Soil

Soil is the biologically active, porous medium that has developed on the uppermost layer of the Earth's crust and is one of the principal substrates of life on Earth. Soil often serves as a reservoir of water and nutrients; it filters and breaks down injurious wastes and is a participant in the cycling of carbon and related elements through the global ecosystem. Soil has evolved through weathering processes driven by biological, climate, and topographic influences.

From a more scientific or soil science perspective, soil can be described as the mineral and organic layer of the earth that has experienced some degree of physical, biological, and chemical weathering. The composition of soil and its main ingredients—minerals, soil organic matter, living organisms, gas, and water— are integrated into a larger system containing soil, rocks, roots, animals, and other parts. Like other interrelated and integrated bodies, soil systems provide integrated functions greater than the parts of the system.

Soil is generally divided into three size classes: clay, silt, and sand. The percentage of particles in any given size class determines the soil's overall texture and can dictate what the soil is best used for. Soils can be very diverse, including clay minerals known as smectite that can shrink and swell upon wetting and drying to such extremes that it could knock over buildings.

Relative sizes of sand, silt, and clay.

In the overall composition of soil, the most common mineral is quartz. The organic matter in soil includes plant, animal, and microbial residue in various states of decomposition. The organic matter of soil is a critical ingredient and one of the best indicators of agricultural soil quality. The color of soil also ranges from common browns, yellows, reds, grays, whites, and blacks, to rare soil colors such as greens and blues. Often the color of the soil offers insight into the mineral and organic composition of the soil.

Distinct soil horizons.

Furthermore, in the body of soil, there are different layers, called soil horizons. These horizons interact with each other and are not independent of each other, despite often being very different from each other. This introduces a great deal of complexity into soil horizons. Below the surface horizons, often more stable layers are found that are formed through a diverse suite of soil formation processes, such as bright white horizons formed through the removal of clays or deep-red, low-fertility horizons formed through millions of years of weathering. Below these horizons, soil transitions into layers that are only partially affected by the soil formation until ultimately forming into layers of parent material.

Soils are often considered renewable resources because they are constantly forming. However, despite this being true, soil formation occurs at an extremely slow rate, with one inch of topsoil taking several hundred years or more to develop. Soil formation rates vary dependent on the local climate, with cold, dry regions requiring over 1000 years to form meaningful layers, while the fastest rates are in hot, wet regions where the formation takes several hundred years.

Because soils are made of horizons, with each layer forming during a specific period of time, these horizons can be used to understand the life of the soil during that period and can yield information about life on Earth during the formation of a given soil horizon. As soil ages, it begins to differentiate its appearance from the parent material, making soil a dynamic and changing material with some components added and some lost.

Soils will also differ depending on the part of the world, even differing from one local region to another; these differences come about based on where and how the soils formed. Over time, there are five major factors to the growth of soil: climate, organisms, relief, parent material, and time; also known as CLORPT.

To identify, understand, and manage soils, soil scientists have developed a soil classification or taxonomy system. Similar to the taxonomy of plants and animals, the soil classification system contains several levels of detail, from general to specific. The most general level of classification in the United States system is the soil order, of which there are twelve; each order is based on one or two dominant physical, chemical, or biological properties that differentiate the types.

One way to determine a soil type is by hand texturing. This is done to understand the behavior, feel, color, sound, and cohesiveness of the soil, which is first achieved by making a bolus. For example, a sandy loam will only just stick together and there will be noticeable sand grains that can be seen, felt, and heard if placed by the ear and squeezed. This is then formed into a ribbon to determine the clay content of the soil, with a longer ribbon having higher clay content. This ribbon is measured against a ruler, and along with the behavior can determine the soil type.

The texture of soil is defined by the particles the soil is composed of: sand, silt, and clay. Sand particles are the largest, and clay particles are the smallest. Although soil can be all sand, all clay, or all silt, most soils are a combination of all three. The percentage of each particle type determines the overall texture of the soil.

The resulting structure of the soil is the arrangement of soil particles into clumps, also called peds. Much like ingredients binding in baking, soil particles bind to form peds. Peds have various shapes, depending on their ingredients and the conditions under which the peds formed—such as getting wet and drying out, freezing and thawing, and even people walking on or farming the soil.

