Abstract
Investigations into water potentials in the soil-plant system are of great relevance in environments with abiotic stresses, such as salinity and drought. An experiment was developed using bell pepper in a Neossolo Fluvico (Fluvent) irrigated with water of six levels of electrical conductivity (0, 1, 3, 5, 7 and 9 dS m-1) by using exclusively NaCl and by simulating the actual condition (using a mixture of salts). The treatments were arranged in a randomized block design, in a 6 × 2 factorial arrangement, with four replicates. Soil matric (Ψm) and osmotic (Ψo) potentials were determined 70 days after transplanting (DAT). Soil total potential was considered as the sum of Ψm and Ψo. Leaf water (obtained with the Scholander Chamber) and osmotic potentials were determined before sunrise (predawn) and at noon at 42 and 70 DAT. There were no significant differences between the salt sources used in the irrigation water for soil and plant water potentials. The supply of salts to the soil through irrigation water was the main factor responsible for the decrease in Ψo in the soil and in bell pepper leaves. The total potential of bell pepper at predawn reached values of -1.30 and -1.33 MPa at 42 and 70 DAT, respectively, when water of 9 dS m-1 was used in the irrigation. The total potential at noon reached -2.19 MPa. The soil subjected to the most saline treatment reached a water potential of -1.20 MPa at 70 DAT. There was no predawn equilibrium between the total water potentials of the soil and the plant, indicating that soil potential cannot be considered similar to that of the plant. The determination of the osmotic potential in the soil solution should not be neglected in saline soils, since it has strong influence on the calculation of the total potential.
Highlights
The dynamics of total water potential is a key variable in environments with the occurrence of abiotic stresses, such as drought and salinity, since it determines water movement and availability in the soil-plant system (Hillel, 1998; Kirkham, 2004)
For soil chemical characterization (Table 1), the following properties were determined in the air-dried fine earth (ADFE): Ca2+, Mg2+, Na+ and K+, extracted using 1 mol L-1 ammonium acetate; the saturation extract was obtained through the preparation of the saturation paste (Richards, 1954), where electrical conductivity and pH in water (Claessen, 1997) were measured and soluble bases and the chloride ion were determined through titration with AgNO3
The electrical conductivity was significant for all the variables, which allowed the fitting of regression models for the osmotic, matric and total potentials (Figure 1)
Summary
The dynamics of total water potential is a key variable in environments with the occurrence of abiotic stresses, such as drought and salinity, since it determines water movement and availability in the soil-plant system (Hillel, 1998; Kirkham, 2004). The knowledge of matric and osmotic components in the soil (Groenevelt et al, 2004) and osmotic and total components in the plant (Souza et al, 2012) allows for understanding and interpreting different management conditions, such as areas irrigated with waters of different electrical conductivities and ionic concentrations. Ben-Gal et al (2009) reported the use of osmotic potential to evaluate the effects of salinity on plants is much more appropriate than electrical conductivity, since it accounts for the influence of all the present ions, whether in the soil solution, irrigation water or in the plant cell. The use of water with high electrical conductivity for irrigation and the excessive application of fertilizers are the main reasons for the problem of the increase in soil salinity. Studies comparing the influence of different ionic compositions of irrigation water on water potential in the soil-plant system are necessary (Melo et al, 2016)
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