ESS Exam 4
ESS Exam 4 ESS 210 001
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This 5 page Study Guide was uploaded by Michaela Humby on Thursday April 7, 2016. The Study Guide belongs to ESS 210 001 at University of Tennessee - Knoxville taught by Andrew Conrad Sherfy (P) in Fall 2015. Since its upload, it has received 40 views. For similar materials see Intro to Soil Science in Environmental Science at University of Tennessee - Knoxville.
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Date Created: 04/07/16
Exam 4 Study Guide Soil Nutrient Cycling Why is phosphorus a necessary plant nutrient? What forms are majority of the soil phosphorus in? What are potential phosphorus losses from soil? Why is phosphorus of concern to the environment? The energy currency in the cell a. ATP -- adenosine triphosphate b. DNA--deoxyribonucleic acid c. RNA--ribonucleic acid enhances many aspects of plant physiology d. photosynthesis, maturation e. N-fixation, flowering, fruiting, seed production P Deficiency Hard to recognize but: ◦ stunted, thin-stemmed, spindly ◦ dark, bluish green foliage P is mobile in the plant, moves from older plant parts to newer, younger plant parts Why is Phosphorus Unavailable? Most soils naturally low in available P, additional P added turns into insoluble forms quickly. Highly weathered soils in warm, humid and subhumid regions ◦ Little capacity to supply P for plant growth ◦ Why? Extensive losses during intense weathering Undisturbed ecosystems contain enough P in plant biomass and organic matter ◦ If undisturbed, sufficient P levels How Does Eutrophication Occur? Low soil P levels means greater application rates ◦ Fertilizer P bound in unavailable forms ◦ Therefore higher rates are needed Manures & biosolids ◦ Applied at N rate ◦ Overapplication of P Erosion must be minimized or excessive aquatic P levels will occur Practical control of P availability Saturate the P-fixing capacity ◦ If done at once, erosion must be kept in check ◦ Once saturated, fertilizer P will be available allowing lower application rates Placement of fertilizer P ◦ If placed as starter, more will be available and less lost to erosion Combine ammonium and P fertilizers ◦ At higher pH ammonium will increase availability of P Choose P efficient plants ◦ Mycorrhizal uptake ◦ Plant efficiency Increase cycling of organic P ◦ Crop residues ◦ Cycling provides constant availability Control soil pH ◦ |b| pH 6-7 is best ◦ Will promote P availability Why is potassium a necessary plant nutrient? f. Third most limiting nutrient in agricultural crops - 1 to 4% of plant dry weight g. Important for: h. osmotic regulation, photosynthesis, starch formation and sugar translocation i. Helps adapt to environmental stress j. drought tolerance, disease resistance, insect tolerance k. Animals l. regulates nervous system, circulatory system What forms of potassium can by up taken by plants, what forms are majority of the soil potassium in? K Availability and Cycle Found at high levels in soils ◦ up to 50,000 kg/ha Most held rigidly as part of primary minerals or fixed A large portion is insoluble and unavailable to growing plants No organic forms + Cycle is mostly uptake and return of K to soil solution What are potential potassium losses from soil? K Deficiency Symptoms Leaf tips begin to yellow and die Can form white necrotic spots along leaf margins Reduced drought tolerance Increased lodging K is mobile, seen in older tissues K losses Considerable amounts of K are lost to leaching ◦ much higher than P ◦ acid soils leach more than neutral Lots of plant uptake… ◦ Luxury consumption occurs with K + Practical Management of K Continuous cropping can deplete soil K Most fertility programs aim for maintaining high levels of exchangeable K in + the soil Liming to pH 6.5 reduces leaching losses Fertilizers supply K as KCl or K 2O .4 Why is sulfur a necessary plant nutrient? Have a general understanding of the sulfur cycle, e.g. what form is majority of the soil sulfur in? What are potential sulfur losses from soil? How does sulfur get in the soil? Amino