Nonlimiting water range
Encyclopedia
The Non-limiting water range (NLWR) represents the range of water content
in the soil
where limitations to plant growth (such as water potential
, air-filled porosity
, or soil strength) are minimal. John Letey (1985) from UC Riverside introduced the NLWR concept in an attempt to integrate several physical properties associated with plant or root
growth to refine the concept of available water capacity
. Alvaro Pires da Silva, Bev Kay. and Ed Perfect (University of Guelph
, Ontario) (1994) refined the concept and termed it least limiting water range (LLWR).
The upper limit (wet end) of LLWR is determined not only at water content at field capacity
(FC), but also the capability of providing adequate aeration for plant roots (usually taken as a minimum air filled porosity of 10%).
The upper limit is then defined as:
min q {air filled porosity = 0.1, FC}.
Rather than air-filled porosity at 10%, LaoSheng Wu from UC Riverside proposed moisture content where Oxygen gas diffusion rate ODR value of 0.2 micro-g/cm2/min as criteria for satisfactory aeration status.
The lower limit (dry end) is not only limited to permanent wilting point
(PWP) but also the ability of root penetration. This is measured as soil mechanical resistance taken at an arbitrary value, say penetration at 3 MPa.
The lower limit is defined as:
max q {mechanical resistance = 3 MPa, PWP}.
Water content
Water content or moisture content is the quantity of water contained in a material, such as soil , rock, ceramics, fruit, or wood. Water content is used in a wide range of scientific and technical areas, and is expressed as a ratio, which can range from 0 to the value of the materials' porosity at...
in the soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
where limitations to plant growth (such as water potential
Water potential
Water potential is the potential energy of water per unit volume relative to pure water in reference conditions. Water potential quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure, or matrix effects such as surface tension...
, air-filled porosity
Porosity
Porosity or void fraction is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0–1, or as a percentage between 0–100%...
, or soil strength) are minimal. John Letey (1985) from UC Riverside introduced the NLWR concept in an attempt to integrate several physical properties associated with plant or root
Root
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
growth to refine the concept of available water capacity
Available water capacity
Available water capacity or available water content is the range of available water that can be stored in soil and be available for growing crops....
. Alvaro Pires da Silva, Bev Kay. and Ed Perfect (University of Guelph
University of Guelph
The University of Guelph, also known as U of G, is a comprehensive public research university in Guelph, Ontario, Canada. It was established in 1964 after the amalgamation of Ontario Agricultural College, the Macdonald Institute, and the Ontario Veterinary College...
, Ontario) (1994) refined the concept and termed it least limiting water range (LLWR).
The upper limit (wet end) of LLWR is determined not only at water content at field capacity
Field capacity
Field capacity is the amount of soil moisture or water content held in soil after excess water has drained away and the rate of downward movement has materially decreased, which usually takes place within 2–3 days after a rain or irrigation in pervious soils of uniform structure and texture...
(FC), but also the capability of providing adequate aeration for plant roots (usually taken as a minimum air filled porosity of 10%).
The upper limit is then defined as:
min q {air filled porosity = 0.1, FC}.
Rather than air-filled porosity at 10%, LaoSheng Wu from UC Riverside proposed moisture content where Oxygen gas diffusion rate ODR value of 0.2 micro-g/cm2/min as criteria for satisfactory aeration status.
The lower limit (dry end) is not only limited to permanent wilting point
Permanent wilting point
Permanent wilting point or wilting point is defined as the minimal point of soil moisture the plant requires not to wilt. If moisture decreases to this or any lower point a plant wilts and can no longer recover its turgidity when placed in a saturated atmosphere for 12 hours...
(PWP) but also the ability of root penetration. This is measured as soil mechanical resistance taken at an arbitrary value, say penetration at 3 MPa.
The lower limit is defined as:
max q {mechanical resistance = 3 MPa, PWP}.
See also
- Integral energyIntegral energyIntegral energy is the amount of energy required to remove water from an initial water content \theta_i to water content of \theta_f...
- Irrigation schedulingIrrigation schedulingIrrigation scheduling is the process used by irrigation system managers to determine the correct frequency and duration of watering.The following factors may be taken into consideration:...
- Limiting factorLimiting factorA limiting factor or limiting resource is a factor that controls a process, such as organism growth or species population, size, or distribution. The availability of food, predation pressure, or availability of shelter are examples of factors that could be limiting for an organism...
- Moisture equivalentMoisture equivalentMoisture equivalent is proposed by Lyman Briggs and McLane as a measure of field capacity for fine-textured soil materials.Moisture equivalent is defined as the percentage of water which a soil can retain in opposition to a centrifugal force 1000 times that of gravity...
- Soil plant atmosphere continuumSoil plant atmosphere continuumThe Soil-Plant-Atmosphere Continuum is the pathway for water moving from soil through plants to the atmosphere.The transport of water along this pathway occurs in components, variously defined among scientific disciplines:...
- Moisture stressMoisture stressMoisture stress occurs when the water in a plant's cells is reduced to less than normal levels. This can occur because of a lack of water in the plant's root zone, higher rates of transpiration than the rate of moisture uptake by the roots, for example, because of an inability to absorb water due...
- Pedotransfer functionPedotransfer functionPedotransfer function is a term used in soil science literature, which can be defined as predictive functions of certain soil properties from other more available, easily, routinely, or cheaply measured properties...