An investigation was made of the comparative effects of calcium and magnesium limestones applied to Carrington loam, Tama silt loam and Grundy silt loam. These soils are all acid in reaction and have a lime requirement of about 3 tons per acre. They occur extensively in Iowa and are among the better agricultural soils of the state.

Studies were made of the effects of the limestones on the hydrogen-ion concentration, the lime requirement, the exchangeable hydrogen, calcium and magnesium and on the degree of saturation of the exchange complex with bases. Studies were also made of the nitrate content and the nitrifying power of these soils as influenced by the two limestones, and of the yields of wheat and red clover on the Carrington loam and the Tama silt loam treated with the two limestones.

The data obtained indicate that the calcium limestone reacted somewhat more rapidly with the soil acids than the magnesium limestone. It reduced the acidity more and stimulated a greater production of nitrates in the soil during the first few weeks after the limestones were applied. This advantage of the calcium limestone was apparently overcome by the magnesium limestone rather quickly and after 8 to 12 weeks there was no apparent difference in the effects of the two limestones on any of the chemical or bacteriological characteristics of the soils studied. Neither limestone was superior in its effects on the yields of wheat and clover.

It is concluded from these experiments that in agricultural practice either limestone may be used to advantage to correct the acidity of soils, their long-time effects being practically identical.