Effects of Long‐Continued Use of Dolomitic Limestone on Certain Chemical and Colloidal Properties of a Sassafras Loam Soil

For a period of twenty-eight years, dolomitie limestone has been used at fiveyear intervals on a Sassafras loam soil on certain of the soil fertility plots at the Uew Jersey Experiment Station. The experiment was started in 1908 for the purpose of comparing dolomitic limestone and high calcium limestone in different amounts, and in connection with different rotations. A number of papers and bulletins have been published giving crop yields and the amount of nitrogen recovered in the crop for the period (6, 7, and 8). Some work has been published relating to the composition of the soil (5), but the long-time treatment with the two forms of limestone in different amounts has established conditions which warrant further soil studies. The authors felt that the conditions were favorable for a more thorough study of the effects of the limestone on the soil, especially with respect -to colloidal content, base exchange powers, and the amounts of exchangeable calcium and magnesium. Also, from the work of other investigators on other soils (9, 15), it seemed quite possible that magnesium was being fixed to a considerable extent in this soil. The soil studied was from two sections of four plots each where two different fiveyear rotations have been carried out. The rotation for the first section (plots 21, 25, 26, and 27) was one of general farm crops: corn, oats, wheat, and hay. The rotation for the second section (plots 35, 39, 40, and 41) was a year of corn followed by four years of vegetable crops. However, in the fall of 1931 this section of four plots was seeded to a grass mixture which has been continued to the present time. The fertilizer treatment has usually been about 300 pounds of superphosphate, 100 pounds muriate of potash, and 100 to 200 pounds of nitrate of soda, or equivalent nitrogenous fertilizer, to the acre. The vegetable crop usually received heavier applications. No farm manure has been used since the experiment was started. Plots 21 and 35 received no lime and are therefore indicated as check plots. Plots 25 and 39 have received a thousand pounds of dolomitic limestone at intervals of five years, plots 26 and 40 two thousand pounds, and plots 27 and 41 four thousand pounds to the acre. The lime treatment was omitted in 1933. The soil samples were taken in the fall of 1936, the surface samples being taken to a depth of six and two-thirds inches while the subsoils represent the next seven inches. These samples represent approximately the A and B horizons respectively. Plots 35, 39, 40, and 41 were in sod when the samples were taken. A thin layer of sod was removed before taking the samples and this resulted in the loss of a small portion of the top soil.