Tilth: Soil Structure and its Management Sonoma County Vineyard Technical Group May 18, 2017 Tilth: Soil Structure and its Management Paul R. Anamosa, Ph.D. Viticultural Soil Scientist www.vineyardsoil.com 707 255-3176 Tilth: Archaic: Integration of many of the characteristics of soil structure and reflects the practical experience of generations of people who have worked the soil and the understanding that they have of conditions that lead to greatest productivity and ease of management. A soil considered to possess good tilth is one that readily fractures whether the stress arises from tillage, emerging seedlings or growing roots, and provides an optimal environment for growth of plants and microorganisms. 1
Tilth is Soil Structure Soil structure is typically defined by its: Geometric form Bulk Density Pore size distribution Strength of these under stress Soil Structural Forms 2
Tilth: Soil Structure and its Management Sonoma County Vineyard Technical Group May 18, 2017 Massive (no Peds) Soil Profile Scale inches Sandy (no Peds) Porosity Porosity is measured at the percent of volume of a soil that is in pores and the pore size distribution (amount of pore with certain dimensions. Due to the geometry of putting an irregularly shaped solids in a fixed volume, the porosity of a soil does not change much and is usually between 46% to 54% of a soil. This means the solid fraction ranges also between about 46 to 54% of the soil volume. However, the pore size distribution, size of the pores, can change considerably. 3
Classification Pore Diameter Properties um Macro-pores > 75 drain by gravity Meso-pores 30-75 drain by gravity Micro-pores 5-30 plant available water Ultra-micro-pores 0.1-5 plant available water Crypto-pores < 0.1 unavailable water Bulk Density Bulk Density is the density (weight per volume) of a soil in its natural state in grams/cubic centimeter 4
Tilth: Soil Structure and its Management Sonoma County Vineyard Technical Group May 18, 2017 Bulk Density Sands are slightly denser than clays (when dry) Sandy loam: 1.38 g/cm Clay loam: 1.26 g/cm Clay 1.20 g/cm However, because the more abundant smaller pores in clay hold water, clays are considered heavy and sands are considered light. Factors Influencing Soil Structure Texture (sand, silt, clay) Clay mineralogy Organic matter - glues Inorganic non-crystalline materials Adsorbed and exchangeable solutes (soluble molecules) Plants Soil organisms Depth in the profile (pressure of the over-burden) 5
Soil Texture Silt 255-3176 6
Tilth: Soil Structure and its Management Sonoma County Vineyard Technical Group May 18, 2017 Clay Mineralogy - 2:1 layered aluminum silicates The 2:1 layered aluminum silicates These minerals have many chemical formulations that impact their shrink-swell behavior. Some swell and shrink more than others. Swelling and shrinking causes intense pressure in the soil. 7
Glues and Cementing Agents: Organic matter Macro-organisms Micro-organisms Non-crystalline minerals (iron oxides, aluminum hydroxides) Adsorbed and exchangeable solutes Calcium (Ca) strengthens particle aggregation. Sodium (Na) and Magnesium (Mg) degrade particle aggregation and enhance dispersion or aggregates. Soil Particle Surface 8
Tilth: Soil Structure and its Management Sonoma County Vineyard Technical Group May 18, 2017 Management of Structure, Porosity, and Bulk Density Goal of soil structural management is to decrease the bulk density of the soil by increasing the porosity. This is done by disorienting the structural blocks, but not pulverizing them. Bulk Density Disorienting the structural blocks to increase micro and mesopore sizes for better air circulation and water storage. Do not pulverize. Do not increase the (ultra-micro-pores). 9
Organic Matter Organic matter has low density. Organic matter increases aggregation of fine particles creating more micro-pores inside the aggregates and more meso- and macro-pores between the aggregates. Organic matter feeds soil fauna (worms, and insects) to pass through the soil and create voids. Encourage Flora and Fauna to make pores and distribute organic matter deeper into the soil. Krotovina: animal burrows 10
Tilth: Soil Structure and its Management Sonoma County Vineyard Technical Group May 18, 2017 Cover-crops Cover-crops keep roots over most of the vineyard floor About 1/3 rd to ½ of the roots die back and decompose during dormancy thereby feeding creating soil organic matter for glues, pore space, and food for animals to do the same. Human induced Impacts: Sculpting hill sides or remove and then re-place soil. Removal destroys structure organization and pulverizes aggregates. Piling destroys structure aggregation Replaced soil has no vertical strength and will compress itself upon wetting. 11
To the untrained eye the physical arrangement of the parts is not appreciated. Tillage Tillage can lift and loosen aggregates especially in the subsoil. Tillage must be done when the soil is dryer than the plastic limit. Tillage can be used pre-plant or in-row after planting to loosen vehicle-track zone. 12
