# Sustainable Management of Water Resources in Supplementary Irrigation Management
## 2 Materials and Methods  
### Site and Soil Description  
The study area lies in the Pannonian Plain, Slavonia region in the northeastern, continental part of the Republic of Croatia. It is a major agricultural and farming region of Croatia due to considerable areas covered by fertile soil (Figure 1). The field and laboratory testing of the selected sensors were performed in the pea (_Pisum sativum_ L.) field at Agricultural Institute Osijek (45\({}^{\circ}\)32\({}^{\prime}\) N and 18\({}^{\circ}\)44\({}^{\prime}\) E, altitude 90 m). In continental, the lowland part of Croatia is a prevalent subhumid climate (Cfwbx) with an average annual temperature of 12 \({}^{\circ}\)C and the annual amount of precipitation from 600 to 700 mm and 360 mm during the growing season, April-September [22]. The soil at the experimental site is classified as anthropogenic eutric cambsiol (WRB), silty clay loamy texture, with its main properties presented in Table 1.  
Figure 1: Map of the study area and location. National classification of soil was used [23], which is genetic and serves as the basis for soil production and ecological assessment and is based on the properties of soils that are morphologically visible or easily measurable. Comparison of national soil classification with The World Reference Base (WRB) [24] classification system was also conducted as well as the separation of the reference group of soils with appropriate prefixes that correspond to lower systematic units than soil type. The anthropogenic horizon is brown to light brown color, classified as silty clay loam soil. The top 50 cm layer is made from coarse-grained particles, high in sesquioxide (R\({}_{2}\)O\({}_{3}\)) contents and free from carbonates. At 50 to 105 cm depth, the soil texture is clay to silty clay, yellowish-brown to brown in color in deeper soil layers. The parent material occurs at 105 to 115 cm depth, yellow, without structure and rich in CaCO\({}_{3}\) (Figure 2). The gley horizon is typically mottled and occasionally saturated with groundwater. For the preparation of the average sample from the selected location, control circular sampling was used according to [PERSON] [25]. Soil samples were prepared for physical and chemical analyses according to ISO 11464 procedures in a drying oven. The determination of soil pH was made in 1:5 (\(v/v\)) suspension of soil in water and a 1M potassium chloride (KCI) solution according to ISO 10390. The soil organic matter was determined using organic carbon (C) by sulfochromic oxidation prescribed in ISO 14235. Plant-available phosphorus (P\({}_{2}\)O\({}_{5}\)) and potassium (K\({}_{2}\)O) were extracted by AL solution (Ammonium Lactate-acetate) and detected by spectrophotometry and flame photometry, respectively. The soil texture and clay content were \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & & & \multicolumn{4}{c}{**Physical Properties**} & \\
**Depth** & **Silt** & **Clay** & **Sand** & **_p_ & **RC** & **AC** & **PWP** & **PD** \\ **(cm)** & **\%** & **\%** & **\%** & **\%** & **\%** & **\%** & **\%** & **g cm3** \\ \hline
0–30 & 64.7 & 32.5 & 2.8 & 44.8 & 39.6 & 5.2 & 23.7 & 2.75 \\
30–50 & 66.4 & 31.3 & 2.3 & 42.1 & 37.8 & 4.3 & 24.5 & 2.66 \\
50–70 & 68.2 & 25.5 & 6.3 & & & & & \\
70–105 & 71.8 & 21.6 & 6.6 & & & & & \\ \hline \multicolumn{8}{c}{**Chemical Properties**} \\
**Depth** & **pH** & & **Al-P\({}_{2}\)O\({}_{5}\)** & **Al-K\({}_{2}\)O** & **Organic Matter** & **CaCO\({}_{3}\)** \\
**(cm)** & **H\({}_{2}\)O** & **KCI** & **mg/100 g** & & **\%** & **\%** & **\%** \\ \hline
0–30 & 5.59 & 6.60 & 26.40 & 29.70 & 2.55 & 1.25 \\
30–50 & 6.85 & 7.64 & 13.75 & 25.33 & 1.63 & 2.51 \\ \hline \hline \end{tabular} \(p\) = porosity; RC = retention capacity; AC = air capacity; PWP = permanent wilting point; FC = field capacity; SAT = saturation; PD = particle density.  
\end{table} 
Table 1: Physical and chemical properties of the soil. Figure 2: Soil profile at the experimental site. determined by sieving and sedimentation method prescribed in ISO 11277.