三,土壤酸度的指标 土壤pH的测定 1.比色法:许多染料随看pH的增减改变颜色,在指示剂反应范内, 便可估计出嵱液近视的pH范围。使用单独的或数种混合的染料,很 容易测定pH3~8范围内的土壤pH。在测定土壤pH肘,土壤样品被 指示剂所饱和,在接触几分钟后,倒出一谪谩提液,在薄层中观察 的颜色,借助于比色卡就可以确定近似的pH.指示剂法可精确到 0.2pH单位。 2.电位测定法是最精确的测定方法。 选择一个电极,其电位决定于与之相接触的嵱液的氢离子浓度; 标准电极为氦电极。另一个电极为参比电极,常选用甘汞电极。廿 汞电极被KC嵱液饱和。用两个电极过程电池,测定其电位差,用 之确定嵱液氫离子浓度。 由于水的稀释、熔解、离子解离等综合作用结果。水土比不同, 其pH测定结果就有所不同,所以,测定时要统一限制水土比 (Soil/solution ratio) 1: 1
三.土壤酸度的指标 土壤pH的测定 1.比色法：许多染料随着pH的增减改变颜色，在指示剂反应范围内， 便可估计出溶液近视的pH范围。使用单独的或数种混合的染料，很 容易测定pH3~8范围内的土壤pH。在测定土壤pH时，土壤样品被 指示剂所饱和，在接触几分钟后，倒出一滴浸提液，在薄层中观察 它的颜色，借助于比色卡就可以确定近似的pH.指示剂法可精确到 0.2pH单位。 2.电位测定法 是最精确的测定方法。 选择一个电极，其电位决定于与之相接触的溶液的氢离子浓度； 标准电极为氢电极。另一个电极为参比电极，常选用甘汞电极。甘 汞电极被KCl溶液饱和。用两个电极过程电池，测定其电位差，用 之确定溶液氢离子浓度。 由于水的稀释、溶解、离子解离等综合作用结果。水土比不同， 其pH测定结果就有所不同，所以，测定时要统一限制水土比 （Soil/solution ratio）为1:1
Soil pH Determination One method to determine soil ph is by a pH indicator dye. This picture shows the indicator dye ph kit called Poly D. It is easy to use and gives a suitable pH value for most soils. The indicator dye is added to the soil in the spot plate until it is saturated the solution is stirred using a small spatula the solution will change color depending on the soil pH. The solution color is compared to a color card that has been calibrated to various pH readings. Be sure to clean the spot plates when you are through Soil ph test kits you get from a garden center for under $15 may give variable results. It is always best to compare the kits with an electronic ph meter The most accurate determination can be made using a ph meter and glass electrode. The electrical conductance of the solution is measured using the meter. The conductance is correlated in the machine to pH values which are read directly Methodology: There are three main internationally accepted methods available for measuring soil pH All of them rely on shaking(or stirring) soil with a solution for 1-2 hours and then determining the ph of the resultant soil slurry 1. Weigh out 5 g of soil into labelled 50 ml plastic(polypropylene)tubes 2. Add one of the following 3 solutions a)25 mL of distilled water. (This is the simplest method and normally oK for most soils. It doesn't remove H+ from the exchange sites and is not very good for soils high salt content) or b)25 ml of 1 M Kcl (used to mask differences in soil's salt content). Useful if determining exchangable cations as both cations and pH can be done on the same sample. It does displace H+ from the soil's cation exchange sites, so the results are usually slightly lower than obtained with methods (a)and(c) or c)25 mL of 0.01 M CaCl2. This is an intermediate between methods (a)and(c)and masks small differences in the soils salt content 3. Shake for 1 h at room temperature(25 C) 4. Let the soil settle for a few minutes(e. g. 3 min) and measure the ph after a two point(pH 4 and pH 7) calibration of the pH meter 5. Normally 2 replicates are performed for each soil sample 6. Field moist soil(store at 5 C)should preferably
