Studies on Nitrogen Tie‐Up as Influenced by Location of Plant Residues in Soils

In field experiments it has been observed that nitrogen availability to corn is frequently depressed where crop residues low in nitrogen remain on the soil surface as compared to where the residues are incorporated in the soil. The purpose of this investigation was to evaluate the immobilization of soil nitrogen as influenced by position of crop residue with reference to the soil. In greenhouse experiments nitrogen uptake by Sudangrass was significantly greater when cornstalk residue was applied to the soil surface than when it was incorporated in the soil. By comparison with a treatment receiving no residue it was concluded that considerable nitrogen was immobilized by cornstalk residue incorporated in the soil, whereas no immobilization occurred with cornstalk residue on the soil surface. On the other hand, in laboratory experiments it was demonstrated that soil nitrogen could be moved to and immobilized in low‐nitrogen residue on the soil surface and that the movement of nitrogen into surface residue was enhanced in treatments which were subsurface irrigated and in treatments held at a low‐air humidity. Also it was found in laboratory experiments that subsurface residue decomposed more rapidly than did surface residue and that this more rapid decomposition resulted in an increase in percent nitrogen but in a decrease in total nitrogen of the residue. Likewise, percent nitrogen of surface residue increased, but total nitrogen increased or decreased, depending upon the conditions of the experiment. The results of a field experiment demonstrated that surface applications of low‐nitrogen residue without added nitrogen fertilizer resulted in decreased nitrogen uptake by corn and yield of corn. However, when nitrogen fertilizer was added along with the residue, yields were increased above the unmulched check.