Phytotoxicity is a term used to describe the degree of toxic effect by a compound on plant growth. Such damage may be caused by a wide variety of compounds, including trace metal

Trace metal

Trace metals are metals in extremely small quantities that reside in or are present in animal and plant cells and tissue. They are a necessary part of good nutrition, although they can be toxic if ingested in excess quantities....

s, pesticides, salinity

Salinity

Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...

, phytotoxin

Phytotoxin

Phytotoxin refers to a substance produced by a plant that is toxic or a substance that is toxic to the plant Many substances produced by plants are secondary metabolites and are the by-products of primary physiological processes...

s or allelopathy

Allelopathy

Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the growth, survival, and reproduction of other organisms. These biochemicals are known as allelochemicals and can have beneficial or detrimental effects on the target organisms...

.

Urea and urine

Phytotoxicity can occur in the application of too much urea

Urea

Urea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....

 either by urea toxicity or by the "ammonia

Ammonia

Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

 produced through hydrolysis

Hydrolysis

Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...

 of urea by soil urease

Urease

Urease is an enzyme that catalyzes the hydrolysis of urea into carbon dioxide and ammonia. The reaction occurs as follows:In 1926, James Sumner showed that urease is a protein. Urease is found in bacteria, yeast, and several higher plants. The structure of urease was first solved by P.A...

". (Ammonia is a fertiliser, in smaller quantities as a source of nitrogen.) Organic compost enables more effective uptake of nitrogen due to higher prevalence of aerobic microbial activity. Ammonia (NH3) can oxidize into ammonium salts (NH4+), bacteria can convert this into nitrites (NO2-)and nitrates (NO3-) and finally nitric acid (HNO3), which may be too acidic for the plant.

Herbicides

Other Approaches This is also an important subject of study in the field of ecotoxicology

Ecotoxicology

Ecotoxicology is the study of the effects of toxic chemicals on biological organisms, especially at the population, community, ecosystem level. Ecotoxicology is a multidisciplinary field, which integrates toxicology and ecology....

. It has also been thought of as a means to control certain populations of plants