Nutrient Content of Lettuce

Plant and Soil Analysis (ESC 515)

Amy Angert

George Scherer

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.

Extractable Soil Macronutrients(* denotes P < 0.05)

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log

scal

e (p

pm)

NH4* NO3* P* K* Ca* Mg* S

SOILCOMPOST

Extractable Soil Micronutrients

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ppm

Cu * Fe Mn * Na * Zn

SOILCOMPOST

Macronutrients in Lettuce

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% d

ry w

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N P K Ca Mg S

SoilCompostRef (M&J)

Micronutrients in Lettuce

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B Cu Fe Mn Zn

SoilCompostRef (M&J)

Metals in Lettuce (ppm)

As Pb Ni

Soil 7.9 4.5 8.8ns

Compost 8.4ns 10.2ns 5.6

Typical 0.1-5 .01-10 1.0

Excessive 15-20 30-300 10-100Reference: Pais and Jones, 1996 for typical metal concentration in plants. Kabata-Pendias and Pendias, 1994for excessive concentrations in plants.

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.

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.

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.

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.

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.

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.