Researchers exposed soybeans to normal (380 parts per million) and high (550 parts per million) levels of CO2 in the field. This high level of CO2 is expected to be the norm in our atmosphere by 2050.
0 parts per million of dissolved oxygen in 90 degree F. water. Koi and goldfish start showing signs of stress at oxygen levels of 4.0 ppm and will start dying at 3.0 ppm. The higher the water temperature goes the less oxygen that's available.
In order to kill soil microorganisms to 6 inch soil depth, water containing 65 parts per million of chlorine was required in one study. Drinking water usually contains much lower chlorine levels. For example, Colorado Springs Utilities water contains between 0.05 to 0.
The acronym PPM stands for "parts per million." Raise the PPM in hydroponics with help from an aquaponics professional in this free video clip. Read More
How to Transplant From Soil to Hydroponics ...
Soils naturally contain copper in some form or other, ranging anywhere from 2-100 parts per million (ppm) and averaging at about 30 ppm. Most plants contain about 8-20 ppm. Without adequate copper, plants will fail to grow properly.
Ian answers: We have a bore in our front yard which we use quite often during summer. The water in the bore is around about 1900 parts per million, so it's moderately salty.
While pH and other levels will vary naturally, aim for a pH of between 6.8 and 9 and an alkalinity level of between 100 and 300 parts per million. You can add substances to adjust the pH, but only use chemicals approved for use with live fish.
The ingredient in peppers that makes the "hot" sensation is called Capsaicin. A sweet green pepper is devoid of this chemical. The hotter the pepper, the more the level of Capsaicin. It is measured in parts per million (ppm).
More on growing peppers at The Gardener's Network ...
See also: What is the meaning of Plant, Soil, Fertilize, Gardening, Gardener?