喜樂、光明、空靈

酸性土壤施用石灰是一項良好的管理措施

LIMING ACID SOILS-A GOOD MANAGEMENT PRACTICE

Jose Espinosa

磷鉀研究所拉丁美洲項目部主任

Director, Potash and Phosphate Institute, Latin American Office, P.O. Box 17-17-980, Quito, Ecuador, South America

1. 引言 Introduction

農用石灰，不管是粉細的白雲石質石灰岩，還是方解石質石灰岩，直接施到酸性土壤是提高作物產量和降低肥料成本的一條廉價途徑。這一土壤改良劑已在全世界廣泛應用。保持恰當的土壤pH值對於保持良好的土壤肥力和制定良好的養分管理方案是必需的。一些導致土壤酸化的因素包括母質、降雨、天然植被、作物種植和施用氮肥等。

Agricultural lime, either finely ground dolomitic or calcitic limestone, applied directly to acid soils is an inexpensive way to increase crop yields and reduce fertilizer input costs. This soil amendment is widely used around the world. Maintaining an adequate soil pH is indispensable in a sound soil fertility and nutrient management program. Several factors contribute to soil acidity including parent material, precipitation, native vegetation, crops grown and nitrogen (N) fertilization.

由基性岩母質發育的土壤通常比那些由酸性岩發育的土壤具有更高的pH值。在高降雨條件下形成的土壤比在乾旱條件下形成的土壤酸性強。土壤有機質不停地被微生物分解成有機酸和CO₂，從而加重土壤酸化。森林植被下發育的土壤比草地植被下發育的土壤酸性強，針葉林土壤比落葉林土壤酸性強。隨著作物收穫部分鹽基養分的移走，土壤酸度增強。氮肥施用由於在硝化過程中產生多餘的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銨態氮轉化為硝態氮的一種自然過程，這裡的氮無論來源於無機肥料、有機肥料和糞肥，還是來源於豆科固定的氮，均發生這一過程，使土壤變酸。

Soils developed from parent materials of basic rocks generally have higher pHs than those formed from acid rocks. Soils formed under high rainfall conditions are more acidic than those formed under dry conditions. Soil organic matter is continually being decomposed by microorganisms into organic acids and carbon dioxide (CO₂)  which add to soil acidity. Soils formed under forest vegetation tend to be more acid than those developed under grasslands, and conifers create more acidity than deciduous forest. Soils become more acid due to base (plant nutrient) removal in harvested parts of the crop. Nitrogen fertilization speeds up the rate at which acidity develops in soil due to excess H⁺ produced in the nitrification process. Nitrification, a natural process mediated by microorganisms, changes ammonium forms of N to nitrate forms. Nitrogen coming either from inorganic fertilizers, organic matter, manure and legume N fixation undergo this process contributing to soil acidity.

土壤酸性是以土壤pH即H⁺活度的對數來度量的。土壤酸性隨著交換複合體固持的和土壤溶液中的H⁺數量的增加而增加。大多數豐產土壤pH變化範圍為4.0~9.0。土壤中鋁表現酸性元素的行為，事實上在大多數pH低於5.5的土壤上鋁是H⁺的主要來源。鋁水解形成氫氧化鋁單體和多聚體，這些過程也產生H⁺，造成土壤酸化。單體鋁的水解以下列方程表示：

Soil pH measures soil acidity as the logarithm of the activity of the hydrogen ion (H⁺). Soil acidity increases according to the increment in H⁺ held in the exchange complex and present in the soil solution. Most productive soils range from 4.0 to 9.0 in pH. Aluminum (Al) in the soil also acts as an acidic element and in fact is the principal source of H⁺ in most soils with pH below 5.5. Aluminum hydrolysis (reacts with water) to form monomeric and polymeric hydroxyaluminum complexes. These reactions also produce H⁺ adding to soil acidity. Hydrolysis of the monomeric forms are shown in the following equations:

