Unit

1. Unit Plant Science

2. Problem Area Managing Inputs for Plant Growth

3. Lesson Plant Tissue Testing

4. Student Learning Objectives • 1. Name the nutrients needed for plant growth. • 2. Explain why nutrients are essential to plants. • 3. Explain where and how plants can obtain nutrients. • 4. Describe environmental conditions that influence nutrient deficiencies. • 5. Explain where plants can obtain nutrients if inadequate amounts are present in the soil. • 6. Discuss the nitrogen cycle and its affect on plant nutrition.

5. Terms • hydroponics • immobilization • incomplete fertilizer • inoculation • legumes • macronutrients • micronutrients • mineralization • atmospheric macronutrients • autotrophs • biogeochemical cycles • complete fertilizer • cortex • denitrification • fertilizer • filler • fixed

6. Terms cont. • prokaryotes • rhizobia • secondary macronutrients • soil • symbiosis • translocation • nitrogen assimilation • nitrogen cycle • nitrification • nitrogen fixation • pH • plant tissue test • primary macronutrients

7. What are the nutrients needed for plant growth? • Plants need a variety of nutrients in order to survive and carry on the necessary metabolic processes of life. Plants require water, carbon dioxide, oxygen, and a variety of essential minerals in order to survive. • A. About 80–85% of the weight of a fresh plant is water. The remaining part of the plant contains elements that are absorbed through the roots and used for plant growth.

8. B. Plants receive most of the nutrients that they need from the growing media, or in the case of hydroponics, the nutrient solution that the roots are exposed to. In order to maintain healthy plants, a grower must provide the right type and amount of nutrients to the media so that the plants can absorb the nutrients and grow. • C. Plant nutrients can be divided into two groups, macronutrients and micronutrients.

9. D. Macronutrientsare needed in large quantities and include atmospheric, primary, and secondary elements. • 1. Carbon, hydrogen, and oxygen make up about 90–95% of the weight of the dry matter. These three atmospheric macronutrientsare nonminerals. Plants acquire carbon, hydrogen, and oxygen from carbon dioxide (CO2 ) and water (H2 O) through the process of photosynthesis. The rest of the dry weight is made up of minerals. • 2. The primary macronutrientsare nitrogen (N), phosphorus (P), and potassium (K). • 3. The secondary macronutrientsinclude calcium (Ca), magnesium (Mg), and sulfur (S).

10. E. Those nutrients that are needed in smaller or trace amounts by the plants, but are still essential to plant growth are called micronutrients. The micronutrients are boron (B), copper (Cu), chlorine (Cl), iron (Fe), manganese (Mn), molybdenum (Mo), and zinc (Zn). • F. A soil test can be performed on the soil or a plant tissue testcan be performed using the tissues of a plant to determine which nutrients are present or deficient (absent or lacking). When nutrients are deficient in the soil, the plant growth is adversely affected. Oftentimes, plants visibly show a nutrient deficiency by turning colors. When nitrogen is deficient in the soil, a plant’s older leaves will start to turn yellow (chlorosis) and eventually die. A plant will show purpling in the stem or leaf when phosphorus is deficient in the soil. Burning or scorching of the leave’s margins may indicate a potassium deficiency.

11. G. Because macronutrients are needed in larger quantities they are usually the ones that are the most limiting to plant production and thus are the ones that producers will add to their crops. • H. Mnemonics (pronounced ni-mon-iks) is the art of improving the memory using a formula. A mnemonic formula has been developed to aid in recalling all sixteen elements. Carbon (C), Boron (B), Hydrogen (H), Oxygen (O), Phosphorus (P), Potassium (K), Nitrogen (N), Sulfur (S), Calcium (Ca), Iron (Fe), Magnesium (Mg), Chlorine (Cl), Manganese (Mn), Molybdenum (Mo), Copper (Cu), Zinc (Zn). • The following mnemonic can be used to help remember the sixteen elements: C. B. HOPKiNS CaFÈ Mighty good Closed Monday Morning See You Zen.

12. Why do plants need nutrients? • In order to be considered essential, an element must meet the following criteria: (a) absence of the element results in abnormal growth, injury, or death; (b) the plant is unable to complete its life cycle without the element; (c) the element is required for plants in general; and (d) no other element can serve as a complete substitute.

