## 4 Discussion  
### Mechanisms of the Drought on SIF and Physiological Parameters  
From jointing to maturity, the biomass produced by plot T1 was significantly higher than that of plots T3 and T4 (Figure 10). These findings were consistent with previous studies, which reported reductions in biomass under water stress. Under moderate and severe stresses, the aboveground biomass decreased significantly, which was attributed to the decreased photosynthetic activities caused by water deficits. As a result, the growth of leaves was affected and could not be fully extended. The intercepted photosynthetic active radiation (PAR) of winter wheat was reduced, leading to a decrease in the plant height and substance assimilation accumulation, resulting in a decrease in the biomass. However, when compared with T1, the aboveground biomass of T2 was not significantly decreased. This could be because photosynthetic activities were not largely affected under mild stresses. The 1000-grain weights of T3 and T4 decreased due to the decreased grain filling time, which resulted in a shorter duration and a lower dry matter accumulation. Thus, the seeds in T3 and T4 developed less, which led to a lower 1000-grain weight. It was interesting that the 1000-grain weight of T2 increased by 1.95% compared to T1, which could be attributed to the fact that the photosynthesis of the winter wheat plants in T2 was not weakened [36]. The grain weight of T2 only decreased by 7.27%, while the grain weights of T2 and T3 decreased by 32.73% and 43.64%, respectively (Table 3). This was similar to the results of Ref. [37], who noted that crop yields decrease under water stress conditions. This study suggested that water stress conditions may reduce the yield by decreasing the 1000-grain weight. As we all know, moderate and severe water stress conditions significantly shortened the duration of carbon assimilation, reduced the photosynthesis rate and affected the transformation of photosynthetic products to the yield, which resulted in a reduction in the yield of winter wheat in plots T3 and T4. Winter wheat maintained a higher photosynthetic rate in T2, which was conducive to full grain filling. Therefore, the yield of T2 was not reduced significantly, which mirrored previous research results [38]. When drought occurs, the decrease in SIF is mainly due to changes in chlorophyll fluorescence quantum yield and absorbed photosynthetically active radiation (APAR) [39]. Drought causes stomatal closure of vegetation, which reduces CO2 uptake and leads to a \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**NO.** & **Category** & **Item Description** & **Unit Quantity** & **Unit Price (S)** & **Amount (S)** \\ \hline
1. & & Data collectors (MC302 L) & 6 & 20.25 & 121.50 \\
2. & & Soil moisture sensors (Hydra Probe II) & 48 & 697.35 & 33,472.80 \\
3. & & Mounting brackets & 6 & 25.86 & 155.16 \\
4. & & Solar panels & 6 & 10.63 & 63.78 \\
5. & Intelligent irrigation & Electrolytic capacitor & 6 & 5.89 & 35.34 \\
6. & control system & Resistors & 6 & 8.62 & 51.72 \\
7. & & 12-V Relay Module External Trigger Delay Adjustable & 6 & 7.59 & 45.54 \\
8. & & Module Light Enmitting Diode & 4 & 3.46 & 13.84 \\
9. & & Digital Temperature, Humidity Sensor Module & 4 & 7.84 & 31.36 \\
10. & & Water Meter & 12 & 4.28 & 51.36 \\
11. & & Air temperature and humidity sensor & 4 & 267.35 & 1069.40 \\ \hline \multicolumn{5}{c}{Subtotal 1} & 108 & 35,111.80 \\ \hline
12. & & QEpro spectrometer & 1 & 17,433.75 & 17,433.75 \\
13. & & electronic switch & 1 & 285.71 & 285.71 \\
14. & Automatic spectral & optical fiber & 2 & 714.29 & 1428.58 \\
15. & monitoring system & cosine corrector & 1 & 166.67 & 166.67 \\
16. & & Robotic arm & 1 & 71.43 & 71.43 \\
17. & & Stepping motor & 1 & 42.86 & 42.86 \\ \hline \multicolumn{5}{c}{Subtotal 2} & 7 & 19,429.00 \\ \hline \multicolumn{5}{c}{Total} & 115 & 54,540.80 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Cost analysis of the Intelligent Irrigation Control System and Automatic Spectral Monitoring System.