   Al³⁺ + H₂O —→ Al(OH) + H⁺

   Al(OH) + H₂O —→ Al(OH)₂ + H⁺

   Al(OH)₂ + H₂O —→ Al(OH)³⁺ + H⁺

這些反應釋放H⁺，H⁺反過來了使Al³⁺數量增加，利於反應的再次發生。有研究顯示，土壤溶液中即使低量Al³⁺對多數作物也是有毒的。因而Al³⁺是這些酸性土壤上的主要限制因子。

These reactions release H⁺ which in turn increases the amount of Al³⁺ ready to react again. It has been demonstrated that even low amounts of Al³⁺ in soil solution are toxic to most crops. The Al³⁺ concentration is the main limiting factor in these acid soils.

石灰通過把一些H⁺轉化為水來提高pH降低酸度。pH高於5.5，Al³⁺形成Al(OH)₃沉澱，毒性影響以及H⁺的主要來源也被消除。一旦需要，施石灰就成為保證高產穩產的一項管理措施。

Lime reduces acidity (increases pH) by converting some of the H⁺ into water. Above pH 5.5 Al³⁺ precipitates as Al(OH)₃ and the toxic action the main source of H⁺- is eliminated. When needed, liming is a management practice that allows higher and sustainable yields.

2. 施石灰是一項良好的管理措施Liming as A Good Management Practice

施石灰是向土壤中摻入含鈣或含鈣鎂的物質來降低酸性和提高pH的一項措施。

Liming is a management practice that incorporates in the soil calcium or calcium + magnesium materials that are capable of reducing acidity and increase soil pH.

2.1 石灰物質  Liming materials

有多種物質能在土壤中反應提高pH。其中最重要的有氧化鈣、氫氧化鈣、方解石和白雲石。

There are several material that can react in the soil increasing pH. The most important include calcium oxide, calcium hydroxide, calcite and dolomite.

氧化鈣（CaO）—-即生石灰，是一種腐蝕性白色粉末，施用時難度較大。工業上生產氧化鈣是通過在熔爐中焚燒方解石質石灰石得到的，其純度取決於原材料的純度。當施入土壤時，它幾乎立即反應，因此在追求立即見效時它是理想的石灰物質。但施用時應與土壤充分混合，否則很快結塊、失效。

Calcium oxide (CaO)- Also known as burned lime or quicklime, is a caustic white powder, disagreeable to handle. It is manufactured by roasting calcitic limestone in an oven or furnace. Its purity depends upon raw material purity When added to soil, it reacts almost immediately, so it is ideal when rapid results are required. It should be mixed completely with the soil, because it rapidly cakes and can become ineffective.

氫氧化鈣［Ca(OH)₂］—-通常稱作水合石灰或建築石灰，是一種具腐蝕性的白色粉末物質，運輸和施用時難度較大。加入土壤後與酸性物質迅速發生中和反應。由氧化鈣水合制得。

Calcium hydroxide [Ca(OH)₂]- Frequently referred to as hydrated lime or builders' lime, is a caustic, white, powdery substance, difficult and unpleasant to handle. Acid neutralization occurs rapidly when it is added to the soil. It is prepared by hydrating CaO.

方解石(CaCO₃)和白雲石［CaMg(CO₃)₂］—-這兩種物質是農業上最常用的石灰物質。白雲石的優點是可向土壤中加入鎂，這一點在一些土壤很重要。二者的質量依賴於其含有粘土或有機質等雜質的多少。

Calcite (CaCO₃) and dolomite ［CaMg(CO₃)₂］- These two materials are the most commonly used lime sources in agriculture. Dolomite has the benefit of adding magnesium (Mg) which in some soils is important. Quality of these materials depends on impurities such as the clay or organic matter they contain.

其它幾種物質也可用來施用石灰，如蠔殼灰、泥灰、鋼渣磷肥（鹼性爐渣）、草木灰和工業水泥的副產品等。

Several other materials can be used for liming purposes, such as, baked or burned oyster shells, marl, basic slag, wood ashes, and cement industry by-products.