Ped shapes resembled balls, blocks, columns, and plates. Between the peds are spaces or pores, in which air, water, and organisms move. The sizes of the pores and their shapes vary from soil structure to soil structure. A soil's texture and structure then tell how a soil will behave. Granular soils with a loamy texture make the best farmland, for example, because they hold water and nutrients well. On the other hand, single-grained soils with a sandy texture do not make good farmland as the water drains out too fast. While platy soils, regardless of texture, cause water to pond on the soil surface.

Color further gives evidence about the soil's mineral content. Soils high in iron are deep orange-brown to yellow-brown. Those with lots of organic material are dark brown or black; in fact, organic matter masks all other coloring agents. Color further indicates how a soil can behave. Generally, soils that drain well are brightly colored. Whereas one that is often wet and soggy has uneven patterns of greys, reds, and yellows.

It is not just the soil type that affects structure and drainage, but also the activities or environmental factors occurring to them. Root and earthworm activity can improve soil structure through creating large pores. Excessive cultivation, removal of crop residues, and increased traffic contribute to soil degradation, as the soil compacts, which reduces pore size and breaks down soil aggregates.

Examples of different soil types.

The chemical composition of soil also determines structure. When high amounts of sodium are present, clay particles separate and move freely in wet soil. These soils are known as sodic soils. When sodic soils contact water, the water turns milky and the clay disperses; when the soil dries out, a crust forms. Sodicity can be overcome by applying gypsum. Slacking describes the breakdown of aggregates on wetting. This generally occurs when intense rainfall hits dry soil and the aggregates collapse through the pressure of the swelling clay and the trapped air expands and escapes. This process further blocks pore spaces and forms a crust as the soil dries, causing infiltration and seedling emergence problems.

Soil has long been an important part of human industry, being the material which homes are built on, being a common raw material, and being the bed in which agriculture occurs. Despite its use as a raw material for earthenware, brick, tile, mud walls, crockery, idols, buildings, highways, roads, dams, embankments, and related infrastructure, it is in agriculture that soil has arguably its greatest importance.

For both gardening and agriculture, there is a manufactured soil industry, which includes soil types such as garden soil, and with companies such as B.D. White Top Soil Company, Boughton Loam & Turf Management, Jiffy International, London Rock Supplies Limited, Resource Management, Inc., The Scotts Miracle-Gro Company, and Time O'hare Associates often leading the market.

This industry is expected to reach $9.9 billion in market share by 2025, according to estimates that see the industry growing at around 6.9 percent from 2020 to 2025. For years, manufactured soil has been used for farming, where it can be an important ingredient for replenishing nutrients in the soil and creating fertile environments, especially in areas where farming has been constant for a long time and the soil has degraded and lots its productivity. Manufactured soil offers an opportunity to increase the productivity of soils, especially with the growing demand for organic farming and horticulture, the increasing global population, and the associated need to improve yield and productivity, which manufactured soil promises to offer solutions for.

Example of a manufactured soil site.

The manufactured soil industry defines soil varieties differently from soil science, and the type used is determined by the properties of the soil and the crops or plants expected to be grown. The materials often used in manufactured soils include the soil, compost, sand, coir fiber, perlite, vermiculite, and others, such as horticulture sand and peat moss. Further, the industry of manufactured soils can be segmented based on application or type. Application includes the use of manufactured soil for cultivation, lawns, commercial developments, sports fields, and green spaces. Whereas, on the basis of type, the manufactured soil market has been segmented into garden soil, soil mix, manure and compost, and others such as turf sand and organic soil improver.

Image of vermiculite, a common inorganic soil additive.

Many of the materials included in manufactured soil are also referred to as soil additives. These are, as the name implies, additions to the soil in order to improve the nutrient content of the soil and improve soil performance. These include compost, peat moss, and vermiculite and perlite.

Compost refers to the decayed organic material that is used as a soil conditioner and fertilizer for growing plants. The materials used in soil are generally the end result of the composting process and are rich in nutrients. Compost can be made of materials such as shredded twigs, grass clippings, leaves, vegetable scraps, and kitchen waste. The use of compost in soil helps to improve soil structure and texture so that it can hold more nutrients, and also hold air and water.

