爱华网LIMINGACID SOILS-A GOOD MANAGEMENT PRACTICE
JoseEspinosa
磷钾研究所拉丁美洲项目部主任
Director,Potash and Phosphate Institute, Latin American Office, P.O. Box 17-17-980,Quito, Ecuador, South America
1. 引言 Introduction
农用石灰，不管是粉细的白云石质石灰岩，还是方解石质石灰岩，直接施到酸性土壤是提高作物产量和降低肥料成本的一条廉价途径。这一土壤改良剂已在全世界广泛应用。保持恰当的土壤pH值对于保持良好的土壤肥力和制定良好的养分管理方案是必需的。一些导致土壤酸化的因素包括母质、降雨、天然植被、作物种植和施用氮肥等。
Agriculturallime, either finely ground dolomitic or calcitic limestone, applied directly toacid soils is an inexpensive way to increase crop yields and reduce fertilizerinput costs. This soil amendment is widely used around the world. Maintainingan adequate soil pH is indispensable in a sound soil fertility and nutrientmanagement program. Several factors contribute to soil acidity including parentmaterial, precipitation, native vegetation, crops grown and nitrogen (N)fertilization.
由基性岩母质发育的土壤通常比那些由酸性岩发育的土壤具有更高的pH值。在高降雨条件下形成的土壤比在干旱条件下形成的土壤酸性强。土壤有机质不停地被微生物分解成有机酸和CO2，从而加重土壤酸化。森林植被下发育的土壤比草地植被下发育的土壤酸性强，针叶林土壤比落叶林土壤酸性强。随着作物收获部分盐基养分的移走，土壤酸度增强。氮肥施用由于在硝化过程中产生多余的H+，因而加速了土壤的酸化。硝化作用是在微生物的作用下把铵态氮转化为硝态氮的一种自然过程，这里的氮无论来源于无机肥料、有机肥料和粪肥，还是来源于豆科固定的氮，均发生这一过程，使土壤变酸。
Soils developedfrom parent materials of basic rocks generally have higher pHs than thoseformed from acid rocks. Soils formed under high rainfall conditions are moreacidic than those formed under dry conditions. Soil organic matter iscontinually being decomposed by microorganisms into organic acids and carbondioxide (CO2) which addto soil acidity. Soils formed under forest vegetation tend to be more acid thanthose developed under grasslands, and conifers create more acidity thandeciduous forest. Soils become more acid due to base (plant nutrient) removalin harvested parts of the crop. Nitrogen fertilization speeds up the rate at whichacidity develops in soil due to excess H+ produced in thenitrification process. Nitrification, a natural process mediated bymicroorganisms, changes ammonium forms of N to nitrate forms. Nitrogen comingeither from inorganic fertilizers, organic matter, manure and legume N fixationundergo this process contributing to soil acidity.
土壤酸性是以土壤pH即H+活度的对数来度量的。土壤酸性随着交换复合体固持的和土壤溶液中的H+数量的增加而增加。大多数丰产土壤pH变化范围为4.0~9.0。土壤中铝表现酸性元素的行为，事实上在大多数pH低于5.5的土壤上铝是H+的主要来源。铝水解形成氢氧化铝单体和多聚体，这些过程也产生H+，造成土壤酸化。单体铝的水解以下列方程表示：
Soil pHmeasures soil acidity as the logarithm of the activity of the hydrogen ion (H+).Soil acidity increases according to the increment in H+ held in theexchange complex and present in the soil solution. Most productive soils rangefrom 4.0 to 9.0 in pH. Aluminum (Al) in the soil also acts as an acidic elementand in fact is the principal source of H+ in most soils with pHbelow 5.5. Aluminum hydrolysis (reacts with water) to form monomeric andpolymeric hydroxyaluminum complexes. These reactions also produce H+adding to soil acidity. Hydrolysis of the monomeric forms are shown in thefollowing equations:
Al3+ + H2O —→ Al(OH) + H+
Al(OH) + H2O —→ Al(OH)2 + H+
Al(OH)2 + H2O —→ Al(OH)3+ + H+
这些反应释放H+，H+反过来了使Al3+数量增加，利于反应的再次发生。有研究显示，土壤溶液中即使低量Al3+对多数作物也是有毒的。因而Al3+是这些酸性土壤上的主要限制因子。
These reactionsrelease H+ which in turn increases the amount of Al3+ readyto react again. It has been demonstrated that even low amounts of Al3+in soil solution are toxic to most crops. The Al3+ concentration isthe main limiting factor in these acid soils.
石灰通过把一些H+转化为水来提高pH降低酸度。pH高于5.5，Al3+形成Al(OH)3沉淀，毒性影响以及H+的主要来源也被消除。一旦需要，施石灰就成为保证高产稳产的一项管理措施。
Lime reducesacidity (increases pH) by converting some of the H+ into water.Above pH 5.5 Al3+ precipitates as Al(OH)3 and the toxicaction the main source of H+- is eliminated. When needed, liming isa management practice that allows higher and sustainable yields.
2. 施石灰是一项良好的管理措施
