In the form of ashes, marl or chalk, lime has been used as a
fertilizer for thousands of years. It serves two very important
purposes: to correct the acidity of sour soils and to supply calcium
and sometimes magnesium as plant food. Burned lime has also been
much used, but in more recent years the development of machinery for
crushing and pulverizing rock--especially in cement manufacture--has
made possible the production of pulverized natural limestone, and at
much less expense than for caustic lime made by burning and slaking.
Where ground limestone can be easily procured it takes the place of
burned lime, and it produces better results at less expense, even
though 1-3/4 tons of ground limestone are required to equal 1 ton of
quicklime in calcium content and in power to correct acidity.

Furthermore, ground limestone can be applied in any amount with no
injurious results, while caustic lime destroys the organic matter or
humus of the soil, dissipates soil nitrogen, is disagreeable to
handle, and may injure the crop unless applied in limited amounts or
several months before the crop is to be planted.

The most valuable and trustworthy investigation on record in regard
to the comparative value of burned lime and ground limestone has
been conducted by the Pennsylvania Experiment Station. A four-year
rotation of crops was practiced, including corn, oats, wheat and hay
(clover and timothy) on four different fields, each crop being
represented every year. After twenty years the results for the four
acres showed that the land treated with ground limestone had
produced 99 bushels more corn, 116 bushels more oats, 13 bushels
more wheat and 5.6 tons more hay than the land treated with about an
equivalent amount of burned lime. At the end of sixteen years the
analysis of the soil showed that the burned lime had destroyed 4.7