Peat moss refers to dead fibrous materials that form when mosses and other living material decomposes in peat bogs. Peat moss can hold large quantities of water and contains air spaces. It is often used as an ingredient in potting soils and for soil amendment. Peat moss is a good source of loose organic matter while containing almost no nutrients. Often it can help the roots of plants to latch on to nutrients and ensure proper water management and distribution.

Example of perlite, an inorganic soil additive.

These are both inorganic products often used as soil additives. Perlite is a white, highly porous and hard substance made by heating volcanic glass and helps with drainage. Vermiculite is a soft and spongy brown-colored material made from heating mica and which helps with moisture retention.

Arguably the most well-known and important aspect of the industrial use of soil, industrial agriculture is also potentially the largest use of soil and has the largest negative effects on soil health and the atmosphere, especially as it reduces organic matter and releases carbon into the atmosphere. The soil in industrial agriculture is increasingly important, as its mismanagement can lead to poor crop yields and a reduction in overall agriculture, which has come increasingly to light as more expect that practices used in industrial agriculture continue to lead to a reduction in soil health. Some of the common practices in industrial agriculture include the following:

Example of a monoculture field.

In the case of monocropping, the practice of growing the same crop on the same plot of land, the practice depletes soil of nutrients, organic matter, and can cause significant soil erosion. In the United States, industrial farming practices often include the rotation of soybeans and corn. Technically, because the crops are grown in rotation, this is not classified as monocropping. However, the simple form of crop rotation does not provide the benefits associated with more complex rotations of crops. These complex systems usually involve the use of three or more crops grown in rotation over a period of one or more years.

Monocropping, and even a simple crop rotation, has been observed to cause a cascade of problems, necessitating not only the use of synthetic fertilizers, but also the use of pesticides to control pests, such as soil fungi, insects, and other agricultural nuisances. Fields that include a diversity of crops, also known as polyculture, are less attractive to insect predators. Soil scientists have found that monocropping alters the microbial landscape of soil, decreasing beneficial microbes and causing poor plant growth over time.

The cascade of effects from monocropping leads to the use of synthetic fertilizers, which replenish the nutrients in the soil. However, the use of these fertilizers have been found to negatively impact soil health in the long term.These fertilizers are often made synthetically or from organic materials and are applied to grow healthy plants in otherwise nutrient deficient soils. The application of synthetic fertilizers has grown as the industrial scale of farming has also grown, and as food demands have necessitated boosts in plant productivity. Some research has found that these fertilizers and their use over time alter or decrease the soil's microbial diversity in favor of more pathological strains. Some fertilizer types have also led to soil acidification, which negatively affects plant growth. Excessive fertilizer use can also cause a buildup of salts in the soil, heavy metal contamination, and an accumulation of nitrate.

The use of pesticides also increases in monocropping as the lack of plant diversity increases the likelihood of specific pests flourishing in an area. The use of pesticides and their residues in the soil are a further cause of contamination and a reduction in soil quality. Pesticides are often used to control weeds, insects, and fungi in food, fiber, and wood production. However, the residue of these products has been found to reside in the soil and last in the soil over time, which can influence the soil type and composition. Depending on the pesticide used, its application quantity, the soil quality, and the larger environment, some pesticides may be broken down by microbial action in the soil or by other chemical reactions, while others accumulate in the soil.

Pesticide spraying in a field.

Some studies have shown that glyphosate, an ingredient in some pesticides, can decrease the soil's natural microbial biodiversity. Others have shown that the chemicals adversely affect earthworms and disturb the necessary ecosystem of the soil. Soil fumigates, another type of pesticide designed to kill organisms before a field is planted, kill nearly all soil organisms. This is not limited to the harmful organisms in the soil, but also kills beneficial bacteria, fungi, and other organisms that have been shown to help maintain healthy soils. in some cases, the fumigants accumulate in the soil and exceed legally imposed limits that further deteriorate soil health and fertility.

The use of heavy farm equipment and mechanical tillage causes both soil compaction and soil erosion when the soil is not properly managed. Soil compaction has become an increasing problem as farm equipment has increased in weight and size. This commonly leads to poor water absorption and poor field aeration, which reduces root growth and results in smaller plant yields.