2.2 石灰質量  Lime quality

石灰性物質應檢驗其中和值和細度。所有石灰性物質的中和值都是以其與純CaCO₃的中和值比較來確定的。把純CaCO₃的中和值設為100，其它物質的中和值就可確定。這個值稱為相對中和值或CaCO₃當量。一些石灰性物質的相對中和值列於表1。

Liming material should be checked for neutralizing value and degree of fineness. Neutralizing value of all liming materials is determined by comparing them to the neutralizing value of pure calcium carbonate (CaCO₃). Setting the neutralizing value of pure CaCO₃ at 100, a value for other materials can be assigned. This value is called the Relative Neutralizing Value or Calcium Carbonate Equivalent. The relative neutralizing values of some liming materials are shown (Table 1).

表1 一些石灰性物質的相對中和值

Table 1 Relative neutralizing values of some liming materials

當一定量的石灰與土壤混合時，它的反應速率和反應程度就受到顆粒大小的影響。粗粒石灰反應慢且不完全，細粒石灰反應更快更完全。

When a given quantity of lime is mixed with soil, its reaction rate and degree of reactivity are affected by particle size. Coarse lime particles react more slowly and less fully. Fine lime particles react more rapidly and much more completely.

石灰成本隨粉碎細度增加而增加。因而最終目標是通過最少量的粉碎卻含有足夠的細質物質以達到快速的pH變化。因而，農用石灰物質同時含有粗粒和細粒。從實踐的角度來看，一種良好的石灰物質應該是完全通過60目篩。

Cost of lime increases with the fineness of grind. The goal is to have a material that requires a minimum of grinding and yet containing enough fine material to cause a rapid pH change. As a result, agricultural liming materials contain both coarse and fine materials. From the practical point of view, a good liming material should have particles that pass completely through a 60 mesh sieve.

2.3 土壤中的石灰反應  Lime reactions in the soil

土壤中石灰反應的機理是中和土壤溶液中的H⁺。石灰與H₂O反應生產OH ^-。因此，只有在土壤水分充足的條件下施石灰才有效。基本的石灰反應可用CaCO₃在土壤中發生的反應來說明。其反應過程是：

Reaction mechanisms of liming materials in soil neutralize H⁺ in the soil solution. Lime reacts with water to produce OH^- ions. For this reason, liming is effective only when adequate soil moisture is present. Basic lime reactions can be illustrated with the reactions that CaCO₃ undergoes in the soil. They areas follows:

    CaCO₃ —→ Ca²⁺ + CO₃^2-

    CO₃^2- + H₂O —→ HCO₃^- + OH ^–

    HCO₃^- + H₂O —→ H₂CO₃ + OH ^–

    H₂CO₃ —→ CO₂↑+ H₂O

         H⁺ (土壤溶液)+ OH ^–—→ H₂O

因而，上述反應的速率，也即CaCO₃的解離速率，與土壤溶液中和H⁺ 時OH ^-的消耗速率和H₂O形成速率有關。只要土壤溶液中有H⁺存在，CaCO₃就會不停地反應，從而提高pH。

Rate of the above reactions, therefore, the dissociation of CaCO₃, is related to the rate OH^- are removed from the soil solution through H⁺ neutralization and H₂O formation. As long as H⁺ is present in the soil solution CaCO₃ will continue reacting, increasing pH.

值得一提的是，上述反應的終產物為CO₂，它散逸到在空氣中。這就解釋了為什麼石灰施用的效果只侷限於石灰顆粒所在的地方。換句話說，表施石灰一定要均勻，然後與土壤充分混合。因此，石灰的均勻混合對於控制酸度是非常必要的。

It is interesting to note that the final product of the above reactions is CO₂ which dissipates to the atmosphere. This is the reason why the effect of liming is restricted to the site where lime particles are located In other words, it is necessary to make a uniform surface application of lime which then needs to be completely mixed with the soil. Good incorporation of lime is essential for effective control of acidity.

