Yield and Nitrogen Utilization by Rice as Affected by Method and Time of Application of Labelled Nitrogen
- K. R. Reddy and
- W. H. Patrick
Recent increases in the cost of N fertilizer make it important to examine methods of improving the utilization of fertilizer N by lowland rice (Oryza sativa L.). The objective of the present investigations was to compare the effects of different methods and times of N application on yield and utilization of N by lowland rice. Field experiments using labelled fertilizer N were carried out during 1974 and 1975 utilizing different times and methods of application of ammonium sulfate on small field plots (2.32 m2). Fertilizer N was applied either by deep placement at the beginning of the season or at one or more times during the growing season as surface application. Relative contributions of native soil N and fertilizer N sources to plant uptake were followed during the growing season, and total uptake of native soil N and fertilizer N by rice was determined at harvest.
Highest grain yields were obtained where all of the N was applied early in the growing season or where part of the N was applied in early season and part applied no later than mid season. Late season application of part of the nitrogen was not as effective. In 1974, recovery of fertilizer N (in grain and straw) was highest in the plots receiving all N by deep placement, while in 1975 split application (half at early season and half at mid season) gave greatest N utilization. For the 2 years, the recovery of fertilizer in grain and straw ranged from 33 to 61% of applied N. Rice plants derived more fertilizer N during the early part of the growing season with the rate of uptake decreasing as the season progressed. Recovery of fertilizer N calculated from labelled N data showed lower values, compared to the recovery of fertilizer N estimated by a method based on total N uptake difference between the plots receiving N and the untreated plots. More native soil N was taken up by the crop from the plots receiving fertilizer IN than from the check plots in 1974, but there was little difference in uptake in 1975.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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