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Estimating the Storage Capacity of the Vadose Zone
Published in L.G. Wilson, Lorne G. Everett, Stephen J. Cullen, Handbook of Vadose Zone Characterization & Monitoring, 2018
Stephen J. Cullen, Lome G. Everett
The term permanent wilting point (PWP) has been used by agriculturalists to identify the water content or soil suction dryer than that at which plants will irreversibly wilt and die. The value generally assigned for PWP suction is 15 bars, although the actual value will vary with the plant life under investigation, and can be as high as 80 bars. PWP water content is of value to hydrogeologic work in that data are readily available in most soil survey interpretations published by the Soil Conservation Service and it has been used as an approximation of the residual water content. When data are not readily available, laboratory determinations (ASTM 1991d and 1991e) of the 15-bar water content can be made from soil samples taken in the field. Undisturbed cores are not required for this analysis.
Biochar effects on soil hydrology
Published in Johannes Lehmann, Stephen Joseph, Biochar for Environmental Management, 2015
Caroline A. Masiello, Brandon Dugan, Catherine E. Brewer, Kurt A. Spokas, Jeffrey M. Novak, Zuolin Liu, Giovambattista Sorrenti
While biochar has been proposed as a mechanism to increase water stored in soil, only a fraction of soil water is plant-available. To understand how biochar may impact plants, we must first understand how plant-available water changes with biochar amendment. Plant-available water is formally defined as the difference between the water held at field capacity and at the permanent wilting point of plants. WHC (also called field capacity in some studies) is the water content of the soil after free, gravity-driven drainage has removed any excess water. This process is assumed to take 24–48 hours and is also assumed to be the water content of the soil when subjected to a pressure of -33kPa (i.e., a soil suction of 33kPa). Permanent wilting point (PWP) is defined as the water content below which a plant will wilt and is often assumed to be the water content of the soil when subjected to a pressure of -1500kPa. The amount of water held between WHC and PWP is considered to be accessible by plants because soils will naturally drain water in excess of WHC and plants do not have the suction capacity to access water below the PWP. Because our knowledge of biochar-driven changes in WHC and PWP remains limited, it is not yet clear under what conditions biochar may alter plant available water.
Sandy Soils
Published in A. Monem Balba, in Arid Ecosystems, 2018
The field capacity (FC) is defined as the percentage of water retained in the pore space of a soil after the excess water from an irrigation has percolated to deeper layers. In practice the field capacity is determined 1–2 days after an irrigation. Permanent wilting point (PWP) is defined as the percentage of water, still remaining in a soil, once the plants are no longer capable of extracting sufficient moisture to meet their needs.
Evaluation of regional soil water retention (SWR) characteristics for soils in Central India
Published in Journal of Applied Water Engineering and Research, 2020
R. K. Jaiswal, J. V. Tyagi, R. V. Galkate, A. K. Lohani
The amount of water stored in the soil depends primarily on retention of water between permanent wilting point and field capacity and are increasingly used in precision irrigation and scheduling. The methodology used to determine SWR with the help of pressure plate apparatus is time-consuming, costly and despite immense importance rarely used in the field. However, data related to soil texture and structure, available for most of the soils in India and abroad, can be used to compute SWR indirectly. The PTFs which are the empirical relationships of physical properties and analytical equations for estimation of SWR can be used for irrigation scheduling in the absence of measured data. The regionalisation approach proposed in the study, if scaled up can be used in precision irrigation on the basin scale.