Soil biodiversity

This article reads like a neutral in tone.

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

According to the Australian

The correlation of soil and biodiversity can be observed spatially. For example, both natural and agricultural vegetation boundaries correspond closely to soil boundaries, even at continental and global scales.^[4]

A "subtle synchrony" is how Baskin (1997) describes the relationship between the soil and the diversity of life above and below the ground. It is not surprising that

These effects occur regardless of the biome. A study in the Netherlands examined the correlation between soil pH and soil biodiversity in soils with pH below 5.^[8] A strong correlation was discovered, wherein the lower the pH the lower the biodiversity.^[8] The results were the same in grasslands as well as heathlands.^[8] Particularly concerning is the evidence showing that this acidification is directly linked to the decline in endangered species of plants, a trend recognized since 1950.^[8]

Soil acidification reduces soil biodiversity. It reduces the numbers of most macrofauna, including, for example, earthworm numbers (important in maintaining structural quality of the

Some plants within the same species have shown resistance to the soil acidity their population grows in.[6] Selectively breeding the stronger plants is a way for humans to guard against increasing soil acidity.^[6]

Further success in combatting soil acidity has been seen in

Soil structure is the arrangement of particles and associated pores in soils across the size range from nanometres to centimeters. Biological influences can be demonstrated in the formation and stabilization of the soil aggregates. Still, it is necessary to distinguish clearly between those forces or agencies that create aggregations of particles and those that stabilize or degrade such aggregations.^[12] What qualifies as good soil contains the following attributes: optimal soil strength and aggregate stability, which offer resistance to structural degradation (capping/crusting, slaking and erosion, for example); optimal bulk density, which aids root development and contributes to other soil physical parameters such as water and air movement within the soil; optimal water holding capacity and rate of water infiltration.^[13]

Well-developed, healthy soils are complex systems in which physical soil structure is as important as chemical content. Soil pores—maximized in a well-structured soil—allow oxygen and moisture to infiltrate to depths and plant roots to penetrate to obtain moisture and nutrients.^[14]

Biological activity helps in the maintenance of relatively open soil structure, as well as facilitating decomposition and the transportation and transformation of soil nutrients. Changing soil structure has been shown to lead to reduced accessibility by plants to necessary substances. It is now uncontested that microbial exudates dominate the aggregation of soil particles and the protection of carbon from further degradation.^[15] It has been suggested that microorganisms within the soil "engineer" a superior habitat and provide a more sound soil structure, leading to more productive soil systems.^[16]

Traditional agricultural practices have generally caused declining soil structure.

Extended exposure to high sodium levels results in a decrease in the amount of water retained and able to flow through the soil and a decrease in decomposition rates (this leaves the soil infertile and prohibits any future growth). This issue is prominent in Australia, where 1/3 of the land is affected by high salt levels.[22] It is a natural occurrence, but farming practices such as overgrazing and cultivation have contributed to the rise of it. The options for managing sodic soils are minimal; one must select sodicity-tolerant plants or change the soil. The latter is the more difficult process. If changing the soil, one must add calcium to displace the excess exchangeable sodium that causes the disaggregation that blocks water flow.^[23]

While very saline soil is not preferred for growing crops, it is important to note that many crops can grow in more saline soils than others.^[26] This is important in countries where resources such as fresh water are scarce and needed for drinking. Saline water can be used for agriculture.^[26] Soil salinity can vary between extremes in a relatively small area;^[27] this allows plants to seek areas with less salinity. It is hard to determine which plants can grow in soil with high salinity because the soil salinity is not uniform, even in small areas.^[27] However, plants absorb nutrients from areas with lower salinity.^[27]

Soil erosion is the removal of the soil's upper layers by water, wind, or ice. Soil erosion occurs naturally, but human activities can greatly increase its severity.^[28] Soil that is healthy is fertile and productive.^[29] But soil erosion leads to a loss of topsoil, organic matter, and nutrients; it breaks down soil structure and decreases water storage capacity, reducing fertility and water availability to plant roots. Soil erosion is, therefore, a major threat to soil biodiversity.^[30]

The effects of soil erosion can be lessened by means of various

Misconstrued soil conservation efforts can result in an imbalance of soil chemical compounds.^[31][34] For example, attempts at afforestation in the northern Loess Plateau, China, have led to nutrient deprivation of organic materials such as carbon, nitrogen, and phosphorus.^[34]

Potassium (K) is an essential macronutrient for plant development^[35] and potassium chloride (KCl) represents the most widely source of K used in agriculture.^[36] The use of KCl leads to high concentrations of chloride (Clˉ) in soil which cause increase in soil salinity affecting the development of plants and soil organisms.^{[37][38][39][40]}

Chloride has a biocidal effect on the soil ecosystem, causing negative effects on the growth, mortality, and reproduction of organisms,^[38][40] which in turn jeopardizes soil biodiversity. The excessive availability of chloride in soil can trigger physiological disorders in plants and microorganisms by decreasing cells' osmotic potential and stimulating the production of reactive oxygen species.^[39] In addition, this ion negatively affects nitrifying microorganisms, thus affecting nutrient availability in the soil.^[38]

Biological systems—both natural and artificial—depend heavily on healthy soils; it is the maintenance of

Maintaining soil health is a regional or catchment-scale issue. Because soils are a dispersed asset, the only effective way to ensure soil health generally is to encourage a broad, consistent, and economically appealing approach. Examples of such approaches as applied to an agricultural setting include the application of lime (calcium carbonate) to reduce acidity so as to increase soil health and production and the transition from conventional farming practices that employ cultivation to limited or no-till systems, which has had a positive impact on improving soil structure. ^[41]

Soils encompass a huge diversity of organisms, which makes biodiversity difficult to measure. It is estimated that a football pitch contains underground as many organisms as equal to the size of 500 sheep. A first step has been taken in identifying areas where soil biodiversity is most under pressure is to find the main proxies which decrease soil biodiversity.^[42] Soil biodiversity will be measured in the future, especially thanks to the development of molecular approaches relying on direct DNA extraction from the soil matrix.^[43]

• Soil carbon
• Soil degradation