Grain Yield and its Components of Triticale as Affected by Silicon Foliar Application, Nitrogen Fertilizer and Water Stress in Reproductive Phase

Introduction In the dry climate of southern Iran including Fars province, most precipitation occurs in winter, thus winter cereals such as triticale (Triticosecale Wittmack) experience water shortage at booting, flowering and grain filling stages in spring. The booting, flowering and grain filling periods are the most sensitive stages to water deficit. Nitrogen fertilizer application is a farmer’s common practice to increase yield, but its performance depends mainly on soil water status than the amount and timing of N applications. On the other hand, matching N fertilization with crop water availability is essential for achieving acceptable grain yield. Farmers of southern Iran use N fertilizer beyond the recommended rate. High N fertilizer application in dry areas that water availability limitations frequently occurred during the grain filling stage of cereals increased severity of water stress. Some authors reported that the silicon application reduces the destructive effects of drought stress by physiological, biochemical, and physical mechanisms (Hattori et al., 2005). Therefore, silicon foliar application may decrease water stress severity, especially in high N crops. Therefore, the aims of this study were to investigate the effects of silicon foliar application, different N rates and irrigation regimes on triticale yield in an arid area of southern Iran (Fars province).      Materials and Methods This research was conducted at the experimental farm of the Darab Agricultural Faculty of Shiraz University. A split factorial experiment in a randomized complete block design with three replications was carried out in the 2017-2018 growing season. Treatments included two levels of irrigation as the main plots [normal irrigation; irrigation based on the plant's water requirement up to the physiological maturity (IRN) and deficit irrigation; irrigation based on the plant's water requirement up to the anthesis stage (cutting of irrigation after anthesis) (IRDI)]. Also, sub plots were two levels of silicon foliar application [0, and 3 mM] and three N fertilizer levels [N0, no nitrogen fertilizer (control); N100, 100 kg N ha-1; N150, 150 kg N ha-1]. Biological yield, grain yield, yield components, plant height, spike length and chlorophyll index of flag leaf were measured. Then, the harvest index (HI) was calculated. Data were analyzed by using SAS 9.1 software (SAS Institute, 2004) and the means were compared using Duncan’s multiple range test at 5% probability level. Results and Discussion The results showed that the IRDI could cause severe water stress in the grain-filling period of the triticale life cycle and consequently reduction of 1000-grain weight, number of grains per spike and number of fertile tillers per m2. However, this reduction was more severe for 1000- grain weight than the other grain yield components and was not constant in different N fertilizer levels (18%, 21% and 36% reduction for N0, N100 and N150 kg N ha-1). Foliar silicon application decreased severity of late-season water stress and consequently improved 1000-seed weight, chlorophyll index, biological yield and finally HI and grain yield. With respect to grain yield, under IRN conditions, the highest grain yield was achieved by N150. Water stress decreased grain yield as a function of N fertilizer (24%, 26% and 46% reduction for N0, N100 and N150 kg N ha-1). Therefore, application of N100 could be acceptable for IRDI conditions. Conclusions According to the results of this study, the highest triticale grain yield (7098 kg ha-1) achieved by N150 in normal irrigation. The IRDI significantly decreased triticale grain yield at all N levels as compared with IRN. However, this reduction was different in N fertilizer rates (24%, 26% and 46% reduction for N0, N100 and N150). Therefore, the highest grain yield under IRDI conditions (4128 kg ha-1) was observed in N100. Therefore, with respect to environmental and economical considerations application of 100 and 150 kg N ha-1 were recommended for late-season water stress and normal irrigation conditions, respectively. Silicon foliar application decreased the severity of water stress and consequently increased grain yield (26%) under IRDI conditions. Therefore, the application of 3 mM of silicon at the anthesis stage is recommended for farms of triticale that expose to late-season water stress in southern Iran (Fars province).