Soils and Cultivation Soils are defined as the loose surface of the earth, or that material which nourishes and supports growing plant, or the material which supports foundations, roads, etc. But common sense tells us that soils are the solid medium in which plants grow.

Functions of Soils l Plant support l Supplies H 2 O, Oxygen l Supplies Nutrients l Protection from stresses l Magic -symbiotic relationships -unknown chemicals/substances

Chemical Composition of Earth’s Crust

Where Do Soils Come From? l Parent Rock breaks down into smaller rocks, then gravel, then further into sand sized particles. Sand is further broken down into silt sized particles. To this point, it is mainly a matter of subdividing the original parent rock. This means that the chemical composition of sand and silt is very similar to the parent rock.

Where Do Soils Come From? l Clay, on the other hand, is very different. In addition to being much smaller than the other particles, it has unique structures, and is unlike the parent rock material. Clay has a very large surface area; surfaces are where things happen in a soil. Clay is chemically very reactive, and dominates the soil in terms of its effect on soil processes.

Where Do Soils Come From? l Weathering is the process that converts parent rock material into a soil. It is a very long term process. Several different components contribute to weathering, including the type of parent material, climate (temperature, rainfall, freeze/thaw cycles), plants, and microorganisms.

Soil Components l Solids - sand, silt and clay, organic matter l Pore spaces - water-filled air-filled Solids Water Air

Balance of Aeration and Moisture Solid Water Air Solid Water Air Ideal balance Waterlogged soil Compacted soil

Characteristics of Soils l Physical Properties l Chemical Properties (Nutrition) l Reactivity (pH) l Organic Matter l Biological Activity

Physical Properties: Soil Separates

Soil Class l Soils are usually composed of several or many “separates”. The proportions of the component separates determines the soil class. For example, a soil might contain 20% clay, 40% silt and 40% sand. This mixture is classified as a loam, based on the soil textural triangle. Soil texture is very important, but so is soil structure.

Soil Textural Triangle

Soil Structure l How the soil particles are arranged and associated with each other is called soil structure. Individual particles aggregate together, glued by attractive forces and by microbial activity plus organic matter. Soil structure can improve a poor soil texture.

Soil Porosity l Pores exist between individual soil particles. These may be either large (macropores) or small (micropores), which is largely determined by the size of the individual particles and aggregates. Pores size is important because it determines permeability and percolation rate.

Fine textured soils, lots of micropores, some macropores Coarse textured soils, mainly macropores

Soil Percolation, Infiltration l Percolation is how quickly water moves through a soil l Infiltration is how quickly water moves into a soil from the surface l Both depend on pore structure. Both are important considerations in water management and drainage design.

Soil Porosity l Macropores are large enough to drain after being filled with water from rain or irrigation. Air enters after water drains, which is very important for root health. l Micropores are small enough to hold water against the downward force of gravity. This water is what the plant uses.

Soil Aeration l Soil aeration is one of the most important factors affecting turf health. Poor aeration can lead to root death. The black layer often found in putting greens is due to poor aeration. l You can improve aeration by encouraging good soil structure and by cultivation.

Soil Compaction l Soil compaction occurs when forces, such as tire or foot traffic, compress the soil and alter pore structure. Bulk density increases, macropores decrease, infiltration decreases, aeration decreases. Compaction is most a problem when soils are wet. A similar problem is caused by shearing forces or puddling of soil surfaces.

Soil Compaction l Soil compaction is controlled by restricting traffic, modifying soils, and cultivation. l Soils can be modified to resist compaction, but it’s not as simple as it sounds. The old dogma about adding a little sand to lighten a heavy soil is just plain wrong. But pure sands are great for resisting compaction. l Cultivation is practiced in many forms.

Soil Cultivation l Cultivation before planting is pretty easy, as long as the soil is not too wet. l Cultivation after planting is the basis of an entire equipment industry. Pieces include hollow and solid tine aerifiers, water injectors, air injectors, slicers, spikers, wing blades, and Klingon disruptor beams.

Ryan Core Aerifier

Rotating Hollow Tines

Soil Cores

Soil Cultivation l What does cultivation do? The idea is to increase the surface area or increase the macropore space to facilitate infiltration and percolation, and to increase air diffusion into the soil. Core cultivation, especially solid tine, can create compaction around the holes. A plow layer can occur when same tine depth is always used.

Soil Cation Exchange Capacity l CEC is a measure of how negatively charged a soil is, and is related to clay content. Sands have very low CEC’s, silts somewhat higher, but clays usually have very high CEC’s. Cation exchange sites occur at the surface of a soil particle, and are negatively charged. They attract cations, such as NH 4, K, Ca, Mg, etc.

Soil Cation Exchange Capacity l CEC is important because it represents a reservoir of some nutrients for the plant. Cations stick fairly tightly to the sites, but on occasion come off and go into solution in the soil water. These cations can then be absorbed by the plant roots.

Cation Exchange Clay particle K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ Ca ++ Mg ++ NH 4 + __ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _

Cation Exchange Clay particle K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ Ca ++ Mg ++ NH 4 + __ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _

Soil Reactivity l Soil reactivity is a measure of how acid a soil is, or soil pH. Soil pH affects root function and nutrient availability, and must be monitored by the turf manager. l Most soils have pH’s between 5 and 9, with somewhere around 6.5 being ideal for most grasses. l Many of our soils are quite acid. Why?

Soil pH l Many of our soils are highly weathered. This means that most of the basic cations (K, and especially Ca and Mg) have been washed out of the soil. They are replaced by protons (H), which are the basic unit of acidity. l This contrasts to younger soils, which are less weathered and more neutral.

Cation Exchange, Acidic Soils Clay particle K+K+ K+K+ K+K+ K+K+ K+K+ H+H+ NH 4 + __ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+

Cation Exchange, Acidic Soils Clay particle K+K+ K+K+ K+K+ K+K+ K+K+ H+H+ NH 4 + __ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+

Soil pH l How do we control soil pH? l If the soil is acid, we need to raise the pH towards neutral. The most common way is to lime the soil. Lime is calcium carbonate, or calcium plus magnesium carbonate. The amount required will depend on the soil, and should be determined by a soil analysis. l Lime granule size is important also.

Soil pH l Lime can be applied either preplant (high rates can be used all at once) or to a mature turf. But then, lower rates are necessary. Do not apply more than pounds of lime per thousand square feet to an existing turf. Water in after application. Several to many applications may be required.

Soil Nutrients l C, H, O, from the air, water l The rest from the soil l C HOPKNS CaFe ClZn, MoB CuMn Mg l See Hopkins Cafe Closin’, Mob Comin’ with Machine Guns

Soil Nutrients l Many nutrients are in adequate supply in the soil, and do not need to be added l Some are readily lost from the soil, or are present but not available. These need to be added as fertilizer. N, P, sometimes K, Fe, rarely S.

Soil Nutrients l The only way to tell if your soil has special needs, or even routine needs, is by a soil test using a reputable lab. Home chemistry kits are not usually practical or accurate. l Samples should represent an entire use area. Collect 12 or more cores, 4- 6”deep and mix them together. A total of about a quart is usually more than enough for the lab.