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Compost Benefits David M. Crohn Department of Environmental Sciences University of California, Riverside.

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Presentation on theme: "Compost Benefits David M. Crohn Department of Environmental Sciences University of California, Riverside."— Presentation transcript:

1 Compost Benefits David M. Crohn Department of Environmental Sciences University of California, Riverside

2 Marketing Healthy Soils for Healthy Plants

3 Soil Nutrients: macronutrients Total N –Organic N –Available N (nitrate and ammonia-N) Total P Total K

4 Soil Nutrients : micronutrients Boron Chlorine Cobalt Copper Iron Manganese Magnesium Molybdenum Sulfur Zinc

5 Soil properties Organic matter Water holding capacity Bulk density Structure Texture ECe pH

6 Low pH = acid soil High pH = alkaline soil Neutral pH = 7

7 ECe = salinity ECe stands for Electrical Conductivity Salts conduct electricity and this is used to measure them in soils High ECe soils may have trouble germinating seeds and supporting growth ECe is a water management indicator, more than a soil property

8 Texture The sand, silt, and clay- sized particles determine soil texture Not affected by structure or OM

9 Bulk density Soil mass. Soil volume Dense soils –Retard water movement –Hold less water –Impede air exchange –Stop root development

10 Fig. Engle et al. WSUE Structure

11 Water holding capacity

12 How Composts Benefit Soils

13 Why compost? To eliminate disease organisms Animal ● Plant ● Human To produce a stable and safe soil amendment Nutrients ● Odors ● Phytotoxins

14 Organic matter: What you are selling Hargrove and Luxmore

15 SOM: Matter of life and death

16 Carbon Source of energy for microbes Not all forms are equally available –sugars (more available) –fats, waxes, proteins –cellulose –lignin (less available)

17 Starches Used by plants and animals for intermediate energy storage. A carbohydrate (CH 2 O) x Readily metabolized by microbes Decomposed during composting

18 Cellulose Most abundant organic compound on Earth Examples: paper, cotton, cellophane, rayon Like starch, a carbohydrate composed of chains of glucose molecules (polysaccharides), but joined by  -linkages Cellulose is used by plants for construction of cell walls Tend to be structured in straight lines Can be metabolized by bacteria, fungi Ruminants, termites use bacteria to break down cellulose

19 Starch and Cellulose

20 Lignin Second most abundant organic compound on Earth Has a complex structure Along with cellulose is used by plants for construction of cell walls Can be metabolized by fungi

21 Lignin molecule

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23 Soil Nutrients: macronutrients Total N –Organic N (slow release ) –Available N (variable) Total P (often rich) Total K (variable)

24 Bacteria 80 – 90% of the microbial community is bacteria Small: 0.5 – 3  m diameter High surface:volume ratio. Important for moving nutrients in and waste products out C:N ratios on the order of 4.3:1 to 6:1 Soil species differ from active compost species –  C: mesophyllic –40-65  C: thermophilic

25 Fungi Fungi include molds and yeasts Larger than bacteria Grow more slowly Able to metabolize lignin C 10 H 17 O 6 N C:N ratios on the order of 9:1

26 Fungi on lignin

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28 Nitrogen Vital nutrient for both microbes and plants Microbes are better than plants at accumulating N C:N ratio –Compost feedstock initially about 35:1 –About 10:1 to 20:1 in cured product –About 8:1 in a soil

29 Soil Nutrients : micronutrients Boron Chlorine Cobalt Copper Iron Manganese Magnesium Molybdenum Sulfur Zinc (Variable, depending on source)

30 pH Low pH = acid soil High pH = alkaline soil Neutral pH = 7 (buffers pH)

31 ECe = salinity ECe stands for Electrical Conductivity Salts conduct electricity and this is used to measure them in soils High ECe soils may have trouble germinating seeds and supporting growth ECe is more of a water management indicator (Contains salts, some of which are nutrients. Improves tilth so salts can leach away)

