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SOIL 205! Quiz #3! March 6, 2013 KEY! NAME ___________________________! ! (please print)! ! 2-digit lottery number: ___ ___! Soil water content! Plant-available water! 0.52! 1. ___________ A loam with 10% clay has a porosity of 0.52. What is θv when the soil is at saturation (ψ = 0)?! ! (at saturation all pores contain water, so θv = porosity! 2. Draw a line or curve to best illustrate the following relationships (1 pt each):! ! !! high! high! ! ! ! ! ! ! ! ! low! low! ! high! low! S! SL! L! SiL! CL! C! Soil water ψ! ! Fineness of texture! ! 3. As a soil goes from field capacity to wilting point, explain whether each of the following increases (I), decreases (D), or stays the same (S)): ! ! D! I! ___________ soil water potential (ψ) __________ air-filled porosity! ! D! D! ___________ soil water content ! ! __________ matric potential! ! ! 4. Consider two pots with sunflowers growing in them. Both pots contain the same volume of! soil, but the soils differ in texture. Answer the following questions (a-e) using these answers: ! Pot A , Pot B , no difference.! ! ! Volumetric Water Content (Θv)! ! ! saturation! wilting point! field capacity! ! Pot A! 0.25! 0.05! 0.11! ! Pot B! 0.53! 0.15! 0.28! ! Pot A! ___________ a. Which pot has less total pore space?! Pot B! ___________ b. Which pot most likely has a more clayey texture?! Pot B! ___________ c. Which pot holds more plant-available water?! no difference! d. When soils in both pots are at wilting point, from which pot will the! ___________ !sunflowers most easily extract water?! Pot A! ___________ e. If Θv = 0.10 in both pots, which pot would better support plant growth?! 0.05! ___________ What is the volumetric water content of Pot A when soil water potential (ψ) = -1500 kPa?! 5. TRUE (+) or FALSE (-): ! ! +! _____ The overall hydraulic conductivity of a soil profile is determined by the horizon with! !the least permeability.! ! –! _____ The Conservation Reserve Program is designed to protect the best farmland.! ! +! _____ Water always moves from areas of high ψ to low ψ.! ! –! _____ Water will move readily from small pores into big pores.! ! –! _____ Hydraulic conductivity of a sand will always be greater than that of a clay.! ! 6. Consider the dripping-sponge demonstration seen in class. Circle the most appropriate! answers to complete the following statement:! !! When the sponge was turned on end, water [ stopped ; started ] dripping !! because of a change in [ osmotic ; gravitational ; matric ] potential.! ! !! percolation! 7. Downward water movement within a soil is called _______________________.! ! 8. The 3 factors that determine a soil s plant-available-water holding capacity are:! ! texture! ___________________ structure! ___________________ organic matter content! ___________________! ! 9. Explain the difference between cohesion and adhesion as it applies to water molecules (2 pts). ! IMAGES! ! silt fence! 10. __________________ What conservation practice is shown in A?! ! conservation tillage! What conservation practice is shown in B?! __________________ ! 11. __________________ The device shown in here is used to measure:! ! ! [ water content ; hydraulic conductivity; infiltration ] ! ! ! ! (circle correct answer)! ! EXTRA CREDIT! ! Draw a diagram of a water molecule that accurately reflects both its composition and structure.! H! H! 105°! O!
