The wood column is fixed at its base and free at its top. Determine the load P that can be applied to the edge of the column without causing the column to fail either by buckling or by yielding. Ew = 12 GPa, sY = 55 MPa.
Spring 2016 CSES 5030 Dr. Monks class Advanced Crop Science EXAM 2 Study Guide Powerpoint: Crop Rotation & Cover Crops by Dr. Delaney Crop rotation: 1. Crop rotation was practiced a long time ago a. Examples i. European study ∙ Field trials over 3 years ∙ Fall: wheat/rye; Spring: Oats, Barley and peas (legume) ∙ Food for humans (wheat, rye, beans, lentils) and oats and barley for horses ii. Thomas Jefferson & George Washington 2. Why crop rotation a. Positives i. Disease control ∙ foliar & root diseases ∙ nematode control ii. Weed Control ∙ some are easier to control than others ∙nutsedges, bermudagrass, concklebur iii. Soil quality ∙ OM is improved along with tilth ∙ Tilth: the condition of tilled soil, especially in respect to suitability for sowing seeds. iv. Labor and equipment management becomes v. Cash flow & risk management ∙ Wheat and corn have earlier seed fill, so can make money in-between harvests vi. Yield goes up sometimes b. Negatives i. equipment costs and damage iv. markets are different ii. traditions v. landowner agreements iii. management and timing may vi. extra management for more become a hassle crops 3. Why does crop rotation systems work a. "Starving out" diseases & insects b. OM Placement and depth - encourages different patterns of roots c. Soil micro and macro organisms are influenced why the increased OM d. Different herbicide modes of action can be used to help curb weed resistance 1 4.Bad crop rotations: a. (soybean with peanuts) legumes and legumes i. low C:N ratio ii. sharing of same diseases iii. both are taproot systems 5. Long-term Rotations a. AL soybean acreage and yield as an example ∙ 1980s decreased acreages and yield because of stem canker b. perennial crops partnering with cash crops i. midwest: alfalfa, then corn ii. south: "sod-based" bahia grass then peanuts iii. hardpan is broken up by perennial deep rooting systems iv. OM increases because of the high amount of residue v. control of nematodes and diseases while increasing income vi. alternating grasses with broadleafs is a good method 6. 7. Cover Crops 1.What is it a. a crop that is not intended to be harvested for feed or sale b. has the purpose of benefiting the soil and the other crop in one or more ways 2.Why do we use cover crops a. controls erosion b. soil and water quality improvement (2-3 yrs) c. increased water infiltration d. nutrient loss is minimized e. legumes give Nitrogen f. habitat for wildlife 3.Maximizing biomass for the maximum in returns a. soil fertility and pH b. seed quality c. incoculate specific and fresh legumes d. early planting e. stand establishment is important f. termination date 4.Residues and Soil Carbon a. the most critical surface soil effects are in the Southern US 5.How to select cover crops: a. What is the summer crop, then what to plant as the cover crop i. cotton --> small grain/legume ii. corn --> rye/triticale/legume iii. peanut --> any small grain - no legume iv. soybean --> any small grain - no legume v. veggies --> rye/triticale/legumes b. What is the experience level of the producer and their cost tolerance 2 i. none: oats, triticale and wheat should be planted ii. some: rye iii. a lot of experience: rye and fertilizer or legumes 6.Planting methods of cover crops a. NOTE: NEVER plant main crop when cover crop still green, wait 2 wks b. Preferred method of Drilling AKA precision planting i. no-till drill: expenses, time and weight ii. conventional: requires tillage usually and must monitor depth for small seed c. Broadcasting seeds - increase seeding rates, aerial broadcast i. do prior to: 1. peanut harvest 2. cotton 3. soy defoliation ii. coincides with fall time Phosphorous and Potassium application iii. this is riskier and depends on rainfall 7.Cover crop seed costs a. legumes are twice as expensive as others b. clover biomass i. plant before frosting date and best return 8.Fertility of cover crops a. depends on what crop you are using b. usually assume nutrients not taken out of cash crop i. Nitrogen in cover crop legumes: ii. fixed Nitrogen from biological sources iii. Nitrogen contribution is highly variable based on: iv. species, weather, dry matter production, N content, existing soil N , time of termination v. MUST synchronize N release with N uptake of cash crop vi. a little bit of Nitrogen can make a big difference c. Terminating cover crops i. factors to consider: 1. timing 2. method 