TISSUE TESTING PLANT TISSUE ANALYSIS COMPLEMENTS SOIL TESTING By Garn A. Wallace, Ph. D. Various tools are available for which can not be readily evaluations. Otherwise, enhancing growth and reducing removed from the soil. can be used as a bioassay to plant problems. Each tool has determine what is really available. it strength and limitations. Soil The are needed The measurement of testing is not always 100% in very low amounts. Boron for uptake by plants eliminates all the adequate in resolving plant instance has a very fi ne line complex interactions of soil and nutritional needs. It is estimated between optimum levels for good gives a picture of what is available. by some to be only 75% accurate. growth and the toxic level. Poorly Soil testing is valuable in resolving buffered soils such as sandy soils RESPONSE OF PLANT GROWTH major problems but does not can be adversely effected with TO NUTRITIONAL STATUS do well with minor adjustments the application of an essential Generally, as the concentration nor does it perform as well in trace metal. A little too much zinc of a nutrient present in tissues soils which have poor physical or copper can induce an iron or increases, the growth rate is found properties. manganese defi ciency. to be faster as shown in fi gure 1. The greatest increase in growth Soil tests can be valuable when Since the root systems of plants occurs when the plant is highly calibrated for a specifi c plant assimilate the nutrients, the defi cient but not severely defi cient. in a specifi c soil. Since there availability of nutrients present in The curve is steepest in the highly are thousands of soil types and the soil depends upon the size and defi cient zone meaning that a numerous plant species which status of the root system. A very small increase of a nutrient in the differ in their responses to soils invasive root system in an infertile, tissue gives a large increase in and nutrition, this is diffi cult. loose, friable soil can give good the growth rate. When mineral growth as well as a more restrictive content of the tissue is suffi cient, The most effi cient procedure root system in a fertile soil. Most there is little change in the growth to assess plant nutritional nutrients move with the fl ow of rate with additional . requirements is with the use of water to the roots. Low levels of As the concentration of nutrients various combined analyses. Visual nutrients over a large root system increases even higher, toxicity symptoms, the result of plant are just as effective as higher occurs with a decreased growth growth to different treatments as levels of nutrients in a smaller rate. well as soil and tissue testing need system. The proper evaluation of to be used. It is best to have a soil when using soil testing should The shape of the growth curve second opinion before applying include fertility as well as physical in the severely defi ciency range PLANT TISSUE ANALYSIS COMPLEMENTS SOIL TESTING Page 2 is “C” shaped. As the growth optimum range, total growth would phosphorus and . rate becomes extremely slow, be 90% of maximum if all cultural The leaves become thinner than the production of biomass is practices and other factors were normal. With a reduced tissue too low to cause much dilution also at optimum. Seldom are all weight, the nonmobile elements of the absorbed minerals. The factors perfect. If two nutrients remaining in the tissue will have concentration of the minerals could were present at 90% of optimum high concentrations based upon be on the curve in the moderately levels, the total growth rate is 90% tissue mass. defi cient range or on the lower times 90% or 81% of optimum. For curve in the severely defi cient three factors at 90%, the result is Toxicity from heavy metals such range. It is best to interpret the 73% (90% x 90% x 90%) and 10 as nickel, chromium, cadmium, data in conjunction with regards factors at 90% would be 35% of vanadium, arsenic, silver etc. to several elements. For example optimum. It is important to correct can be detected in leaf tissue with iron defi ciency, phosphorus all factors to near 100% if the goal analyses. For some elements such and calcium are also depressed. is to have good growth. as silver, nickel, chromium and It is wise to evaluate the results as others, the root system is a barrier a whole and not rely on absolute Some experts believe that the ratio to the movement of the metals values. of the concentration of one nutrient into the upper parts of the plants. relative to the concentration of Root analysis is more reliable in Frequently, laboratories will use another element is more important detecting these possible problems. a critical value for an elements. than the absolute concentration Normally the “critical value” for of either. This concept has led to Multiple Testing approach to the defi cient nutrient level is the a method for the interpretation Nutritional Status concentration present for 90% of multi-element analyses of Soil testing is helpful to determine of the optimum growth rate. plant nutrients often called by the broad problems such as salinity, The “critical toxicity level” is the acronyms such as DRIS or TEAM. acidity and major problems with concentration present where the The method has given some defi ciencies. Soil testing can growth rate is depressed 10% from success. Its main advantage is not provide precise answers for the optimum