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Lecture 23 biology

Lecture 23 biology - Lecture 23 Nutrient Procurement T...

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Lecture 23: Nutrient Procurement T: 37 (789-800) 41 (875-897) 37.2-end 41: entire chapter Chapter 37: Plant Nutrition 37.2 S OIL Q UALITY IS A M AJOR D ETERMINANT OF P LANT D ISTRIBUTION AND G ROWTH -conditions for plants to grow well: texture and composition of the soil -texture: soil’s general structure -composition: soil’s organic/inorganic chemical components Texture and Composition of Soils -solid rock weathered by freezing of water seeping into crevices and acids dissolved in water also help break soil -some organisms secrete acids dissolving the rock -roots that grow in fissures mechanical fracturing -RESULT: topsoil : mixture of particles derived from rock, living organisms, & humus - humus : remains of partially decayed organic material - horizons : distinct layers -topsoil (aka A horizon): richest in organic material -texture: depends on sizes of particles: classified from coarse sand to microscopic clay particles - loams : made up of roughly equal amounts of sand, silt (particles of intermediate size), and clay -most fertile, provide air spaces containing oxygen and have surface area -composition: organic components and minerals -organisms in soil, as well as bacteria -plant roots affect pH by releasing organic acids and reinforce soil against erosion -humus: decomposing organic material formed by bacteria and fungi on dead organisms, feces, fallen leaves, and other organic refuse…prevents clay from packing together & builds crumby soil that retains water but is still porous enough for adequate aeration of roots…also reservoir of mineral nutrients that are returned to soil as microorganisms decompose the organic matter -rain: water drains away from larger spaces but smaller spaces retain water (attraction to neg charged surfaces of clay) -mineral ions must be released from soil particles into soil solution (anions (-) not bound to neg charged soil particles and easily released but during heavy rain, drained quickly into ground water..less available for roots -cations (+) less likely to be drained -mineral cations become available for absorption when they enter the soil solution after being displaced from soil particles by cations in the form of H+ called cation exchange , which is stimulated by the roots which add H+ Soil Conservation and Sustainable Agriculture -soil mismanagement: recurring problem in history (dust bowl) -mineral nutrients usually recycled by decomposition of dead organic material in soil -when farmers harvest a crop, essential elements diverted from chemical cycles -3 goals of soil conservation: fertilization, irrigation, and prevention of erosion Fertilizers -usually enriched in nitrogen, phosphorus, and potassium -NPK ratio: content of minerals (in percents)
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-before plants can use organic material, must be decomposed into inorganic nutrients that roots can absorb -pH fertilizer affects cation exchange Irrigation -problems of irrigation: waste water resources, gradually makes soil salty is infertile Erosion -top soil lost by water and wind erosion - sustainable agriculture
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Lecture 23 biology - Lecture 23 Nutrient Procurement T...

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