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Tilth is a physical condition of soil, especially in relation to its suitability for planting or growing a crop. Factors that determine tilth include the formation and stability of aggregated soil particles, moisture content, degree of aeration, soil biota, rate of water infiltration and drainage. Tilth can change rapidly, depending on environmental factors such as changes in moisture, tillage and soil amendments. The objective of tillage (mechanical manipulation of the soil) is to improve tilth, thereby increasing crop production; in the long term, however, conventional tillage, especially plowing, often has the opposite effect, causing the soil carbon sponge to oxidize, break down and become compacted. [1]


Soil with good tilth is spongy with large pore spaces for air infiltration and water movement. Roots only grow where the soil tilth allows for adequate levels of soil oxygen. Such soil also holds a reasonable supply of water and nutrients. [2]

Tillage, organic matter amendments, fertilization and irrigation can each improve tilth, but when used excessively, can have the opposite effect. [2] Crop rotation and cover crops can rebuild the soil carbon sponge and positively impact tilth. A combined approach can produce the greatest improvement.[ citation needed ]


Good tilth shares a balanced relation between soil-aggregate tensile strength and friability, in which it has a stable mixture of aggregate soil particles that can be readily broken up by shallow non-abrasive tilling. A high tensile strength will result in large cemented clods of compacted soil with low friability. Proper management of agricultural soils can positively impact soil aggregation and improve tilth quality. [3]

Aggregation is positively associated with tilth. With finer-textured soils, aggregates may in turn be made up of smaller aggregates. Aggregation implies substantial pores between individual aggregates. [4]

Aggregation is important in the subsoil, the layer below tillage. Such aggregates involve larger (2- to 6-inch) blocks of soil that are more angular and not as distinctive. These aggregates are less impacted by biological activity than the tillage layer. Subsurface aggregates are important for root growth deep into the profile. Deep roots allow greater access to moisture, which helps in drought periods. Subsoil aggregates can also be compacted, mainly by heavy equipment on wet soil. Another significant source of subsoil compaction is the practice of plowing with tractor wheels in the open furrow. [4]

Pore size

Soil that is well aggregated has a range of pore sizes. Each pore size plays a role in soil's physical functioning. Large pores drain rapidly and are needed for good air exchange during wet periods, preventing oxygen deficiency that can drown plants and increase pest problems. Oxygen-deficient wet soils increase denitrification - conversion of nitrogen to gaseous forms. In degraded soil large pores are compressed into small ones. [4]

Small pores are critical for water retention and help a crop endure dry periods with minimal yield loss. [4]


Soil tilth is naturally maintained by the interaction of plant roots with the soil biota. [5]

Short lived tilth can be obtained through mechanical and biological manipulation.


In 2021, the globally tilled soil volume was estimated at 1840 km3/yr. This value exceeds by two orders of magnitude the global total of all engineering earthworks. [6] For comparison globally, the natural process of soil bioturbation by plant roots and earthworms, was estimated at 960 km3/yr. [7]

Mechanical soil cultivation practices, including primary tillage (mold-board or chisel plowing) followed by secondary tillage (disking, harrowing, etc.), break up and aerate soil. Mechanical traffic and intensive tilling methods have a negative impact on soil aggregates, friability, soil porosity, and soil-bulk density. When soils become degraded and compacted, such tillage practices are often deemed necessary. The tilth created by tillage, however, tends to be unstable, because the aggregation is obtained through the physical manipulation of the soil, which is short lived, especially after years of intensive tillage. [4] The compaction of soil aggregates can also decrease soil biota due to the low levels of oxygen in the top-soil. The resulting high soil-bulk density results in lower water infiltration from rainfall or conventional irrigation (surface, sprinkler, center-pivot); in turn, the series of processes will naturally erode and dissolve small soil particles and organic matter. [8] The consequences from these processes cyclically require more tilling and intervention, thus tillage practices have the capability to disrupt biological mechanisms that stabilize soil structure, the soil carbon sponge and tilth quality. [9]


