# Advancing Crop Yield Predictions: AQUACROP Model Application in Poland's JECAM Fields
## 2 Materials and Methods
### Aquacrop Model Overview  
The software AquaCrop (Version: 7.0, Manufacturer Name: Food and Agriculture Organization of the United Nations (FAO), City: Rome, Country: Italy), developed by the FAO's Land and Water Division, aims to enhance water-efficient agricultural methods [14]. This approach utilizes the water balance concept to integrate soil, plant, and atmospheric components [15]. To simulate the growth and yield of agricultural products, AquaCrop considers various factors including atmospheric conditions (such as precipitation, temperature, evapotranspiration, and carbon dioxide concentration), physical and hydraulic processes of soil (including soil profile and groundwater characteristics), plant physiological and productivity parameters (such as phenology, crop cover, rooting depth, biomass production, and harvestable yield), as well as field management practices (including irrigation and field cultivation techniques) [16].  
The simulation process comprises four stages, executed consecutively at every time step of the day, involving the following calculations [17].  
The first step involves the development of canopy cover. AquaCrop indicates foliage growth using green (canopy cover) (CC), indicating the proportion of the soil surface covered by green canopy:  
\[\text{CC}=\frac{\text{soil surface covered by the green canopy}}{\text{unit ground surface area}} \tag{1}\]  
Crop transpiration is calculated by multiplying the reference evapotranspiration (ETo) by the crop transpiration coefficient (K\({}_{\text{CT}}\)) and a water stress coefficient (K\({}_{\text{s}}\)) [18]:  
\[\text{T}_{\text{r}}{=}\text{K}_{\text{s}}\text{K}_{\text{CTr}}\text{ET}_{ \text{o}} \tag{2}\]  
This coefficient is equal to 1 when water stress does not induce stomatal closure.  
The crop transpiration coefficient (K\({}_{\text{CTr}}\)) is proportional to the green canopy cover (CC):  
\[\text{K}_{\text{CTr}}{=}\text{K}_{\text{CTr},\text{xC}}{\text{CC}^{*}} \tag{3}\]  
where CC* is the canopy cover adjusted for micro-advective effects, and K\({}_{\text{CTr},\text{x}}\) is the crop coefficient for maximum crop transpiration, which is determined by the characteristics distinguishing a crop with full canopy cover from reference grass. Typically, K\({}_{\text{CTr},\text{x}}\) varies between 1.05 and 1.20 for most crops [18].  
The total biomass (B) is calculated by the model using normalized water productivity (WP) and the cumulative crop transpiration over the growing season as follows:  
\[\text{B}=\text{WP}*\sum\text{Tr} \tag{4}\]  
Through the utilization of parameter B and the harvest index (HI), one can determine the harvestable yield (Y) from [19]:  
\[\text{Y}=\text{HI}*\text{B} \tag{5}\]  
AquaCrop provides a yield value by converting the daily simulated crop transpiration into equivalent biomass, which is then subsequently translated into yield using harvest index values [20].  
The model is designed to serve as a planning tool to support management decisions in both rainfed and irrigated agriculture, used by practitioners employed in extension services, government agencies, non-governmental organizations, and farmer associations. It is also employed as a tool to examine how water affects crop productivity [21].