An Inquiry into the Reason for the Large Accumulation of Nitrates in Soil Following the Growth of Clover or Alfalfa 1

The beneficial effect of the growth of clover on the productiveness of soil is common to almc st all regions. E ven when the hay is removed and only the stubble and roots are incorporated in the soil the effect on succeeding crops may usually be noted, except where nitrogen is not the limiting factor in plant growth. It is rather common to assume that this property of the clover plant is due to the store of nitrogen which it lays up in the soil, as the result of its fixation of that element from the atmosphere. While there may usually be an increase in the nitrogen content of soil resulting from the growth of clover or alfalfa, such is not always the case, as has been definitely shown by Swanson (i) and indicated by the experiments of Lyon and Bizzell (2). In spite of the fact that there appeared to be little' or no more total nitrogen in the soil on which alfalfa had grown for six years than .in that on which timothy had grown for the same length of time, the nitrate nitrogen was found, by Lyon and Bizzell (3), to be more abundant following a crop of alfalfa than following timothy. It was with the purpose of attempting to determine why nitrate nitrogen is more abundant in a soil following the growth of clover