The preferred scenario for good tilth is as the result of natural soil-building processes, provided by the activity of plant roots, microorganisms, earthworms and other beneficial organisms. Such stable aggregates break apart during tillage/planting and readily provide good tilth. [4] Soil biota and organic matter work in unison to bind soil aggregates and establish a natural soil stability - a soil carbon sponge. Plant root exudates feed bacteria that emit extracellular polysaccharides (EPS), and feed the growth of fungal hyphae, to form a soil carbon sponge with the dispersed clay particles. These active tilth-forming processes contribute to the formation and stabilization of soil structure. [3] The resulting soil structure reduces tensile strength and soil-bulk density while still forming soil aggregates through their abiotic/biotic binding mechanisms that resist breakdown during water saturation. The fungal hyphae networks can establish a role of enmeshment with EPS and rhizodeposition, thus improving aggregate stability. [3] However, these organic materials are themselves subject to biological degradation, requiring active amendments with organic material, and minimal mechanical tillage. [4] Tilth quality is heavily dependent on these naturally binding processes between biotic microorganisms and abiotic soil particles, as well as the necessary input of organic matter. All constituents in this naturally binding network must be supplied or managed in agriculture to ensure the sustainability of their presence through growing seasons.


Crop rotation can help restore tilth in compacted soils. Two processes contribute to this gain. First, accelerated organic matter decomposition from tillage ends under the sod crop. Another way to achieve this is via no-till farming. Second, grass and legume sods develop extensive root systems that continually grow and die off. The dead roots supply a source of active organic matter, which feeds soil organisms that create aggregation - the soil carbon sponge. Beneficial organisms need continual supplies of organic matter to sustain themselves and they deposit the digested materials on soil aggregates and thereby stabilize them. Also, the living roots and symbiotic microorganisms (for example, mycorrhizal fungi) can exude organic materials that nourish soil organisms and help with aggregation. Grass and legume sod crops therefore deposit more organic matter in the soil than most other crops. [4]

Some annual rotation crops such as buckwheat also have dense, fibrous, root systems and can improve tilth. Crop mixtures with different rooting systems can be beneficial. For example, red clover seeded into winter wheat provide additional roots and a more protein-rich soil organic matter. [4]

Other rotation crops are more valuable for improving subsoils. Perennial crops such as alfalfa have strong, deep, penetrating tap roots that can push through hard layers, especially during wet periods when the soil is soft. These deep roots establish pathways for water and future plant roots, and produce soil organic matter. [4]

Crops rotation can extend the period of active growth compared to conventional row crops, leaving more organic material behind. For example, in a corn-soybean rotation, active growth occurs 32% of the time, while a dry bean–winter wheat–corn rotation is active 72% of the time. Crops such as rye, wheat, oat, barley, pea and cool-season grasses grow actively in the late fall and early spring when other crops are inactive. They are beneficial both as rotation and cover crops, although intensive tillage can negate their effects. [4]

Soil types

The soil management practices required to maintain soil tilth are a function of the type of soil. Sandy and gravelly soils are naturally deficient in small pores and are therefore drought prone, whereas loams and clays can retain and thus supply crops with more water. [4]

Coarse-textured, sandy soils

Sandy soil has lower capacity to hold water and nutrients. Water is applied more frequently in smaller amounts to avoid it leaching and carrying nutrients below the root zone. Routine application of organic matter increases sandy soil's ability to hold water and nutrients by 10 times or more. [2]

Fine-textured, clay soils

Clay soils lack large pores, restricting both water and air movement. During irrigation or rain events, the limited large pore space in fine-textured soils quickly fills with water, reducing soil oxygen levels. In addition to routine application of organic matter, microorganisms and earthworms perform a crucial assist to soil tilth. As microorganisms decompose the organic matter, soil particles bind together into larger aggregates, increasing large pore space. Clay soils are more subject to soil compaction, which reduces large pore spaces. [2]