growth. More reliable that it organizes the nutrients into nutrient needs. Soil testing data recommendations are made within a series from mostly likely defi cient are used to predict that there may a range of concentrations. to least likely defi cient (or most be a probability of a increased toxic). growth response to the application Optimum growth occurs over of a nutrient in question. It is not a range of nutrient contents. Tissue Analysis as a Forensic uncommon in relying on soil data Defi ciency also occurs over a Tool predicting that a nutrient is low range of concentrations. In lieu of a Some plants suffer from stress that one fi nds upon supplying an “critical value”, it is more accurate from excess salts which result element in large amounts that to use a “critical nutrient range” in damaged leaves and roots. there is no response to increased for diagnostic needs. As with all Necrotic leaves can be analyzed to growth. Thus the test can be organisms, variation occurs from determine the source of the stress. considered as inaccurate. In individual to individual. What is Excess salts in the plant are reality, the test is accurate but the optimum for one differs a little for extruded on the margins of leaves interpretation is inadequate. The another. causing a marginal burn. Analyses same problem occurs with tissue Guidance with the use of critical of leaves can determine the actual analysis. values can cause poor growth if salts causing the problem. multiple elements are defi cient. When several different methods If just one nutrient were slightly Moisture stress can cause the of assessing nutritional status are defi cient and results in a 10% nutrients to be recycled from combined, the results are more decrease in growth while all of leaves prior to leaf loss. These dependable. Evaluation methods the other nutrients were in the leaves lose nitrogen, potassium, are soil testing, tissue testing, PLANT TISSUE ANALYSIS COMPLEMENTS SOIL TESTING Page 3 visual symptoms and responses to Nitrogen Low nitrogen causes a pale green coloration. Since the nitrogen the testing of nutrient application - is mobile, new growth is greener than the older growth. typically foliar application. Iron The old growth versus new growth symptoms for low iron are reversed for nonmobile elements such as iron. The newest Soil properties can vary from spot growth is yellower for iron. In addition, iron defi ciency, if not too to spot. The manner in which defi cient, will have green veins in the leaves with yellowness in plants grow is the total sum of between the veins. the differences for each spot. Soil testing may not give a true picture Manganese Manganese defi ciency is similar to iron. However, the width of the green veins is greater. of the soil properties in a particular location but plant appearances Phosphorus Phosphorus defi ciency causes slow, weak growth. Newer refl ect these problem areas. leaves may be dark green while the older leaves have a purple pigmentation. Tissue content varies within the plant. Leaves from the same Potassium Potassium defi cient plants are sensitive to disease infestation. Older leaves will be as if they had been burned along the edges, age vary. Also tissues change a defi ciency known as “scorch.” Plants defi cient in potassium with age. The newest growth may become sensitive to ammonium toxicity. has higher levels of nitrogen, potassium and phosphorus than do Calcium The growing tips of plants turn brown and die with calcium older leaves. As the tissue ages, defi ciency. Leaves curl and their margins turn brown with newly mobile elements such as nitrogen, emerging leaves sticking together at the margins, leaving the expanded leaves shredded on their edges. potassium and phosphorus are transported to new tissues and Zinc Zinc defi ciency causes a chlorosis of the interveinal areas of the concentrations are lowered. new leaves. The chlorosis is mosaic. With increasing severity of Nonmobile elements such as defi ciency, growth is stunted and leaves die and abscise. Excess calcium, increase with phosphorus can induce zinc defi ciency. Excess zinc can induce age. The selection of tissue for iron defi ciency. testing needs to be selective. Tissue analysis is a valuable tool to aid those growing, establishing Visual Indications OF or maintaining vegetation. As with all tools, the proper ones are DEFICIENCIES needed at the appropriate time. With the correct interpretation and Visual interpretation of the recommendations, valuable plantings can be maintained for many years. nutritional status of plants can help diagnose problems. The following Garn A. Wallace, pH. D. earned his doctorate degree from UCLA in the Department of Biochemistry. He worked as a research biochemist in the symptoms are helpful if only one Laboratory of Biomedical and Environmental sciences before forming Wallace element were defi cient. With Laboratories with Arthur Wallace, professor emeritus, Department of Agricultural multiple defi ciencies or toxicities in Sciences [ and Soil Science] UCLA. Jointly the Wallaces have addition to defi ciencies, the use of over 600 publications in the fi elds of plant nutrition, soil science, microbiology, visual signs is diffi cult plant physiology, ecology, soil conditioners, mineral excesses, water relationship in plants, mineral toxicities etc. They are located at

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