## 2 Materials and Methods
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Calibration 1** & **Calibration 2** & \multicolumn{3}{c}{**Average**} \\  & **Calibration 1** & **Calibration 2** & \multicolumn{3}{c}{**Calibration 1**} & **Calibration 2** \\ \hline N & 20 & 20 & cbar & kg & cbar & kg \\  & & 81.43 & 0.746 & 74.51 & 0.763 \\ Min. & 0.00 & 0.00 & & & \\ Max. & 199.00 & 199.00 & & Correlation coefficient & \\ Std. Dev. & 55.87 & 62.90 & \(-\)0.91 & & \(-\)0.86 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Granular matrix sensors’ (GMSs’) calibration results. Four maize hybrids with similar maturity groups were used in the study: c1--OSSK596, c2--OSSK617, c3--OSSK602, and c4--OSSK552. Maize crop was sown on 6 May, 3 May, and 27 April with a hand planter. The planting space between the maize rows was 0.70 m, with a 0.25 m inter-row spacing. Maize was planted in two rows, 10 m long per experimental plot, with a total plant density of 58333 plants/ha. The sowing was preceded by soil tillage with a rotary narrow on 19 April in all three years of the study. As for the maize crop protection, weed control was done using Radazin T50 at 2 L ha\({}^{-1}\) and Dual Gold 960 EC at 1.4 L ha\({}^{-1}\). The maize crop was harvested at a mature stage on 12 (2010), 3 (2011), and 5 November (2012). Grain samples were collected at harvest time from each experimental plot and taken to a laboratory for grain composition analysis. Measurement of the grain moisture was done in the field immediately after the grain samples were collected. The GY was determined for each experimental plot (study treatment) and standardized to a 14% grain moisture content. The GSC (%), GPC (%), and GOC (%) contents were analyzed using a spectrophotometer (Infratec 12141, Foss Tecator). The climatological characteristics classification for each study year was done according to the analysis of the distribution of the climatic elements, probability percentiles, and estimation of the extremes made by the Croatian Meteorological and Hydrological Service [65]. Then, climate data were collected from a weather station located near the experimental field--the amount of rainfall (mm), air temperature (\({}^{\circ}\)C) and humidity (%), wind speed (km day\({}^{-1}\)), and radiation (MJ m\({}^{2}\) d\({}^{-1}\))--and were used for the calculation of crop water requirements (CWR) with the use of the CROPWAT 8.0 computer model. Effective rainfall was determined with the use of the USDA method, which is integrated into the CROPWAT 8.0 model. Monthly values of rainfall and average monthly air temperatures were compared to the long-term averages (LTA, 1981-2010) to highlight deviations. The Penman-Monteith methodology [66] was applied to calculate the reference evapotranspiration (ETo), while the crop evapotranspiration (ETc) was determined by multiplying the ETo and single crop coefficient (kc), which integrates differences in the soil evaporation rate and crop transpiration rate between the crop and the grass reference surface and was taken from [PERSON] et al. [66]. An observation well that was located near the experimental field was used for monitoring the groundwater level two times per week on average. Soil samples were collected in springtime, before pre-sowing fertilization, and in autumn after the maize harvesting (before autumn fertilization). Soil samples were collected from five points of each irrigation and N fertilizers subplot in the 20 cm horizontal direction and 0-30 cm vertically downward. In total, 180 soil samples (5 soil samples from each irrigation (3) and N fertilizers (3) treatment, two times per growing season (pre-sowing and after harvesting)) were collected during the three-year study and analyzed for the total N content. The total N content was determined using the dry combustion method (RM: ISE 910, ISE 882, and ISE 955, Nepal, recovery <5%). The accuracy of the analyses was controlled by repeating the analysis of the samples (3 times) and was satisfactory (RSD < 10%).