Gravelly and decomposed granite soils

Such soils natively have little tilth, especially once they have been disturbed. Adding organic matter up to 25% by volume can help compensate. For example, if tilling to a depth of eight inches, add two inches of organic materials. [2]

See also

Related Research Articles

Soil Mixture of organic matter, minerals, gases, liquids, and organisms that together support life

Soil is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Earth's body of soil, called the pedosphere, has four important functions:

Tillage Preparation of soil by mechanical agitation

Tillage is the agricultural preparation of soil by mechanical agitation of various types, such as digging, stirring, and overturning. Examples of human-powered tilling methods using hand tools include shoveling, picking, mattock work, hoeing, and raking. Examples of draft-animal-powered or mechanized work include ploughing, rototilling, rolling with cultipackers or other rollers, harrowing, and cultivating with cultivator shanks (teeth).

Crop rotation Agricultural practice of changing crops

Crop rotation is the practice of growing a series of different types of crops in the same area across a sequence of growing seasons. It reduces reliance on one set of nutrients, pest and weed pressure, and the probability of developing resistant pests and weeds.

Soil structure describes the arrangement or the way of soil in the solid parts of the soil and of the pore space located between them. It is determined by how individual soil granules clump, bind together, and aggregate, resulting in the arrangement of soil pores between them. Soil has a major influence on water and air movement, biological activity, root growth and seedling emergence. There are several different types of soil structure. It is inherently a dynamic and complex system that is affected by different factors.

In agriculture, a green manure is a crop specifically produced to be incorporated into the soil while still green. Typically, the green manure's biomass is incorporated with a plow or disk, as is often done with (brown) manure. The primary goal is to add organic matter to the soil for its benefits. Green manuring is often used with legume crops to add nitrogen to the soil for following crops, especially in organic farming, but is also used in conventional farming.

Topsoil Top layer of soil

Topsoil is the upper, outermost layer of soil, usually the top 5–10 inches (13–25 cm). It has the highest concentration of organic matter and microorganisms and is where most of the Earth's biological soil activity occurs. Topsoil is composed of mineral particles, organic matter, water, and air. Organic matter varies in quantity in different soils. The strength of soil structure decreases with the presence of organic matter, creating weak bearing capacities. Organic matter condenses and settles in different ways under certain conditions, such as roadbeds and foundations. The structure becomes affected once the soil is dehydrated. Dehydrated topsoil volume substantially decreases and may suffer wind erosion.

No-till farming Agricultural method which does not disturb soil through tillage.

No-till farming is an agricultural technique for growing crops or pasture without disturbing the soil through tillage. No-till farming decreases the amount of soil erosion tillage causes in certain soils, especially in sandy and dry soils on sloping terrain. Other possible benefits include an increase in the amount of water that infiltrates into the soil, soil retention of organic matter, and nutrient cycling. These methods may increase the amount and variety of life in and on the soil. While conventional no-tillage systems use herbicides to control weeds, organic systems use a combination of strategies, such as planting cover crops as mulch to suppress weeds.

Nutrient management

Nutrient management is the science and practice directed to link soil, crop, weather, and hydrologic factors with cultural, irrigation, and soil and water conservation practices to achieve optimal nutrient use efficiency, crop yields, crop quality, and economic returns, while reducing off-site transport of nutrients (fertilizer) that may impact the environment. It involves matching a specific field soil, climate, and crop management conditions to rate, source, timing, and place of nutrient application.

Agricultural soil science Branch of soil science

Agricultural soil science is a branch of soil science that deals with the study of edaphic conditions as they relate to the production of food and fiber. In this context, it is also a constituent of the field of agronomy and is thus also described as soil agronomy.

