Nitrogen fertilization and fungicide mixtures in wheat: how do they affect the severity, yield and dynamics of nitrogen under leaf rust infections?

Nitrogen (N) fertilization and fungicides are important tools in order to achieve high yields and quality in wheat (Triticum aestivum L.), although its use may affect the expression of foliar diseases such as leaf rust (LR) (Puccinia triticina Eriks.). An approach focused on the impact of LR and its interaction with fungicides mixtures and N fertilization rates could be useful to improve the modelling of crop N dynamics and enhance grain yield and quality in the context of the integrated management. Our study was designed to determine the additive effects of carboxamide fungicides (TSC) to a double triazole-strobilurin (TS) mixture under three N fertilization rates on the LR disease progress, healthy area duration (HAD), grain yield and N dynamics during two years. Main plots corresponded to three fungicide treatments and three N doses were the sub-plots. LR disease progress, HAD, yield, N remobilization (NREM), N post-anthesis absorption (NPA), N stored in grains (NG) and %N in grains (%Ng) were evaluated. LR severity increased at higher N rates. TSC applications produced the major decreases on LR severity and the main increases in HAD, which resulted in the higher yield increases (+2726 kg/ha). The %Ng increased with the application of fungicides when LR was controlled. LR infections generated reductions in NREM, NPA and NG, a response that could be explained by decreases in aboveground biomass and yield, coupled with reductions on N harvest index and N remobilization efficiency. Combined effect of TSC fungicides and increases in N dose showed the largest increases in NREM, NPA and NG.