Tilth: Soil Structure and its Management Sonoma County Vineyard Technical Group May 18, 2017 Conventional Straight Shank Very ineffective. Vector force of tillage is horizontal into compacted profile. Requires repeated ripping at different directions, which causes destruction and pulverization of surface soil structure due to repeated passes. Does not create uniform rootzone. Some vines feel one rip, intersection of two rips, intersection of three rips, and some are where the soil was not ripped at all. Paul R. Anamosa, Paul R. Anamosa, Ph.D. - Vineyard Ph.D - Vineyard Soil Technologies Soil Technologies - 707 255-3351 13
Vector Force Winged Shank Vector force is up. Lifts soil up and drops it off of the back. Loosens but does not compress or pulverize soil structure Paul R. Anamosa, Paul R. Anamosa, Ph.D. - Vineyard Ph.D - Vineyard Soil Technologies Soil Technologies - 707 255-3351 14
Tilth: Soil Structure and its Management Sonoma County Vineyard Technical Group May 18, 2017 Ripped to 24 with Winged Shank on 6 ft. centers Sine curve Paul R. Anamosa, Paul R. Anamosa, Ph.D. - Vineyard Ph.D - Vineyard Soil Technologies Soil Technologies - 707 255-3351 Ripped to 30 with Winged tine on 4 ft. centers Paul R. Anamosa, Paul R. Anamosa, Ph.D. - Vineyard Ph.D - Vineyard Soil Technologies Soil Technologies - 707 255-3351 15
In-Row Tillage Used to remove compaction zone from sprayers. Very effective due to winged shank Limited by equipment that can pass the row width and still pull to 18 depth. Mould-board Plow Mixes and inverts soil. Overworks aggregates and causes structural degradation. Brings low fertility and possibly toxic material subsoil (Na, Cl, B, Al) to top. Disperses nutrients that are naturally concentrated near surface: organic matter, phosphorus, nitrogen. Usually not bad - but not as good as winged tine. 16
Tilth: Soil Structure and its Management Sonoma County Vineyard Technical Group May 18, 2017 What tine is it? Straight shank should be used on land that has slightly fractured bedrock or very hard soil such as a duripan or cementation within the deep tillage zone. A Winged shank will skip across these layers. Winged shank should be used on all other soils: clayey, deep, rounded rock, etc. Paul R. Anamosa, Paul R. Anamosa, Ph.D. - Vineyard Ph.D - Vineyard Soil Technologies Soil Technologies - 707 255-3351 How wet should a soil be to till? 17
Very Highly Plastic Clay Very highly plastic clay will deform and compress upon application of a sheer or compressional stress. The compression causes the removal of air pores. Soil becomes more dense. If wetter than the plastic limit, the soil will become puddled like modeling clay. Puddled soils have many fewer air pores, become hard even when moist, restrict root penetration, and restrict water and air drainage. Great for rice and the lining of reservoirs. Thus soil must be dryer than the plastic limit in order to till it effectively. Soil dryer than the plastic limit is brittle. Very Highly Plastic Clay Management Rice farmers puddle their soils to prevent water from leaking out the bottom of their rice paddies. Drying plastic clays sufficient to be effectively ripped is typically very difficult for depths below 18 to 24. Monitoring the soil moisture prior to deep tillage will be imperative. Consider a deep rooted winter cover crop of safflower, barley, triticale, etc. Till with a winged shank to get vector force up. 18
Tilth: Soil Structure and its Management Sonoma County Vineyard Technical Group May 18, 2017 Same soil before and after puddling 2006 2011 Examples of Puddled subsoils 19
Field Assessment of the Plastic Limit 1. Auger in 12 increments to intended ripping depth. 2. Knead soil to press out all pebbles and structural aggregates. Field Assessment of the Plastic Limit 3. Roll soil into a sphere > 4. Slowly roll the soil between the palms to try and form a noodle 1/8 th of an inch in diameter. 20
Tilth: Soil Structure and its Management Sonoma County Vineyard Technical Group May 18, 2017 The soil is still too moist if it soil can be rolled into an unbroken noodle to a diameter of 1/8 th inch Do not till! Field Assessment of the Plastic Limit Broken noodle at ¼ inch - this is dryer than the plastic limit and can be tilled. 21
Summary: Soil tilth and structure are important because they govern soil water and air movement, and penetrability by roots. The goal of managing soil structure is to reduce the bulk density by increasing the porosity. Porosity can be increased by organic matter, vegetation roots, and tillage. The choice of tillage implement is dependent on soil properties, and the timing is dependent on the current soil plasticity. Monitor soil plasticity prior to deep tillage to ensure it is sufficiently dry to till. If too wet, either let dry more or rip shallower to the depth of non-plastic soil. Best covercrop for drying clayey subsoils is Safflower. 22