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Introduction to Soils

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Introduction to Soils Introduction to Soil Science UC Master Gardener Training Feb. 11, 2015 Chuck Ingels UC Cooperative Extension, Sacramento County http://cesacramento.ucanr.edu Components of Soil ● Solid particles (sand, silt, clay) ● Soil pores (air, water) ● Soil organisms (OM) ● Chemistry (nutrients) Most Soils Are Not Ideal! High water percentage = waterlogged High air percentage = dry High mineral percentage = compacted Soil Characteristics Physical Components Physical Properties Texture Water holding Structure Nutrient holding Water infiltration Aeration Soil Texture vs. Structure Texture: size distribution of individual particles (sand, silt, clay) Impractical to change Structure: arrangement of particles into larger units (aggregates, clods, crusts, pans) Can be changed – for better or worse Surface Area of Soil Surface area Soil texture (cm2/g) Very coarse sand (<2 mm) 11 Coarse sand 23 Medium sand 45 Fine sand 91 Very fine sand (>50 micron) 227 Silt (2-50 micron) 454 Clay (<2 micron) 8,000,000 (=8,600 ft2) The Soil Triangle Soil Texture Loamy sand LIGHT Sandy loam Loam Silty loam Clay loam Clay Silty clay Sandy clay HEAVY Sandy Clayey Soil Particle Sizes Sand 2.00 to 0.05 mm Silt 0.05 to 0.002 mm Clay 0.002 to <0.0002 mm Soil Texture Affects Soil Moisture Permeability Water Holding Capacity Clay Loam Soil in Davis Soil Structure Structure - the arrangement of soil particles into aggregates Good structure: holds water (micropore space) and has air space (macropore space) Poor structure: lacks adequate macropore space Soil structure & texture can be highly variable across small areas Soil Aggregate Formation Physical Wetting (shrink/swell) Animal & earthworm activity Root growth Chemical Soil glues Soil Glues glucose cellulose hemi cellulose Humus, roots and soil microbes produce glues that aggregate soils Organic Matter Content % Organic Matter 0 to 6 inches Venice peaty muck 60 Sacramento silty clay 5 Yolo loam 1 Hanford sandy loam 0.5 Most Sacramento soils 0.75-1.5 Hardpan, Compacted, and Clay Soils (Working with Sacramento Area Soils) Some Soil Layers Restrict Air, Water, and Root Penetration Hardpan – cemented (by silica, iron, carbonates) Claypan – higher clay than overlying layer Crust – brittle, compact/hard when dry Traffic or compaction pan – caused by vehicles, tillage implements, feet, hooves Cemented Hardpan Hardpan vs. Compaction Compacted soil Cemented hardpan Cemented hardpan Compacted soil Cemented Hardpan Primary cementing agent » In our area – silica » In Southwest: (caliche) – carbonates Sand, silt, & clay grains are cemented together into a hard, impermeable layer of varying thickness Not always continuous across the landscape Cemented Hardpan How it Forms Precipitation of silica or carbonate at the edge of the wetting front at some depth It starts beneath pebbles & slowly forms around particles, pebbles and aggregates until they are covered These coatings thicken until they touch and begin to plug pores Cemented Hardpan How it Forms Pores completely fill with particles A horizon of clay often forms on top of the hardpan because downward translocation of clay has been interrupted by the cemented horizon Effects of Grading Fair Oaks Horticulture Center, 1997 Soil Compaction Effects of Compaction on Soil Soil structure is destroyed – pore space is severely reduced Soil drains slowly and is prone to being anaerobic Compacted soil physically impedes root growth Soil Compaction Dry and Compacted Soil Deep soil improves drought tolerance and anchorage (You Are Here) Compacting the Planting Site Fair Oaks Horticulture Center Soil Stratification Stratified Layer Loam Sand Loam Sand Dealing with Compacted and Layered Soils The Main Goal Create & maintain soil conditions most favorable for root growth and water movement It’s best to evaluate It’s difficult to make soil conditions changes after planting! before planting. Dealing with Compacted Soils and Cemented Hardpan Break it up – down to good soil Rip / Drill Jackhammer / clay Backhoe spade / pick ax Trencher Dynamite Use raised planters With walls or barriers Without walls (raised mounds) Provide drainage Sell Deep Ripper -For Vineyards Shallower Ripper - FOHC Mix the Soil Backhoe Plow Drill or Trench Soil Provides some drainage, root growth Backhoe or Excavate Jackhammer with clay spade attachment Pickaxe Then add compost… …and mulch Use Raised Beds… …Or Raised Planters Use subsurface drainage, but… (Eco-landscape principle)…maximize soil drainage to minimize off-site movement FOHC, 2003 Clay Soils Dealing with Clay Soils Cultivation helps, but clay particles resettle Avoid compacting, especially when wet » Equipment, foot traffic, etc. Provide drainage Use raised beds Dealing with Clay Soils Amendments Incorporate well decomposed organic matter »Avoid pockets of OM Use mulch to prevent crusting and runoff Incorporate sand? Incorporate gypsum Organic Amendments Composts Manures Peat moss Ground fir bark Gypsum Can Gypsum Improve Your Soil? Yes If soil is impermeable due to excess Na, Or due to low Ca:Mg ratio Probably Not If soil is impermeable due to fine texture, compaction, or hardpan Definitely Not If soil is permeable and water penetrates well Mulching with Wood Chips Mulch vs. Compost Mulch = Organic or inorganic material spread on the soil surface Compost = Rotted organic matter made from plant material and/or manure »Thermophilic decomposition (heat) »Finished compost is not hot »Usually incorporated into the soil Potential Benefits of Mulch Reduces weeds & erosion Insulates roots from temp. extremes Conserves soil moisture ↑ root growth Increases microbial activity Increases water penetration Improves plant establishment Potential Problems with Mulch May prolong saturation in heavy soils »Favors root and crown rot May host plant diseases, insects, and nuisance fungi Some wood chips poor quality Can’t see soil moisture Time consuming to spread Mulch Basics (Wood Chips) Softwood mulches (pine, cypress, etc.) last longest – less microbial feeding Keep mulch 6-12 in. away from the base of trees & shrubs when soil wet, poorly drained Application rate: Generally 2-4 in. deep »Fine = <2 in. Coarse = 4-6 in. Keep mulch on top of soil to prevent N tie-up Do Wood Chips Affect Soil Nutrients? Tie-up of N? »N immobilization from high C:N mulch »Generally N tie-up at interface only »Avoid mulch in planting holes Soil pH – little effect (pine needles acidic) Mulch Reduces Weeds if Deep Enough Some Weeds Blend Mulch Doesn’t in With Mulch Control Perennials! Bermudagrass Spotted spurge Bindweed Sheet Mulching Layering mulch to suppress weeds »Knock down or mow existing weeds »Add compost, weed barrier, mulch, water Biodegradable – plant right into it Sheet Mulching Albany, CA Nuisance Fungi that Grow on Wood Chips Dog Vomit Fungus (Slime Mold) Other Mulch Fungi Mushrooms Bird’s nest fungus Stinkhorn Questions? .
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