acid constituent m. Necessary for some proteins Aromatic character of cabbage and onions n. Require large amounts of S Plant foliage contains up to 0.45% S, one tenth of N S deficiencies Spindly, slow growth with delayed maturity Chlorotic Similar to N in deficiency symptoms Changes in pollution led to S deficiencies: ◦ Clean air standardsà SO reduction 2 ◦ High analysis fertilizers no longer contain S No ammonium sulfate or ssp that contained 24 or 12% S Higher yielding varieties have greater S needs Burning of crop residues common in developing countries have greater S fertilizer needs Why is nitrogen important in the soil? What is plant available nitrogen? How much nitrogen is typically plant available at any given time in the soil? How does nitrogen get into the soil? Usually most limiting for plant growth Importance: proteins, chlorophyll, nucleic acids Low N = low yields Total soil N: < 400 to >8000 kg/ha Available soil N = < 5% of total at any time o. Available N = NH 4+ and NO 3 i. only nutrient taken up as cation and anion 2. Atmosphere = 79% N - UNAVAILABLE a. lightning converts small amounts to NH 4+ and NO 2 3. Biological N-fixation (nitrogenase enzyme) a. bacteria only b. symbiotic c. non-symbiotic 4. Industrial N-fixation - Haber-Bosch process a. fertilizers b. N 2 + 3H 2 2NH 3 c. requires inputs of natural gas for H 2nd energy d. high temp and pressure required N Fertilizer Materials Ammonium Nitrate (NH NO ; 34-0-3) Anhydrous ammonia gas (NH ; 82-0-3) Urea [(NH ) 2 2; 46-0-0] Ammonium sulfate [(NH ) SO 4 21-040] Organic sources (1 -12 % N) ◦ manures ◦ sludges ◦ fish and bone meals Understand the nitrogen cycle (e.g. inputs, losses, and transformations) Why is nitrogen of concern to the environment? Why is it important to manage how much nutrients we add to the environment? What are some practical aspects of nutrient management? What is fertilizer grade? How much and in what forms do we typically recommend applying nutrients? Soil Organic Matter How much of organic matter is carbon? C = 45-50% of all organic matter What are the end products of the organic matter decomposition process? + - - 2- CO 2 NH ,4NO , 3 PO2, S4 , H4O 2 Anaerobic conditions: e. CH 4 H 2, NH 3 Microbial biomass Humus What happens to the carbon in organic residues when they decompose? If residue has low N, degrades slowly Residue with high N, degrades quickly Microorganisms require N to make proteins Can’t use the C without the N If C:N > 30, residue is N-deficient If C:N < 20, residue is N-rich If residue C:N > 30 - Net immobilization Residue C:N < 20 - Net mineralization C:N of 20-30 - depends on many factors Practical implications: ◦ composting of high C materials ◦ mulching ◦ surface application of N to soils with wheat residue Factors Affecting Decomposition and Humus Formation Temperature ◦ Cold - low production of biomass, low humus ◦ Temperate - good production of biomass, high humus as go north, humus increases ◦ Tropical - high production of biomass, low humus Moisture High rainfall = high production of biomass Nutrients pH 6 - 8 best poor below 4.5 and above 8.5 Texture clayey soils accumulate more humus. WHY? Tillage Water-logging = high humus What is soil humus and why is it important? What are the different types of humic substances? Humic and non-humic substances Humic Substances f. Very high specific surface area g. Very high CEC h. Very water holding capacity Non-humic i. polysaccharides, other simple C and N compounds How would you suggest to increase or improve soil organic matter content? Source of plant nutrients: N, P, S Soil aggregation CEC and buffering capacity Water holding capacity, air movement, etc... Chelation of metals (Zn, Cu) C supply for microorganisms Surface mulches regulate temperature, moisture Minimize soil disturbance Maximize surface residues minimize tillage increases oxidation of OM keep residues on the soil surface to slow the decay process conservation tillage can increase soil OM levels 0.1% per year perennial vegetation should be encouraged
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