| MadSci Network: Botany |
I don't think there is any plant that has a really wide soil pH optimum, say pH 4 to 8. However, a lot of plants will grow in a wide soil pH range if they are provided with optimal levels of mineral nutrients. The classic bar graph showing soil mineral nutrient availability versus pH gives a mineral soil pH optimum of 6.5 and an organic soil pH optimum of 5.5. However, those graphs are broad generalizations and are partly based on natural levels of mineral nutrients found in soils of that pH, hence they assume no fertilizer has been added. Low pH soils are often deficient in calcium and magnesium, which means non-acid-loving plants will suffer from lack of calcium and magnesium. However, it is possible to add calcium and magnesium without raising the soil pH. Similarly, acid-loving plants suffer from lack of iron at higher soil pH, however, it is possible to increase iron availablility at high pH by applying iron chelates. You can find lists of pH optima for plants but they are not necessarily that accurate for the reasons discussed above. Thus, it is not particularly important what kind of plant you use if you want to examine soil pH effects on a plant. Depending on the plant you use, you will get different results but the results are still valid. A more important consideration is to pick a plant that is easy to grow and possibly grows fast so you can get results in a short time period. Other considerations are the size of the plants and their light and temperature requirements relative to the space and environment you can provide. You might want to try Wisconsin fast plants, houseplants easily grown from cuttings such as wandering jew, coleus, piggyback plant, devil's backbone, Swedish ivy or pothos, or flower or vegetable seeds such as marigold, impatiens, zinnia, corn, bean, radish or lettuce. Also extremely important is to have replication, ideally five or more plants per treatment so you can average the results and do statistics. You also have to be able to measure soil pH with a pH meter or pH paper. Metal probe pH meters sold for gardening are worthless. A good method of doing soil pH experiments in pots is to grow plants in sphagnum peat moss, which has a natural pH of about 4.0. You can raise the pH to various levels by adding different amounts of lime or calcium carbonate. To assure that the low pH treatments have the same amount of calcium as the higher pH treatments, add a comparable amount of calcium sulfate or gypsum. You would also need to apply a complete liquid fertilizer to all pots so all plants would have optimal nutrition. It is also possible to do pH experiments in plant solution culture or hydropnics. References Hershey, D.R. 1995. Plant Biology Science Projects. NY: Wiley. Hershey, D.R. 1992. Evaluating metal probe meters for soil testing. 54:436-438 Hershey, D.R. 1992. Plant nutrient solution pH changes. Journal of Biological Education 26:107-111. Hershey, D.R. 2000. "Hydroponics: Iron Deficiency of Piggyback Plants" pp. 147- 155. IN Gerry M. Madrazo, Jr. and Steven E. Dyche (editors). Exciting Plant Science Activities for the Secondary Classroom Chapel Hill, NC: University of North Carolina Press. Mineral soil pH and nutrient availability bar graph Another mineral soil pH and nutrient availability bar graph Organic soil pH and nutrient availability bar graph Liming Acid Soils List of Optimal Soil pH for a Variety of Crops
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