32 Texture (no effect) The sand, silt, and clay- sized particles determine soil texture Not affected by structure or OM

33 Bulk density (decreases density) Soil mass. Soil volume Dense soils –Improves water movement –Holds more water –Increases air exchange –Promotes root development

34 Bacteria and fungi Bacteria are much smaller than fungi Both decompose composts in the soil

35 Encourages the formation of soil aggregates Aggregates are soil clusters held together as a result of compost decomposition –Fungal hyphae bind particles together –Bacterial polysaccharides serve as glue Compost in soil

36 Structure Fig. Engle et al. WSUE

37 Aggregated soils Hold water while allowing air to penetrate Facilitate drainage and salt removal Allow roots to penetrate Are more stable, resisting erosion –Sheet –Rill

38 Water holding capacity

39 Overcome worry… …with knowledge and information Photo credit: aur2899

40 Compost Use Index Derived from focus groups asking experts and users what they care about. Measureable using STA/TMECC values Designed to indentify quality composts for specific uses Not all parameters matter for all uses Currently implemented for –Avocado –Lettuce –Tomato –Grape –Strawberry

41 Use Index Parameters C:N Ratio Organic Matter Salinity (EC) Total N Total P Stability Phytotoxicity pH Boron Chloride Sodium Manmade Inert Impurities Particle Size Distribution Safety –Metals –Pathogens

42 Carbon:Nitrogen Ratio Low C:N do not tie up N and are biologically most active High C:N Ratios (>25) imply lignin and cellulose which resist decay. –Good for mulches. –May immobilize N in soils, stealing N from plants UseC:N ratio Mulch  15 : 1 Soil amendment  20 : 1

43 Organic Matter Carbon based Derived from the tissue of living things Substrate for soil microbes that improve soil structure Helps hold plant nurtients > 65% O.M. suggests immaturity UseOM Mulch  25 % Soil amendment  25 %  65 %

44 Salinity (EC) Most significant issue for arid and semi-arid areas All charged ions, including nutrients, contribute to salinity Compost and soil salinities are measured differently. –Compost: EC 5:1 (5:1 water to compost) –Soil: EC e (saturate paste extract) Plant toxicity levels are in terms of EC e Formula needed to predict the EC e of a Soil/compost mix –Soil texture –Soil organic matter content –Compost organic matter content –Mixing depth Salinity is a transitory property Salts added with irrigation water usually far exceed compost salts Crop Soil/compost mix EC e, dS/m Avocado4 Lettuce1.3 Tomato2.5 Grape1.5 Strawberry1

45 Macronutrients Total N –Source of crop nutrients –Too much ammonia can harm crops Total P –Not a crop health concern –Eutrophication concern

46 Maturity Stability –Unstable composts are still decomposing rapidly. This emits CO 2. And odors. Phytotoxicity –Germination test UseC:N ratio Mulch  8 mg CO 2 /g OM/day Soil amendment  8 mg CO 2 /g OM/day UseC:N ratio Mulch  80 % emergence Soil amendment  80 % emergence

47 pH Describes the acidity of the compost Low pH (acid) composts may not be mature. Phytotoxic organic acids produced during composting must be decomposed as they are phytotoxic. High pH (alkaline) composts may be contaminated. UseC:N ratio Mulch 6.0  pH  8.5 Soil amendment 6.0  pH  8.5

48 Boron Naturally present in some soils and irrigation waters. More available under acid conditions. Controlled through leaching. Once commonly added to plywood glue, therefore found in MSW, demolition debris, coal or wood ash feedstock More available under lower soil pH conditions Hard to say how a compost will affect available soil levels UseC:N ratio Mulch  100 mg kg -1 Soil amendment  100 mg kg -1 Toxic B Levels: Crop Concentration in saturated extract, mg L -1 Avocado0.5 – 0.75 Lettuce0.5 – 0.75 Tomato4.0 – 6.0 Grape0.5 – 0.75 Strawberry0.75 – 1.0 Boron toxicity thresholds (Hanson et al., 1993, Maas, 1986).

