Between-Bed pH

1. 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 11 10 Mid-Inner Bed Group 16 17 Mid-Outer Bed Group Outer Bed Group Bed number 2 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 Goals Background and Introduction • Answer questions posed by the growers at the Jones Farm: • How does SOM differ among the raised beds as a result of different approaches to developing the soils? • Is pH significantly different at the edge of beds where it is in close proximity to the limestone paths? • 2. Establish baseline data for future studies on the effects of varying management practices applied to the beds. • 3. Gather data to help inform future management decisions. 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. Hypotheses • We expect: • 1. Higher %SOM in the outer group of beds where more leaves were used in the construction. • 2. Higher %SOM, and thus more decomposition in the outer beds compared to the inner beds, will lead to lower pH values in the outer beds. • 3. Limestone from the pathways may interact with soil on the bed edges, thus raising pH relative to the center of the beds. • 4. Relatively uniform %SOM within each bed due to the fat that the beds were well mixed prior to planting, 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. Methods 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. Conclusions • Using primarily shredded leaves to build a raised bed leads to higher %SOM than using primarily compost. • Lower pH in the outer beds is due to more decomposition as a result of higher %SOM relative to inner bed groups. • The limestone pathways did not alter soil pH in any significant way. • Soil filling the beds is homogenized with regard to pH and %SOM. Results Between-Bed SOM 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. Literature Cited Between-Bed pH 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