Soil Moisture Regime
Soil moisture regime (SMR) refers to the presence or absence of water in soil at different time of year . (refers to the presence or absence of water saturated conditions or plant-available soil water at a defined section of the soil (control section) e.g.
- Moist soil: soil moisture tension <15 bar within the soil moisture control section(SMCS)
- Dry soil: greater than 15-bar.
SMR is a partial function of climate, soil and landform or topography in broad sense. It is defined in terms of the number of days the SMCS remains moist with moisture tension between 1/3 bar and 15 bar. SMR is important when crop growth is concerned. It is also important to understand pedogenesis (soil forming process) and nutrients availability. SMR has use in classification of soil at different categoric levels such as soil family, suborder and occasionally at order level.
In nature there are three dominant soil moisture regimes
- Saturated: it is a condition when soil pores are completely filled with water resulting in anaerobic condition. Not suitable for normal crop growth. Taxonomic equivalent – Aquic
- Non-leaching: arid climates; dry in all portions of profile most of the time. Water moves into SMCS for very short period in a year and gets completely withdrawn by high potential evapo-transpiration, or very low rainfall and loss of soil moisture through excessive evapotranspiration. Taxonomic equivalent – Aridic.
- Humid climates; moisture usually exceeds evapotranspiration
Leaching: water moves in soil profile almost throughout the year if not frozen. Taxonomic equivalent – udic
Two more intermediary horizon between leaching and non-leaching are as follow
- Ustic – between aridic and udic (sufficient moisture for crop growth) wet summer and dry winter
- Xeric – Mediterranean climates; cool, moist winters and hot dry summers
This is very broad scale categorization and if precise study of soil is desired further classification is required for specific soil.