AP Environmental ScienceAP Environmental ScienceEdinburg North High SchoolEdinburg North High School

Increased salinity of a soil can occur in arid regions where crops are irrigated (Miller and Spoolman 2009).

The salts decrease the osmotic potential of the soil making it difficult for plants to take up water (Molnar 2005).

The Lower Rio Grande Valley (LRGV) of south Texas has been characterized as having a subtropical and semi-arid climate (Lonard et al. 1991).

Objective: Describe the salt tolerance of the Grand Rapids Lettuce.

We tested the null hypothesis that salt concentration will not have an effect on germination rates of this lettuce cultivar.

The following salt (NaCl) concentrations, by weight, were tested: 0.01%, 0.05%, 0.10%, 0.50%, 1.0%, 1.5%, 2.0%, 2.5%, and 3.0%

In addition, a control group used water only.

Nine replicates for each test concentration as well as for the control group were established

For each replicate, 10 lettuce seeds were placed on a paper towel, in a Petri dish.

The paper towel in each dish was completely saturated with the respective test salt solution.

Seeds were allowed to germinate for 7-days.

After 7-days, the number of seeds germinated was recorded for each replicate.

Mean germination frequencies were calculated for each test group, then plotted against concentration.

The median lethal dose (LD50) for the lettuce cultivar was interpolated from the graph.

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

0.00% 0.01% 0.10% 1.00% 10.00%

Aver

age

Freq

uenc

y of

Ger

min

ation

(ou

t of 1

0)

Percent Concentration of NaCl (w/w)

Effects of Salt Concentration on Germination Rates of a Lettuce Cultivar

LD50 = 0.80 % NaCl

No response was observed between 0 and 0.01%.

Ten out of 10 (or 100%) of the seeds germinated.

The threshold of toxicity of NaCl was observed at between 0.01% and 0.50%.

Viability dropped precipitously above 0.50%. One-hundred percent mortality was observed at 1.50%.

The median lethal dose was estimated to be 0.80%.

The null hypothesis that salt concentration would have no effect on germination rate of Grand Rapids Lettuce was rejected.

Salt tolerance of Grand Rapids Lettuce was moderate.

Feasibility of growing this lettuce cultivar in the LRGV requires further investigation.• Water requirements• Soil salinity• Projected increases

in soil salinity from irrigation requirements