Unit 7:  Organism  Organic Residues

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Unit 7: Organism Organic Residues

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1. Unit 7: Organism & Organic Residues Chapter 5

2. Objectives Understanding of beneficial & nonbeneficial roles of soil animals Impact of photosynthetic organisms Knowledge of the role of bacteria in the soil Identification of the conditions in which microbe growth is maximized/decreased Enzymatic role in decomposition Appreciation for role of soil organic matter in soil chemical & physical properties Value of manure, crop residue, compost, sewage

3. Introduction Weight of bacteria in an acre of soil = 1500+ lbs. Microbes – mix, aerate soil, fix atmospheric N, decompose organic substances, recycle nutrients Two most important processes on earth Decomposition Photosynthesis

4. Animalia: Rodents, Worms, & Insects Large, burrowing animals to mites Earthworms major contributor to soil biomass Most biomass comes from soil bacteria & fungi Burrowing Animals Aerate the soil Alter its fertility & structure Also eat & destroy vegetation Can be more detrimental than beneficial

5. Animalia: Rodents, Worms, & Insects Earthworms Feed on animal/plant residues Excretions are small, granular aggregates w/ readily available plant nutrients Aerate/stir the soil Increases water infiltration Improves root penetration Borrowing depth Some as deep as 20’ Most in the common root zone (6.6’)

6. Animalia: Rodents, Worms, & Insects Prefer moist, well-aerated soils (70° F), w/ pH 5.0-8.4 Plenty of materials to eat Low salt concentrations High available Ca Deep soil w/ medium to fine texture Undisturbed by tillage Hindrances of earthworms Farm machinery Sandy, salty, arid, acidic soils Cold Barren soils

7. Animalia: Rodents, Worms, & Insects Mice, mites, moles, millipedes, insecticides Arthropods & Gastropods Arthropods – joint-footed invertebrate organisms Mites, spiders, scorpions, millipedes, centipedes, ants, termites, etc. Feed on decaying plant vegetation Aerate soil Can be pests feeding on living plant materials

8. Animalia: Rodents, Worms, & Insects Gastropods Slugs, snails Feed on decaying vegetation Can eat/damage living plants Nematodes Microscopic, unsegmented, threadlike worms Omnivorous nematodes – feed on decaying organic matter, most common soil nematode Predaceous nematodes – prey on soil bacteria, fungi, algae, other nematodes

9. Animalia: Rodents, Worms, & Insects Parasitic nematodes – infest plant roots Nearly all field, vegetable crops & trees are affected How do they cause damage? What other problems can they introduce? Very hardy Extremely difficult to control Also very expensive Must use resistant varieties, more natural control means

11. Plantae: Plants Play the most important role in the cycle of life Most root systems account for 30-50% of the total plant mass Range from older/thicker roots, to single-celled root hairs Which are most active? Which absorb nutrients? Secrete important materials into the soil that can be used by other organisms for food, or provides protection from disease

12. Plantae: Plants Area around roots is very important to organisms & usually contains highest percentage of microbes = rhizosphere Rhizosphere soil may be quite different than the soil mass Different proportions of soil nutrients Different soil pH

13. Fungi: Molds, Mushrooms, Mycorrhizae Fungi – can’t use sun for energy…live off of live/dead plant/animal tissue Unicellular yeasts Molds Mildews Smuts Rusts Mushrooms

14. Fungi: Molds, Mushrooms, Mycorrhizae Typically consist of small filaments stretching through the soil Most important role is as decomposer in the soil Organic Matter Decomposers First sign of decomposition of organic materials is presence of filaments (hyphae) Readily attack cellulose Can compete for soil nutrients Help hold soil aggregates together

15. Fungi: Molds, Mushrooms, Mycorrhizae w/out fungi, carbon cycle would slow greatly Deleterious Fungi Predators/parasites on living cells Penetrate other microbes or nematodes & digest Cause plant diseases Smut Rust Wilt Powdery mildew, etc.

