CSIRO PUBLISHING www.publish.csiro.au/journals/ajar Australian Journal of Agricultural Research, 2007, 58, 39–45 Wheat development as affected by nitrogen and sulfur nutrition Fernando Salvagiotti A,C and Daniel J. Miralles B A Dep. de Agronom´ ıa, EEA Oliveros INTA, Oliveros, Argentina; present address: 243 Keim Hall, Department of Agronomy and Horticulture, PO Box 830915, Lincoln, NE, USA. B Dep. de Producci ´ on Vegetal, Facultad de Agronom´ ıa, Univ. de Buenos Aires, Av. San Mart´ ın 4453, C1417DSE, Buenos Aires, Argentina. C Corresponding author. Email: fsalvagiotti@correo.inta.gov.ar Abstract. Sulfur (S) is one of the essential nutrients for crop growth, which is linked to nitrogen (N) in many physiological functions. The rate of leaf emergence (RLE) and final leaf number (FLN) determine the duration of the emergence (Em)– anthesis (Ant) period in wheat. Although some studies showed effects of N and phosphorus on RLE and the length of the Em–Ant period, no reports studied the effect of N and S interaction on the phasic development and the coordination of RLE with tillering appearance. A bread-wheat genotype was grown with 4 N and 2 S fertiliser rates during 2000 and 2001 in field plots. In addition, an experiment with 4 combinations of N and S rates (N0S0, N0S1, N1S0, and N1S1) was arranged in containers using nutrient solutions in 2001. Under field conditions, additional N and S did not modify the duration of the different phenological stages or the Phy value and FLN. However, the stronger N and S deficiency in the experiments conducted in containers affected RLE. A higher S rate delayed the period Em–Ant by 65 ◦ degree-days under no N restrictions, mainly by a delay in the duration of terminal spikelet (TS)–Ant period. Phyllochron (Phy) changed with crop ontogeny (inflection point occurred on 7th leaf) and N and S did not affect the timing when Phy changed; however, a lower N supply increased Phy in earlier leaves without effect of S on this trait. Treatments without S or N deficiency achieved the highest maximum tiller number (MTN) and the greatest tiller mortality rate (TMR); however, tiller number at maturity was 76% higher in this treatment with respect to the rest of the treatments because of the MTN attained. The number of tillers per emerged leaf was significantly increased when plants were grown under high N supply. Under no N restrictions, additional S increased the number of tillers per emerged leaf by 24%. Additional keywords: phyllochron, tillering. Introduction Crop growth and biomass partitioning can be successfully simulated if developmental processes are accurately predicted. In wheat, as in other cereals, the occurrence of anthesis (Ant) depends on the rate of leaf emergence (RLE) and final leaf number (FLN) on the main stem. Temperature, day length, and vernalisation are the main environmental factors that govern the rate of development in wheat, and determine the duration of the different phenological phases (Fischer 1984; Davidson et al. 1985; Hay and Kirby 1991; Slafer and Rawson 1994). Water and nutritional stress may affect crop development depending on the phenological stage and the timing of the stress; however, their effects are of less magnitude in comparison with the main environmental factors mentioned above. Some studies in the literature analysed the effect of nitrogen (N) or phosphorus (P) on wheat development and examined the consequences in specific development traits (e.g. FLN, RLE). However, only few studies have examined the effect of sulfur (S) on development, and there are no reports in the literature studying the effect of the interaction of N and S on the phasic development and on the coordination of different developmental processes occurring in the wheat plant. Dale and Wilson (1978), Longnecker et al. (1993), and Kernich and Halloran (1996) showed evidence regarding the effects of nutrient stress on the rate of development, but this information is sometimes contradictory depending on the author. Fischer (1993) found, in field conditions, a delay in the occurrence of terminal spikelet (TS) and Ant when N was deficient, whereas other evidence carried out under controlled conditions showed no important effects of N deficiency on the duration of different phenological stages (Frank and Bauer 1982; Longnecker et al. 1993). The coordination of FLN and RLE determines the duration of pre-heading phases. Nutrient supply could affect the duration of this period by altering one or both of those processes. Several reports describe nutritional effects on leaf emergence in rice (Nemoto et al. 1995), barley (Prystupa et al. 2003; Arisnabarreta and Miralles 2004), corn (Uhart and Andrade 1995), and wheat (Rodr´ ıguez et al. 1998), although under most field conditions the initiation of leaf primordia, i.e. FLN, appears to be unaffected by nutrients, and experiments carried out under controlled conditions have shown that nutrient starvation affected both FLN and RLE. Some studies observed low RLE in N-deficient plants (Frank and Bauer 1982; Longnecker et al. 1993), but others © CSIRO 2007 10.1071/AR06090 0004-9409/07/010039