The Effect of Acidity on Turf and the Chemistry of Acid Soils

T FIRST fertilizer plats on this continent devoted to lawn grasses were started by the Rhode Island Agricultural Experiment Station. Sulphate of ammonia and nitrate of soda, alone and in combination, were used as the source of nitrogen. Superphosphate and muriate of potash were added to make a complete fertilizer. The plats were laid down in 1907 and were fertilized continuously until 1942, when the experiment was concluded. The 55th annual report of the station summarizes the results in an interesting manner. Turf on the nitrate of soda was unsightly because of its non-uniform character and invasion of weeds. The ones fertilized with a combination of nitrate of soda and ammonium sulphate were very slightly acid, and the turf was satisfactory. There was considerable "winter kill" or dying out on the sulphate of ammonia piats. The soil was strongly acid, pH 4.0. The winter kill was first noticed in the spring of 1938. Very severe raking to remove the dead grass helped restore the turf so there were few vacant spaces by the end of the growing season. Without raking in June and September the turf on the acid plats would have died and disappeared. But recovery of the injured areas was very slow in 1939-1940 and 1941. Raking showed that three times more clippings and dead grass accumulated on the acid soils (pH 4.0) than on the alkaline ones (pH 7 to 8). The slightly acid plats (pH 5 to 6) produced twice as much undecomposed grass as the alkaline ones. The accumulation of dead stems and roots produced a "sod bound" condition of the turf. The action of sodium arsenite and lead arsenate, used for weed and worm control, showed that the grass on the acid plats was in a weakened condition. The turf on the sulphate of ammonia plats was damaged severely by both materials. Little or no injury occurred on the alkaline or slightly acid soils. The concluding statements about these "old classic" plats, which were plowed under in 1942, are illuminating: "The plats that received sulphate of ammonia continuously as the source of nitrogen rather than nitrate of soda remained free of weeds and it was from the results of these tests that the "weedless lawn" dream was realized by the discovery of a long sought fertilizer that would grow grass and kill weeds. This gave rise to the 'sulphate of ammonia era' in turf culture. But as more research was undertaken and further observations were made, it was found that continuous applications of either sulphate of ammonia or nitrate of soda were inadvisable, due to the high acidity produced by the sulphate of ammonia, and the alkalinity produced by the nitrate of soda. However, sulphate of ammonia, when mixed with an equal weight of limestone to prevent the soil from becoming more acid, proved very satisfactory, and was also superior to nitrate of soda in maintaining desirable turf."