16. Fungi: Molds, Mushrooms, Mycorrhizae Cause molds (Aspergillus) growing on grains/peanuts Produces aflatoxins Very potent and poisonous Mycorrhizae Fungus root Mutualistic relationship between fungus & plant roots Symbiosis Share nutrients & water back & forth w/ plant roots Can extend root’s reach 100x

17. Fungi: Molds, Mushrooms, Mycorrhizae Particularly helpful in absorbing more nutrients that aren’t as mobile (P, Zn, N, etc.) Increase drought tolerance of the plant, disease resistance, extreme soil acidity Can have endo- or ectomcycorrhizae relationship Nursery soils that are sterilized can be reinoculated to help develop this relationship

18. Protista Algae, protozoa, slime molds Algae photosynthesize Not important decomposers Producers of: Polysaccharides Oils Other organic substances Algae inhabit only surface areas of soils In fertile soils, can produce hundreds of kg of organic material/yr

19. Protista Protozoa Unicellular organism, w/out cell wall Ingest bacteria, fungi, other microbes, nematodes, etc. Numerous in the soil Can cause serious disease Influence microbe populations & recycling of plant nutrients

21. Monera: Bacteria Actinomycetes & cyanobacteria Actinomycetes Source of numerous beneficial antibiotics & important decomposers Cyanobacteria Tiny prokaryotic bacteria No cell wall Aka – mycoplasma

22. Monera: Bacteria Soil Bacteria Most numerous soil microbe 1g soil – 1m bacteria Can survive even most extreme environment Populations can double in 30 min Some may take hours/days Autotrophic Manufacture their food by synthesis of inorganic materials Get C from CO2

23. Monera: Bacteria Can oxidize materials in soils to make them available to plants Convert ammonium to nitrite them nitrate NH4 can be used by plants Nitrite is toxic & volatile Nitrate can be absorbed also, but can leach to water sources Convert CO to CO2 & methane gas making these gasses much less lethal Also can reduce toxicity of some materials

24. Monera: Bacteria Heterotrophic Get food & energy directly from organic substances Most soil bacteria are in this group Can be N-fixers or not Account for much decomposition in the soil Symbiotic Bacteria Also heterotrophic bacteria Fix atmospheric N in plant root nodules Can you give an example?

25. Monera: Bacteria Provide usable N to the plant, plus return excess to the soil Infect roots hairs of plants & form nodules where bacteria can fix N in an anaerobic environment Crops can be inoculated to help this relationship develop Free-Living N2-Fixing Heterotrophic Bacteria Don’t need a host plant Still have a mutual relationship with nearby plants Populations may be altered due to presence/absence of O2

26. Monera: Bacteria Bacterial Diseases Cause of numerous diseases in both plants & animals Most disease causing bacteria in humans has little to do w/ soil bacteria Blight, wilt, salmonella, etc. Actinomycetes Small heterotrophic organisms (similar to fungi) No nucleus

27. Monera: Bacteria Many antibiotics have origins w/ this bacteria group Neomycin, tetracycline, etc. Generally live on dead tissue Important decomposers in the soil Don’t compete well w/ fungi early in decomposition Adverse conditions Cold Anaerobic soils Acidic soils

28. Monera: Bacteria Very drought tolerant Recently found to have a symbiotic N-fixing relationship w/ some plant families Prompting research in this area

29. Soil Viruses & Viroids Nonliving nucleic acids surrounded by protein coat Can be a replicated protein Do carry genetic material, but only perform few life functions Prion – various nucleic acids w/out protein coat – may be most deadly No warning symptoms Difficult to detect Viroid – no protective coat w/ RNA Virus – protective coat w/ RNA or DNA

30. Soil Viruses & Viroids Can cause many plant diseases Control by removing carriers of viruses Enzymes in soil help decompose viruses Most viruses can only over winter if inside a host Otherwise will survive only 1-4 wks Over wintering can inoculate the following crop No chemical control for field virus infections

31. Conditions for Microbial Activity Constant competition among microbes for food sources Depend greatly on: temp, moisture, soil acidity, soil nutrient levels, competition, air Ideal temp for maximum microbe growth w/ near neutral pH - 86°

