Editing Nitrogen deficiency (section)

== Detection ==
The visual symptoms of nitrogen deficiency make it relatively easy to detect in some plant species. Symptoms include poor plant growth, and leaves become pale green or yellow because they are unable to make sufficient chlorophyll. Leaves in this state are said to be [[chlorosis|chlorotic]]. Lower leaves (older leaves) show symptoms first, since the plant will move nitrogen from older tissues to more important younger ones.<ref>http://www.rainbowplantfood.com/agronomics/efu/nitrogen.pdf {{Bare URL PDF|date=March 2022}}</ref> Nevertheless, plants are reported to show nitrogen deficiency symptoms at different parts. For example, Nitrogen deficiency of [[tea]] is identified by retarded shoot growth and yellowing of younger leaves.<ref>{{Cite web | url=http://www.upasitearesearch.org/soil-nutrition/ |title = Soil & Nutrition &#124; Upasi Tea Research Foundation (TRF)}}</ref>

However, these physical symptoms can also be caused by numerous other stresses, such as deficiencies in other nutrients, toxicity, herbicide injury, disease, insect damage or environmental conditions. Therefore, nitrogen deficiency is most reliably detected by conducting quantitative tests in addition to assessing the plant's visual symptoms. These tests include [[soil test]]s and [[plant tissue test]].<ref>{{Cite web | url=https://www.scribd.com/doc/15085476/CROP-NUTRIENT-DEFICIENCIES-TOXICITIES |title = CROP NUTRIENT DEFICIENCIES - TOXICITIES &#124; Plant Nutrition &#124; Nutrients}}</ref>

[[Plant tissue test]]s destructively sample the plant of interest. However, nitrogen deficiency can also be detected [[Plant tissue test#Non-destructive tissue tests|non-destructively]] by measuring chlorophyll content.<ref>{{Cite journal |last1=Ji-Yong |first1=Shi |last2=Xiao-Bo |first2=Zou |last3=Jie-Wen |first3=Zhao |last4=Kai-Liang |first4=Wang |last5=Zheng-Wei |first5=Chen |last6=Xiao-Wei |first6=Huang |last7=De-Tao |first7=Zhang |last8=Holmes |first8=Mel |date=2012-05-01 |title=Nondestructive diagnostics of nitrogen deficiency by cucumber leaf chlorophyll distribution map based on near infrared hyperspectral imaging |journal=Scientia Horticulturae |volume=138 |pages=190–197 |doi=10.1016/j.scienta.2012.02.024 |issn=0304-4238|doi-access=free |bibcode=2012ScHor.138..190J }}</ref>

Chlorophyll content tests work because leaf nitrogen content and chlorophyll concentration are closely linked, which would be expected since the majority of leaf nitrogen is contained in chlorophyll molecules.<ref>http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=2349&context=extensionhist {{Bare URL PDF|date=March 2022}}</ref> Chlorophyll content can be detected with a [[Plant tissue test#Chlorophyll content meters|Chlorophyll content meter]]; a portable instrument that measures the greenness of leaves to estimate their relative chlorophyll concentration.

Chlorophyll content can also be assessed with a [[Chlorophyll fluorescence#Chlorophyll fluorometers|chlorophyll fluorometer]], which measures a [[chlorophyll fluorescence]] ratio to identify phenolic compounds that are produced in higher quantities when nitrogen is limited. These instruments can therefore be used to [[Plant tissue test#Chlorophyll fluorometers|non-destructively test]] for nitrogen deficiency.