Jenny Equation

Origins

The Jenny Equation was created by Hans Jenny to explain the soil formation process. It was first internationally recognized when Hans Jenny published his book “Factors of Soil Formation” in 1941. The Jenny Equation is a formula used to help determine the properties of the soil such as fertility and mineral composition, as well as the organisms living within the soil and the chemical reactions that will occur around plant roots and the other organisms.

Hans Jenny

A photograph of Hans Jenny

Hans Jenny was born in Switzerland in 1899. His college career started with the Swiss Federal Institute of Technology (Zurich) where he received a bachelor in agriculture in 1922. He later received degrees in chemistry and ion exchange reactions by 1927, also from Zurich. In 1936 he joined The University of California, Berkeley as a member of the faculty. His intensive education helped him formulate the Jenny Equation, which is S = f(cl, o, r, p, t, …). In this equation the “S” represents soil formation, "cl" is climate, "o" is organisms in the soil, "r" is relief such as the topography, “p” is the parent material, “t” is the time that takes place. He left the “…” in case something new was discovered or needed to be added later.

Uses of Jenny Equation

The Jenny Equation helps determine the physical properties of soil based on several independent factors. These factors known as the pedogenic processes which in this equation are; climate, organisms, topography, parent material, time and any other factors that may apply. The Jenny equation is used to help make soil maps, this will show you what the soil contains and helps determine what it is useful for.

Climate

The climate has a big effect on the soils, rainfall has the impact of weathering and erosion. This helps to break down the larger rocks and other soil particles into smaller pieces. Two of the most influential factors of climate are temperature and moisture. Temperature has a direct effect on the rate that chemical reactions can occur in the soil. The higher the temperature the quicker the reactions will happen with in the soil. Moisture also affects the rates of chemical reactions that can happen in the soil. The higher the moisture levels the higher the rate of chemical reactions will occur. This will allow plants to grow faster, as well as allowing the bacteria and fungus to be more active. This includes the decomposers to decompose dead organisms much faster when the temperature and moisture levels are high.

Organisms

Main article: Organisms

The organisms in the soil also influence the soils processes and functions. The vegetation and animals have a significant role. Plants roots help to break up the soil by creating more surface area for water to seep into. This allows chemical reactions to occur here as plants excrete chemicals that help these chemical reactions to take place. These chemicals also attract bacteria and fungi, which allow them to help speed up the roots' ability to uptake nutrients as well as fend off harmful chemicals and organisms. Bacteria and fungi also can multiply and decompose detritus more easily. Dead organisms in the soil allow for more nutrients to be available for plant uptake after decomposition begins, which also enhances soil fertility.

Topography

The next factor that is in the equation is topography. Topography is the slope of the land, whether there is a hill or a valley or a flat plain. The topography of the land has a big effect on the moisture content of the soil. For example, a hill will have a lower moisture content because of the increased runoff. A valley will have a very high moisture content because the amount of water that can go into the soil is higher as the water will puddle up and have more time to infiltrate. A plain will have a medium amount of moisture in the soil. The slope also effects the type of vegetation that can grow as there will be more moisture in some areas than others.

Parent Material

The parent material of the soil is determined from what type of rock it is derived from. Igneous, metamorphic, or sedimentary rock break down and create different types of soil, whether it is sandy, silt or clay dominated soil. The breaking down of the soil increases the surface area which allows more reactions to happen, the soil can hold more water, and more organisms can live within it. The parent material will also determine what kind of minerals make up the soil. For example, if some rock rich in phosphorous, breaks down due to weathering, the soil that it creates will have a higher content of phosphorus. The minerals in the soil, will affect the types of organisms and plants that can thrive in the soil. In a soil is darker colored it is from a volcanic eruption these are metamorphic rocks, and lighter soils are formed from igneous rocks.

Time

Time is the next variable in the equation, the amount of time directly effects the weathering rates. As the time increases the more weathering can occur, this allows the parent material to break down further and create different minerals and smaller soil particles. Time also effects the amount of growth a plant will have. And interact with the soil, through roots and the chemicals released by them, as well as the uptake of nutrients.

Additional Factors

Hans Jenny also left room in the equation for any other factor that he could not think of, or has yet to be discovered. However, nothing since has been added to Hans Jenny’s equation since it was wrote in 1941. As no new factors have been discovered that influence the way soils react with its environment.