The effect of cyanamid and potash when plowed under with organic refuse on the yield of corn and succeeding crops

The value of cyanamid as a supplement to the nitrogen supply of the rotation was studied by plowing it under with organic matter preceding a corn crop. The residual effect of this nitrogen was measured by succeeding crops. It is apparent that the corn crop can utilize fairly efficiently the nitrogen supplied as cyanamid when it is plowed under with organic refuse and that considerable quantities of this nitrogen remain in the soil and can be utilized by succeeding crops in the rotation. While this efficiency was much greater on the lighter colored soils, very significant increases were obtained in almost all cases. The inter-relationship of the utilization of nitrogen and potassium was noticed in much of the work reported. The need for nitrogen was made more apparent whenever potash was applied and whenever the higher rates of nitrogen failed to provide additional increases, the plant tissue test indicated that potassium had become the limiting element. Whenever there was a deficiency during the last of July or first of August, as determined by the tissue tests, this deficiency was always reflected in the yield. The importance of climatic influences, especially rainfall, must be recognized in a study of this kind because such factors often make the averaging of data obtained in different seasons misleading, unless a sufficiently large number of years is involved to weigh the data properly. On the Clermont silt loam in 1939 and 1940, and on the Crosby silt loam in 1940, approximately 1 bushel of corn was obtained for each 2 pounds of nitrogen plowed under as cyanamid when the supplies of phosphorus and potassium were ample. Since this was true at the higher levels of application, apparently the maximum of production was not reached on these soils. It is well understood that this great efficiency would not be maintained indefinitely, since some other element, or the plant's capacity to produce would become a limiting factor. This is probably the case in some of the more fertile soils used in these experiments which gave smaller or no responses. It is evident from the field results that a considerable amount of the nitrogen from cyanamid persists in the soil in one form or another and is available to the following crops. Since most rotations contain limited soil-building crops and must be used for a long period at relatively low production levels before the soil organic matter and nitrogen supply are built up, the use of cyanamid on light colored soils to step up the production rapidly to a profitable level and to avoid the expensive delay has practical possibilities. When this profitable level is rapidly attained, the good rotation practices can be followed.