32. Conditions for Microbial Activity Optimum Soil Water & pH for Soil Microbes Water content near/just greater than field capacity is best (wet, but well aerated) Dryness is often lethal, or they go dormant Anaerobic bacteria thrive in saturated conditions Prefer soil pH close to 7.0 Most don’t like pH <5.0 Lower the pH, more thrifty fungi

33. Conditions for Microbial Activity Optimum Temp & Other Conditions for Microbes Activity accelerates as temp increases Microbes nearly dormant at freezing Activity rate almost doubles from 50° to 68°F Some strains thrive at low temps, or high temps High nutritive demand Especially N, P, S, Ca Competition helps to maintain a healthy population of microbes in the soil As long as soil remains healthy & well managed

34. Conditions for Microbial Activity Encouraging Beneficial Organisms Very difficult to regulate/manipulate soil microbe populations Response to changes in environment can cause quick changes in microbe populations Typically, conditions for good plant growth also good for microbe growth Ways to encourage desirable microbe population Inoculate the soil w/ desired microbes, especially in a soil where a host plant hasn’t grown prior

35. Conditions for Microbial Activity Lime the soil (keep pH >6.0) Minimize fumigation/sterilization of soil Kills harmful & beneficial microbes Keep organic matter content high Avoid contamination from problem soils Avoid causing stress conditions Drought High salt content Water logging Excessive fertilizer Reduced tillage

36. Conditions for Microbial Activity Controlling Harmful Microbes Can inject poisonous gasses into soil Methyl Bromide Used in greenhouses to ensure pest control Also kills helpful organisms Should be used only in desperate situations Other methods of control Introduce natural enemies Change soil conditions in favor of different microbial growth

37. Conditions for Microbial Activity BMP’s Start w/ disease-free plants & use resistant varieties Pay attention to sanitation Can spread easily from equipment, clothes, rodents, etc. Minimize mechanical injury to plants Control water Excessive irrigation invites diseases Improve ventilation Control soil pH Control any infestations quickly

38. Composition of Organic Matter Composed of 45-50% Carbon Lesser amounts of H, O, N, P, S, etc. Most are long C chains w/ different arrangements of organic materials Proteins Lignin's CHO’s Oils Fats Waxes Etc.

39. Composition of Organic Matter Humus – substances remaining after chemical/biological breakdown of fresh plant/animal residues & microbial biomass Most soluble organic matter in form of humic acid or fulvic acid Other specific organic substances: Sugar amines Nucleic acids Lipids Polysaccharides Chains of sugar molecules that help hold soil aggregates together

40. Decomposition of Organic Matter Energy from sun is released when materials decompose Activation energy must first be obtained before decomposition can occur (enough heat to start the fire) Enzymes help reduce activation energy in soils Enzymes & Biological Reactions Enzyme – lowers activation energy enough to allow the breaking or formation of a particular bond in nature

41. Decomposition of Organic Matter These enzyme-influenced reactions = biological reactions Helps split bonds and open up substances Enzyme is not destroyed/altered in the process Do decompose, denature over time due to other substances in the soil Products of Decomposition End products of decomposition (in well aerated soils) Carbon dioxide Ammonium Nitrate Phosphate

42. Decomposition of Organic Matter Sulfate Water Other Can be significantly different under anaerobic conditions Factors Affecting Decomposition Decomposition rate directly affected by number of microbes present Absorb nutrients produced & use for growth & reproduction (N & C)

43. Decomposition of Organic Matter N is key, as bacteria need it to drive decomposition C:N Ratio – ratio of carbon:nitrogen in the soil High C:N – low N content, low C:N – high N content Alfalfa residue – 13:1 Soil microbes – 10:1 Straw – 80:1 Sawdust – 500:1 Affects rate of microbe growth, therefore, speed of decomposition Plants growing in high C:N ratio soils often N deficient because microbes use N to help w/ decomposition before the plant can use for growth

44. Decomposition of Organic Matter As decomposition occurs, C lost as CO2 to atmosphere, N kept in soil Easily decomposed residues go first (sugars, cellulose) Some microbes may die after these are gone & release their N to plants/soil solution Lignin may take 10 yrs to decompose fully Dense microbe populations in the upper soil surface Decomposition of plant residues w/ C:N <20:1 occurs quickly & N returned to the soils/plants

