Plant tissue test
Encyclopedia
The nutrient
content of a plant
can be assessed by testing a sample of tissue from that plant. These tests are important in agriculture
since fertilizer
application can be fine-tuned if the plants nutrient status is known. Nitrogen
most commonly limits plant growth and is the most managed nutrient.
s. Soil tests measure the concentrations of nutrients in the soil that are potentially available for uptake by plant root
s.
Although soil testing is widely used, it does not always accurately estimate the nutrient status of the crop. Even if soils have the recommended level of nutrients, the crop can still be nitrogen deficient
if it has a nutrient uptake problem. Only tissue tests tell growers the actual nitrogen status of the crop.
Another drawback of soil nutrient tests is that they do not take account of factors such as soil structure or biological activity, which affect the rate at which nutrients leave the soil. These factors mean that the concentration of nutrients in the soil can rapidly deviate from the results of a soil test.
Another reason why soil tests do not always guarantee the best management of nutrient treatments is that cultivar
s vary in their ability to scavenge soil nutrients. Some cultivars can produce their optimum yield when grown in soil with less than the recommended levels of nutrients. Directly testing the nitrogen status of the crop helpd growers adjust fertilizer applications to the specific needs of that crop.
Another issue with laboratory tissue tests is that the results are often difficult to interpret.
To non-destructively assess nitrogen content, one can assess the chlorophyll content. Nitrogen content is linked to chlorophyll
content because a molecule of chlorophyll contains four nitrogen atoms.
can be detected with a chlorophyll content meter. Many studies have used chlorophyll content meters to predict N-content of leaves, and generally a good correlation is obtained. Researchers at the University of Nebraska concluded that a producer’s ability to manage nitrogen is enhanced by using a Chlorophyll Meter in combination with the researcher's new technique to fine-tune N-management during the growing season.
Peer-reviewed studies have concluded the CCM-200plus Chlorophyll Meter accurately measures leaf nitrogen content. For instance, researchers at the Universidad Politécnica de Madrid used a CCM-200plus to measure a Chlorophyll Content Index (CCI), and concluded that leaf chlorophyll content performed well as an indicator of nutritional status in sugar beet. The CCI was responsive to differences in nitrogen availability and was able to discriminate between treatments. The CCI parameter was concluded to be quick, easy and non-invasive.
Researchers at the University of Vermont
assessed the ability of the CCM-200plus to estimate Chlorophyll Content Index (CCI) and nitrogen content. The N-content was laboratory analysed, and was found to have a significantly linear relationship with CCI (P < 0.001). The CCM-200plus was concluded to be an effective tool for estimating relative chlorophyll and nitrogen content.
Nitrogen deficiency tests based on the fluorescence emission of leaves have been developed. Certain spectrums of laser
-induced fluorescence are used, since this particular spectrum is able to distinguish nitrogen and sulphur deficiency. Only N-deficiency significantly increases the fluorescence induced by 360nm- and 440nm-laser pulses. A test protocol based on this fluorescence spectrum has been developed and is incorporated into the latest chlorophyll fluorometers, such as the OS-5p (in which it is called the FRFex360/FRFex440 test). This spectrum of laser-induced fluorescence changes prior to or simultaneously with plant growth inhibition, allowing this fluorescence ratio to detect N-deficiency in a timely manner.
Another test protocol based on fluorescence that is incorporated into the OS-5p fluorometer is the OJIP test. This test analyses the increase in fluorescence emitted from dark-adapted leaves, when they are illuminated. The rise in fluorescence during the first second of illumination follows a curve with intermediate peaks, called the O, J, I, and P steps. In addition, the K step appears during specific types of stress, such as N-deficiency. Research has shown the K step is able to measure N-stress.
