Improving Soil Quality for Healthy Plants and Drought Tolerance CAPCA ED Sacramento November 4, 2015 Chuck Ingels UC Cooperative Extension, Sacramento County http://cesacramento.ucanr.edu Topics to Be Covered Soil Texture and Structure Soil Organic Matter and the Soil Food Web Soil Fertility and Plant Nutrition Dealing with Soil Compaction and Restrictive Soil Layers Soil Texture and Structure A Soil Profile Components of Soil ● Solid particles (sand, silt, clay) ● Soil pores (air, water) ● Soil org. matter, including organisms ● Chemistry (nutrients) Soil Characteristics Physical Physical Properties Components Water infiltration Texture Water holding capacity Structure Nutrient holding capacity Aeration Soil Texture vs. Structure ● Texture – The percent sand, silt, & clay, based on the soil triangle » e.g., sandy loam, clay loam ● Structure – The arrangement of primary particles into secondary units (aggregates) » Affected by compaction 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 Soil Structure Structure - the arrangement of soil particles into aggregates Good structure: holds water but has plenty of air space Except for sands, soil particles don’t exist as single particles but as aggregates Soil Aggregation Humus, plant & microbial exudates, and earthworm & soil insect feces act as “binding” agents Components of Soil Organic Matter Living organisms Fresh organic residue < 5% < 10% Humus 33% - 50% Decomposing org. matter 33% - 50% Soil Organic Matter Serves as energy source (food) for microorganisms, which promote stable aggregation of the soil particles Nutrients are obtained by plants as organic matter decomposes Enhanced by OM additions but destroyed by cultivation Humus What’s left over after organic matter decomposes Cannot be seen by naked eye Very reactive (CEC), similar to clay In equilibrium with organic matter additions Cation Exchange Capacity (CEC) A measure of soil fertility Cations in soil solution in dynamic equilibrium with clay & humus particles Varies by soil type and % organic matter Typical CECs Based on Soil Texture Soil Texture Typical CEC Range meq/100g Sand 2 – 6 Sandy Loam 3 – 8 Loam 7 – 15 Silt Loam 10 – 18 Clay & Clay Loam 15 – 30 High vs. Low CEC CEC 11-35 CEC 1-10 High clay or OM content High sand content Greater capacity to hold N & K leaching more nutrients likely More lime or sulfur Less lime or sulfur needed to adjust pH needed to adjust pH High water-holding Low water-holding capacity capacity Dealing with Soil Compaction and Restrictive Soil Layers 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 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 ● Often not continuous or uniform across the landscape Effects of Grading 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 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 Deep Tillage Slip Plow Deep Ripper Deep Tillage Backhoe Plow Clay Soils Dealing with Clay Soils ● Cultivation helps, but clay particles resettle ● Avoid compacting, especially when wet » Equipment, foot traffic, etc. ● Provide drainage ● Add organic matter (cover crops, compost) Is the Problem Physical or Chemical? Determine if problem is physical or chemical Improving Ca:Mg ratio more likely to improve surface infiltration than drainage thru subsoil Sodic or high Mg soil profiles should be tilled deeply before planting trees/vines » May require precision ag applications of Ca because soils are highly variable Dig backhoe pits before planting! Dig Backhoe Pits, Examine Soil 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 Ca:Mg Ratios Plant Growth and Soil Structure Plant growth not generally affected over wide range of Ca:Mg ratios, from 6:1 to 1:1 Ca:Mg ratios – use saturated paste extract conc. (meq/L) or base saturation % Unfavorable plant growth along with poor soil structure may occur when Mg concentrations are greater than twice those