Nutrient Content of Lettuce

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Nutrient Content of Lettuce

• Plant and Soil Analysis (ESC 515)
• Amy Angert
• George Scherer

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Hypotheses

• Ho Soil nutrients equal compost nutrients.
• Ho Soil grown lettuce nutrients equal compost
  grown lettuce nutrients.
• Ho Soil grown lettuce metals equal compost grown
  lettuce metals.

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Extractable Soil Macronutrients( denotes P lt
0.05)
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Extractable Soil Micronutrients
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Macronutrients in Lettuce
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Micronutrients in Lettuce
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Metals in Lettuce (ppm)
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Conclusions

• Significant differences in soil vs. compost
  nutrient concentration.
• Macros p-values .002 to .005, except S,
  extractable.
• Micros p-values .0015 for Cu and .0055 for Mn,
  extractable.
• No significant differences in soil grown lettuce
  nutrient concentration vs. compost grown lettuce.
• Some metals are higher in garden, regardless of
  soil treatment, than in production grown lettuce.

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References

• Kabata-Pendias, A. and H. Pendias. 1994. Trace
  Elements in Soils and Plants. CRC Press, Boca
  Raton, FL
• Mills, H.A. and J.B. Jones.1996. Plant Analysis
  Handbook. MicroMacro, Athens, GA.
• Pais, I. and J.B.Jones. 1996. The Handbook of
  Trace Elements. St Lucie Press, Delray Beach, FL.

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Text of slide talk.

• The goal of our class project was to examine the
  properties of compost-amended vs. non-amended
  soil and to see if differences in soil treatment
  led to differences in plant tissue nutrients.
  Plant tissue measurements included determinations
  of total C, total N, and total H and total
  elemental composition. Soil measurements included
  the above and, in addition, pH, electrical
  conductivity, cation exchange capacity,
  extractable ions (NO3- and NH4), and
  exchangeable cations.
• This presentation will focus on the soil,
  compost-amended soil, and tissue data for lettuce
  grown in the four replicate plots. We will show
  information that compost-amended soil has greater
  content of nutrient elements than soil only
  plots. We will show that concentrations of the
  nutrient elements in lettuce tissue grown in
  these two media do not differ. We compare these
  tissue nutrient concentrations with published
  data. And finally, we explore the tissue content
  of some heavy metals that were found in lettuce
  during the analysis.
• In examining the data, we used paired t-tests of
  four samples for each nutrient element of
  interest, comparing compost-amended soil vs. soil
  only substrate, and lettuce grown in
  compost-amended vs. non-amended soil. Our null
  hypotheses were 1) no difference in soil only and
  compost-amended nutrient concentration for the
  soils alone 2) no difference in the nutrient
  content of lettuce grown on soil vs.
  compost-amended soil 3) no difference in
  selected heavy metal concentrations in lettuce
  tissue grown on soil vs. compost-amended soil.
• For the macronutrients, N, P, K, Ca, Mg, there
  were significantly greater concentrations of
  these in compost-amended soil vs. soil only.
  There was not a significant difference between
  the two soils for concentrations of S. This is
  shown here in parts per million on a logarithmic
  scale to capture both large and small values. K,
  Ca and Mg in compost were 10 to 100 times greater
  in concentration than other nutrients.

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Text continued

• This slide shows values of extractable elements.
  We chose to focus of extractable elements rather
  that total elements because extractable elements
  are more likely to be available to plant. For
  nitrogen we show values for NH4-N and NO3-N as
  determined by KCl extraction
• For the micronutrients Cu, Mn and Na there were
  significant greater amounts in compost-amended
  soil than for soil only. Iron (Fe) and Zn
  concentrations were not significantly different
  between the two soil materials. These are shown
  here in parts per million in normal scale.
• For the soil materials, it pretty clear the
  compost-amendments add and apparently make
  available greater concentrations of most nutrient
  elements.
• The next slide shows concentrations of
  macronutrients for lettuce tissue. Literature
  generally shows these values in percent dry
  weight for N, P K, Ca, Mg, and S. Here we compare
  values from our analysis with those published in
  Mills and Jones, Plant Analysis Handbook II
  (1996) for plantation grown lettuce- leafy
  lettuce (not head lettuce). There was not a
  significant difference in the macronutrients
  content of lettuce grown in compost-amended soil
  vs. lettuce grown in soil only.

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Text continued

• It also appears that our lettuce has slightly
  less nutrient content overall than the plantation
  grown lettuce.
• For micronutrients content in lettuce, we found
  no significant differences in that grown in
  either of the two soil materials used in this
  experiment. Typically in literature, these data
  are reported in parts per million, as they are
  here. We point out here that, in comparison with
  plantation grown lettuce, our data shows that our
  lettuce has four times the amount of Fe and about
  twice the amount of Mn and Zn for both soil only
  and compost-amended soil grown plant tissue.
• We were curious about some other metals since
  information was available in our analytical data.
  
• The next slide shows data about arsenic (As),
  lead (Pb) and nickel (Ni) content in lettuce
  tissue grown in both soil only and
  compost-amended soil. Here again we compare our
  values with that available in literature by
  KabatapPendias and Pendias (1994) and Pais and
  Jones (1996) for higher plants in general, not
  specifically lettuce. They report data in ranges
  to account for considerable variability in the
  ability of specific plants to sequester different
  metals in different concentrations.
• The content of As, Pb and Ni in the lettuce here
  is clearly not excessive. However, in near all
  cases reported here for both soil and
  compost-amended soil the concentrations are
  greater than typically known for higher plants in
  general. Nickel is eight times typical values for
  soil grown lettuce. We note that compost-amended
  grown lettuce has twice the concentration of Pb
  in its tissue than does soil only grown lettuce.

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Text ending

• The presence of these metals in these tissue
  concentrations may be one of the properties of
  urban soils and urban grown produce. There was
  class discussion about use of industrial metal
  and material products such as is found in
  building materials, packaging and other
  consumable items finding it way into soil and
  subsequently plant and animal tissue. Metal
  refining mills and manufacturing facilities are
  located in this general region and have a history
  of discharging waste particulates into air, water
  and soil resources.
• We conclude that compost-amended soil did have
  greater amount of many nutrients available than
  did non-amended soil. However, this did not
  translate into greater amounts of the nutrients
  appearing in lettuce tissue grown in
  compost-amended soil. Perhaps the additional
  nutrients available in compost-amended soil were
  used to make more biomass and larger plants
  relative to plants grown in non-amended plots. An
  interesting extension of this experiment might be
  to measure the root and shoot biomass of
  vegetables grown in compost and no-compost soils.
  Another variable to examine might be water
  availability, to see whether compost addition
  changes the texture and water-holding capacity of
  soil. Furthermore, we observed higher than
  typical levels of metals in lettuce plants grown
  in both soils.