In-season nitrogen fertilizer calibration based on optical sensoron breading and turkey wheat varietien under watery conditions inŞanlıurfa

In wheat cultivation, various varieties can yield higher grain and protein levels than expected with optimal nitrogen fertilization, but the nitrogen needs vary regionally and annually, highlighting the crucial role of Seasonal Nitrogenous Fertilizer Management Systems. This 2022 study, conducted at Şanlıurfa Gap Agricultural Research Institute's Gündaş location, aimed to determine the most suitable fertilization method using these systems. Four winter wheat varieties (Polathan, Serince, Edessa, İlkan) were studied, measuring their responses to nitrogen fertilization and vegetation indices via GreenSeeker and SPAD devices.The experiment was carried out in a factorial trial design in randomized blocks and with 6 different nitrogen ratios (0,5,10,15,20,25). Vegetation index readings (NDVI) were carried out in four different periods: Zadoks 2.4 (tillerization), Zadoks 3.0 (beginning of stem erection), Zadoks 3.1 (1 node period of stem erection), Zadoks 3.2 (2 node period of stem erection). Along with the spectral readings, protein analyzes and biomass analyzes were performed in the plant and grain. Grain yield was calculated after harvest. Looking at the results of the SPAD meter measuring leaf chlorophyll value; Among the periods, the highest yield was given in the Zadoks 3.0 (beginning of sticking) period (47.24). Looking at the varieties; İlkhan variety gave the highest value (48.37) at 20 kg N. However, SPAD meter measurements are not used in fertilizer recommendation methods whenever possible due to both difficulty of use and measurement differences between users. Regression analyzes were conducted in which grain yield was taken as the dependent variable and in- season yield estimates (INSEY) were taken as the independent variable. The highest R2 values were given by the Edessa variety (R2= 0.65) in the Zadok3.2 (stem up and 2 node formation) period, respectively. Regression analyzes were performed in which biomass was taken as the dependent variable and intraseasonal yield estimates (INSEY) as the independent variable. The highest R2 values were respectively in the Edessa variety Zadok3.0 (beginning of stemming) period (R2= 0.958). As a result, the highest correlation between the Yield Provision Index and the NDVI Provision Index was again given in the Zadoks 3.0 and Zadoks 3.1 periods, and the period that we would recommend and most suitable for implementation was determined as the Zadoks3.0 period. More such studies need to be done in order to give the most accurate advice from the equations we obtained.