Soil chemistry is the study of the chemical characteristics of soil. Soil chemistry is affected by mineral composition, organic matter and environmental factors. Back in the early 1850s a consulting chemist to the Royal Agricultural Society in England, named J. Thomas Way, performed many experiments on how soils exchange ions. As a result of his diligent and strenuous work, he is considered the father of soil chemistry. But after him, many other big-name scientists also contributed to this branch of ecology including Edmund Ruffin, Linus Pauling, and many others.

Soil biodiversity refers to the relationship of soil to biodiversity and to aspects of the soil that can be managed in relation to biodiversity. Soil biodiversity relates to some catchment management considerations.

The term cropping system refers to the crops, crop sequences and management techniques used on a particular agricultural field over a period of years. It includes all spatial and temporal aspects of managing an agricultural system. Historically, cropping systems have been designed to maximise yield, but modern agriculture is increasingly concerned with promoting environmental sustainability in cropping systems.

Soil management is the application of operations, practices, and treatments to protect soil and enhance its performance. It includes soil conservation, soil amendment, and optimal soil health. In agriculture, some amount of soil management is needed both in nonorganic and organic types to prevent agricultural land from becoming poorly productive over decades. Organic farming in particular emphasizes optimal soil management, because it uses soil health as the exclusive or nearly exclusive source of its fertilization and pest control.


Peds are aggregates of soil particles formed as a result of pedogenic processes; this natural organization of particles forms discrete units separated by pores or voids. The term is generally used for macroscopic structural units when observing soils in the field. Soil peds should be described when the soil is dry or slightly moist, as they can be difficult to distinguish when wet.

Soil compaction (agriculture)

Soil compaction, also known as soil structure degradation, is the increase of bulk density or decrease in porosity of soil due to externally or internally applied loads. Compaction can adversely affect nearly all physical, chemical and biological properties and functions of soil. Together with soil erosion, it is regarded as the "costliest and most serious environmental problem caused by conventional agriculture."

Particulate organic matter

Particulate organic matter (POM) is a fraction of total organic matter operationally defined as that which does not pass through a filter pore size that typically ranges in size from 0.053 to 2 millimeters.

Soil aggregate stability

Soil aggregate stability is a measure of the ability of soil aggregates to resist degradation when exposed to external forces such as water erosion and wind erosion, shrinking and swelling processes, and tillage. Soil aggregate stability is a measure of soil structure and can be impacted by soil management.

This glossary of agriculture is a list of definitions of terms and concepts used in agriculture, its sub-disciplines, and related fields. For other glossaries relevant to agricultural science, see Glossary of biology, Glossary of ecology, Glossary of environmental science, and Glossary of botany.

The physical properties of soil, in order of decreasing importance for ecosystem services such as crop production, are texture, structure, bulk density, porosity, consistency, temperature, colour and resistivity. Soil texture is determined by the relative proportion of the three kinds of soil mineral particles, called soil separates: sand, silt, and clay. At the next larger scale, soil structures called peds or more commonly soil aggregates are created from the soil separates when iron oxides, carbonates, clay, silica and humus, coat particles and cause them to adhere into larger, relatively stable secondary structures. Soil bulk density, when determined at standardized moisture conditions, is an estimate of soil compaction. Soil porosity consists of the void part of the soil volume and is occupied by gases or water. Soil consistency is the ability of soil materials to stick together. Soil temperature and colour are self-defining. Resistivity refers to the resistance to conduction of electric currents and affects the rate of corrosion of metal and concrete structures which are buried in soil. These properties vary through the depth of a soil profile, i.e. through soil horizons. Most of these properties determine the aeration of the soil and the ability of water to infiltrate and to be held within the soil.

Soil carbon sponge is porous, well-aggregated soil in good health, better able to absorb and retain water. Australian microbiologist and climatologist, Walter Jehne, articulated the concept of the soil carbon sponge in his 2017 paper, Regenerate Earth, connecting soil carbon with a restored water cycle able induce planetary cooling through evaporative cooling and higher reflectance of denser green vegetation. Cooling from increased cloud formation is another benefit of soil regeneration anticipated by Jehne.


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