Comparison of the use of total phosphorus concentration and acetic acid soluble phosphorus concentration in petioles for assessing the phosphorus status of potato crops

Abstract

We studied the effect of rate of applied phosphorus on total phosphorus concentration (17 sites) and acetic acid soluble phosphorus concentration (12 sites) in petioles of youngest fully expanded leaves of potatoes (cvv. Kennebec, Coliban and Exton) when their largest tubers were 5-10 mm long. We showed that the internal requirements for phosphorus are similar for the cvv. Kennebec and Coliban. Taken over all sites, mean total phosphorus concentrations and acetic acid soluble phosphorus concentrations ranged from 0.22 to 0.84% and 0.10 to 0.63%, respectively depending on phosphorus supply. For each site a coefficient of determination (r2) was calculated based on the mean total phosphorus concentration versus acetic acid soluble phosphorus concentration data for all treatments. The r2 values varied from 0.969 (site 14) to 0.997 (site 17). On the pooled data for all sites, the Cate-Nelson separation and the Mitscherlich and Smith-Dolby bent-hyperbola models were used to investigate the correlations between relative yield [(mean treatment yields/maximum treatment yie1d)x 100] and total phosphorus concentration (n = 16 1, 17 sites) and acetic acid soluble phosphorus concentration (n = 112, 12 sites) and to calculate the critical values. Depending on the model fitted the critical total phosphorus concentrations varied from 0.41 (r2 = 0.62) to 0.53% (r2 = 0.72). The critical acetic acid soluble phosphorus concentrations varied from 0.29 (r2 = 0.62) to 0.52% (r2 = 0.72). Critical concentration ranges of 0.41-0-53% for total phosphorus and 0.29-0.52% for acetic acid soluble phosphorus have been proposed to assist in the assessment of the phosphorus status of irrigated potato crops in South Australia. Based on sensitivity, reproducibility and sharpness of the transition zone between adequacy and deficiency we found no advantage in determining acetic acid soluble phosphorus concentration rather than total phosphorus concentration to assess the phosphorus status of potato plants.