Often the animal waste collected from concentrated animal feeding operations, also known as factory farms, is spread on fields as a form of fertilizer. However, this animal waste, dependent on the conditions of the farm where it is collected and the methods of collection, can contain harmful microbes. As well, depending on how the animals are maintained, the waste can contain antibiotic and other pharmaceutical residues. While these residues are in small concentrations, the accumulation of them in the soil can lead to antibiotic-resistant bacteria in the soil. These antibiotics have been found to be capable of remaining in soil from a few days to up to hundreds of days. Other studies have found that certain classes of antibiotics, such as tetracyclines, can be taken up by the crops themselves.

In agriculture, soil erosion usually refers to the wearing of topsoil through wind, water, and farming activities, such as tillage. Erosion is caused by different factors, but poor soil management can cause significant erosion over time, as can practices such as not planting cover crops in winter and not mulching.

Example of soil erosion in an agricultural setting.

Soil erosion is a problem for several reasons. When topsoil is lost, soil fertility is often lost as well. In some cases, this can cause a change in the structure of the soils, which can further increase the susceptibility of the soils to drought. Eroded soil can turn into runoff and wash into local waterways, which carry with them not only soil particles but any contaminants that reside in the soil. While soil erosion due to wind can cause significant topsoil loss, as well as health problems, property damage, and harm to crops. Erosion can also be a cause of flooding, as the damaged soil may be unable to absorb as much water as healthy soil.

Besides offering a place to grow crops, soil stores a tremendous amount of carbon, with nearly 80 percent of carbon in terrestrial ecosystems residing in soil. Local loss of soil-sequestered carbon has been seen to have global consequences, with scientists estimating that approximately one-third of carbon dioxide emissions are a result of clearing forests and the cultivation of the cleared land for agriculture. Unsustainable agriculture techniques that cause erosion and do not improve the overall soil health, such as excessive tillage, further release carbon dioxide into the atmosphere.

Regenerative agriculture focuses on building soil health through ecosystem-centered techniques, such as composting or adding animals to complex crop rotation practices. This is often considered to be in contrast of the industrial agriculture model, which whether by design or otherwise, is responsible for stripping the soil of nutrients and often creates destructive feedback loops that require more inputs over time, such as synthetic fertilizers or pesticides. In regenerative agriculture, farmers use different techniques to maintain healthy soil structures, create a rich nutrient environment for crops, and restrict or completely remove the use of synthetic fertilizers or pesticides.

The benefits of regenerative agriculture are generally understood to include no need for synthetic fertilizer. This is based in part on the use of plant-based compost and animal manure, green manure, and cover cropping to amend the soil, while also employing crop rotation—all to contribute to healthier soil. Healthier soil can also increase water retention, with at least a one percent increase in soil organic matter, helping soil hold 20,000 gallons more water per acre.

This can help plants grow in biologically diverse soil with plenty of nourishment and thriving microbes, which helps the plants be less susceptible to plant pests and better able to defend themselves, thereby removing or reducing the need for pesticides. And the techniques in regenerative agriculture can help soil sequester carbon, which can help with climate change and help produce healthy plants.

The following techniques are used in regenerative agriculture:

• Complex crop rotating
• Composting
• Green manure, cover cropping, and mulching
• No-till or low-till techniques to reduce soil compacting
• Limited to zero pesticide use and sustainable pest management techniques, such as using buffer zones and courting beneficial insects
• Adding animals on pasture and animal manure to farm systems and crop rotation

Sustainable soil management is often considered a part of regenerative agriculture, except where regenerative agriculture can include the types of crops and rotation of crops, and the use of pasturing and animal waste. Sustainable soil management has a greater focus on the soil itself and includes techniques that some do not consider a part of regenerative farming, such as micro-dosing fertilizer or pesticides. However, the goals of sustainable soil management are the same as regenerative agriculture, which are to build healthy soil; reduce soil erosion; and reduce the need for fertilizers, pesticides, and herbicides. This includes a variety of practices:

• Planting cover crops, especially in the fall to prevent erosion and add nutrients and organic matter to the soil
• Using mulch around plants when possible to prevent erosion, suppress weeds, hold moisture, and add nutrients and organic matter to the soil
• Rotating crops to disrupt disease and pest life cycles and reduce excess nutrients
• Reducing soil compaction which helps fungal and insect life in soil thrive, and whenever possible reduce tilling and using equipment that results in soil compaction
• Providing habitats for beneficial insects like cover crops, mulch, wildflower patches, and insect hotels

Example of a diversified crop rotation in sustainable soil management.

