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Relationships of petiolar-nitrate concentrations with growth and yield of sunflower

J.W. Kerage and B.T. Steer

School of Agriculture, University of Western Australia, Nedlands WA 6009

The monitoring of petiolar nitrate concentrations could offer a useful management tool in predicting nitrogen requirements for sunflower, Helianthus annuus, crops (2). Glasshouse and field experiments have been used to test the relationships between petiolar nitrate concentra- tions and yield.


In the field, sunflower cv. Hysun 33 was sown in October into fallow soil or after a winter lupin crop, Lupinus angustifolius cv. Gungurru). Only lupin root material remained in the soil following removal of the shoots from the site. Nitrogen (N) fertiliser was applied to sunflower at 36 and 75 days after sowing (DAS). Petioles from the three uppermost recently matured leaves were collected at intervals up to physiological maturity. Their nitrate-N concentrations were measured colorimetrically (1).

Results and discussion

Petiole nitrate concentrations (PETN) were significantly influenced by the lupin/fallow treatments at the 4-6 leaf stage, and later by fertiliser-N application (Fig. la). The concentra- tions were greatest at the 4-6 leaf stage (23 DAS) and declined as the season progressed. Seed and dry matter yields at physiological maturity were significantly affected by lupin/ fallow and nitrogen fertiliser treatments (Fig. lb). PETN were correlated with yields, but because there was an early effect of lupin residues and later an effect of fertiliser application, measurements of PETN were needed at two times . The relationships found are shown below:

Seed yield (g) = 1.0 + 13.9*(PETN @ 33 DAS) + 10.9*(PETN @ 46DAS) (r2 = 0.83) Shoot DW (g) = 23.9 + 38.9*(PETN @ 33 DAS) + 28.2*(PETN @ 46DAS) (r2 = 0.80)

Figure 1.
(a) PETN at various times after sowing in response to previous lupin (—) or fallow
(- -), and fertiliser-N application 60 kg N (...) or 120 kg N (—).
(b) Seed (—) and shoot DW(...) as a function of fertiliser N application and previous -) or fallow (...,—).


Best, E.K. 1976 Queensland Journal of Agriculture and Animal Sciences 33, 161-166.

Nocking, P.J. and Steer, B.T. 1982. Tenth international sunflower conference, Surfers Paradise pp. 73-78.

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