Effects of nitrogen fertiliser on potato (Solanum tuberosum L., cv. Russet Burbank) in Tasmania. 2. Petiole and soil analysis

Abstract

Thirteen field trials were conducted on ferrosols and tenosols in Tasmania to assess the response of potatoes (Solanum tuberosum L., cv. Russet Burbank) to basal and topdressed nitrogen fertiliser. The objectives of this study were to assess whether petiole nitrate concentrations could be used to indicate potato nitrogen status and crop response to nitrogen topdressing, and whether various soil nitrogen measures could be used to determine the responsiveness of potatoes to nitrogen fertilisation. Petiole nitrate-nitrogen concentrations in the youngest fully expanded leaves were found to be an indicator of nitrogen status. Critical nitrate concentrations varied in a linear fashion from about 25 000 mg/kg at tuber initiation to less than 5000 mg/kg when tubers were 100 mm long (about 100 days after planting). These concentrations are consistent with those determined for Russet Burbank in other studies. In contrast to petiole measures, various pre-plant and early season soil nitrogen measures (mineral, mineralisable and total nitrogen) did not adequately (adjusted R2<0.25) explain variation in crop nitrogen responsiveness and could not be recommended as diagnostic or predictive tests. Soil nitrogen mineralisation rates in spring varied from 0.4 to 5 kg N/ha.day and were higher at sites previously in pasture than at continuously cropped sites. Although petiole nitrate concentrations responded to nitrogen topdressing, most nitrogen-deficient crops in this study did not show yield responses to topdressed nitrogen. This limited the usefulness of petiole nitrate-nitrogen tests.