of Ca Mg deficiencies likely if Ca:Mg > 8:1 Ca:Mg Ratios Plant Growth and Soil Structure 1930s & 40s – Researchers proposed ideal ratio of 6.5:1 for midwest & eastern soils » Cation exchange sites –Ca (65%), Mg (10%), K (5%), H (20%) » But % can vary greatly without affecting yields Ca:Mg Ratios Plant Growth and Soil Structure UC: Economic benefits unlikely from applying gypsum to orchards with ratio of 1.1 to 1:2 Sunland Analytical: Review of 25,000 soil samples analyzed in 2005 (CA, AZ, NV, OR) » Avg. Ca:Mg ratio = 3.4 » Avg. Ca & Mg values = 2085 ppm & 622 ppm » Amount of amendment needed to modify top 6” of soil to a Ca:Mg ratio of 6.5 = over 6 T/A lime or 9 T/A gypsum Ca Additions vs. Mg and pH Gypsum (CaSO4) adds Ca, no soil pH effect Ag Lime (CaCO3) adds Ca, increases pH Dolomitic lime CaMg(CO3)2 increases pH » 22% Ca, 11% Mg Use only if Mg is low (rare) Improving Infiltration Improve soil pore volume Increase access to surface pores Increase salinity of irrigation water Use soluble Ca to reduce Na effects Organic mater additions / management Soil Crusting Problems Increase with: » Soils with <26% clay » Alkaline soils and/or irrigation water » Compacted soils » Large droplet sprinklers » High velocity erosive surface irrigation » Rain hitting bare soil Infiltration Rate after 2 Hrs. (mm/hr) 20 Early Season 18 Late Season 16 14 12 10 (mm) 8 6 4 2 0 clover resident brome chemical residual veg. mow herb Source: Terry Prichard Conservation Tillage 1. A range of crop production practices that minimize or eliminate primary or intercrop tillage operations such as disking, plowing, chiseling, ripping 2. Manage residues to enable efficient planting, harvesting and pest management Conservation Tillage Tillage operations should ensure that 30% residue cover remains on the field after planting Conservation Tillage Potential Benefits Saves fuel, soil, time, labor, machinery Permits timely planting Reduces run-off Increases soil moisture Increases soil organic matter Improves habitat for beneficial organisms Conservation Tillage Potential Benefits 2008 to 2010: Central Valley row crop farmers switched to CT on >344,000 acres 2012: CT systems accounted for about 17% of the total corn, grain, tomato, cotton, dry bean, and melon acreage in Central Valley 2011: UC researchers achieved record yields in cotton and tomato using no-tillage practices Cover Crops Prevent structural crusting »Rain »Sprinklers Increase soil pores »Root channels »Soil aggregation Soil Management Options Clean tillage Complete herbicide Resident vegetation Cover crop Vetch Cover Crop in Tomato Field Mainly for N Addition Cover Crops Potential Advantages Reduced soil erosion Addition or conservation of N Addition of organic matter Improved soil structure & water penetration Improved accessibility Enhanced pest management Grass vs. Legume Roots Root Cap •Covers apical meristem •Grouping of cells held within slimy “mucigel” •Protects & lubricates root tip as it grows •Cells slough off Cover Crops Potential Drawbacks Increased water use Competition with trees or vines Increased frost hazard Increased pests Increased costs and management Additional equipment required Alternate Row Management 1998-2000 Vineyard Cover Crop Trial Experimental Methods Treatments » Calif. native grass mix No-till » Bell bean/vetch/pea/oat mix Disked » Annual clover/medic mix No-till » Barley/oat mix Disked » Disked control Disked Two adjacent middles planted Calif. Native Grass Mix Legume-Grass Mix, Annual Clovers, Barley/Oats Bloom Petiole Nitrate 2000 (After 3 years) 800 a 600 Native Grass (ppm) 3 BB/Vetch 400 b b Clovers Cereals 200 Disked c bc Petiole NO Petiole 0 (LSD, p>0.05) Soil Microbial Biomass 30 25 Native Grass 20 BB/Vetch 15 Clovers 10 Cereals PLFA (nm/g) PLFA 5 Disked 0 Berm Cover Crop Questions? A PDF of this presentation is online at http://cesacramento.ucanr.edu .