Soil pH Determination One method to determine soil pH is by using a pH indicator dye. This picture shows the indicator dye pH kit called Poly D. It is easy to use and gives a suitable pH value for most soils. The indicator dye is added to the soil in the spot plate until it is saturated. The solution is stirred using a small spatula. The solution will change color depending on the soil pH. The solution color is compared to a color card that has been calibrated to various pH readings. (Be sure to clean the spot plates when you are through.) Soil pH test kits you get from a garden center for under $15 may give variable results. It is always best to compare the kits with an electronic pH meter. The most accurate determination can be made using a pH meter and glass electrode. The electrical conductance of the solution is measured using the meter. The conductance is correlated in the machine to pH values which are read directly. Methodology: There are three main internationally accepted methods available for measuring soil pH. All of them rely on shaking (or stirring) soil with a solution for 1-2 hours and then determining the pH of the resultant soil slurry. 1. Weigh out 5 g of soil into labelled 50 ml plastic (polypropylene) tubes 2. Add one of the following 3 solutions a)25 mL of distilled water. (This is the simplest method and normally OK for most soils. It doesn't remove H+ from the exchange sites and is not very good for soils high salt content) or b) 25 ml of 1 M KCl (used to mask differences in soil's salt content). Useful if determining exchangable cations as both cations and pH can be done on the same sample. It does displace H+ from the soil's cation exchange sites, so the results are usually slightly lower than obtained with methods (a) and (c). or c) 25 mL of 0.01 M CaCl2. This is an intermediate between methods (a) and (c) and masks small differences in the soil's salt content. 3. Shake for 1 h at room temperature (25°C) 4. Let the soil settle for a few minutes (e.g. 3 min) and measure the pH after a two point (pH 4 and pH 7) calibration of the pH meter 5. Normally 2 replicates are performed for each soil sample 6. Field moist soil (store at 5°C) should preferably
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三,土壤酸度的指标 (二)土壤酸度的数量指标-固相指标(容量因素 1.交换性酸度( soil exchangeable acidity)(pHkc) 当用中性盐熔液如 Imol Kcl或0.06 mol bacl嵱液(pH=刁)浸提土壤 肘,土壤胶体表面吸附的铝离子与氨离子的大部分均被浸提剂的阳离 子交换而进入嵱液,此肘,不仅交换性氦离子迸入嵱液变酸,交换性 铝离子由于水解作用也增强了嵱液酸性 A3+3H2O→A1OH)3↓+3H 浸出液中氩离子及其有铝离子水解产生的氫离子,用标准碱液滴 定,根据消耗的碱量换算,为交换性氢与交换性铝的总量,即为交换性 酸量(包括话性酸)。以厘摩尔(十)/千克)为单位,宅是土壤酸度 的数量指标。 阳离子交换反应是一种可以反应,所以,所测定的交换性酸度仅是 潜性酸度的一部分。 交换性酸量在进行调节土壤酸度,估算石灰用量肘,有重要参考 价值
三.土壤酸度的指标 （二）土壤酸度的数量指标---固相指标（容量因素） 1. 交换性酸度(soil exchangeable acidity)（pHKCl) 当用中性盐溶液如1mol Kcl或0.06mol BaCl溶液(pH=7)浸提土壤 时,土壤胶体表面吸附的铝离子与氢离子的大部分均被浸提剂的阳离 子交换而进入溶液，此时,不仅交换性氢离子进入溶液变酸,交换性 铝离子由于水解作用也增强了溶液酸性. Al3++3H2O→Al(OH)3↓+3H + 浸出液中氢离子及其有铝离子水解产生的氢离子,用标准碱液滴 定,根据消耗的碱量换算,为交换性氢与交换性铝的总量,即为交换性 酸量(包括活性酸)。以厘摩尔（＋）/千克）为单位，它是土壤酸度 的数量指标。 阳离子交换反应是一种可以反应,所以,所测定的交换性酸度仅是 潜性酸度的一部分。 交换性酸量在进行调节土壤酸度，估算石灰用量时，有重要参考 价值
土壤酸度的指标 2.水解性酸度 soil hydrolytic acidity)( pANadA 用弱酸强碱的盐类嵱液(常用的为pH8.2的 Imol nasa嵱液) 浸提,再以0. moiNa○H标准液滴定谩出液,根据所消耗的NaOH 的用量换算为土壤酸量。这样测得的潜性酸的量称之为土壤的水 解性酸。 浸提的机理①交换程度比之用中性盐类嵱液更为完全,土壤吸附 性氫、铝离子的绝大部分可被Na离子交换。②水化氣化物表面 的羟基和腐殖质的某些功能团(如羟基、羧基)上部分H解离 而进入浸提液被中和。 CH:COONa t Ho CHI COOH Naoh Naw H-胶粒 Al +4CH COONa 胶粒M N +Al(oH): 4CH. 氧化物」一0m+[氧化物」一0x+cH
三.土壤酸度的指标 2.水解性酸度(soil hydrolytic acidity)(pHNaoAc) 用弱酸强碱的盐类溶液（常用的为pH8.2的1mol NaOAc溶液） 浸提, 再以0.1molNaOH标准液滴定浸出液,根据所消耗的NaOH 的用量换算为土壤酸量。这样测得的潜性酸的量称之为土壤的水 解性酸。 浸提的机理①交换程度比之用中性盐类溶液更为完全，土壤吸附 性氢、铝离子的绝大部分可被Na+离子交换。②水化氧化物表面 的羟基和腐殖质的某些功能团（如羟基、羧基）上部分H+解离 而进入浸提液被中和