Determination of critical nitrogen concentrations of lettuce (Lactuca sativa L. cv. Montello) grown in sand culture

• Published in: Australian journal of experimental agriculture Vol. 32; no. 6
• Main Authors: Huett, D.O. (New South Wales Agriculture, Alstonville (Australia). Tropical Fruit Research Station), White, E. (New South Wales Agriculture, Wollongbar (Australia). Wollongbar Agricultural Inst.)
• Format: Journal Article
• Language: English
• Published: 1992
• Subjects: ABONOS NITROGENADOS; ANALISIS DE TEJIDOS; ANALYSE DE TISSUS; AZOTE; BESOIN NUTRITIONNEL; ENGRAIS AZOTE; FEUILLE; HOJAS; LACTUCA SATIVA; NECESIDADES DE NUTRIENTES; NITROGENO
• ISSN: 0816-1089; 1446-5574
• DOI: 10.1071/EA9920759

A gamma x cubic response surface model was used to predict the dry matter yield of lettuce cv. Montello over the 8-week growth period in sand culture. Growth was consistently depressed at 2 mmol N per L due to N deficiency, and at 36 mmol N per L due to salt toxicity. Petiole sap nitrate concentrations were more responsive than leaf total N concentrations to N application levels. Leaf N concentrations at N application levels of 18 and 36 mmol per L were often similar. Critical leaf total N concentrations in youngest leaves decreased from 2 weeks after transplanting to maturity, whereas the opposite trend occurred for petiole sap nitrate concentrations. Nitrogen application levels of 2 and 36 mmol N per L reduced K, Ca and Mg concentrations in all leaves. This confirms the importance of optimising N supply when determining critical levels of these nutrients for lettuce. Petiole sap nitrate-N concentrations, which can be determined rapidly in the field, can be used to distinguish between a deficient and an adequate N supply. The marked increase in critical concentration over the growth period requires consecutive determinations to verify the N status of lettuce.