Table 2 Root diameter, root fresh weight, leaf fresh weight, relative chlorophyll content (SPAD_chlorophyll value), and leaf area index of sugar beet plant as influenced by indole‒3‒acetic acid (IAA) and nitrogen (N) rate (data average for 2022/23 and 2023/24 cropping seasons)

IAA (mg L^− 1)

IAA₀

12.82 ± 0.29c

1.57 ± 0.07c

0.61 ± 0.03c

53.4 ± 1.6c

4.56 ± 0.28c

IAA₁₅₀

13.14 ± 0.29b

1.70 ± 0.07b

0.66 ± 0.04b

54.7 ± 1.6b

4.97 ± 0.33b

IAA₃₀₀

13.50 ± 0.32a

1.82 ± 0.07a

0.79 ± 0.06a

56.2 ± 1.6a

5.57 ± 0.40a

N rate (kg ha^− 1)

N₂₄₀

12.19 ± 1.24c

1.38 ± 0.03c

0.50 ± 0.01c

50.5 ± 1.3c

3.63 ± 0.11c

N₂₉₀

13.04 ± 0.24b

1.71 ± 0.03b

0.66 ± 0.02b

55.0 ± 1.5b

4.66 ± 0.12b

N₃₄₀

14.22 ± 0.22a

2.01 ± 0.05a

0.89 ± 0.04a

58.7 ± 1.5a

6.80 ± 0.21a

IAA × N rate

IAA₀

N₂₄₀

11.94 ± 0.44 g

1.22 ± 0.04a

0.45 ± 0.02 g

48.9 ± 2.4a

3.36 ± 0.17 g

N₂₉₀

12.80 ± 0.45e

1.61 ± 0.03a

0.62 ± 0.03ef

53.8 ± 2.5a

4.31 ± 0.16e

N₃₄₀

13.71 ± 0.35c

1.90 ± 0.05a

0.77 ± 0.04bc

57.4 ± 2.7a

6.00 ± 0.17c

IAA₁₅₀

N₂₄₀

12.20 ± 0.42 fg

1.39 ± 0.02a

0.49 ± 0.01 g

50.6 ± 2.3a

3.61 ± 0.19 g

N₂₉₀

13.05 ± 0.43de

1.71 ± 0.04a

0.67 ± 0.03de

55.0 ± 2.7a

4.55 ± 0.18e

N₃₄₀

14.15 ± 0.36b

2.00 ± 0.06a

0.81 ± 0.04b

58.5 ± 2.8a

6.73 ± 0.23b

IAA₃₀₀

N₂₄₀

12.43 ± 0.46f

1.52 ± 0.02a

0.56 ± 0.02f

52.1 ± 2.3a

3.92 ± 0.17f

N₂₉₀

13.27 ± 0.39d

1.80 ± 0.05a

0.71 ± 0.03 cd

56.2 ± 2.8a

5.11 ± 0.16d

N₃₄₀

14.81 ± 0.34a

2.14 ± 0.09a

1.10 ± 0.06a

60.2 ± 2.9a

7.67 ± 0.29a

p-value

IAA

< 0.001^**

< 0.001^**

< 0.001^**

< 0.001^**

< 0.001^**

N rate

0.031^*

< 0.001^**

< 0.001^**

< 0.001^**

< 0.001^**

IAA × N rate

0.006^**

0.670^ns

< 0.001^**

0.964^ns

< 0.001^**

CV (%)

1.2

1.5

5.5

2.0

3.4