在一些種植制度下，如多年生草皮或種植園作物，混施石灰只能在種植前才有可能。一旦作物長出以後，石灰就只能表施了。表施石灰反應較慢，不像石灰與土壤混合一樣反應完全。然而現已證明，在免耕系統中，表施石灰是有效的，主要是由於在土壤剖面中發生的物理和化學變化使得0~10cm的表層土壤保持較高的根系活性。

In some cropping systems, such as perennial sods or plantation crops, mixing is only possible before seeding. Once the crop is established, lime must be topdressed. Surface applied lime reacts more slowly and not as completely, as lime mixed with the soil. However, it has been proven that in no-till systems surface lime application is effective mainly due to the physical and chemical changes in the soil profile that concentrate root activity in the 0-10 cm superficial layer.

3. 石灰需要量Lime Requirement

雖然土壤pH是土壤酸度很好的指標，但並不能確定出石灰需要量。石灰需要量是指在某一種植系統中把pH調至一定範圍所需的農用石灰數量。測定pH時，只能測定土壤水中的活性酸度，被土壤粘粒和有機質吸持的潛在酸度也必需考慮。

Although soil pH is an excellent indicator of soil acidity, it does not determine lime requirement. Lime requirement is the amount of agricultural lime needed to establish the desired pH range for the cropping system being used. When pH is measured, only active acidity in the soil water is determined. Potential acidity, that is held by soil clay and organic matter, must also be considered.

石灰需要量不僅與土壤pH有關，而且與陽離子交換量(CEC)有關，而CEC又與主要粘粒的數量、類型和土壤有機質的含量有關。這些因素決定土壤緩衝性的強弱，即抵禦pH變化的能力，其緩衝容量隨粘粒和有機質數量的增加而增加。砂土含粘粒和有機質少，緩衝性弱，需要很少的石灰就能改變pH。

Lime requirement is not only related to soil pH, but also to cation exchange capacity (CEC) which in turn is related to total amount and type of clay predominant and soil organic matter content. These factors determine how strongly soils are buffered or how strongly they resist a change in pH. Buffering capacity increases with amount of clay and organic matter. Sandy soils, with small amounts of clay and organic matter, are weakly buffered and require less lime to change pH.

3.1 溫帶土壤的石灰需要量  Lime requirement for temperate soils

有證據表明，施用石灰時必須考慮該土壤的主要粘土礦物。我們常在溫帶地區發現的2:1型粘土礦物（蒙脫石、蛭石、伊利石）為主的土壤，也出現在熱帶和亞熱帶地區。這些土壤不同於世界範圍內廣泛分佈的典型的熱帶紅壤(以鐵鋁氧化物和高嶺石為優勢粘土礦物的老成土和氧化土)，也不同於由火山灰（以水鋁螢石、伊利縞石和腐殖質-Al複合體為優勢粘土礦物的火山灰土）發育的土壤。這些重要的差別決定了評價石灰需要量的方法。

It has been demonstrated that successful liming has to take into account the dominant soil clay minerals in the soil to be limed. Soils dominated by 2:1 clays(montmorillonite, vermiculite, illite), more frequently found in temperate zones, but also present in tropical and subtropical areas; behave different from the typical tropical red soils (Ultisols and Oxisols dominated by Fe and Al oxides and kaolinite) and from the soils developed from volcanic ash (Andisols dominated by allophane, imogolite, and humus-Al complexes) that are widely spread over the world. These important differences determine the approach to evaluate lime requirements.

以2:1型粘土礦物為主的土壤（軟土、變性土），由於脫鹽基（K、Ca、Mg等離子減少）作用導致土壤酸性，由此引起粘土礦物的解體和Al的釋放並佔據鹽基損失後的交換位點。這些土壤通過施用石灰很容易把pH調至6.5~7.0，以挖掘最大的生產潛力。在這個過程中，CEC（永久電荷土壤）的變化極小。表2的數據顯示了在阿根廷的軟土上施用白雲質石灰石對土壤pH和大豆、玉米產量的影響。

In soils dominated by 2:1 clays (Mollisols, Vertisols), the reduction in base saturation (loss of K, Ca, Mg) leads to acidity. This increment in acidity in turn leads to the breakdown of clay material and release of Al which occupies exchange sites left by the lost bases. These soils can be easily limed to reach a pH range of 6.5 to 7.0 to obtain the highest productivity. During this process there is very little change in CEC (soils of permanent charge). Data (Table 2) illustrates the effect of dolomitic lime on soil pH, and soybean and corn yields in a Mollisol from Argentina.

