Sharing the results of “in-class exercise” of Sept. 14

1. Sharing the results of “in-class exercise” of Sept. 14 • Remember the scale . . . Completely agree . . . . . Completey disagree 1 . . . . . . . . . . . . 5 . . . . . . . . . . . . 10 • Science education is important – 24 students marked “1” w. ave. of 1.6 • I have a good foundation in science – 9 students marked “1” w. ave. of 2.6 • My science education is typical – mid-scale “5” received more marks. Ave. of 47

2. Sept 14 “in-class” cont. • 4) More science could and should be taught K-12. • 15 chose “1”, with ave. of 2.4 • Which areas merit more attention? • Biology – 11, Chemistry – 9, Physics – 7, Agriscience – 6, Environment – 4, Ecology – 3, with Anatomy, Botany, Earth Science, Meteorology, “All” receiving “2” votes

3. Obs. on “in-class” Sept. 14 • Quite apparent that students tried to respond using good English. • Several students pointed out that science teaches students “critical thinking skills.” • One statement merits some discussion - “not everyone meant to be a scientist”

4. Crop Physiology – Ch. 3 -71 • How can we harvest the sun more efficiently, while using/conserving the natural resources of soil and fresh water in the most prudent manner possible?

5. Yield -71 • Product per unit area (per unit time), usually as dry matter, or specified moisture content (e.g., corn grain yield is calculated at 15.5% moisture.)

6. Types of Yield -71 • Biological = total dry matter produced per plant or per unit area, everything, including roots. However, often, just the above-ground parts are used. Need to check. • Economic = weight or volume produced per unit area of the marketable portion, at standardized market moisture content.

7. Harvest Index ! -72 • Ratio of economic yield to biological yield. • **** This is the characteristic that plant breeders have modified to increase economic yield. • Meanwhile, biological yield has changed very little, if any.

8. Components of grain yield -72 • YIELD = • Plants/area • Heads/plant • Seeds/head • Weight/seed • * increasing one,usually results in decrease in one or more of the others

9. Plant Growth Curve -72

10. Plant Growth Regulators – 72+ • Auxins – cell elongation – “master regulator,” e.g., IAA • Gibberellins – elongation, but chemically different than auxins, e.g., gibberellic acid • Cytokinins – cell division, differentiation, e.g., zeatin • Growth Inhibitors – inhibit growth and development, e.g., abscisic acid, or phosphon • Ethylene – hastens fruit ripening

11. Demo results, to be reported later • The exercises described on pp 73-76+ are expected to be reported in time for Quiz 3, via lecture.

12. Photosynthesis and Respiration -77

13. Photosynthesis -77 • 6CO2 + 6H2O + light (in presence of chlorophyll) produces . . . C6H12O6 (sugar) + O2

14. Respiration - 78 • Oxidative breakdown of organic compounds • Energy (stored in high energy bonds–ATP) and growth are products of respiration

15. Ps. and Resp. compared -78 PS . Resp. in green cells in every cell occurs w/light all the time uses H2O and CO2 burns sugars releases O2 releases energy weight increases weight decreases accumulates food breaks down food

16. Terminology - 78 • Net Photosynthesis (Pn), also NAR = Photosynthesis minus respiration • Leaf Area Index (LAI) = ratio of total leaf area of crop plants divided by land area occupied • Canopy = aerial portion of plants

17. PS – Respiration = NAR

18. Sunlight, factors • 1) Quality (think of rainbow) • 2) Intensity (interception) • Efficiency of interception is a sub-factor • 3) Duration (daylength, photoperiod) • Compare June 21 daylength for Miami and New York City – which city has longer days?

19. The visible light spectrum -79

20. Plant tissue and light quality • Wavelengths absorbed – blue and red • Wavelengths reflected – green and yellow • Wavelengths which penetrate leaves and inhibit germination of species which require light for germination – far-red

21. Light quality -80

22. Importance of good plant distribution within canopy • 1) light needed for Ps • 2) inhibit germination of weed species needing light • 3) reduce moisture loss through evaporation • 4) for species depending on N-fixation, shading the soil benefits N-fixing bacteria

23. Example of light interception benefits - 80 • Table 6 – Light interception/soybean yields • Row width - % light intercept. - % yield in. • 20*” 84 115 • 40*” 75 100 * = Same population densities

24. Species differ in light utilization

25. Comparisons of C3 and C4 -83 • C3 plants C4 plants Primarily cool season Prim. warm season Max of ~60% intensity Uses 100% intens. Low C02 uptake Higher CO2 uptake Lower yielding Higher yielding Less efficient water use Higher ef. H2O use

26. Notes on carbon fixation (Ps) • Calvin cycle (all plants) produce 3-carbon chain products – known as C3 species • Hatch & Slack (discovered another pathway in 1960s) in tropical grasses+, producing 4-carbon products – known as C4 species • Increasing levels of CO2 help C3 close Ps gap with C4 species.

