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

1
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
Lauren C. Cunningham, Benjamin J. Mew, Gabriel D.
Goldthwaite Systems Ecology (ENVS316) Fall 2008
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 (R20.76) positive correlation between
SOM and soil moisture and a weaker (R20.12)
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