Influence of soil type on the wilting of plants

Abstract

A b s t r a c t. It has been shown that the water remaining in soil when plants wilt due to soil limitations and the residual water content as observed when soils are de-watered in pressure cell apparatus are essentially the same. Both are produced by immiscible displacement of water by air, and this leads to the water remaining in soil not being in thermodynamic equilibrium. Water removal by immiscible displacement ceases when hydraulic cut-off is reached. The point of hydraulic cut-off may be calculated by fitting waterretention data to equations for both the non-equilibrium case and the equilibrium case, and then solving these simultaneously. This has been done for water retention data for 52 soil horizons in Poland. These results are used to obtain a pedotransfer function for the permanent wilting point due to soil limitations and the results are presented for the different soil texture classes. The pore water suction when wilting occurs is estimated to be 1.0 MPa. The methods and findings in this paper are used to explain a range of published results on plant wilting. K e y w o r d s: hydraulic cut-off, pedotransfer function, permanent wilting point, residual water content, water retention INTRODUCTIONThe de-watering of moist soil by transpiring plants and the de-watering of soil samples in a pressure plate apparatus both occur by the physical process of convective movement of water in the soil by immiscible displacement ie air displaces the water . This explains why the water remaining in soil when plants of many species wilt is very close to the amount of water remaining in soil samples when they are de-watered in a ceramic pressure plate extractor with an applied air pressure of P a = 1.5 MPa (Richards and Weaver, 1943). This convective movement is completely different from the movement of water by diffusion. Whereas diffusion leads to water in thermodynamic equilibrium, immiscible displacement can lead to systems not in thermodynamic equilibrium. When a system is in thermodynamic equilibrium, all the water has the same specific free energy. In contrast, when it is not in thermodynamic equilibrium, different 'packets' of water within the soil can have different values of specific free energy: for example, they can have different values of pore water pressure or suction. Dexter et al. (2012) concluded that for every drying soil, two different water retention curves are needed: one for cases where de-watering occurs by immiscible displacement and one for cases where de-watering occurs by diffusion. Another curve is needed for soil wetting because of the hysteresis effect, but this case is not considered here.A water retention curve for a soil shows how the water content decreases with increasing pore water suction. The subject of water retention curves was discussed in detail by Fredlund and Xing (1994), however those authors did not distinguish between the above two physical processes of de-watering. Here, we follow Dexter et al. (2012) The Dexter et al. (2008) equation is based on the concept of a bi-mo...

SoilFlex‐LLWR: linking a soil compaction model with the least limiting water range concept

“…Ratliff et al . () found that there is little effect of crop type on CLL for a given soil, and Czyż & Dexter () demonstrated that plant wilting is in most cases soil limited due to hydraulic cut‐off (i.e. plant wilting is a soil property).…”

Role of fungal endophyte of tall fescue ( Epichloë coenophiala ) on water availability, wilting point and integral energy in texturally-different soils

“…Similarly, Czyż and Dexter (2012) showed that h at hydraulic cut-off of drainable pores (which might be assumed similar to h PWP ) would increase with CC and plant wilting due to the soil alone would occur at h values lower than 15000 hPa for CC < 28 kg 100 kg −1 . Analyses of Czyż and Dexter (2013) using a data set for 52 coarse-textured soils (i.e., CC < 25 kg 100 kg −1 ), showed that the mean h at hydraulic cut-off is 10300 hPa (i.e., much lower than 15000 hPa). These findings showed that h PWP depends not only on the plant species but also on the soil.…”

“…It is because water flow to the roots stopped due to hydraulic cut-off (i.e., continuity of liquid water practically diminishes), which is a soil physical property and not a plant property Dexter, 2012, 2013). Czyż and Dexter (2013) by using a data set for 52 coarse-textured soils (i.e., clay percent <25), predicted the mean h PWP (i.e., matric suction at hydraulic cut-off) to be 10300 hPa (i.e., much lower than 15000 hPa).…”

Available water capacity from a multidisciplinary and multiscale viewpoint. A review

“…PTF predictors must be adapted to the target of interest, and should differ when estimating FC and PWP, as different pore sizes are involved in water retention at these two potentials (Tomasella et al 2003). Thus, specific PTFs have been developed for FC (Ottoni et al 2014) and for PWP (Czyz and Dexter 2013).…”