45. Decomposition of Organic Matter Decomposition of plant materials w/ C:N 20-30:1 – enough N for decomposition, not much released for the plant Residues >30:1 decompose slowly, lack enough N to feed microbes from residue, microbes feed on soil N (robs from plants) Conditions favoring microbe growth & higher decomposition rates Temp: moderate/warm temps Water: moist soils Soil texture: soils higher in clays retain more organic matter, nutrients for use by microbes

46. Effects of Soil Organic Matter Benefits of Soil Organic Matter Source of all soil N not treated w/ mineral fertilizer Major source of available P & S Supplies major soil aggregate forming cements Contributes to CEC (usually 30-70% of total soil CEC) Increases available water content at field capacity, increases air/water flow

47. Effects of Soil Organic Matter Chelate minerals to help protect them in the soil C supply for many microbes Reduce erosion, shade soil, moderate soil temps Buffers soil from acidity or toxicity Leaving mulch on soil surface increases water infiltration, decreases soil erosion, stabilizes temp changes

48. Effects of Soil Organic Matter Organic Matter as a Source of Nutrients Depends on whether the nutrients can be supplied at the right time to the plants As temps, decomposition rates, and plant growth increases, more nutrients become available Nutrients supplied depends on: Kind of organic matter Soil texture Crop needs

49. Effects of Soil Organic Matter No single soil condition can supply all/optimum nutrients That’s why we still have to fertilize Conservation of soil nutrients Protects nutrients from leaching losses Store for future use Continual release of nutrients As material decomposes, microbes die more nutrients are mineralized and become available to the plant

50. Effects of Soil Organic Matter Must be careful not to add too much organic matter to the soil Nitrate pollution of groundwater Phosphate pollution of surface water Allelopathy – beneficial or harmful effect of chemicals produced by one plant on another plant These toxins in the form of phytotoxins Alfalfa on alfalfa Wheat on barley seedlings

51. Effects of Soil Organic Matter Can help w/ natural weed suppression Some suspect that weeds have an advantage in this way over crops Maintenance of Soil Organic Matter Wide ranges of organic matter contents exist, due to climate Uncultivated soils are highest in organic matter Plants can grow in soils w/ no organic matter A single amount is not recommended

52. Effects of Soil Organic Matter Usually, organic matter increases, helps plant growth Can be costly to increase (if you’re buying it, or taking out of production to do so) Utilize all available residues

53. Organic Waste Materials Animal Manure Safe, environmentally friendly disposal is key Best when added to soil, nutrients are recycled Great fertilizer Good soil conditioner How are we going to deal with the environmental concerns?

54. Organic Waste Materials Manure Composition & Use Cattle manure – 3% N, .8% P, 2% K, 25% organic carbon Manures supply relatively low quantities of nutrients/unit dry wt. Micronutrient content higher Varies due to the feeding program & livestock Potential problems: High soluble salts May be high in weed seeds

55. Organic Waste Materials Sewage Sludge Solids settled from sewage treatment plants Widely usable 4% N, 2% P, .4% K Problems: May contain toxic elements & heavy metals Can be toxic to plants, animals, people Some pathogenic organisms can remain present Cholera, diarrhea, hepatitis, tapeworms, etc.

56. Organic Waste Materials Composting Usually don’t occur naturally Must have a pile of organic materials Don’t commonly supply a lot of available nutrients <2% N, P, K Fresh materials: manure, vegetable wastes – don’t have to be composted – will decompose quickly Materials w/ high C:N – composting will greatly improve their effectiveness when added to soils

57. Organic Waste Materials Requires conditions favorable for microbe growth Best if it is aerobic Temps should reach ~160° F for > 1hr to help destroy pathogens Compost should be turned regularly Monitor compost moisture level to increase effectiveness of compost Can kill weed seeds if conditions are right Usually requires several weeks of composting

58. Organic Waste Materials Can finish compost in ~1 mo or >6 mos, depending on what is composting & how it’s managed

59. Assignment

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