3. use growth stage rather than planting date ii. influenced by: 1. soil temp, soil moisture, weed suppression, allelopathic compounds, N release from residues 2. pest potential 3. disease potential iii. allow 2-3 weeks to allow rainfall to replace usage iv. mineralization and immobilization v. methods: 1. chemical 3 a. glyphosate - roundup, glufosinate - liberty, tank mixes- residuals 2. physical - a. tillage, b. mowing, c. mechanical rolling - residue lays flat on soil surface, provide max soil coverage 9.Cover crops a. Cereal Rye i. stemmy, slow to break down, winter annual grass, rapid growth, tolerance high of low fert and ph, allelopathic, deep rooted b. Winter wheat i. winter annual, produces good dry matter but manageable c. oats d. winter annual grass, i. fibrous root system, tolerant of low fert and ph, winterkilled e. Crimson clover i. winter annual, upright easy to handle, legume f. Hairy vetch i. winter annual, winter hardy, vine (hard to manage, hard to kil BEFORE bloom), legume g. Sun hemp i. summer annual, newer, planted after corn h. Tillage radish i. cool season, deep rooted, fast grower ,plant after summer crops, natural nematicide, cavity when roots die i. Can lessen leaching of Nitrogen j. Winter cover crops: i. lessen effects of Fe chlorosis in high ph soils ii. moisture related (Fe chlorosis), nitrates trigger it, iii. grass cover crops may incrase moisture of soil and lessen nitrates 8. Word Documents Notes: Seed classes based on temperature requirements and plant adaptations to do some plants to tolerate freezing temperatures. 9. Classes of seed based on requirements: temperatures 1. Cool temperature: a. Required: do not germinate at ++ temps, lettuce and radish b. Tolerant: temperate zone plants, 4 i. Wide temperature ranges for the germ ii. Cold crops 2. Warm temperature: a. Required: do not germinate at lower temperatures (require ++ temps) i. Tropical and sub-tropical (near equator, south Florida is subtropical) ii. Can be injured at the lower temps 3. Temperature requirements alternate: a. Must have alternating temperatures to break dormancy of the seed 10. Plant "barriers" to "harsh" temperature exposure: 1. Physical barriers: a. Enhancement of heat retention and reduce penetration of the cold: i. Overwintering stage b. Plant architecture & canopy c. Plant population d. Thickened structures: maintenance of internal temperatures during short durations, i. Especially root systems (example: tillage radish) 2. Soil: a. Mulch effects: insulate soil and the roots from rapid changes b. Color differences, texture differences, etc. 3. Question: What about leaf characteristics like angle, color, pubescence, age 4. Question: In the spring, which will heat up faster- no-till soils or conventional-tilled soils 11. 12. Cold (freezing temps) toleration adaptations of some plants: 1. 2 cell level responses that enable plants (cold plants) to tolerate these temps: a. -- decrease of internal freezing point i. solute concentration in the INTRAcellular spaces increase (sugars) b. solution movement out of the cell into the INTERcellular areas i. plasmolysis (desiccation) is tolerated by some plants within the cell moreso than other plants ii. fluidity of the membrane can be increased when the membrane (plasma) is changed with an increase in unsaturated fatty acids 1. pliable cell wall 2. membrane more permeable 13. 5 14. Environmental factors that add to plant stress 15. Water: 1. Processes are affected by water, temp, and nutrient stresses: a. seed germination, growth processes, individual survival, reproduction 2. "Our interests" a. availability amount, timing of the stress, how long it lasts, water amounts during season, and the response from the plants 3. Determines how much water is available: a. soil texture and structure i. coarser versus finer soils 1. field capacity potential, 2. pore space: clay> silt>sand 3. amount held: clay> silt >sand 4. movement in and out of the soil: sand> silt > clay 5. gravitational and capillary movement a. adhesion versus cohesion b. events of the water i. application- fate of the water: run off, percolation through soil ii. cover crops, tillage of land, quality of the water applied c. roots i. structure type ii. pressures from pathogens iii. age iv. health 4. Cover crops: a. lessen run off b. open root channels and pores c. long term soil aggregation stablization d. uptake of water and nutrient increases 5. Water Quality: a. ph of soil b. salinity: i. ++ osmotic potential: lessens water availability to the plants ii. needs more energy from from plant to take in water iii. ion concentration increases and lessens