Atmospheric interactions

The atmosphere directly influences the biogeochemical processes of soil by depositing and removal of materials. For atmospheric deposition, elements can be added to soils from wet processes (precipitation such as snow, rain, sleet, fog), dry processes (particulates or dust) or a mix (aerosols).

Wet deposition is an important source for dissolved compounds from the atmosphere to soils, ranging from nitrogen and carbon compounds to inorganic nutrients like calcium and magnesium. In and near marine coastlines, wet deposition may also deliver a wide array of elements that generally occur in low concentrations soils. Wet deposition can also affect the acidity of soils by depositing weak to moderate concentrations of acids, such as carbonic acid, nitric, and sulfuric acid. This is has been particularly impactful for soils downwind of anthropogenic emitters where coal and industrial processes occur. This drove the acid rain problems across the northeastern United States

Dry deposition is the movement of particulates, either natural or human-derived, from the atmosphere to soils. Dry deposition can move clay, silt, and sand sized particles from one area to another. Generally clay and silt are the most susceptible to deposition and can be sourced from thousands of miles away. For example, clay sized particles from North Africa frequently traverse the Atlantic ocean, reaching homes and forests across the southern United States, from Mobile, Alabama to Atlanta, Georgia (Propsero, 1999).

The atmosphere can affect soil biogeochemistry removing soil materials or serving as a sink for elements. Fine particulates like clay and silt can undergo suspension in wind. Larger particles like coarse sand and gravel are too heavy to be transported by suspension in wind. However, they can travel hundreds of miles by saltation, a type of ‘hopping’ and ‘bouncing’ along soil surface. For even larger particles, they can creep along the ground from strong enough gusts and wind bursts. The atmosphere can also move materials from soil surfaces by blowing away leaves and vegetation, especially during hurricanes, tornadoes, and other extreme weather events.

Soil biogeochemistry of inorganic compounds is strongly affected by diffusion and deposition of volatile elements. For example, carbon dioxide can volatilize straight to the atmosphere, but wet soils with dissolved compounds can capture carbon dioxide. This is very important as the sequestration of carbon dioxide in calcium carbonate deposits is a large global carbon sink. Metals with low vapor pressures can also volatilize as well, such as mercury.

Rock and mineral weathering
Inorganic nutrients, like phosphorus, potassium, and calcium, are derived from weathering of rocks and minerals. Chemical weathering occurs in by chemical reactions when water and dissolved compounds interact with rock and mineral surfaces. Physical weathering is the disintegration of rocks by heating, cooling, and physical stresses. Both processes serve to increase the surface area and dissolution of minerals from solid compounds into dissolved solutes or secondary solid compounds. There are many types of chemical weathering reactions but two of the most important are the oxidation of elements or dissolution from acid reactions. Oxidation occurs when elements become exposed to oxygen and transition to more oxidized states, like iron being exposed to water and rusting. Minerals react with acids and dissolve, like limestone statues or inscriptions wearing away to unrecognizable features due to acid rain. Physical weathering can occur from rocks become exposed to high temperatures in the summer in deserts or during cold snaps during winter. And much like cooling a hot glass to fast or putting an ice cube into a warm drink, stresses build in the rock at the molecular and visible scales. In both cases, if rocks undergoing stresses are unable to endure it, they can crack and crumble. 
Plant cycling
In terrestrial ecosystems, plants exert a substantial influence on how elements are cycled in surface soils. Plants affect the mobility, distribution and abundance of elements in soils. Their roots affect the chemistry of soils, their nutritional needs move elements aboveground, and their death and shedding of wood and leaves are a source for elements to soils from litterfall. To meet their nutritional need, plants can increase the mobility and availability of elements from rocks and minerals. Plant roots excrete organic acids and other compounds that directly and indirectly help dissolve minerals. Organic acids can bind directly to elements on mineral surfaces and bring them into solution. Other carbon compounds from plant roots can support fungi and bacteria, which secrete their own mineral dissolving compounds. Plants also influence the distribution and abundance of elements in soils. Plants move elements from belowground in the soil to aboveground in their leaves and woody materials. This action serves as a ‘biological pump’, moving elements from within soil, and concentrating them in surface horizons, specifically the forest floor and A horizon (sometimes referred to as topsoil). In addition, plants biologically pump the specific elements they need. Plant roots have specialized tissues that promote the accumulation of nutrient elements they need from soil while keeping out elements that are not essential.
Leaching and water movements

Leaching is the process of water carrying soluble substances or small particles through soil or rock. Leaching is captures two important processes simultaneously, chemical interactions with rock and mineral surfaces and physical movement of water. As the water passes through the rock and soil, it interacts with the surfaces of the materials. Compounds on the surface of minerals can be become dissolved. In addition, the physical movement of water can dislodge and moving small clay and silt particles downward.

In semi-arid areas, leaching preventing salt accumulation in soil but can remove nutrients from the plant rooting zone. The Food and Agriculture Organization of the United States estimates 45 million hectares of the 230 million hectares of irrigated croplands are salt-affected. The accumulation of sodium, potassium, calcium, and magnesium can interfere with the ability for plants to obtain water, causing them to wilt and dry-out easier. On the opposite end, excessive leaching can move nutrients from soils and into surface and groundwater. This is a double problem as farmers lose the inorganic nutrients they paid for and contributes to eutrophication and algae blooms in lakes, rivers, and even oceans.