## 3 Results
### Growth Parameters  
The increase in plant weight per unit of area covered by the plant over a predetermined period is known as the crop growth rate (CGR). As leaf area increased over time, it was likewise noted that CGR increased until 60 DAT and then declined at 80 DAT in all cultivars except Jagliboro, Rata boro and Lakhai (Figure 1). At 20-40 (1 st), 40-60 (2 nd), and 60-80 (3 rd) DAT, Binadhan-10 produced maximum CGR values of 5.99, 7.88, and 7.15 g cm\({}^{-2}\) day\({}^{-1}\) respectively, while the cultivar Jagliboro had the minimum CGR values were 3.84, 4.6, and 6.07 g cm\({}^{-2}\) day\({}^{-1}\), respectively. RGR was higher in the early stages and began to decline as the plants got older (Figure 2). The rise in metabolically active tissue, which makes a smaller contribution to plant growth, is likely what caused the reduction in RGR. At 20-40 (1 st) DAT, Jagliboro had the highest RGR (47.33 mg g\({}^{-1}\) day\({}^{-1}\)) and Binadhan-10 had the lowest RGR (36.10 mg g\({}^{-1}\) day\({}^{-1}\)). The maximum RGR value was documented in BRRI dhan74 \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Cultivars** & **Root Number** & **Root Length** & **Root Volume** & \multirow{2}{*}{**Root Porosity (\%)**} & **Total Dry Mass** & **Leaf Area** \\  & & **(cm)** & **(cm\({}^{3}\) hill\({}^{-1}\))** & & **(g plant\({}^{-1}\))** & **Index** \\ \hline BRRI dhan 29 & 330.33 b & 1467.66 bc & 8.01 bc & 21.03 ab & 22.72 bc & 4.80 b \\ BRRI dhan58 & 315.33 d & 1460.08 de & 7.88 d & 19.76 bc & 21.97 d & 4.77 d \\ BRRI dhan67 & 304.66 e & 1454.83 g & 7.59 f & 18.18 c & 20.97 f & 4.75 e \\ BRRI dhan74 & 262.33 h & 1447.41 h & 7.21 h & 18.46 c & 19.74 h & 4.72 h \\ BRRI dhan81 & 288.00 f & 1452.41 f-h & 7.50 fg & 19.30 bc & 20.45 g & 4.74 f \\ Binadhan-8 & 275.00 g & 1450.83 g & 7.43 g & 18.61 c & 20.16 g & 4.73 g \\ Binadhan-10 & 340.66 e & 1476.16 a & 8.15 a & 22.18 a & 24.12 a & 4.82 a \\ Hira-2 & 332.00 b & 1470.66 b & 8.08 ab & 22.02 a & 23.02 b & 4.81 ab \\ Tej gold & 322.33 c & 1463.50 cd & 7.95 cd & 19.96 bc & 22.44 c & 4.79 c \\ SLSH & 308.00 e & 1456.75 e & 7.75 e & 19.45 bc & 21.59 e & 4.77 d \\ Jagliboro & 195.66 k & 1426.00 j & 5.90 k & 14.55 d & 15.98 j & 4.64 k \\ Rata boro & 237.33 i & 1437.33 i & 6.31 i & 15.94 d & 16.84 i & 4.68 i \\ Lakhai & 227.66 i & 1427.50 j & 6.10 j & 15.18 d & 16.76 i & 4.65 j \\ \hline Sx & 7.5 & 8.13 & 0.01 & 1.08 & 0.03 & 0.01 \\ \hline Level of sig. & ** & ** & ** & ** & ** & ** \\ \hline CV (\%) & 0.95 & 0.19 & 0.76 & 5.53 & 0.90 & 0.12 \\ \hline \hline \end{tabular} Columns with treatment means that have similar letters do not vary significantly. ** = Significant at a 1% level of probability.  
\end{table} 
Table 2: The root morphological traits, total dry mass (TDM), and leaf area index (LAI) of 13 _boro_ rice cultivars at 80 DAT. (17.79 mg g\({}^{-1}\) day\({}^{-1}\)), while the minimum value was reported in Binadhan-10 at 40-60 (2 nd) DAT (16.27 mg g\({}^{-1}\) day\({}^{-1}\)).Finally, between 60 and 80 (3 rd) DAT, Lakhai had the highest RGR (11.79 mg g\({}^{-1}\) day\({}^{-1}\)), while Hira-2 had the lowest RGR (8.54 mg g\({}^{-1}\) day\({}^{-1}\)). The net assimilation rate (NAR) refers to the amount of dry matter synthesized per unit of LA per unit of time. This implies that the synthesis of assimilation is driven by factors such as leaves and light. The wider the leaves and the more light they can absorb, the more assimilation will be detected. NAR increases if all the leaves block the light and are not shaded. This indicates that, while the LAI produced is high, the shade of the underlying canopy reduces the number of leaves that can be blocked, resulting in a decrease in NAR. In our study, the trends in NAR were more or less consistent, and decreased for all cultivars (Figure 3). Figure 1: Crop growth rate (CGR) in 13 rice cultivars at 20–40 (1 st), 40–60 (2 nd), and 60–80 (3 rd) DAT. In figure, same letter(s) do not differ significantly whereas dissimilar letter differ significantly.