defect action levels

Levels of natural or unavoidable defects in foods that present no health hazards for humans.

deficiency diseases

Diseases caused by an insufficient intake of essential nutrients, i.e., protein (or amino acids), vitamins, and minerals or inadequacy intake of calories.

delignification

Removal of part or all of the lignin from wood by chemical treatment

demeclocycline

A tetracycline analog having a 7-chloro and a 6-methyl. Because it is excreted more slowly than tetracycline, it maintains effective blood levels for longer periods of time.

demonstration forests

Forests which provide models of forest ecology and exhibitions of various forest management techniques and silvicultural practices.

dendrochronology

The study of annual growth rings of a tree in order to determine the historical date of their formation and the age of the tree.

dendroclimatology

The study of the annual growth rings of a tree to determine historical patterns of climate variation.

dendroecology

The use of tree ring data to investigate the past histories of ecological processes such as, forest dynamics with precise spatial and temporal resolution.

dermis

A layer of vascular connective tissue underneath the epidermis.

determinate growth

Plant growth in which the growth of the main axis is terminated. Typically applied to inflorescences, where the terminal flower is the first to mature along the inflorescence.

detoxification

The removal or inactivation of a poison or toxic substances from a nonliving substance or product.

diffuse solar radiation

Diffuse solar radiation is that fraction of the solar radiation that is reaching Earth's surface after been scattered downwards by the molecules or particulates in the atmosphere.

digestible dry matter

Amount of digestible fibre in a feed or forage.

disease resistance

Describing any organism which has low susceptibility or has the ability to withstand a disease caused by infectious agents (i.e., viruses, bacteria, fungi) or by parasitic nematodes, protozoa and helminths.

disease susceptibility

A constitution or condition of the body which makes the tissues react in special ways to certain extrinsic stimuli and thus tends to make the individual more than usually susceptible to certain diseases.

DNA

he chemical substance from which genes are made. DNA is a long, double-stranded helical molecule made up of nucleotides which are themselves composed of sugars, phosphates, and derivatives of the four bases adenine (A), guanine (G), cytosine (C), and thymine (T). The sequence order of the four bases in the DNA strands determines the genetic information contained.

domestication

The process of breeding for one or more desirable characteristics in plants�

double cropping

Two different crops grown on the same area in one growing season.

draft animals

Animals used to supply power to pull farming implements, carts, vehicles, heavy loads, etc.

drainage system

Manmade systems of furrows, ditches, tile drains, pipes, etc. which collect and remove water from a central location.