17. Where do plants obtain nutrients and how do they absorb the nutrients? • Nutrients are supplied through the growing medium or nutrient solution. Plant analysis can provide very valuable information to the grower as they make management decisions. When asked what plants need to grow, most people would respond with water, sunlight, and soil. In all actuality, soil is only one type of media that can be used to grow plants. There are a number of substances that allow plants to grow. • A. Soilis the outer portion of the Earth’s crust that supports plant growth. Soil contains air, water, minerals, and organic matter. • B. A Soilless medium (one that contains no topsoil) can be used to grow plants since plants need the minerals and water from the medium. Examples include perilite and vermiculite.

18. C. Hydroponicsis a method of growing plants in a nutrient solution. The plants in a hydroponics unit could be supported in a sand or gravel substrate for support or the roots could be left bare. With bare roots, the plants’ root system can float in the nutrient rich solution, or the nutrients could be sprayed directly onto the roots. • D. These essential minerals are dissolved in a water or aqueous solution. This solution moves from the soil or surrounding environment through the root into the xylem. Translocationis the movement of organic molecules throughout plant tissues. Most of the water and nutrients are absorbed through the root hairs. With the help of adhesive and cohesive properties of water, the solution moves upward against the force of gravity to the various parts of the plant usually the leaves. Most of the water is lost through transpiration via the stomata. This also aids in the movement of water from the roots to the rest of the plant. Metabolic processes use the nutrients for a variety of purposes.

19. What environmental conditions influence nutrient deficiencies? • A. The measure of alkalinity or acidity of a substance is known as pH. The pH scale runs from 0 to 14, with 0 being extremely acidic, 7 as neutral, and 14 as extremely basic. • 1. Changes in pH can be made by adding sulfur or gypsum to lower pH (make more acidic) and by adding limestone to increase pH (make more basic). Generally plants grow best within the pH range of 5.5 to 8.0. • 2. The pH value of soil is important to agriculturists because certain nutrients become unavailable to plants if the pH value is too high or too low. The amount of nitrogen, phosphorus, and potassium that are available is dependent upon soil pH.

22. B. The soil must be of good tilth and permeable enough for roots to expand and feed extensively. A crop will develop a root system 6 feet or more in depth in some soils to get water and nutrients. A shallow or compacted soil does not offer this root feeding zone. Wet or poorly drained soils result in shallow root systems. • C. Cool soil temperature slows organic matter decomposition. This lessens the release of nitrogen, sulfur, and other nutrients. Nutrients are less soluble in cool soils, and that increases deficiency potential. Phosphorus and potassium diffuse more slowly in cool soils. Root activity is decreased. • D. Acid soil conditions reduce the availability of calcium, magnesium, sulfur, potassium, phosphorus, and molybdenum, and increase the availability of iron, manganese, boron, copper, and zinc.

23. E. Insect damage is often mistaken for deficiency symptoms. Examine roots, leaves, and stems for insect damage that may look like or may induce a nutrient deficiency. • F. Close study will show the difference between plant disease and nutrient deficiency. • G. Dry soil conditions may create deficiencies such as boron, copper and potassium. Drought slows movement of nutrients to the roots. • H. Soluble salts and alkali are problems in some areas. They may cover only part of the field. They are usually present where a high water table exists, where salt water contamination has occurred, or where poor quality water has been used for irrigation.

24. I. Herbicides and mechanical controls are more important today than ever before. Weeds rob crop plants of water, air, light, and nutrients. Some weeds may even release substances that inhibit crop growth. • J. Some soils develop hardpans (compaction) and require deep tillage. This requires more phosphorus and potassium to build up fertility. • K. Row width, spacing of plants in the row, and number of plants per acre have important effects on yields. • L. Irrigation water can contain nitrate, sulfate, boron, potassium, bicarbonate, chlorine and other salts. A water analysis should be used to modify production practices for utilization of various water sources. • M. Other pollutants can also cause nutrient deficiencies as well as other problems.

25. If insufficient levels of nutrients are found in the soil, where do the plants get the nutrients that they need? • A. Nutrients may become depleted by growing crops. Since crops are harvested, the organic matter does not break down and return to the soil to replenish the nutrients. Additionally, nutrients might leach or run out of the medium via water, causing the grower to continually add the nutrients. The nutrients can sometimes be present in the growing medium, but they are not available for the plants to take up into their roots because the pH level in the soil is not conducive to plant growth. Plants have different pH requirements.

