Radiation interception, biomass production and grain yield as affected by the interaction of nitrogen and sulfur fertilization in wheat

Grain yield response to sulfur (S) fertilization in wheat (Triticum aestivum L.) has been reported several times. However, the effects of S and its interaction with nitrogen (N) on the physiological attributes that determine biomass and grain yield at field scale have not been deeply studied. This research was conducted to determine the influence of N, S and their interaction on grain yield (GY), crop growth rate (CGR), leaf area index (LAI), intercepted radiation (IPAR) and radiation use efficiency (RUE) in wheat. Field experiments were conducted in 2000 and 2001 in the Argentinean Pampas using a bread-wheat genotype grown under different combinations of N and S fertilizer rates. Nitrogen and sulfur increased biomass at anthesis, with increments of 62 and 13% in LAI, and 20 and 7% in IPAR, due to N and S addition, respectively. However, the effect of S on LAI and IPAR were higher as N fertilizer rate increased. Nitrogen addition increased biomass at physiological maturity from 7 to 19% at the lower S rate, but at the highest S supply, these increments ranged from 20 to 35%, evidencing a clear interaction between both nutrients. This increase in biomass was sustained by a large fertile spike population that increased grain number per unit area and consequently, grain yield. Harvest index was not affected by the different N and S fertilizer rates. Sulfur effects were evident between anthesis and physiological maturity, increasing CGR by 41%. Plants under low S levels produced ca. 10.8 kg of grain per unit of fertilizer N; however, S addition increased this efficiency by 51%. Therefore, the positive interaction between N and S was reflected in a higher N use efficiency when the crop had no S deficiency.