Plant part selection and evaluation of factors affecting analysis and recovery of nitrate in irrigated durum wheat tissue

Periodic nitrate tissue tests are used to determine nitrogen (N) fertility status of a variety of crops. Data on the importance of plant part selection, sample handling techniques, grinding criteria and extraction conditions in NO₃-N analysis of wheat tissue are essential if the procedure is to achieve widespread adoption and use. Detailed partitioning of field grown durum spring wheat (Triticum durum) plants at the Feekes 2 (3–4 leaf), 6 (joint) and 10 (boot) growth stages was conducted to document which plant part exhibits the greatest accumulation of NO₃-N. Sample handling, fineness of tissue grinding, different tissue: extractant ratios and extraction times were examined to determine their effects on NO₃-N recovery. Partitioning data confirmed previous findings which identified the basal stem between ground level and the seed prior to jointing and the 5 cm of stem just above ground level thereafter as the plant parts showing the greatest accumulation of NO₃-N. Therefore, these plant parts have the greatest potential as indicators of the N nutritional status of durum spring wheat. Optimal recovery of tissue NO₃-N was obtained when stem tissue was separated immediately in the field and dried within 8 hours of sampling, ground to pass a 0.55 mm mesh screen, and extracted for at least 30 minutes when using a sample size of 0.1000 g in conjunction with 25 ml of extractant (i.e. 1:250 plant tissue to extractant ratio).