26. B. As a result, growers must add artificial fertilizers, manure, or other organic matter to the soil or nutrient solution for the plants to use. Soil or plant tissue tests should be conducted before fertilizers are added. • 1. A fertilizeris any material that is provided to plants to supply the nutrients needed for plant growth. Fertilizers vary in the components they contain, the way they are applied, and the function they serve. • 2. When choosing a fertilizer to use, one should always look for the fertilizer analysis on the bag or box. The fertilizer analysis states the percentage of primary nutrients (nitrogen, phosphate, and potash) present in the fertilizer. The analysis is written as 3 numbers, for example, (15-10-26). The numbers, always in this order, represent the percent of nitrogen, phosphorus, and potash, present in the fertilizer. So the example above has 15% nitrogen, 10% phosphate, and 6% potash.

27. Fillersare made up of the remaining essential plant nutrients and are used to ensure a more even application of the fertilizer. The amount of filler in the above example can be calculated: 100-(15 + 10 + 16) = 59. This means that 59% of the fertilizer is filler. • 3. If a fertilizer contains all three primary nutrients, it is called a complete fertilizer. If a fertilizer is lacking any of the three primary nutrients, it is an incomplete fertilizer. • C. Local fertilizer and horticulture companies employ specialists that can help in determining an appropriate nutrient program based on your varying conditions. • D. Remember that high yields are not the only goal of a plant nutrition program, but that overall quality and economics play vital roles as well.

29. What influence does the nitrogen cycle have on plant nutrition? • A. The nitrogen cycleis the recycling of nitrogen as it moves between the abiotic (non-living) and biotic (living) parts of the environment. The largest proportion of nitrogen at any given time is found in the biomass or in dead organisms. • 1. Every nutrient that an organism uses is recycled throughout the ecosystem. These cycles are referred to as biogeochemical cycles. The water cycle is another well-known example of this process. The phosphorus and potassium cycles act in a similar manner. • 2. The key concept is that no element is lost or consumed in the environment, but rather it changes form and moves between the abiotic and biotic components of the environment and is recycled.

31. B. Nitrogen is essential to all living organisms because of its use in the synthesis of enzymes, proteins, and chromosomes. In plants, nitrogen is an important component of chlorophyll. • C. Plants absorb nitrogen as inorganic nitrate ions (NO3 - ) and in a few cases as ammonium (NH4 + ) or amino (NH2 + ) ions. • 1. The positive charge of ammonium causes it to easily bond to clay soils making it unavailable. • 2. The negative charge of nitrate causes it to easily leached away; this can become a cause for water contamination. High nitrite levels in water can cause illness especially in children. • 3. Nitrogen that is absorbed by the plant is reduced to N2 - ,NH - or NH2 which then is synthesized into more complex compounds and amino acids and proteins. • 4. Nitrogen assimilationis the incorporation of nitrogen into organic cell substances by living organisms.

32. D. Most natural soil nitrogen is in the organic form meaning that it is combined in some manner with carbon. Manures, decomposing organic matter, and urea are all forms of organic nitrogen. These must be oxidized before plants can use them. • 1. The transformation of organic matter to the inorganic or mineral form (NH4 + , NO2 - ,or NO3 - ) is called mineralization. • 2. Immobilizationis the conversion of nitrogen from an inorganic or mineral form to an organic form. This process occurs naturally during initial decomposition or nitrogen can be immobilized during chemical fertilizer composition to make it available to the plant at a later time.

33. E. Nitrogen fixationis the conversion of atmospheric nitrogen into oxidized forms that can be assimilated by plants. • 1. A symbiotic relationship that exists between bacteria and legume plants is utilized to convert nitrogen gas (N2 ) to ammonium ions (NH4 + ) that are usable to plants. • 2. Certain blue-green algae and bacteria are capable of biochemically fixing nitrogen. • 3. Legumes such as beans, peas, alfalfa, clover, chickpea, and soybeans are able to take in the nitrogen through their roots. Legumesare plants that are members of the family Leguminosae; they have the characteristic capability to fix atmospheric nitrogen in nodules on their roots with the aid of certain bacteria.