The rationale for sustainable soil management often comes from the perspective of soil as a non-renewable resource and the necessary goods and services soil provides that can be vital to human and non-human ecosystems. Soils are fundamental for producing crops, feed, fiber, and fuel, and they filter and clean tens of thousands of cubic kilometers of water each year. The balance between supporting and provisioning services for plant production and the regulation service for the soil to provide water quality and availability and for atmospheric carbon dioxide composition and sequestration are often a part of the consideration of sustainable soil management.

Sustainable soil management comes down to the development of healthy soil, which can be determined by soil high in organic matter content, a balanced structure, and high nutrient availability, which provides a basis for good plant production. It can also decrease the amount of inputs a grower needs to use, since many of the nutritional requirements of the crops will be supplied through the soil. This increased nutrient availability also increases stronger roots and creates crops more resistant to environmental stressors.

Soil erosion, either by wind or by water, has been identified as a significant threat to global soils and the ecosystem services soil provides. Soil erosion causes the loss of surface soil layers, which are often the most nutrient rich layers of the soil, and can result in partial or complete loss of soil horizons. Soil erosion can also result in off-site impacts, such as damage to private and public infrastructure, reduced water quality, and sedimentation. Soil erosion has been accelerated by the reduction of plant or residue coverage, tillage, and other field operations. And a reduced soil stability has also led to soil creep and landslides. Using techniques such as low or no-tillage and using plant or residue coverage can maintain soil and reduce overall erosion as well.

Soil organic matter (SOM) plays a role in maintaining soil functions and preventing soil degradation. The millions of microbes making their homes in the soil are a part of the nutrient cycling of breaking crop residue into organic matter in the soil and making those nutrients available for plants. This can help growers reduce their use of additives of fertilizers.

Appropriate land use, or the use of soil following sustainable soil management techniques, can improve the soil quality and can help sequester carbon dioxide in the soil, and the loss of SOM can cause an increase in atmospheric carbon dioxide levels. Besides carbon dioxide, soil organic matter also applies to nutrient dynamics in the soil, which follows along the soil-water-nutrient-plant root continuum. Plant nutrients also need to be based on the crop needs, local soil characteristics and conditions, and local weather patterns. Plant nutrition can be enhanced through nutrient recycling or additions, including mineral fertilizers, organic fertilizers, and other soil amendments. It can be crucial in this process to select an appropriate plant management system and approach, and to assess the land for a given land use. For example, trying to grow crops not native to a region can introduce stresses to the soil and lead to the use or over-use of fertilizers and pesticides.

Whereas, the appropriate use of land and a sufficient and balance nutrient supply for plant needs are well-established and the benefits can include production of food, feed, fiber, timber, and fuel at levels close to the optimum potential in the specific geographical context; a reduced need for pest control measures, external application of organic and inorganic amendments, and mineral fertilizers; less pollution resulting from inappropriate use of agro-chemicals; and enhanced soil carbon sequestration through biomass production and restitution to the soil.

Salinization is another problem in soil, which is caused by the accumulation of water-soluble salts of sodium, magnesium, and calcium in the soil. It is a consequence of high evaporation and transportation rates, inland sea water intrusion, and human-induced processes. Salinization reduces crop yield, and above certain thresholds, eliminates crop production.

Example of contaminated soil in a forest.

Besides salinization, another major issue is the prevention of soil contamination with other possibly toxic or dangerous elements in the soil. Contaminants can enter soils from a variety of sources, including agricultural inputs, land application, atmospheric deposition, flood and irrigation water, accidental spills, inappropriate urban waste, and wastewater management. And while soil is capable of filtering and removing contaminants, a contaminant can exceed the possible rate of removal of a soil, which can lead to contamination that can cause plant toxicities, productivity declines, contamination of water and off-site areas, and increased human and animal health risks.

Part of a prevention of the soil contamination includes working to prevent soil from acidifying. Acidification can, and often is, a result of human activity, and is primarily associated with the removal of base cations and the loss of soils buffering capacity or increases in nitrogen and sulfur inputs. Soils with low pH-buffering capacity or high aluminum content are most prevalent when the soil has a low content of weatherable minerals.