表2 在阿根廷的軟土上白雲石對土壤pH和大豆、玉米產量的影響

Table 2 Effect of dolomite application on soil pH, and soybean and corn yield in a Mollisol from Argentina

通常確定2:1型土壤的石灰需要量是依據緩衝溶液與土-水懸浮液的pH變化。最常用的就是SMP方法，該法用來測定美國溫帶地區酸性土壤的石灰需要量。土壤-水-緩衝溶液三者的懸浮液的平衡pH值，與用CaCO₃培養法使同一土壤樣品達到一定的pH所需的石灰量是相關的。應用這種方法就能推算出使土壤pH達到一特定值所需的石灰量。該方法使我們能夠對永久電荷酸性土壤石灰需要量進行快速測定。表3是一個應用SMP緩衝液校正法進行石灰推薦的例子。

Common methods of determining lime need in soils dominated by 2:1 clays are based on pH change of a buffered solution compared to pH of a soil-water suspension. The most popular of these methods is the SMP (Shoemaker, McLean and Pratt) method developed to determine lime needs in acid soils of the temperate zones of the USA. The equilibrium pH value of a suspension made of soil water buffer solution is correlated with the amount of lime needed to increase soil pH to a certain value, using a CaCO₃ incubation procedure, in the same soil sample In this way, recommendations can be developed to indicate the amount of lime required to bring soil pH to a particular value. This method allows a rapid determination of lime requirement in acid soils of permanent charge. An example of liming recommendations based on calibration of a SMP buffer solution is presented (Table 3).

表3 應用SMP緩衝溶液方法確定的石灰量

Table 3 Liming rates determined using SMP buffer solutions

*土-水-緩衝液的pH。pH of the suspension soil-water-buffer solution

3.2 熱帶土壤的石灰需要量  Lime requirement for tropical soils

確定熱帶紅壤石灰需要量的方法是不同的。在這些土壤中，pH低到5.0時粘土礦物的Al和Fe是穩定的，此時Al被包埋在粘土顆粒中，對植物不構成威脅，直到pH降低到使氧化物和高嶺石溶解，把Al³⁺ 釋放到土壤溶液中，有時會達到毒害水平（pH<5.3）。當這一情況發生時就要把土壤pH提高到5.5以上，這就能使Al³⁺ 沉澱下來，同時大幅度增加土壤可變電荷CEC（如表4、表5）。在這一pH下作物生長和產量最佳的。

However, determination of lime requirement of tropical red soils is different In these soils, Al and Fe present in mineral clays are stable at pH values as low as 5.0. In this case Al is buried in the clay particle and is not a threat to plant growth until pH reaches values where the oxides and kaolinite dissolve bringingAl³⁺, sometimes in toxic quantities, into the soil solution (pH < 5.3). When this arises it is advisable to raise soil pH to values of about 5.5. This allows Al³⁺ precipitation and appreciable increment in CEC (soils of variable charge) as presented (Tables 4 and 5). At this pH, crop growth and yields are excellent.

表4 巴拿馬紅色老成土施用石灰的效果

Table 4 Effect of lime application to a red Ultisol from Panama

表5 巴西氧化土施用石灰對土壤pH和作物產量的影響

Table 5 Liming effects on soil pH and the yield of various crops in Oxisols from Brazil

在熱帶土壤上應用緩衝溶液方法確定石灰需要量很不適用。用該方法推薦的石灰量過大，使pH升到6.0~7.0，而實際上相對少量的石灰就能使pH升高足以沉澱Al³⁺，因此，石灰推薦應依據表層土壤交換態Al的數量來確定。按照這一概念，大部分熱帶土壤的石灰需要應根據下述方程來確定：

