# Enhancing Smart Agriculture by Implementing Digital Twins: A Comprehensive Review
## 4 Reviewing DT Applications in Agriculture and Farming Domain
### The First Categorization of Researched Literature, According to the Main Research Objectives
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Citation** & **Type of** & **Case Study** & **Smart Farming** & **DT Case** & **Application Domains** & **Target Applications** \\ \hline
[84] & Review Paper & - & \(\surd\) & - &
\begin{tabular}{c} Greenhouse \\ horticulture, indoor \\ farming smart \\ agriculture \\ \end{tabular} & IoT Data-driven food production. \\ \hline
[85] & Review Paper & - & \(\surd\) & - &
\begin{tabular}{c} Industry 4.0 \\ approaches to the \\ agricultural sector \\ \end{tabular} & Virtualization of an agro-food supply chain \\ \hline
[45] & Review Paper & - & \(\surd\) & - & \
\begin{tabular}{c} Food safety and \\ quality, supply chain \\ \end{tabular} &
\begin{tabular}{c} Authentication and \\ traceability of food \\ supply in the \\ agricultural \\ production process \\ \end{tabular} \\ \hline
[86] & Review Article & - & \(\surd\) & future study & \
\begin{tabular}{c} Sustainable and \\ precision agriculture \\ \end{tabular} &
\begin{tabular}{c} Remote detection \\ and monitoring of \\ vegetation and crop \\ stress in agriculture \\ \end{tabular} \\ \hline
[87] & Review & - & \(\surd\) & \(\surd\) & \
\begin{tabular}{c} Urban farming, \\ vertical farming, \\ indoor farming, \\ hydroponics, \\ aeroponics, \\ aquaculture, and \\ aquaponics. \\ \end{tabular} &
\begin{tabular}{c} Monitor, control, \\ coordinate, and \\ execute farm \\ operations at \\ agricultural sites \\ \end{tabular} \\ \hline
[88] & Review Paper & - & \(\surd\) & \(\surd\) & \
\begin{tabular}{c} DTs applied to \\ precision agriculture. \\ \end{tabular} &
\begin{tabular}{c} Predictive control, for \\ improving \\ soil quality \\ \end{tabular} \\ \hline \end{tabular}
\end{table} 
Table 2: _Cont._  
Figure 10: Review paper type distribution. Fourteen articles either being descriptive as in [9] or practically using a case study project as in [9; 19; 26; 28; 35; 64; 74; 75; 76; 77; 79; 80; 81; 82] address the significance of a DT case study in agriculture. The concept of DTs is mainly addressed in all reviewed papers. In 16 papers though [19; 26; 27; 28; 64; 73; 82], the DT concept is analyzed and utilized in more detail, thus posing the significance of using DTs in smart farming and agriculture. According to the reviewed literature summarized in Table 2, smart farming as an implementation of agriculture 4.0 [19; 26; 27; 28; 29; 45; 63; 75; 76; 77; 79; 80; 81; 82] includes smart irrigation strategies by monitoring and controlling various farming stages [28], implementing data acquisition techniques [27] for automatically controlling actuator systems in agriculture or even in high-tech data-driven greenhouses [79]. Furthermore, via simulation, monitoring, controlling, coordinating, and executing farm operations at agricultural sites [87], DTs improve predictive control in precision irrigation [28; 73; 88], greenhouse horticulture, and organic vegetable and livestock farming. Smart farming enhances remote detection and monitoring of vegetation and crop stress in agriculture [86], developing DT stages and forecasting plant yield in greenhouses, vertical farms, or outdoor fields [76; 77], or even in urban and indoor farming, of vertical agriculture utilizing hydroponics, aeroponics, aquaculture, and aquaponics. Smart farming approaches the smart agriculture [85] as well as the sustainable agriculture 4.0 [80] sector to address precision farming and management [75; 76] via the adoption of digital technologies and techniques in agriculture [27; 29; 64], leading the way to digital representations of plants [9], inventory quality in agriculture, greenhouse production flow, and food safety and quality within the food supply chain [45]. Although the DTs remain a major issue in our research criteria, in papers [29; 45; 63; 83; 84; 85], they are implied as such. In [9], authors propose a functional DT model; in [86], they are proposed as a significant future issue to address and study.