Editing Soil (section)

== Soil moisture ==
{{Main|Soil moisture}}
Soil [[water content]] can be measured as volume or [[Specific weight#Soil mechanics|weight]]. Soil moisture levels, in order of decreasing water content, are saturation, [[field capacity]], [[wilting point]], air dry, and oven dry. [[Field capacity]] describes a drained wet soil at the point water content reaches equilibrium with gravity. Irrigating soil above field capacity risks [[percolation]] losses. [[Wilting point]] describes the dry limit for growing plants. During growing season, soil moisture is unaffected by plant functional groups or species richness while it varies with species composition.<ref name="auto1">{{Cite journal |last1=Spehn |first1=Eva M. |last2=Joshi |first2=Jasmin |last3=Schmid |first3=Bernhard |last4=Alphei |first4=Jörn |last5=Körner |first5=Christian |date=2000 |title=Plant diversity effects on soil heterotrophic activity in experimental grassland ecosystems |url=https://www.academia.edu/24032411 |journal=[[Plant and Soil]] |volume=224 |issue=2 |pages=217–230 |doi=10.1023/A:1004891807664|bibcode=2000PlSoi.224..217S |s2cid=25639544 |access-date=26 January 2025 }}</ref>

[[Available water capacity]] is the amount of water held in a soil profile available to plants. As water content drops, plants have to work against increasing forces of [[adhesion]] and [[sorptivity]] to withdraw water. [[Irrigation scheduling]] avoids [[moisture stress]] by replenishing depleted water before stress is induced.<ref>{{cite web |title=Water holding capacity |work=[[Oregon State University]] |date=24 June 2016 |url=https://forages.oregonstate.edu/ssis/soils/characteristics/water-holding-capacity |quote=Irrigators must have knowledge of the readily available moisture capacity so that water can be applied before plants have to expend excessive energy to extract moisture |access-date=26 January 2025 }}</ref><ref>{{cite web |title=Basics of irrigation scheduling |work=[[University of Minnesota Extension]] |url=https://extension.umn.edu/irrigation/basics-irrigation-scheduling |quote=Only a portion of the available water holding capacity is easily used by the crop before crop water stress develop |access-date=26 January 2025 }}</ref>

[[Capillary action]] is responsible for moving [[groundwater]] from wet regions of the soil to dry areas. [[Subirrigation]] designs (e.g., [[wicking bed]]s, [[sub-irrigated planter]]s) rely on [[Capillary action|capillarity]] to supply water to plant roots. Capillary action can result in an evaporative concentration of salts, causing [[land degradation]] through [[Soil salinity#Dry land salinity|salination]].

[[Soil moisture measurement]]—measuring the water content of the soil, as can be expressed in terms of volume or weight—can be based on ''in situ'' probes (e.g., [[capacitance probe]]s, [[neutron probe]]s), or [[remote sensing]] methods. Soil moisture measurement is an important factor in determining changes in soil activity.<ref name="auto1"/>