Comparative value of alfalfa and sweet clover on soils in the Lower Yakima Valley

In this experiment a comparative study was made of the carbon dioxide evolution and nitrate nitrogen accumulation in irrigated soils that had and those that had not grown alfalfa and sweet clover, in soils that had not grown legumes and soils to which legume hays were added as a fertilizer, and in alfalfa and sweet clover land. Soil from sweet clover land had 102% greater carbon dioxide evolution and 95% greater nitrate nitrogen accumulation than soil from alfalfa land during the 44 days of this experiment. The comparative yield of corn was 14.92 tons of silage per acre on sweet clover land and 8.25 tons on alfalfa land. The two soils after having produced a crop of corn proved to be very similar in carbon dioxide and nitrate nitrogen accumulation, consequently a very similar yield of the following crop might be expected. Both the virgin arid soil and the same soil after it had been irrigated and cropped to non-legumes for two years showed a low carbon dioxide evolution and nitrate nitrogen accumulation, evidently because of their low organic matter content. When a legume hay was added to either a virgin or a non-legume cropped soil the amount of carbon dioxide evolution and nitrate nitrogen accumulation was practically equal to that for the same soils which had grown a legume in the field. There is a greater carbon dioxide evolution during the first ten days and a greater final nitrate nitrogen accumulation from sweet clover than from alfalfa, whether they are grown in the field or applied as a residue. For purposes of supplying available soil nitrogen to new land for establishing a short rotation, for seeding a pasture, or for seeding an orchard cover crop, sweet clover is especially adapted because of its high nitrogen content and its rapid decomposition when returned to the soil.