radiocarbon dating

The determination of the age of an organic substance by measuring the loss rate of radiocarbon (carbon-14). The method is based on the principle that all living plants and animals take in small amounts of radiocarbon, and the intake ends when they die.

rainfed farming

A system of producing crops without the use of irrigation.

rain gauges

An instrument that measures the amount of rain that has fallen in a particular place.

rain intensity

The rate at which rain is falling at any given instant, usually expressed in inches per hour.

ranchers

People who raise livestock on rangeland.

range pastures

An area devoted to the production of forage (introduced or native) and harvested by grazing.

rare species

A rare species, or subspecies, is one that, although not presently threatened with extinction, is in such small numbers, throughout its range, that it may be endangered if its environment worsens.

ratooning

Production of a subsequent crop that results from the regrowth from roots of the previous harvested crop, as in sugarcane, pineapple, and banana

raw milk

Fresh, unprocessed milk as it comes from a cow, goat or other mammal.

reciprocal crosses

A pair of crosses where the first cross is the progeny of breeding a male from population A with a female from population B, and the second cross is the progeny of breeding a male from population B with the female from population A.

recombinant DNA

A molecule of DNA formed by joining different DNA segments using recombinant DNA technology.

refined grains

Grain products whose natural chemical and nutrient composition has been altered by processing, such as with milling, debranning or germ removal. Refined grain products generally have a finer texture than whole grains.

relay cropping

The seeding of one crop into another standing crop, e.g., winter wheat into standing soybeans. A practice of starting one crop in another.

replicon

Any DNA sequence capable of independent replication or a molecule that possesses a replication origin and which is therefore potentially capable of being replicated in a suitable cell.

risk

The probability that an adverse event will occur, including measures of the probability of an unfavorable outcome.

roof top gardens

A specialized roof structure for a building that is partially or completely covered in vegetation. Green roofs can reduce water runoff, improve air and water quality, provide energy conservation and improve aesthetics.

root crown

The growing point where the roots meet the stem.

root shoot ratio

The ratio of roots to shoots in a plant, either measured by dry weight or fresh weight.

rootstock-scion compatibility

The ability of the graft union to survive after the scion and the stock are grafted together.

rough rice

Unmilled rice that still contains the husk.