Acid rain is rain or any other form of precipitation that is unusually acidic. It has harmful effects on plants, aquatic animals, and infrastructure. Acid rain is mostly caused by human emissions of sulfur and nitrogen compounds which react in the atmosphere to produce acids. In recent years, many governments have introduced laws to reduce these emissions.

Soil biology and chemistry can be seriously damaged by acid rain. Some microbes are unable to tolerate changes to low pHs and are killed. The enzymes of these microbes are denatured (changed in shape so they no longer function) by the acid. The hydronium ions of acid rain also mobilize toxins, e.g. aluminium, and leach away essential nutrients and minerals.

Soil chemistry can be dramatically changed when base cations, such as calcium and magnesium, are leached by acid rain thereby affecting sensitive species, such as sugar maple (Acer saccharum).

Adverse effects may be indirectly related to acid rain, like the acid's effects on soil or high concentration of gaseous precursors to acid rain. High altitude forests are especially vulnerable as they are often surrounded by clouds and fog which are more acidic than rain.

Other plants can also be damaged by acid rain but the effect on food crops is minimized by the application of lime and fertilizers to replace lost nutrients. In cultivated areas, limestone may also be added to increase the ability of the soil to keep the pH stable, but this tactic is largely unusable in the case of wilderness lands. When calcium is leached from the needles of red spruce, these trees become less cold tolerant and exhibit winter injury and even death.

The radish (Raphanus sativus) is an edible root vegetable of the Brassicaceae family that was domesticated in Europe in pre-Roman times. They are grown and consumed throughout the world. Radishes have numerous varieties, varying in size, color and duration of required cultivation time. There are some radishes that are grown for their seeds; oilseed radishes are grown, as the name implies, for oil production.

Summer radishes mature rapidly, with many varieties germinating in 3-7 days, and reaching maturity in three to four weeks. A common garden crop in the U.S., the fast harvest cycle makes them a popular choice for children's gardens. Harvesting periods can be extended through repeated plantings, spaced a week or two apart. Radishes grow best in full sun and light, sandy loams with pH 6.5 - 7.0. They are in season from April to June and from October to January in most parts of North America; in Europe and Japan they are available year-round due to the plurality of varieties grown. As with other root crops, tilling the soil helps the roots grow. Most soil types will work, though sandy loams are particularly good for winter and spring crops, while soils that form a hard crust can impair growth. The depth at which seeds are planted affects the size of the root, from 1 cm deep recommended for small radishes to 4 cm for large radishes.

Radishes are rich in ascorbic acid, folic acid, and potassium. They are a good source of vitamin B6, riboflavin, magnesium, copper, and calcium. One cup of sliced red radish bulbs provides approximately 20 Calories or less, coming largely from carbohydrates, making radishes, relative to their size, a very filling food for their caloric value.

Radishes are suggested as an alternative treatment for a variety of ailments including whooping cough, cancer, coughs, gastric discomfort, liver problems, constipation, dyspepsia, gallbladder problems, arthritis, gallstones, kidney stones and intestinal parasites.

The seeds of the Raphanus sativus species can be pressed to extract seed oil. Wild radish seeds contain up to 48% oil content, and while not suitable for human consumption the oil has promise as a source of biofuel. The oilseed radish grows well in cool climates.

Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License)

For More Information:
Acid Rain: K-12 Experiments & Background Information
Radish