
TY  - JOUR
A1  - Huett, DO 
A1  - White, E 
T1  - Determination of critical nitrogen concentrations of lettuce (<I>Lactuca sativa</I> L. cv. Montello) grown in sand culture
JF  - Australian Journal of Experimental Agriculture
JO  - Aust. J. Exp. Agric.
Y1  - 1992
VL  - 32
IS  - 6
SP  - 759
EP  - 764
KW  - 
UR  - https://doi.org/10.1071/EA9920759 
N2  - 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 with nitrogen (N) levels of 2, 5, 11, 18 and 36 mmol/L. At 1, 2, 3, 5, 7 and 8 weeks after transplanting, dry matter yield relative to maximum was plotted against tissue N concentration to derive diagnostic concentrations of petiole sap nitrate-N and leaf total N in youngest fully opened leaf (YFOL), youngest fully expanded leaf (YFEL) and oldest green leaf (OL), and total N in bulked leaf samples. Critical concentrations corresponding to 90% maximum yield are presented. Growth was consistently depressed at 2 mmol N/L due to N deficiency, and at 36 mmol N/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/L were often similar. Critical leaf total N concentrations in YFOL and YFEL decreased from 2 weeks after transplanting to maturity, whereas the opposite trend occurred for petiole sap nitrate concentrations. Critical total N concentration ranges in YFEL were 0.30-0.95 g/L for petiole sap nitrate-N, and 4.00-5.30% for leaf total N concentration. Critical leaf total N and petiole sap nitrate concentrations clearly differentiated between inadequate and adequate N application rates. Critical values in most cases, differentiated toxic concentrations. Nitrogen application levels of 2 and 36 mmol N/L reduced (P<0.05) potassium, calcium and magnesium 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. 
ER  -