Soil sealing refers to the reduction of arable land to human settlement and infrastructure, which can reduce a region's capability of growing food and increasing food production. Urban sprawl can be an especially difficult problem for the loss of arable land and often removes some or all of the soil functions form the ecosystem.

Soil compaction, on the other hand, is related to the degradation of the soil structure due to imposed stresses by machinery and livestock trampling. Soil compaction reduces soil aeration by destroying soil aggregates, and collapsing macropore density, and reduces the ability for soil to drain and infiltrate water and generates higher runoff rates. Compaction also limits root growth and seed germination by high mechanical impedance.

Example of compacted soil complication crop growth.

In soil management or regenerative agriculture, tilling should be retained for the improvement of problem areas, including where the soil is compacted or where drainage issues are heavily impacted. Tilling can increase the number of weeds in a field by bringing them to a surface, where they can germinate and grow, which can reduce overall field space and nutrients. The machinery used for tilling can also cause soil compaction in sub-layers or horizons, despite being capable of recovering soil compaction.

Sustainable soil management requires rapid water infiltration, optimal soil water storage, and efficient drainage when the soil is saturated. Waterlogging and water scarcity are problematic conditions for crop growth. Waterlogging, which relates to the oversaturation of soil, creates rooting problems and can reduce overall yields. It can also cause contaminants such as arsenic and methylmercury to become mobile in the soil. While water scarcity can cause crop failure through crop dehydration.

Example of cover crops and crop waste being used as soil cover.

Soil coverage, or cover crops, has become an increasingly popular method of maintaining soil health in sustainable soil management. Not only do cover crops offer another opportunity for farmers to improve their soil, their use can also increase the availability of nutrients in the soil and reduce the possible erosion of the soil. Whereas, when fields are left uncovered after harvest, they become susceptible to erosion from wind and rain, which reduces the possible healthy foundation for spring growth.

The type and amount of nutrients used by different crops vary depending on what is being grown and what the target crop is. However, different crops can also increase the availability of different nutrients, which can be used to replenish the soil for the crops that follow. And crop rotation, especially a complex multi-crop rotation, can include crop coverage and plays a part in preventing soil erosion through the root growth. The root growth can help develop the soil structure at different depths throughout the seasons and maintain its stability against heavier rains and winds.

In a joint report developed by the RSC, the University of Sheffield, the Natural Environment Research Council (NERC) and the Environmental Sustainability Knowledge Transfer Network (ESKTN), called "Securing soils for sustainable agriculture - a science led strategy," the organizations highlight areas of concern and related actions with possible technological solutions that could be taken to develop advances in soil science.

The report focuses on soil research and innovation in the United Kingdom, with each agricultural zone arguably dealing with different soil conditions and different soil concerns. It highlights four areas with possible interdisciplinary research that could be developed to generate technologies for increased crop production and reduced resource consumption. This includes the possible technologies:

• Biosignalling and sensors for precision monitoring and control of crop conditions
• Closed-loop systems for recovering plant nutrients, such as phosphorous from waste
• Integrated computational models of plant-soil-water to design crop technologies
• Innovation in plant nutrient and water use efficiency to reduce resource demands

With that, there are existing approaches to soil management that are seen as relative innovations, either because they rely on newer technology or because they represent a shift in the understanding and approach to agriculture. These include things like micro-dosing fertilizer, using wastewater for irrigation, reintegrating livestock into a field, and preventing nitrogen leaching.

Micro-dosing fertilizer has been suggested as a possible innovation in soil health. Defined as the application of small, affordable quantities of fertilizers with the seed at planting time or as top dressing at three to four weeks after emergence, the process is intended to be precise and stand in contrast with field-wide fertilization often associated with industrial agricultural techniques.

Micro-dosing fertilizer.

Fertilizers are also often expensive, especially in developing areas, such as sub-Saharan Africa. Micro-dosing in these cases can reduce fertilizer costs while increasing overall field and soil health. Programs to test the viability of micro-dosing fertilizer undertaken in Mali, Burkina Faso, and Niger, with over 25,000 small-holder farmers participating, found that sorghum and millet yields responded well to the technique and boosted yields by 44 to 120 percent, while also increasing incomes for those farmers by as much as 130 percent for some families.