49 Chloride Toxic to some crops, but not to others. Almost all composts can meet the 1% dry wt. limit Toxic C Levels Crop Concentration in saturated extract, meq L -1 Avocado5 – 7.5 Lettuce n.a. Tomato n.a. Grapes30 – 40 Strawberry5 – 7.5 CropChloride content Avocado  0.2 % dry weight Lettuce  1 % dry weight Tomato  1 % dry weight Grape  1 % dry weight Strawberry  0.2 % dry weight

50 Sodium CropSodium content Avocado  0.2 % dry weight Lettuce  1 % dry weight Tomato  1 % dry weight Grape  1 % dry weight Strawberry  1 % dry weight Sodicity Sodium disperses clay particles collapsing soil structure This is offset by compost organic matter, calcium and magnesium Phytotoxicity Mainly woody plants

51 Manmade Inert Impurities Plastic, in particular, can litter the soil. Remember that runoff water is often reused and plastic can clog water systems UseInerts Soil amendment  0.75 % dry weight Mulch  0.75 % dry weight

52 Particle size distribution Mulches should have larger particles than soil amendments. Large particles in soils can tie up nutrients. Too many small particles in mulches can support weed development. UseSize Characteristics Soil amendment  95% passing though a 5/8” screen  70 % passing through a 3/8” screen Mulch  99% passing though a 3” screen  25 % passing through a 3/8” screen

53 Metals Current numbers based on assumption of 100 years of biosolids applications at 4.5 t/ac and a detailed risk assessment. Compost applied at higher rates than biosolids so those number are not conservative. Mulches are applied at higher rates still, though less often. Constituent Amendments (ppm) Mulches (ppm) Arsenic (As) Cadmium (Cd) Chromium (Cr) Copper (Cu) Lead (Pb) Mercury (Hg) Nickel (Ni) Selenium (Se) Zinc (Zn)

54 Pathogens UseSize Characteristics AvocadoFecal coliforms: < 1,000 MPN per gram of total solids Salmonella sp. < 3 MPN per 4 g of total solids LettuceFecal coliforms: < 1,000 MPN per gram of total solids Salmonella sp. < 3 MPN per 4 g of total solids E. coli O157:H7: non detect TomatoFecal coliforms: < 1,000 MPN per gram of total solids Salmonella sp. < 3 MPN per 4 g of total solids GrapeFecal coliforms: < 1,000 MPN per gram of total solids Salmonella sp. < 3 MPN per 4 g of total solids StrawberryFecal coliforms: < 1,000 MPN per gram of total solids Salmonella sp. < 3 MPN per 4 g of total solids E. coli O157:H7: non detect Many diseases are spread through a fecal-oral transmission route. Both humans and animals can deposit infectious bacteria, viruses, and helminths. Because there are so many infectious organism out there, we use indicator organisms. Because E. coli O157:H7 is so dangerous, suggest checking when applied to produce eaten fresh.

55 My Advice to Growers on Choosing a Compost Trust your judgment! Compost should have an earthy smell An off smell suggests that the compost is not ready yet. It may damage young plants Composts have different amounts of organic matter. 25 – 75%. More is usually better Local stuff will be cheaper to deliver Value the reputation of the composter STA certification

56 Soil amendments: modify soil properties Improve tilth Improve water holding capacity Improve aeration Improve infiltration capacity Adjust pH Promote microbial activity

57 Mulches: cover the soil Protect soils against erosion Conserve water by slowing evaporation Control weeds Control certain plant diseases Decorate landscapes

58 Organic fertilizers: slow release sources of Nitrogen Phosphorus Potassium Micronutrients

59 Summary on uses Mulches, soil amendments and organic fertilizers are uses, not products. Composts may serve any of these. Different composts have different properties, and will therefore be more suitable for some uses than for others.

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61 Think long-term. Focus on the soil and your plants will thrive.


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