peering into the processes: soil functions

plant growth

when a seed is planted, it is already packed full of the carbohydrates and other nutrients needed for the plant’s initial growth.

photosynthesis

as plant shoots grow aboveground, they act like solar panels, using energy from the sun to convert CO2 from the atmosphere into the building blocks of life (i.e. carbohydrates, proteins, fats, nucleic acids).

nutrient uptake

building these organic molecules also requires water and nutrients. as roots grow, they take up nutrients dissolved in water (the "soil solution") or from the surfaces of soil particles.

nutrient cycling

some nutrients are more mobile than others, making it easier for plants to access and take them up

mobile nutrientslarger uptake zoneimmobile nutrientssmaller uptake zone

carbonic acid

plants respire some carbon out of their roots as CO2, which forms carbonic acid in water, and can lead to increased mineral weathering and nutrient availability.

root ion exchange

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plant roots also release H+, or protons, which can replace other positively charged ions (often plant nutrients) on soil surfaces, making them available for plant uptake.

ph & nutrient availability

ph determines the amount and type of charge on soil minerals and organic matter (the exchange complex), as well as the amount of protons (H+) or hydroxyls (OH-) in the soil solution; driving overall nutrient availability.

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metabolism

meanwhile, up to 60% of the plant's carbon is being pumped underground in the form of organic compounds (i.e. sugars, amino acids); providing food/fuel for soil microbes.

decomposition

plant residues fall to the surface, roots slough off, and the soil food web eats and is eaten; cycling carbon and nutrients throughout the soil system.

with sufficient nitrogen, microbes don’twork as hard to build biomass, respiring less CO2 and mineralizing nitrogen for plant uptake.alfalfalowcarbon:nitrogenplant roots release sugars into the rhizosphere,which microbes convert to biomass more easily than residues.without enough nitrogen, microbes mine the soil for it, reducing availabilityfor plants and blowing off more CO2 overall.barleyhigh carbon:nitrogenprotozoa and nematodes graze on soil fungi and bacteria, releasing plant-available nitrogen.microbes break down soil organic matter, releasing all 17 plant essential nutrients and building biomass.microbes eat, convert into biomass & grow/multiplymicrobes die or are preyed ondead microbes and their byproducts are bound upwith minerals (newSOM)nativesom

mineral weathering

as microbes consume carbon based compounds, they also excrete acids thatweather minerals, releasing nutrients for plant uptake.

animal inputs

above ground, animals nibble on plants. in response, plants change their root growth patterns and pump more carbon underground, in search of nutrients for regrowth. this herbivory has been shown to increase soil microbial biomass and activity.

urine and feces that grazers leave behind provides nutrient-rich food for microbes, enhancing nutrient cycling/availability. applications of these inputs have been found to increase soil organic matter.

trampling from animal hooves helps break up the soil and vegetation. this increases water infiltration, promoting decomposition and seed germination, allowing the cycle to begin again!