CaCO₃當量（噸/公頃）= 因子×釐摩爾Al/公斤土壤

In tropical soils, determination of lime requirements using buffered solutions does not work adequately. Using this approach large amounts of lime are recommended to force soil pH to values in the 6.0-7.0 range while only moderate amount of lime is needed to raise soil pH enough to precipitate Al³⁺. In this case it has been suggested that lime recommendations be based on the amount of exchangeable. Al in the top soil Following this concept, lime requirement for most tropical soils can be predicted applying the following equation :

CaCO₃ equivalent (t/ha)=Factor×cmol Al/kg soil

因子值因作物特性和土壤類型不同，其變化範圍是1.5~3.0。這可通過在某一特定地點工作的農學家或農民來精細地調整。

The factor used can vary from 1.5 to 3.0 depending on the crop characteristics and the soil type. This factor can be fine tuned by the agronomist or farmer working at a specific site.

該方法的主要目標是中和全部Al³⁺，但有一類耐鋁作物在土壤交換複合體處於中度鋁飽和時能夠生長良好並獲取令人滿意的產量。既然不需要沉澱所有的Al³⁺，施用較少量的石灰就能把鋁飽和度降到所需的水平。多數情況下，施用石灰是為了克服在低CEC的風化土上生長的作物缺乏Ca和Mg。咖啡、香蕉、油棕和許多熱帶牧草和豆科植物都屬於高度耐鋁植物。通過作物育種已經培育出水稻、高粱和玉米等一些作物的高度耐鋁品種。

The primary goal of this approach is to neutralize all Al³⁺ but, there are Al tolerant crops that can grow and yield satisfactorily at moderate aluminum saturation of the exchange complex. Since not all Al³⁺ needs to be precipitated, a lower amount of lime can be used to reduce Al saturation to the desired level. Inmost of these cases, applied lime is used to overcome Ca and Mg deficiencies which can limit plant growth in weathered soils of low CEC. Coffee, banana, oil palm, and a number of tropical grasses and legumes are among the crops that tolerate high Al saturation. Plant breeding has developed cultivars of certain crops like rice, sorghum, and corn that are also tolerant to high Al saturation.

另外一種計算石灰需要量的方法與鋁的飽和度有關，是以土壤的鹽基飽和度為依據的。儘管鹽基飽和度不影響生長在2︰1型礦物上作物的產量，但其在低CEC和低Ca、Mg含量的高度風化土壤（老成土和氧化土）上卻非常重要。上面提到的白雲石，其不僅用來較正這些土壤的酸性，而且可以補充土壤的鈣和鎂。有研究證明，風化土壤較高的鹽基飽和度可在一定程度上改善土壤肥力和提高作物產量。

Another common method used to calculate lime requirements, related to Al saturation, is based on soil base saturation. Though it has been determined that base saturation does not influence yield in soils dominated by 2:1 clays, this parameter is very important in highly weathered soil (Ultisols and Oxisols) of low CEC and low Ca and Mg content. As indicated above, dolomitic lime is used not only as an amendment in these types of soils, but also as a source of Ca and Mg. Research has demonstrated that, within certain limits, higher base saturation in weathered soils improves fertility and increases crop yields.

一種考慮施石灰後獲得目標土壤鹽基飽和度來確定石灰需要量的方法逐步完善起來。巴西的經驗表明，咖啡在鹽基飽和度為60％時產量最佳，換句話說，即咖啡在土壤為鋁飽和度為40%時生長良好。根據這一標準，石灰需要量可根據下式計算：

A method for determining lime requirement was developed taking into account a targeted soil base saturation attained by lime application. Brazilian experience indicates, for example, that the best coffee yields are obtained at 60 percent saturation. In other words, coffee can grow satisfactorily in a soil having up to 40 percent Al saturation. According to these criteria, lime requirements can be calculated using the following equation:

CaCO₃(噸/公頃)=(BS₂-BS₁)×CEC/100

式中 BS₁＝起始鹽基飽和度

 BS₂＝目標鹽基飽和度

CaCO₃ (t/ha)=((BS₂BS₁)×CEC/100)

