精选课件第6讲_土壤磷素转化.ppt

本章重要知识点: 土壤磷的形态及分级 土壤磷的吸附机理及其影响因素 土壤磷的生物转化及其影响因素 土壤供磷能力及其影响因素 土壤磷素循环 Soil P transformations Phosphorus “Fixation”* Precipitation from soil solution -- pH driven Adsorption to soil minerals -- soil chemistry (mineralogy) determines * Note: with K and NH4+, “ fixation” refers to insertion into the lattice of certain clays 影响土壤生物活性的土壤物理和化学因素，均可能影响有机磷的矿化。 Factors controlling organic P mineralization C:P ratio of organic residues 200 矿化 Soil temperature 最适温度35℃ Soil moisture Soil texture Tillage The Phosphorus Cycle in Soil Phosphorus in the Environment P is an essential element for plants and animals High P is generally non-toxic to plants or animals Relatively immobile in soil P causes accelerated eutrophication Excessive growth of algae and aquatic plants Limits use of water for drinking, fishing, recreation, etc. PHOSPHORUS AND WATER QUALITY Phosphorus additions to natural waters can stimulate weed and algae growth. Vegetative growth and oxygen depletion reduce water quality. Phosphorus losses from agriculture can be a major source of P entering lakes and streams. Phosphorus (P) Loss Processes In surface runoff: Soluble (dissolved) P Particulate P (soil particles) By leaching Does phosphorus leach? Soil P to Water: Transport P Losses due to Runoff from SERA-IEG 17 Potential P loss related to soil test P Soil P, Crop yield Environment Eutrophication and phosphorus Eutrophication N vs P Behavior The Phosphorus Cycle 思考题 1.比较磷的吸附与沉淀发生的条件？ 2.淹水为什么能提高土壤磷的有效性？ 3.试述根系对于土壤磷的有效化的作用机理 ? 4.影响土壤供磷能力的主要土壤因素有哪些？其 各自的影响机理是什么？ 5.描述土壤磷素的循环,及其可能产生的环境效应? 三、土壤磷的 化学沉淀和溶解(了解) 3.1、磷的化学沉淀 由磷化学沉淀作用产生的化合物种类很多，据研究大约有60多种。在中性和石灰性土壤中以磷酸钙盐为主，而在酸性土壤中以磷酸铁铝盐为主。 化学沉淀反应一般发生在土壤溶液中磷浓度高的微域环境内，如肥料颗粒周围。 当水溶性磷肥如过磷酸钙施入土壤后，磷肥颗粒开始吸收土壤水分，并发生异成分溶解（Incongruent dissolution)，使颗粒内部磷的浓度升高至饱和或接近饱和，同时pH下降(约1.5)。由于存在着浓度梯度，磷和质子以扩散的方式进入周围土壤，扩散过程中将会溶解土壤中大量的铁、铝、钙、镁等离子。当溶液中磷与这些阳离子的活度积高于相应难溶性化合物溶度积时，发生磷的化学沉淀。 3.2 难溶性含磷化合物的溶解 土壤中难溶性含磷化合物的溶解