To Mulch Or Not To Mulch:

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To Mulch Or Not To Mulch
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COMPARING BROCCOLI PRODUCTIVITY IN MULCHED AND
UNMULCHED AREAS IN NAZARE PAULISTA
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Zena Lee Park Center for Environmental Research
and Conservation, Columbia University, New York,
New York, 10027 U.S.A ZLP1_at_COLUMBIA.EDU
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INTRODUCTION

• Mulch acts as the skin of the soil, a protective
  layer covering the surface of the soil. Often the
  mulching technique can eliminate fertilizing,
  thereby economizing the workload of the gardener.
  Mulch takes away the sunlight weeds need
• The existence of mulch lessens water evaporation
  and adds essential microorganisms and nutrients
  to the soil. Areas that are mulched sustain
  balanced and healthy soil. The use of mulch is
  an important strategy to minimize the risks of
  soil degradation. Since mulching avoids excess
  watering, it avoids the passage of nutrients into
  subsoil.
• The Natural Resources Conservation Service-United
  States Department of Agriculture claims mulch
  does the following protects the soil from
  erosion, reduces compaction from the impact of
  heavy rains, conserves moisture, reduces the need
  for frequent waterings, maintains a more even
  soil temperature, prevents weed growth, keeps
  fruit and vegetables clean.
• Mulching a garden mimics the natural setting of a
  forest. Since, in nature, there will always be
  some kind of organic litter or some type of
  protection on the ground. For example, leaves
  fall and then cover the soil, thereby cooling and
  shielding the soil and root system from rain that
  might cause soil erosion or hardening. In an
  unmulched area, sun exposure often kills many of
  the microorganisms that make the soil healthy.
• The main objective of this study was to determine
  if there were any differences between mulched and
  unmulched areas of broccoli, indicating possible
  differences in productivity. If so, then whether
  or not there was any correlation between type of
  treatment and factors that show broccoli
  productivity.
• The question was Does the existence of mulch
  increase the productivity of an organic garden?
  The null hypothesis (Ho) was The existence of
  mulch does not effect the productivity of an
  organic garden. The alternative hypotheses were
  The existence of mulch increases the level of
  productivity in an organic garden (Ha). The
  existence of mulch decreases productivity (Hb).

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METHODS

• Description of Study Area
• The studied area was an organic garden,
  privately operated by the Center of Light
  community, in the Atlantic Rainforest of Nazare
  Paulista, Sao Paulo State, Brazil. On June 16,
  2001, all data was collected. The observed eight
  broccoli plants were found at the following
  location, according to the GPS unit used (Trimble
  GeoExplorer3) 23 ? 1156.907 S,
  46?21234.408W, at an altitude of 798.3m. The
  mulched and the unmulched gardens lay evenly,
  side by side, in a combined rectangular area of
  880cm x 300cm. The mulched garden included
  African Red Grass (Melinis minutiflora) that lay
  on top of the soil.
• Summary of Procedures
• In order to compare broccoli (Brassica oleracea)
  productivity in mulched versus unmulched treated
  areas, the following characteristics were
  calculated and measured plant height, plant
  width, number of stalks on each plant, leaf
  areas, number of leaves on each plant, and soil
  temperature taken at the base of each plant.
• There was only one crop of the same species that
  had been divided equally between mulched and
  unmulched treatments, located in the same area,
  and planted at the same time. This crop of
  broccoli was three months old at the time of the
  study.
• Eight individual broccoli plants were chosen for
  observation within this half mulched, half
  unmulched area of broccoli. Four rows were
  chosen randomly, each row had two broccoli
  plantsone in the mulched area and one in the
  unmulched.

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RESULTS

• Significant differences were found in two
  out of the six variables looked at number of
  broccoli stalks and the leaf sizes (Table 1).
  According to the statistical test used (t-test),
  the two variables gave calculated t values that
  were greater than the critical t values. This
  indicated that the null hypothesis should be
  rejected. The average number of broccoli stalks
  for the mulched area was much greater than the
  average number of broccoli stalks for the
  unmulched area (Figure 1, Table 2). The average
  leaf size found on each broccoli plant in the
  mulched area was higher than the average leaf
  size found on each broccoli plant in the
  unmulched area (Figure 2, Table 3). As for the
  other variables, leaf abundance (Figure 3, Table
  4), plant height (Figure 4, Table 5), plant width
  (Figure 5, Table 6), and soil temperature (Figure
  6, Table 7), t-tests showed no significant
  differences.

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Statistical Analysis t-test
Table 1
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Figure 1
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Number of Broccoli Stalks
Plant Row Mulched Unmulched
A 15 4
B 29 1
C 9 4
D 21 10
Mean 18.5 4.75
Variance 73 14.25
Standard Deviance 8.544004 3.77491722
Table 2
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Figure 2
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Leaf Size Results
Table 3
The three larges leaf areas were taken from each
area.
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Figure 3
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Number of Leaves Results
Plant Row Mulched Unmulched
A 55 23
B 58 19
C 29 45
D 46 51
Mean 47 34.5
Variance 170 251.6667
Standard Deviance 13.0384 15.8640
Table 4
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Figure 4
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Broccoli Plant Height
Plant Row Mulched Unmulched
A 90cm 50cm
B 72cm 44cm
C 67cm 52cm
D 48cm 63cm
Mean 69.25cm 52.25cm
Variance 298.250 62.917
Standard Deviance 17.270 7.932
Table 5
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Figure 5
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Broccoli Plant Width Results
Plant Row Mulched Unmulched
A 58.0cm 40.0cm
B 55.0cm 40.0cm
C 70.0cm 63.0cm
D 59.0cm 44.0cm
Mean 60.5cm 46.75cm
Variance 43.0 120.916667
Standard Deviance 6.557439 10.9962115
Table 6
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Figure 6
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Soil Temperature Results
Plant Row Mulched Unmulched
A 18.0C 18.4C
B 18.4C 18.5C
C 18.6C 19.0C
D 18.4C 19.0C
Mean 18.35C 18.725C
Variance .063333 .1025
Standard Deviation .2516611 .32015621
Table 7
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CONCLUSIONS

• The original hypothesis was that the existence of
  mulch increases productivityin this case, of
  broccoli. Of the six variables tested, two of
  them rejected the null hypothesis, recognizing a
  significant difference between the mulched and
  unmulched areas. The two variables that
  supported the hypothesis were the number of
  broccoli stalks and leaf sizes found.
• But it is important to remember that even with
  the two variablesnumber of broccoli stalks and
  average size of the leavesthat rejected the null
  hypothesis, there was still a five percent chance
  that the results were inconclusive.
• There were several possible reasons (sources of
  error) that the four other variables did not
  support my hypothesis the smallness of the
  sample sizes used, soil quality was not one of
  the variables, characteristics of the broccoli
  stalks found on the plants were not considered,
  more than one crop in an organic garden that has
  been divided equally into mulched and unmulched
  sections, the type of mulch used, amount of
  mulch, the type of mulch used is dependent on the
  type of crop, and the time of day and the number
  of times the temperatures were taken.
• Studying the soil and the effects of mulch can
  help gardeners all over the world maximize their
  productivity. The process of mulching protects
  the soil from weather, efficiently uses the water
  and heat, protects the plants and soil from
  harmful insects, and organic mulching enriches
  the soil. Such advantages provide a better,
  healthier growing environment for a vegetable or
  fruit.
• Researchers and gardeners should be aware that
  the way to have a productive garden is to have
  healthy soil. Since mulch is a protective
  covering that improves the quality and the
  condition of the soil, it can only be beneficial
  for the crop and increase productivity.