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...
content of a plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
can be assessed by testing a sample of tissue from that plant. These tests are important in agriculture
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
since fertilizer
Fertilizer
Fertilizer is any organic or inorganic material of natural or synthetic origin that is added to a soil to supply one or more plant nutrients essential to the growth of plants. A recent assessment found that about 40 to 60% of crop yields are attributable to commercial fertilizer use...
application can be fine-tuned if the plants nutrient status is known. Nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
most commonly limits plant growth and is the most managed nutrient.
Comparison to Soil Tests
Plant tissue tests are often used in combination with soil testSoil test
In agriculture, a soil test is the analysis of a soil sample to determine nutrient and contaminant content, composition and other characteristics such as acidity or pH level. Tests are usually performed to measure the expected growth potential of a soil...
s. Soil tests measure the concentrations of nutrients in the soil that are potentially available for uptake by plant root
Root
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
s.
Although soil testing is widely used, it does not always accurately estimate the nutrient status of the crop. Even if soils have the recommended level of nutrients, the crop can still be nitrogen deficient
Nitrogen deficiency
All plants require sufficient supplies of macronutrients for healthy growth, and nitrogen is a nutrient that is commonly in limited supply. Nitrogen deficiency in plants can occur when organic matter with high carbon carbon content, such as sawdust, is added to soil. Soil organisms use any...
if it has a nutrient uptake problem. Only tissue tests tell growers the actual nitrogen status of the crop.
Another drawback of soil nutrient tests is that they do not take account of factors such as soil structure or biological activity, which affect the rate at which nutrients leave the soil. These factors mean that the concentration of nutrients in the soil can rapidly deviate from the results of a soil test.
Another reason why soil tests do not always guarantee the best management of nutrient treatments is that cultivar
Cultivar
A cultivar'Cultivar has two meanings as explained under Formal definition. When used in reference to a taxon, the word does not apply to an individual plant but to all those plants sharing the unique characteristics that define the cultivar. is a plant or group of plants selected for desirable...
s vary in their ability to scavenge soil nutrients. Some cultivars can produce their optimum yield when grown in soil with less than the recommended levels of nutrients. Directly testing the nitrogen status of the crop helpd growers adjust fertilizer applications to the specific needs of that crop.
When Tissue Testing is Most Useful
Tissue tests are almost always useful, since they provides additional information about the physiology of the crop. Tissue tests are especially useful in certain situations;- For monitoring the nitrogen status of the crop throughout the growing season. Soil tests are commonly performed before planting.
- In highly controlled environments, such as hydroponic production in greenhouses, crops require a constant feed of nutrients in their water supply. Even a transient lack of nutrients can reduce yields. In these controlled environments, soil testing is unlikely to be sufficient to manage crop nitrogen status. Soil testing is more suitable when growing crops in slow-release composts and manures.
- When there is a risk that the nutrient applications are toxic to the crop, such as during the application of poultry litter that contains micro nutrients such as copper.
- To guarantee that nitrogen levels in the crop do not exceed a certain limit. High concentrations of nitrateNitrateThe nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
s has implications to human health because nitrates can be converted into nitriteNitriteThe nitrite ion has the chemical formula NO2−. The anion is symmetric with equal N-O bond lengths and a O-N-O bond angle of ca. 120°. On protonation the unstable weak acid nitrous acid is produced. Nitrite can be oxidised or reduced, with product somewhat dependent on the oxidizing/reducing agent...
s in the human digestive tract. Nitrites can react with other compounds in the gut to form nitrosamines, which appear to be carcinogenic. Crops contain high concentrations of Nitrate when excess fertilizer is used. This is an issue in crops with high levels of nitrates, such as spinachSpinachSpinach is an edible flowering plant in the family of Amaranthaceae. It is native to central and southwestern Asia. It is an annual plant , which grows to a height of up to 30 cm. Spinach may survive over winter in temperate regions...
and lettuceLettuceLettuce is a temperate annual or biennial plant of the daisy family Asteraceae. It is most often grown as a leaf vegetable. It is eaten either raw, notably in salads, sandwiches, hamburgers, tacos, and many other dishes, or cooked, as in Chinese cuisine in which the stem becomes just as important...
