1. The pH (potential Hydrogen ions) scale ranging from 0 to 14 is used to indicate acidity and alkalinity. A pH of 7.0 is neutral, values below 7.0 are acid, and those above are alkaline. The lower the pH the more acid is the soil. The higher the pH, the more alkaline. The pH values of some common items are: 
Rain water: 7.0; Lemon juice, 2.2 to 2.4; Orange juice, 3.4 to 4.0; Milk, 6.3 to 6.6; mild soap solution, 8.5 to 10.0.

Why pH is important in soil?:
Soil pH can affects the biological and chemical activity of the soil significantly. 
Acid soils: often low in magnesium and calcium. 
Calcium: an important neutralizing agent. If calcium is depleted by leaching and plant uptake, hydrogen and 
aluminium ions increase and soil become acid.

Iron, manganese, boron, copper and zinc: 
These elements are essential to plant growth in very small amounts. Plant uptake is better in neutral or slightly 
alkaline soils. Decreasing acidity by liming can influence manganese uptake significantly. 

Alkaline soils: high in basic ions, mainly calcium and magnesium and to a lesser extent potassium and sodium. Leaching and rain removes calcium, magnesium and potassium from soils over hundreds or thousands of years the natural trend is for soils to become more acid. 

Acids soil: result in poor yields. Neutralise with lime. It is generally easier to make soils more alkaline than it is to make them more acid.

Lime application: lime must be mixed with the soil. Should be worked into the soil to a depth of 250mm. Also 
effective: ground limestone, marl, ground oyster-shells.
To increase pH by 1.0 point and make soil more alkaline:
Add 115grams of hydrated lime per square yard in sandy soils 
Add 8 ounces of hydrated lime per square yard in loamy soils 
Add 230 grams of hydrated lime per square yard in clay soils 
Add 700 grams of hydrated lime per square yard in peaty soils.
NOTE: Use protection such as dusk-mask and gloves. The best way to adjust pH is gradually, over several seasons. Lime should be applied only when tests show it to be necessary. 

How long will it take for lime to work?
It takes water to activate the lime reaction, so lime works slowly in dry soil. Even with adequate soil moisture, 
it may take a year or more for a measurable change in pH. Since neutralization involves a reaction between soil and lime particles, mixing lime with soil increases the efficiency of acidity neutralization. 
Plants that can benefit from liming: asparagus, celery, beets, spinach, carrots. 

Plants that will not tolerate lime in soil: Rhododendrons and heathers.