Chapter 29, Problem 10TYU

SCIENTIFIC INQUIRY

A Minnesota gardener notes that the plants immediately bordering a walkway are stunted compared with those farther away. Suspecting that the soil near the walkway may be contaminated from salt added to the walkway in winter the gardener tests the soil. The composition of the soil near the walkway is identical to that farther away except that it contains an additional 50 mM NaCl. Assuming that the NaCl is completely ionized, calculate how much it will lower the solute potential of the soil at 20°C using the solute potential equation

${\psi }_{\text{S}}=-iCRT$

where i = the ionization constant (2 for NaCl), C = the molar concentration (in moles/liter), R = the pressure constant [R = 0.00831 (liter MPa)/(mole K)] and T = temperature in Kelvin (273 + °C) Describe how this change in the solute potential of the soil would affect the water potential of the soil. Explain how the change in the water potential of the soil would affect the movement of water in or out of the roots