| Placement of the point-banded urea 5 cm deep, 5 and 10 cm horizontally from the corn seeds depressed the grain yield especially with the higher N rates applied. Incorporated urea prills broadcast on conventionally tilled soil tended to give the highest grain and stover yields. The corn seedlings, with point-banded urea prills applied at close proximity and high N rates, were subject to growth retardation and death.;The greenhouse experiments showed that root growth in soil was eliminated within a spherical region of a diameter of 10-15 cm with a USG at the centre. The inclusion of a nitrification inhibitor, dicyandiamide (DCD), in the USG did not improve the early growth of corn. The urease inhibitor, NBPT, however, improved the seedling growth and nitrogen and potassium uptake.;Urea hydrolysis was significantly retarded by NBPT in USG in a ten-day period following placement in soil. The soil pH, moisture content, ammonium and nitrate concentrations were lower around a USG with NBPT in soil compared with a USG without NBPT.;The apparent concentration of urea in soil extracts obtained with a colorimetrical method was decreased by the presence of NBPT. (Abstract shortened by UMI.). |
