. 8. 8. %SOM. pH. 7. 6. 4. 6. 2. 5. 0. Inner. Mid-inner. Outer. Mid-Outer. 1. 2. Beds 1. -5. Beds 6-9. Beds 16-21. Beds 10-15. 19. N. 20. 13. 14. 8. 5. 9. 4. 1. 12. 15. 18. 21. 2. 3. 7. 6. Inner Bed Group.
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Inner Bed Group
Mid-Inner Bed Group
Mid-Outer Bed Group
Outer Bed Group
Lauren C. Cunningham, Benjamin J. Mew, Gabriel D. Goldthwaite
Systems Ecology (ENVS316) Fall 2008
Comparison of Soil Organic Matter and pH Between and Within Raised-Beds of a Newly Constructed Organic Learning Garden in Northeast Ohio: Implications for Future Management
Background and Introduction
Soil organic matter (SOM) and pH are important indicators of soil fertility (Manlay et al. 2007). SOM is dead organic matter that is decomposed into inorganic nutrients by fungi, bacteria, and other soil fauna. SOM correlates with important soil properties including cation exchange capacity (CEC), moisture retention, soil drainage, and soil biota diversity (Weil and Magdoff, 2004). Conventional agriculture often depletes SOM (Pulleman 2003) while sustainable agriculture techniques focus on developing SOM by application of organic inputs. Lime is occasionally applied to fields to raise the soil pH and maintain optimum acidity for crop productivity.
The organically managed George Jones Memorial Farm in Oberlin, OH has been working since 2002 to restore the fertility of soil degraded by decades of conventional farming (New Agrarian Center). In 2008, the farm built a “learning garden” of raised beds to help educate students and the public about environmentally sustainable food production and consumption. Although previous research has examined soil fertility on other areas of the Jones farm (e.g. Bishop et al. 2007), this study establishes baseline data in a highly controllable environment. The learning garden can act as a research tool to monitor the effects of initial bed composition and subsequent soil management strategies on %SOM, pH, and other aspects of soil fertility.
We compared soil between beds grouped in concentric circles separated by limestone paths. Inner beds contain more compost while outer beds contain an increasing amount of shredded leaves due to limited compost during construction.
1Bed 1 was an outlier and not included in SOM analysis. 2 Bed 21 was an outlier and not included in SOM analysis. Error bars indicate standard deviations
Within-Bed pH and SOM
Contrary to our hypotheses, no significant difference was found between the middle and edge of any of the four beds analyzed for pH and SOM. This suggests that the limestone paths had a negligible effect on the soil pH and that the soil was well-mixed during construction.
We collected soil samples using a 15 cm soil corer with a 2 cm diameter. For between-bed comparisons we took 4-5 cores distributed over all regions of each bed to adjust for possible within-bed variability, then homogenized them prior to analysis. To assess within-bed heterogeneity, we sampled multiple transects within one bed from each group (9 cores from Bed 2, 9 cores from Bed 6, 5 cores from Bed 10 and 15 cores from Bed 16) (See garden schematic). We measured %soil moisture, pH, and %SOM, taking one replicate for each sample. We used a single factor ANOVA (p = 0.05) for pH and %SOM variability and a linear regression between %SOM and %moisture as well as pH and %SOM.
A linear regression of between-bed SOM plotted against between-bed pH and soil moisture reveals a strong (R2=0.76) positive correlation between %SOM and %soil moisture and a weaker (R2=0.12) inverse relationship between %SOM and pH.
We found that the outer group of beds has significantly higher %SOM than the three inner groups of beds. This corresponds to the higher percentage of shredded leaves in the soil of these beds.
pH is significantly higher in the two inner groups of beds relative to the outer two groups. Decomposition of the shredded leaves in the outer beds likely contributes to the lower pH.
-Manlay, R. J., C. Feller, & M Swift. 2007. Historical evolution of soil organic matter concepts and their relationships with the fertility and sustainability of cropping systems. Agriculture, Ecosystems and Environment, 119(3-4): 217-233.
-New Agrarian Center. www.gotthenac.org
-Weil R.R. and F. Magdoff. 2004. Significance of Soil Organic Matter to Soil Quality and Health. Soil Organic Matter in Sustainable Agriculture. CRC Press, Boca Raton.
-Pulleman, M., Jongmans, A., Marinissen, J., & Bouma, J. (2003). Effects of organic versus conventional arable farming on soil structure and organic matter dynamics in a marine loam in the Netherlands. Soil Use and Management, 19(2), 157-165.
Schematic of George Jones Memorial Farm Learning Garden