NRES 201 Lecture 18 Outline of Last Lecture I. The global hydrological cycleII. Fate of precipitation and irrigation waterIII. The soil - plant - atmosphere continuumOutline of Current Lecture IV. Control of evapotranspirationV. Fundamentals of irrigationVI. Enhancing soil drainageCurrent LectureControl of evapotranspiration - Weed controlo Transpiration by weeds depletes soil watero Options for control: Cultivation- Uproots or smothers weeds- Disadvantages:o Root pruningo Erosion of bare soil Herbicides- Advantages:o Requires less labor and energy than cultivation o Does not disturb residue cover- Disadvantageso High input costso Escalating weed resistanceo Drift and carryovero Environmental toxicity Fallow in dry land cropping:- Arid or semiarid cropland kept free of vegetation in alternate years- The purpose is to increase soil water storage by preventing transpiration o Can promote soil degradation from:These 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. Organic matter depletion Wind erosiono Conservation tillage is better optionFundamentals of irrigation- Importance of irrigationo Water is the most limiting fact for crop productiono Irrigation was crucial to many ancient civilizations And is no less crucial to the modern worldo Irrigated land area has doubled since the 1960s A major consequence of the Green Revolution- When is irrigation necessary?o When potential evapotranspiration exceeds precipitation and soil storage (PET > P + SS)- Irrigation in the USAo Mostly in the 17 conterminous western states- Furrow Irrigationo Water applied to graded furrows from a supply ditch or gated pipeo Uniformity of water delivery depends on: Infiltration rate Slope Length of runo Excess water problems: At the upper end with sandy soils At the lower end with clayey soils- Advantages over furrow irrigationo Supplies cooler, better, aerated watero More precise water deliveryo Allows application of fertilizers and pesticideso Wider range of application to sandy soils and sloping soils- Disadvantageso Energy intensive - High volume, high pressure, large pumpo Wet foliage increase evaporative losses and can promote fungal diseasesEnhancing soil drainage- Extent of artificial drainageo 50% of Illinois farm land tile - drainedo Often essential for removing gravitation water from: Poorly drained soils Compacted soils Irrigated soils- Benefits of soil drainageo Improved aeration Plant roots need O2 for respiration Surface ponding quickly kills many crops Drainage replaces water in the macro-pores with air- Not only promotes root growth and activity, but also enhances microbial activities and prevents the accumulation of toxic substanceso Soil heating and frost heaving Dry soils heat faster in the spring because water has a high specific heat Frost heaving occurs because water expands upon freezingo Timeliness of field operations Drainage increases the field season- Negative aspects of soil drainageo Wetland degradation - reduced nutrient retentiono Loss of wildlife habitat o Increases leaching of nitrateo Accelerated loss of soil organic mattero Greater flooding hazard- Surface draining- Subsurface
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