A comparison of several legumes with respect to nitrogen accretion
1934
Lyon, T.L. | Bizzell, J.A.
Various legumes, alone and in combination with other crops, were grown for 10 years on a soil with an initial nitrogen content of 0.0842%. Nitrogen was determined in the soil at the beginning and at the end of the experiment, and in all the crops grown during the period. Alfalfa and the cereals alternated with it contained more nitrogen than did any other combination of legumes and cereals. Red clover and alsike clover were approximately equal in nitrogen contained in the crops, but the mixture of the two clovers was superior to either one separately. Of the legume grain crops, soybeans was the most effective. The rotation without legumes contained the smallest quantity of nitrogen. The gains in soil nitrogen in some cases were large. Generally the larger gains in soil nitrogen were associated with large amounts of nitrogen in crops. Of the legumes, those grown for hay were the most effective in increasing soil nitrogen. Field beans caused the greatest reduction of soil nitrogen of any crop grown. The greatest apparent fixation of nitrogen was shown by alfalfa followed by sweet clover and a mixture of red and alsike clovers. The mixture of red and alsike clovers was superior to either grown alone. All rotations which included legumes showed significant apparent fixation. Non-symbiotic fixation amounted to 17 pounds of nitrogen to the acre annually. Comparison of the data obtained with those secured on a soil with a higher initial nitrogen content showed that the gains of soil nitrogen were greater and the losses less in the low-nitrogen soil. These differences are accounted for by the larger quantities of nitrogen removed by the crops from the high nitrogen soil.
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