Example of a farm using wastewater irrigation.

The proper disposal of sewage and wastewater has become more challenging as urban areas have grown, and the United Nations Food and Agriculture Organization notes that wastewater contains most of the essential elements of fertilizer in the proper amounts. Treating and applying wastewater, effectively, could contribute both to healthier urban areas, and provide a vital and organic fertilizer for rural areas. This could provide an easy way for farmers, especially those near cities, to fertilize their crops. However, it also presents some risks, as wastewater often contains biological and chemical substances harmful to human health. Further innovations into sanitation could provide a better infrastructure for waste and create a more efficient wastewater for use in energy and fertilizer.

Livestock integrated into a field as part of its crop rotation.

Animals are important for their egg and meat production, but they can also be integrated into a larger agricultural system. This is as animal manure, or animal feces, especially when the animals are on a diet of grasses and similar crops, can be an effective and inexpensive method of boosting the health of organic topsoil.

Nitrogen is an essential nutrient to soil health and for productive crops. Chemical fertilizers and nitrogen-fixing plants, such as legumes, can help provide nitrogen to soils. However, nitrogen, same as water, follows cycles that include leaching from the ground as a gas. Poor land management, erosion, over-fertilization, and chemical runoff all contributes to nitrogen depletion. This leaves land in a different state of dehydration and degradation and reduces the possible productivity of plants.

To combat nitrogen loss, soil scientists have experimented with chemical inhibitors to keep those nutrients in the ground for longer. These have been shown to actively stimulate the nitrogen cycle, keep nitrogen in the soil for longer, and could increase crop yields. Tests into chemical nitrogen inhibitors in Brazil found an increase in sugarcane production. However, these inhibitors do not present an absolute solutions for nitrogen depletion, but these could be used in small doses in combination with natural nitrogen-fixers and better land management to rebuild healthy soil.

Soil moisture monitoring systems include sensors and software systems that provide information for different soil conditions, including sensors for agricultural systems, systems for sandstorm warnings, and systems for environmental protection or detecting environmental hazards. Monitoring the moisture helps farmers understand when crops are getting the right amount of water and when is the right time to water crops. This can lead to higher yields, better product quality, improved plant vigor, reduction in plant disease, more effective use of water, and reduced irrigation costs.

Example of soil moisture monitors.

These sensors come in different versions and for different use cases. For example, there are portable instruments, also known as instant read devices, which are best suited for growers accustomed to walking their fields regularly. There are similar devices, known as "bury in place" instruments, which also require farmers to walk the field, but do not require them to carry the instrument. The "bury in place" instruments tend to offer automated data logging, some of which are capable of communicating to a central computer and others that still require walking to log the data.

Also known as soil conditioners, soil amendments often are differentiated into three classes of amendments. The first is the most well known, fertilizers, which can be organic or synthetic and works to provide nutrients, especially nitrogen, phosphorus, and potassium, and also known as macro nutrients.

The second is soil inoculants which work to add biology to the soil to improve the soil food web; this usually includes an emphasis on bacteria and fungi, but can include beneficial nematodes and related biological entities that can play vital role in the carbon cycle or nitrogen cycle.

The third is soil conditioners, which work to enhance soil properties and are as often called soil enhancers. These products work to alter the soil structure and may affect properties of the soil including cation exchange capacity, soil pH, water holding capacity, and soil compaction. Soil conditioners can be organic, inorganic, or a combination of synthetic and natural matter. Some of the following ingredients in these can be included:

• Animal manure
• Compost
• Cover crop residue
• Sewage sludge
• Sawdust
• Ground pine bark
• Peat moss

Some inorganic soil conditioner ingredients include the following:

• Pulverized limestone
• Slate
• Gypsum
• Glauconite
• Polysaccharides
• Polyacrylamides

Although not precisely an innovation in soil, it is an innovative use of soil, with recent studies showing the several carbon-beneficial agricultural practices in increasing soil carbon sequestration. Part of this has been shown to be the use of compost, which has increased carbon stored in both grassland and cropland soils, and has increased primary productivity and water-holding capacity. Similarly, restoration on riparian areas on working lands has the capacity to sequester significant amounts of carbon. Related practices have also produced co-benefits, such as increased water retention and hydrological function, biodiversity, and soil resilience.