Hi Christina,
Do you know any plant that I can use instead of rice?
I've never tried to grow rice, but this web page claims it is not hard to do:
http://www.kidsregen.org/howTo.php?sect ... arden&ID=4
Would that work for you? If not, did you try the search for "flood tolerant plants"? You could also try searching for "wetland plants" or you could visit a plant store and ask what plants they have that can live in saturated or intermittently flooded soils. Also, if you look in the link that I gave to the abstract, there are some plants mentioned in there that were used for iron toxicity experiments.
how can I make soil anaerobic or make ph to go down?
To make soil anaerobic, mix in some organic material (e.g. manure) and flood the soil. To lower the pH, you could add some acid, but unless you would like to study acid mine drainage, the effects of pH are probably not as important for your project.
Can you explain how those can cause iron toxicity?
The short explanation is that anaerobic conditions (or low pH) make iron more soluble and therefore more available to plants. In most soils that contain some oxygen (aerobic soils), iron exists in solid minerals that plants can not absorb. As a result, plants in aerobic soils usually get too little iron rather than too much, and iron toxicity is rare. In anaerobic soils, the higher solubility of iron allows more iron to enter the water and possibly to induce iron toxicity.
Iron chemistry in soil is a very interesting and somewhat complicated topic. Here is a more detailed explanation of how anaerobic conditions make iron more soluble:
Are you familiar with the term "redox" which stands for "reduction-oxidation"? Basically, redox reactions occur between what we can call an "oxidizer" and a "reducer". For example, gaseous oxygen (O2) is an oxider, and our bodies use that oxidizer to react with organic carbon (the reducer) from our food to generate energy. Many microbes in soil also use O2 to generate energy for themselves, and they are called "aerobes". Some microbes are called "anaerobes" because they survive without O2 by using oxidizers such as NO3, Mn, and Fe.
In simple terms, different oxidizers produce different amounts of energy. O2 produces more energy than Fe, so microbes tend to use O2 exclusively if it is available, and they do not use much Fe if O2 is available. In drained soils, atmospheric O2 is able to penetrate through open pores into the soil to replenish the O2 that is being consumed by aerobes. When the soil becomes flooded, the open pores fill with water, and there are no open pathways for atmospheric O2 to penetrate directly into the soil. Some O2 is dissolved in water, but not a lot. Once the aerobes have used up the available O2, they switch (or anaerobes out-compete them) to use the other oxidizers, including Fe. So, after soil has flooded and oxygen in the pore spaces has been consumed by aerobes, anaerobes will eventually reduce Fe from a form known as "ferric iron" or "Fe3+" to a form known as "ferrous iron" or "Fe2+".
This is where it becomes very important for your project and experiments. Fe3+ has very low solubility and typically exists in soils as solid minerals, which do not interact with plants. In contrast, Fe2+ is much more soluble than Fe3+. In flooded soils lacking O2, anaerobes convert Fe3+ to Fe2+, and the amount of dissolved iron goes up enormously. Plants interact with dissolved iron (and not the solid minerals), so the plants are more likely to experience iron toxicity as the concentration of Fe increases in the soil water due to the flooded soils and lack of O2.
I realize that might be a lot of information to absorb if you are not familiar with redox reactions or soil chemistry. Please feel free to ask about anything.