.
Disadvantages of traditional tests
Traditional tissue tests are destructive tests where a sample is sent to a laboratory for analysis. Any laboratory test (soil or tissue test) performed by a commercial company will cost the grower a fee. Laboratory tests take at least a week to complete, usually 2 weeks. It takes time to dry the samples, send them to the lab, complete the lab-tests, and then return the results to the grower. This means the results may not be received by the grower until after the ideal time to take action. Nitrogen tissue tests that can be performed quickly in the field make tissue testing much more useful.Another issue with laboratory tissue tests is that the results are often difficult to interpret.
Non-destructive Tissue tests
Non-destructive tissue tests have advantages over traditional destructive tests. Non-destructive tissue tests can be performed easily in the field, and provide results much faster than laboratory tests.To non-destructively assess nitrogen content, one can assess the chlorophyll content. Nitrogen content is linked to chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
content because a molecule of chlorophyll contains four nitrogen atoms.
Chlorophyll content meters
Nitrogen deficiencyNitrogen deficiency
All plants require sufficient supplies of macronutrients for healthy growth, and nitrogen is a nutrient that is commonly in limited supply. Nitrogen deficiency in plants can occur when organic matter with high carbon carbon content, such as sawdust, is added to soil. Soil organisms use any...
can be detected with a chlorophyll content meter. Many studies have used chlorophyll content meters to predict N-content of leaves, and generally a good correlation is obtained. Researchers at the University of Nebraska concluded that a producer’s ability to manage nitrogen is enhanced by using a Chlorophyll Meter in combination with the researcher's new technique to fine-tune N-management during the growing season.
Peer-reviewed studies have concluded the CCM-200plus Chlorophyll Meter accurately measures leaf nitrogen content. For instance, researchers at the Universidad Politécnica de Madrid used a CCM-200plus to measure a Chlorophyll Content Index (CCI), and concluded that leaf chlorophyll content performed well as an indicator of nutritional status in sugar beet. The CCI was responsive to differences in nitrogen availability and was able to discriminate between treatments. The CCI parameter was concluded to be quick, easy and non-invasive.
Researchers at the University of Vermont
University of Vermont
The University of Vermont comprises seven undergraduate schools, an honors college, a graduate college, and a college of medicine. The Honors College does not offer its own degrees; students in the Honors College concurrently enroll in one of the university's seven undergraduate colleges or...
assessed the ability of the CCM-200plus to estimate Chlorophyll Content Index (CCI) and nitrogen content. The N-content was laboratory analysed, and was found to have a significantly linear relationship with CCI (P < 0.001). The CCM-200plus was concluded to be an effective tool for estimating relative chlorophyll and nitrogen content.
Chlorophyll fluorometers
A novel method of detecting nitrogen deficiency is with a chlorophyll fluorometer.Nitrogen deficiency tests based on the fluorescence emission of leaves have been developed. Certain spectrums of laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
-induced fluorescence are used, since this particular spectrum is able to distinguish nitrogen and sulphur deficiency. Only N-deficiency significantly increases the fluorescence induced by 360nm- and 440nm-laser pulses. A test protocol based on this fluorescence spectrum has been developed and is incorporated into the latest chlorophyll fluorometers, such as the OS-5p (in which it is called the FRFex360/FRFex440 test). This spectrum of laser-induced fluorescence changes prior to or simultaneously with plant growth inhibition, allowing this fluorescence ratio to detect N-deficiency in a timely manner.
Another test protocol based on fluorescence that is incorporated into the OS-5p fluorometer is the OJIP test. This test analyses the increase in fluorescence emitted from dark-adapted leaves, when they are illuminated. The rise in fluorescence during the first second of illumination follows a curve with intermediate peaks, called the O, J, I, and P steps. In addition, the K step appears during specific types of stress, such as N-deficiency. Research has shown the K step is able to measure N-stress.