NRES 201 Lecture 17 Outline of Last Lecture I. Measurement of soil waterII. Movement of water in soilsIII. Factors affecting soil water availability Outline of Current Lecture I. The global hydrological cycleII. Fate of precipitation and irrigation waterIII. The soil - plant - atmosphere continuumCurrent LectureThe global hydrological cycle:- Fundamental realitieso The world's water resources are not evenly distributed Annual precipitation varies Seasonal variation can also be extensive when flooding is followed by droughto Water management has changed From the old way: adapt culture to environment- Settle near water- Harvest the rain- Live as nomads To the new way: adapt environment to culture- Irrigate arid lands to make them productive- Build cities in the desert- Deplete the aquifers- Global Water Use:o Dominated by irrigated agricultureo Increases by 10% per decadeo Highest per capita consumption in the USA- Water Cycles:o Solar energy drives evaporationo Water vapor forms cloudso The clouds move and form precipitationo Rain and Snowfall return water to land and seasThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. Lead to runoff and percolation that resupply streams, rivers, and the oceans- Water balanceo The usual focus is a watershed Land area is drained by a single system of streamso Precipitation falling on a watershed can be Stored in the soil Returned to the atmosphere by evaporation or transpiration Discharged by surface or subsurface flowo Represented as: P = SS + ET + D where - P - precipitation (+ irrigation) SS - Soil Storage ET - Evapotranspiration D - Dischargeo Impact by management Irrigation increases the input of water and calls for strategies to maximize soil storage by minimizing dischargeFate of precipitation and irrigation water:- Water that reaches the ground may:o Enter the soil by infiltration More likely with good soil structureo Or remain on the surface if rainfall exceeds infiltration The result is ponding or runoff- Water that enters the soil may leave by:o Evaporationo Plant uptake/transpiration o Subsurface drainage Can account for up to 50% of water input Some availability through capillary rise during dry periods- Factors affecting infiltration:o Type of vegetationo Stem flowo Snow Fallo Soil Managemento Furrow dikingo Minimizing compactiono Urban watershedso Soil propertiesThe soil - plant - atmosphere continuum- Water flows from the soil to the plant, from the plant to the atmosphere, from higher to lower potentials- Two critical factors: o Rate of water supply to rootso Rate of water loss from leaves
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