27. Leaf angle and light interception - 82

28. Chalkboard explanation • Gain from upright leaves – diminishing returns from higher sunlight • Light demo (with leaves)

29. Remember: one leaf shape does not fit all farmers • Upright leaf varieties have allowed farmers to increase yields provided that they had the nutrients and water • Limited input farmers (e.g., developing world) get higher yields from traditional, more-horizontal leaf varieties

30. Mid-Chapter review • There are many practical applications of the info on auxin effects (produced in rapidly growing tissue): • 1) promotes elongation • 2) inhibits lateral bud development – (lateral buds have three options – • Develop into stem replacement • Develop reproductive organs (seed) • Remain dormant) • ****Destroyed by sunlight (see next)

31. Review, continued • Applications: • 1) population densities result in shading differences – and consequences – • - barrenness, if too high a density (e.g., corn) • - excessive branching (e.g., soybeans) if density too low • 2) make your landscape plants and trees “bushier”

32. Transport and Uptake - 83 Defined as “movement of organic and inorganic solutes from one part of plant to another” Amino acids (formed in leaves and roots from sugars and nitrogen) move in phloem Water and minerals move in xylem

33. Transpiration/Evapotranspiration -84 Keeps the plants cool – necessity (graph) Requires considerable water to evaporate Evapotranspiration adds the evaporation component. Good plant spacings minimize evaporative losses, keep soil from overheating – esp. imp’t in legumes which rely on N-fixing bacteria

34. Water requirement (ETR) - 85 Also known as “evapotranspiration ratio” Defined as “units of water to produce unit of dry matter” Varies from about 325 to 1500+ Sorghum and millets being in 325 range (C4 species) Rice at upper end of ETR (C3 species) *** When ETR is divided by harvest index (HI) in grain crops, we get the units of water to produce unit of grain (e.g., 325 / 0.50 = 650 for most efficient crops)

35. Reviewing imp’t concepts Plant breeders, working on grain yield improvement, have changed the harvest index (esp. wheat and rice, but others too). Most species had HI of 0.20-0.25 when pl. breeders started making crosses and selections for higher grain yield. Now, those improved crops are in range of 0.50 His. Theoretical maximum =~ 0.60

36. So, what constitutes drought tolerance then? Several aspects: C4 species use water more efficiently – lower ETRs Perennial crops have dormancy mechanism Indeterminate more tolerant than determinate species (Indeterminate have longer flowering period – the most susceptible stage to moisture stress) Plant crops during cool season to avoid heat Deep roots

37. Let’s look at some examples CropMechanism Cotton dormancy Millets C4, some short cycle Sorghum C4 and dormancy Alfalfa Deep root system Small grains Grow in early spring (low stress period) Indeterminate soybeas - flower over longer period

38. Why wasn’t corn on that list? Corn is monoecious – imperfect flowers, same plant Corn plant is efficient but problem with grain production Problem arises as result of apical dominance – the top of the plant takes precedence over lower parts (tassel gets limited resource while silk is retarded – if and when moisture returns and silk emerges, there may not be any pollen available)

39. Mineral uptake methods -86 Root growth, interception (here is where unusually wet spring weather can result in lower yields – roots not well distributed) Fungi (mycorrhizae) help contact more nutrients Nutrient flow with moisture flow in soil Diffusion, from high to low concentration

40. Nutrient absorption thru roots -86 May be passive (mass flow) uptake Or may be active (energy expended to absorb nutrients)

41. Biological N-Fixation (BNF) - 87 Rapidly growing interest, with increasing cost of chemical fertilizers Organic farmers depend on BNF Legumes fix more N than all of fertilizer manufacturers

42. Process of Rhizobium infection • Bacteria survive in soil, and build up pop’n when suitable host present • Bacteria infect root hair, resulting in tetraploid cell formation and nodule formation • Nodules may be visible after about two weeks, and N-fixation starts about 7-10 days later • Nodules need sugars from Ps (graph)

43. Symbiosis (symbiotic organisms) • Defined as “two or more organisms living together for the benefit of each other” • Legume plant and N-fixing bacteria (Rhizobium) is example • For contrast – • Parasite (mistletoe) • Epiphyte (e.g., Spanish moss)

44. Imp’t concepts: • Some bacteria infect more than one crop – cross-inoculation groups – the “cowpea” group, for example, includes: • Cowpeas • Peanuts • Pigeonpea • Some weeds (FL beggarweed, for example)

45. Other symbiotic (?) N-fixers -87 • Azospirillum lives in the rhizosphere (not in roots) of some grass species – • live on exudates from the grass roots and fixes some nitrogen. • seems to be most productive in moist environments

46. Non-symbiotic N-fixers -87 • Azotobacter and Clostridium – “free-livers” inhabiting soil and fixing low level of nitrogen, without associating with living plants • Cyanobacteria (formerly blue-green algae) – important in rice cultures

47. What is the approximate amount of N fixed by each category? • Rhizobium (Bradyrhizobium in soybeans) is most productive – 50 ~ 300 lbs N/year • Azospirillum – 40 lbs N/year probably is upper expectation – there interesting research • Azotobacter – 20-40 lbs N/year • Cyanobacteria (the blue-green algae) – possibly as high as 60 lbs N/year • **for comparison -130 bu corn requires ~175 lbs N~ from various sources

48. Germination requirements -88 • 1) water • 2) suitable temperature (see Fig. 12) • Note that differences in temps for germination are factors in use of “nurse” crops to establish forage, and reduce weed competion – small grains germinate at low temps • 3) oxygen • 4) light – some species • Tobacco • Grassy weeds

49. Etiolation -88 • Def: elongation of plant stems grown in absence of light, or low light intensity (shaded). Why? (high levels of auxin) • Recall that sunlight destroys auxin

50. Tillering, Branching, Barrenness - 89 • Tillering is the production of secondary stems from crown area, promoted by – • Sunlight • Moisture • Fertility • Cool temperatures in small grains • Warm temperatures in rice