NRES 201 Lecture 18 Outline of Last Lecture I The global hydrological cycle II Fate of precipitation and irrigation water III The soil plant atmosphere continuum Outline of Current Lecture IV Control of evapotranspiration V Fundamentals of irrigation VI Enhancing soil drainage Current Lecture Control of evapotranspiration Weed control o Transpiration by weeds depletes soil water o Options for control Cultivation Uproots or smothers weeds Disadvantages o Root pruning o Erosion of bare soil Herbicides Advantages o Requires less labor and energy than cultivation o Does not disturb residue cover Disadvantages o High input costs o Escalating weed resistance o Drift and carryover o 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 erosion o Conservation tillage is better option Fundamentals of irrigation Importance of irrigation o Water is the most limiting fact for crop production o Irrigation was crucial to many ancient civilizations And is no less crucial to the modern world o 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 USA o Mostly in the 17 conterminous western states Furrow Irrigation o Water applied to graded furrows from a supply ditch or gated pipe o Uniformity of water delivery depends on Infiltration rate Slope Length of run o Excess water problems At the upper end with sandy soils At the lower end with clayey soils Advantages over furrow irrigation o Supplies cooler better aerated water o More precise water delivery o Allows application of fertilizers and pesticides o Wider range of application to sandy soils and sloping soils Disadvantages o Energy intensive High volume high pressure large pump o Wet foliage increase evaporative losses and can promote fungal diseases Enhancing soil drainage Extent of artificial drainage o 50 of Illinois farm land tile drained o Often essential for removing gravitation water from Poorly drained soils Compacted soils Irrigated soils Benefits of soil drainage o 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 substances o 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 freezing o Timeliness of field operations Drainage increases the field season Negative aspects of soil drainage o Wetland degradation reduced nutrient retention o Loss of wildlife habitat o Increases leaching of nitrate o Accelerated loss of soil organic matter o Greater flooding hazard Surface draining Subsurface draining
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