bio activity and CAN BE toxic iv. Sodium and Magnesium INDUCED Calcium deficiency 1. Na or Mg CAN replace Ca in the cell membrane structures c. ***sensitivity of crop to bad water quality i. (most sensitive) clover > corn, soybean >wheat, oats > cotton, peanuts (least sensitive) ii. metals become more available at lower ph and become a problem 6. Health and root area of ROOTS a. structure type: fibrous vs. taproot b. pathogen pressures: nematodes, insects, diseases 6 c. age of root: older ones have LOWER uptake capacity d. health of root : declining of roots causes less function 7. NOTES: a. Drought ++ --> WATER POTENTIAL ---- but ABA(abscisic acid - controls hormones) +++ AND stomatal resistance ++++ as stomata close b. Rain: Water potential ++++but ABA --- and stomatal resistance --- as stomata open 8. Water stress regulation: a. Osmotic adjustment: i. UP regulate potential of solutes to make the adjustments to the osmotic potential ii. keeps a positive turgor pressure and reduces wilting b. Stomatal control: i. guard cells have chloroplasts ii. chloroplasts make sugars and actively pump potassium ions iii. reduces the transpirational stream at night and during droughts iv. leaf temperature increases internally v. K status is CRITICAL 9. TOO MUCH WATER a. ATP energy production --- b. ethylene is increased c. system of root declines and is re-adjusted d. the canopy of the vegetation is adjusted, too i. corn: 2to4 days flooded; 1/3 yield loss ii. soybean: 48 hours flooded, bacteria DIES, diseases +++ iii. cotton: 36-48hours, perennial so kind of tolerant iv. peanut: fair tolerance depending on growth stage 10. H2O pathway a. What happens in the plants with water stress b. short term: stomates close, roots send signals and it makes it harder to pull water in c. reduced surface area on leaves d. metabolic acclamation e. PERMANENT wilting point f. increased root to shoot ratio 16. 17. Temperature 1. Processes affected: a. germination of seeds b. processes of growth c. survival d. reproduction 2. Interests: a. soil temp 7 b. ambient temp c. duration of extreme temps d. timing and changes in temp e. graduients of temp 3. Processes involved in germination responses: a. deterioration of seeds - TEMPERATURE DEPENDENT b. seed dormancy is inversely related to temperature c. CONCEPTS: generalized: i. each species has their own functional temperature range ii. plants can vary in their responses 4. Plants exposed to temperature: 5. plant architecture a. High temp: i. lower leaf area index ii. # of stomata lessen on BOTTOM of leaf iii. stomates become larger and opening of stomate changes iv. petioles elongate to increase leaf separation b. Low temp: i. rosette, closer to the soil ii. root structures thicken, seed coats thicken 6. leaf angle, olor, pubescence, 7. environment 8. plasticity THRESHOLDS OF PLANT TEMPERATURE 9. cell changes: a. photosynthesis reduced: i. chloroplasts are damaged, enzyme activity lessens, b. chlorophyllase activity +++, --- in chrlorphyll production c. balance of metabolites produced changes d. phytohormones increase: abscissic acid and ethylene e. growth promoting hormones ---- : cytokinins, auxins, gibberlic acid f. internal transport adjusted 10. other responses to temperature extremes a. plant cell membrane characteristics b. fluidity of membrane c. saturated lipids +++ = tolerance to higher temps i. carotenoids protect the integrity of the membrane 1. reactions in plant energy may become too high so this helps stabilize voltage regulators and plant turns white (carotenized bleaching) d. root life span 11. Vernalization a. causes a reduction in RNA levels of repressors which remains THROUGHOUT the rest of development b. genetically controlled 8 c. PERMANENTLY down regulated d. FLC : flowering locus C 12. Processes affected by hot temperature: a. pollination b. carbohydrate and production c. Silk and pollen activity: i. example in corn: 1. silk formation is delayed 2. dessication of silk occurs 3. pollen production lessens 4. pollen shed lessens 5. viablity of pollen also is reduced 13. Temperature related seasonal plants: a. eastern asia warm season perennial: Lespedez cuneata i. +++ temp = +++activity b. native North American cool season annual Lupinus perennis i. +++ temp = --- activity 14. Climate change affects nodulation: a. pushes plants north towards cooler (cold loving plants) 15. Correlating plant growth with Temperature: a. GDD : growing degree days i. adjust planting date not degrees ii. ex cotton: base temps 60F iii. KNOW THIS: GDD60= max+min temps DIVIDED BY/ 2 - minus 65 =DD60 (per day) iv. helps predict plant maturity 9