Determination of the nitrogen status of irrigated potato crops: I. Critical nutrient ranges for nitrate‐nitrogen in petioles

Abstract

This paper describes the derivation of critical nutrient ranges (CNR) for nitrate‐N in petioles of potato plants (Solanum tuberosum L.) at different sampling times during crop growth for use as interpretation standards or ‘target’ levels when assessing plant nitrogen (N) status. Nine rates of N from 0 to 320 kg/ha were applied in randomised block experiments to the cultivars Atlantic, Coliban or Kennebec at 5 sites over 2 years. Petioles of the youngest fully expanded leaves were analysed for nitrate‐N at 5 sampling times. Petiole samples were collected when the length of the longest tuber was <2, 10, 25, 35 and 50 mm.

Rates of applied N required for 95 and 100% of maximum yield ranged from 87 ‐ 261 kg/ha across sites. Sensitivity of nitrate‐N levels to variations in N supply depended on site and petiole sampling time. The first sampling time was too early to reliably detect N deficiency except in very deficient situations. However, at later sampling times coefficients of determination (R²) for the relationships between nitrate‐N concentrations and tuber yield were significant except on one occasion for the cultivar Atlantic.

The CNR decreased from 2.71 ‐ 2.97% nitrate‐N at the first petiole sampling time to 0.99 ‐ 1.60% at the final sampling time. CNR for nitrate‐N at each sampling time was relatively narrow. Effects of site and cultivar on the CNR values established for nitrate‐N were not significant, however sampling time had a significant effect on CNR values. Hence the importance of carefully specifying petiole sampling time to ensure correct interpretation of plant test data.

We have shown that CNR can be established for nitrate‐N concentrations in petioles and that these are useful to monitor the N status of potato plants during crop growth.