Isotopic studies on the uptake of nitrogen by pasture plants. V. ¹⁵N balance experiments in field microplots

Abstract

Recovery of 15N from labelled fertilizers was measured in open microplots on pastures at three sites in southern Queensland. Very little 15N was recovered from plants growing further than 15-30 cm from the area of application. Most of the 'N found in soil and roots was in the top 15 cm of the profile. The following total recoveries of 15N (with their standard errors) were recorded: 83.0¦2.7% from ammonium sulphate applied to Rhodes grass; 76.6 ¦3.7 % from potassium nitrate on a Townsville stylo-spear grass pasture; and 97.9¦6.7% from urea applied to a Nandi setaria pasture. The weather during the three experiments was relatively dry, and it is unlikely that any ISN was leached below the depth of sampling. The advantages and disadvantages of open and enclosed microplots are discussed in some detail. It is suggested that while open microplots are satisfactory for some purposes, the use of plots enclosed by steel cylinders pressed into the soil is probably the most accurate technique available for 15N balance studies in the field.