Using SPAD for the early detection of nitrogen deficiency on different vine varieties in pots or in the field

Abstract

In recent years, the total N content in the leaves has been estimated through the use of non-destructive spectral methods, among them the N-tester and the SPAD-502. The SPAD-502 (Minolta) is an instrument for rapid detection of chlorophyll content and N concentration in plant leaves, which is widely used in N nutrition diagnosis in annual crops. The use of these tools could be useful in vineyards to guide fertilization management. We studied the response of N status through the use of SPAD for Shiraz plants grown in pots and from field experimentations in the South of France using the cultivar Grenache Noir. The pot experiment includes five N regimes supplied as NH₄NO₃ to explore a wide range of N stress: excessive fertilization (12 g N plant : 12N), control fertilization (2.4 g N plant^–1: 2.4N) or three N deficiency treatments of decreasing intensity (0 g N plant^–1, 0.6 g N plant^–1 and 1.2 g N plant^–1 ). The field trial includes different soil management and organic or mineral fertilization strategies. For each plant in both pots and field trial conditions, five successive readings on one single fully expanded leaf were taken by a SPAD-502, across the whole surface of the leaf at three phenological stages (flowering, bunch closure and veraison). The pot experiment revealed that the N status of the plants became significantly different between treatments from flowering. The SPAD values in the field pots ranged from 6 to 45. At flowering, only the 0N treatment differed significantly from the well supplied treatments (1.2, 2.4 and 12 N). From bunch closure to veraison, all the treatments were significantly different and varied according to the soil-N dose applied. We tested this method on a field trial with other varieties. The SPAD in field conditions was useful to compare two situations but was less accurate for deficiency diagnosis due to the narrow range of SPAD values observed in the field and the natural N supply from organic matter mineralization.