Where BS₁= Initial base saturation

  BS₂= Required base saturation

3.3 火山灰土壤的石灰需要量  Lime requirement for soils derived from volcanic ash

火 山灰土壤的石灰需要量的計算方法有些不同，主要是高的緩衝容量使得石灰需要量難以計算，而且其緩衝容量的強度隨著海拔、降雨和溫度等影響火山灰風化的因素 變化而變化。因此，評價這些土壤的石灰需要量並不是遵循一個簡單的原則。應用交換態鋁為標準有時會對石灰需要量估計偏低（表6）。

Liming approach for soils derived from volcanic ash (Andisols) is somewhat different. The high buffering capacity (resistance to pH change) complicates lime requirement evaluation. Intensity of the buffering capacity varies from one place to another according to altitude, rainfall and temperature the factors controlling volcanic ash weathering. For this reason, there is not a simple rule to evaluate lime requirement in these soils. Use of the exchangeable Al criterion sometimes underestimates lime needs as illustrated (Table 6).

表6 厄瓜多爾高原的火山灰土壤施用石灰對土壤化學性質和作物產量的影響

Table 6 Effect of lime application on soil chemical properties and crop yield in an Andisol of the highlands of Ecuador

*以中性鹽計算的陽離子交換量  *CEC evaluated with an indifferent salt

火山灰風化形成的水鋁螢石、伊利縞石和腐殖質-Al複合體粘土顆粒表面非常活躍。當施用石灰時，其與粘土顆粒產生電荷（CEC增加）的表面反應，使pH升高和沉澱Al難以進行。沉澱Al所需的石灰需要量應隨火山灰形成的時間及其風化的程度而變化。因此，為了準確計算某一地點的石灰需要量，應佈置一些簡單的田間試驗。

Clay particles resulting from volcanic ash weathering (allophane, imogolite and humus-Al complexes) have a very reactive surface. When lime is applied to these soils it reacts with clay surfaces creating charge (increment in CEC) failing to increase pH and to precipitate Al. The amount of lime needed to precipitate aluminum varies with the age and weathering of the volcanic ash. For this reason, it is necessary to conduct simple field trials which can indicate precisely the amount of lime needed in an specific site.

在熱帶土壤，不管應用何種方法計算石灰需要量，均要注意石灰施用量不能過大，通常把土壤調至中性就會出現這種情況。熱帶土壤僅需中和鋁，這只需把pH調至5.5~6.0即可。過量施石灰會導致土壤結構退化，B、Zn、Mn的有效性下降，產量降低。

Regardless of the method used to determine lime requirement in tropical soils, it is advisable to avoid excessive lime applications. Usually this happens when such soils are limed to neutrality. Tropical soils should only be limed to neutralize Al, which generally brings soil pH to values in the 5.5 to 6.0 range. Over liming leads to soil structure deterioration, reduced boron (B), zinc (Zn) and manganese (Mn) availability, and lower yields.

4. 結論Conclusions

土壤酸性在多方面影響作物生長，最終對產量影響也很大。合理施用石灰能控制由低pH帶來的有害作用，也能降低鋁錳毒害，這可能是酸性土壤施用石灰主要的積極作用。其它作用還有改變土壤的物理條件、刺激土壤的微生物活性和共生固氮作用，提高其他營養元素的有效性，增加可變電荷土壤的CEC含量。酸性土壤中，一項精細設計的石灰施用計劃對於作物的高產穩產是非常重要的。

Soil acidity affects plant growth in many ways, in consequence, crop yields are also affected significantly. Properly applied lime controls the detrimental effects of low pH. A good liming program reduces Al and Mn toxicity. This is perhaps the main favorable effect of liming acid soils. Other benefits include an improved soil physical condition, stimulation of soil microbial activity and symbiotic N fixation, increment of availability of other nutrients, and increase in CEC in soils of variable charge. In acid soils, a well designed liming program is fundamental to high sustainable crop yields.

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