34. 4. Aquatic ferns and Gunnera macrophylla (tropical plant) form symbiotic relationships with blue-green algae to attain their nitrogen. Acacias, mesquites, alder, buckthorn, Casuarina, and paloverde plants also rely on bacteria. Lichens form a relationship with cyanobacteria which enables them to be one of the first organisms seen in primary succession. Cyanobacteria also aid the water fern Azolla and cycads. • 5. Azotobacter, Beijerinckia, Klebsiella (some), Cyanobacteria (some), Clostridium (some), Desulfovibrio, Purple sulphur bacteria, Purple non-sulfur bacteria, and Green sulphur bacteria are free living nitrogen fixing organisms. Those that form symbiotic relationships with other organisms include Rhizobium, Frankia, and Azospirillum. • a. All nitrogen fixing organisms are prokaryotes. • b. Prokaryotesare one celled organisms that lack membrane bound organelles and a central nucleus.

35. 6. Rhizobiaare aerobic bacteria that are naturally found in soils. They cause excessive growth in the form of nodules on the cortex of the roots of legumes. Cortexis an outer layer of tissue in the roots of dicotyledonous plants located between the stele and epidermis. • a. Rhizobia are autotrophic bacteria. Autotrophsare organisms that create their own food rather than obtaining it from other organisms. They get their energy from the oxidation of mineral constituents, as well as carbohydrates from their host plant. • b. The rhizobia and the plant live in a symbiotic relationship. Symbiosisis where two dissimilar organisms live together in a mutually beneficial relationship.

36. 7. The soil bacteria enter the plant through openings in the root hairs and extend into the cortex (outer cells) of the rootlets. This causes the growth of nodules to occur and is where nitrogen fixation occurs. • 8. The rhizobia “fix” atmospheric nitrogen (N2 ) by converting it to ammonia (NH4 + ). • a. Fixedis when a compound resists decomposition. • b. Ammonia is then converted to nitrite (NO2 - ) and then to nitrate (NO3 - ). This process is known as nitrification. • c. Nitrite is toxic to higher plants, but the conversion from nitrite to nitrate occurs so quickly that no nitrite buildup in the soil or plant roots occurs. • 9. It appears that nitrogen, in the form of nitrate, is then diffused through the walls of the bacteria located in the root nodules and is absorbed by the host plant through the nodule root system.

37. F. To complete the nitrogen cycle, nitrogen can be removed from the soil by the uptake of nitrogen by the plant, losses due to leaching, or by denitrification. • 1. Denitrificationis when nitrates are converted to nitrogen gas. • 2. Denitrification occurs in soils that have no oxygen because of saturation from water; the nitrogen is then lost to the atmosphere. • G. Seeds are inoculated with rhizobia in order to increase the bacterial populations in the soils of leguminous plants. Inoculationis the bulk treatment of leguminous seeds with rhizobia. • 1. Increased rhizobia populations will “fix” more nitrogen, making more nitrogen available to the plant. • 2. The increased supply of nitrogen by rhizobia lessens the need for supplemental nitrogen and generally increases the yield and quality of crops. • 3. However, these bacteria are crop-specific, with certain strains affecting only certain crops.

38. H. Factors affecting rhizobium activity include: • 1. As soil temperature increases, soil bacteria become more active. This explains why nodules are not present in legumes during the winter months. Research has also shown that nodules slough off immediately after crop harvest, and then begin to return several days after harvest. • 2. Their populations are increased by soil moisture, soil oxygen, and soil aeration. • 3. A pH of 6.0–8.0 supports the greatest rhizobia populations. • 4. Also, the greater the exchangeable calcium in the soil, the greater the soil bacteria populations. • I. Nitrogen can also be added to the soil by lightning, application of commercial fertilizers, and through decomposition of dead organisms.

41. Review/Summary • What are the nutrients needed for plant growth? • Why do plants need nutrients? • Where do plants obtain nutrients and how do they absorb the nutrients? • What environmental conditions influence nutrient deficiencies? • If insufficient levels of nutrients are found in the soil, where do the plants get the nutrients that they need? • What influence does the nitrogen cycle have on plant nutrition?