3.1 Effect of different fertilizer treatments on growth and yield of garlic
In this study, the fresh weight of garlic plants, garlic bulb and bulb yield per m2 was determined to evaluate the effects of different fertilizer treatments on the growth of garlic under field condition (Fig. 1 and Table 2). In 2021, the average fresh weight of garlic plants under T1 treatment was the highest (200.7 ± 0.67 g), followed by T2 treatment (164.3 ± 2.73 g) and control treatment (136 ± 4.73 g). This corresponded well with the average fresh bulbs weight per plant. Garlic plants under T1 treatment recorded the highest average fresh bulbs weight per plant (74.3 ± 0.33 g), whereas the garlic plants under control treatment have the lowest average fresh bulbs weight per plant (58 ± 1.16 g). At harvest, the bulb yield per m2 was the highest under T1 treatment (2.23 ± 0.01 kg), followed by T2 and control treatment (Table 2). A similar finding was observed in year 2022. For the average fresh weight of garlic plant, the highest was recorded under T2 treatment (182.0 ± 7.02 g), followed by T1 treatment (168.5 ± 4.19 g) and control treatment (146.3 ± 11.06 g). Meanwhile, the average fresh weight of garlic bulb was the highest under T1 treatment (97.3 ± 9.88 g), followed by T2 treatment (91.2 ± 5.66 g) and control treatment (69.2 ± 8.41 g). Similarly, the bulb yield per m2 of the garlic grown under T2 and T1 treatment were approximately 14% and 6% higher than that of control, respectively (Table 2). These findings indicated that the addition of microbial biofertilizer and germanium-containing controlled release nanofertilizer had positive effects on the growth and yield of garlic even under the conditions of reduced P and K supply.
Furthermore, we showed that the allicin concentration in garlic increased significantly with the application of microbial biofertilizer. In 2021, the allicin concentration in the garlic under T1 treatment was the highest (0.355 g/kg), however there was no significant difference between control (0.243 g/kg) and T2 treatment (0.283 g/kg) (Fig. 2a). On the other hand, in 2022, both treatments significantly increased the allicin content with T1 treatment recorded the highest allicin concentration (0.65 g/kg) followed by T2 treatment (0.53 g/kg) (Fig. 2b).
Table 2 Fresh weight (FW) of garlic plant, garlic bulb and bulb yield per m2 of garlic harvested in 2021 and 2022. Values are means ± SE (n≥6). Significant difference (P<0.05) is indicated by different lower case letters above bars as determined by Duncan’s multiple range test.
3.2 The nitrate concentration and content in garlic under different fertilization treatments
In this study, we observed that the fluctuation patterns of nitrate concentration in the shoot and root of garlic plants at different growth stages are consistent, regardless of the types of fertilizer treatment (Fig. 3). The concentration of nitrate in garlic leaf peaked at the spring garlic stage and began to decline sharply during the bulb development stage. However, we found that the shoot nitrate concentration at spring garlic stage increased significantly under T1 and T2 treatment. In 2021, T1 and T2 treatment increased the shoot nitrate concentration by 44% and 37%, respectively (Fig. 3a). Meanwhile, in 2022, the shoot nitrate concentration of garlic at spring garlic stage increased by 51–52% under the treatment of both biofertilizers (Fig. 3b).
In 2021, the garlic under T2 treatment had the highest root nitrate concentration, which was approximately 39% and 53% higher than that of control and T1 treatment, respectively (Fig. 3c). In 2022, T1 treatment recorded the highest root nitrate concentration at spring garlic stage, which was about 36.6% and 33.6% higher than that of T2 treatment and control treatment, respectively (Fig. 3d). However, there was no significant difference in nitrate concentration in the shoot and root of garlic plants under different treatments at harvest stage.
3.3 The nitrogen concentration and content of garlic under different fertilization treatments
In 2021, the shoot concentration of nitrogen in garlic peaked at the spring garlic stage and declined gradually from the bulb developmental stage to the harvesting stage (Fig. 4). The highest shoot concentration of nitrogen was recorded by control treatment (25.24 ± 0.75 g/kg) at spring garlic stage, followed by T2 (15.54 ± 1.9 g/kg) and T1 treatment (11.41 ± 0.33 g/kg) (Fig. 4a). In 2022, the shoot concentration of nitrogen peaked at the seedling stage and reached its lowest value at harvest stage, irrespective of the treatments. The highest shoot concentration of nitrogen was recorded by the control treatment which was 23.55 ± 1.41 g/kg (Fig. 4a). Meanwhile, the maximum nitrogen content in the shoot was recorded at bulb developmental stage, irrespective of treatments and location (Fig. 4b). In 2021, we observed that the shoot nitrogen content in garlic plant under control treatment was the highest throughout different growth stages, except for harvest stage. At bulb developmental stage, the shoot nitrogen content of control garlic plant was 59% and 38% higher than that of T1 and T2 treatments, respectively. However, in 2022, the garlic under T1 treatment had the highest shoot nitrogen content (192.93 ± 0.99 mg) during bulb development stage (Fig. 4b).
For the root concentration of nitrogen, the garlic grown in 2021 had the highest root concentration of nitrogen in spring garlic stage. Among which, T2 treatment recorded the highest root concentration of nitrogen (27.29 ± 2.55 g/kg), followed by control (24.35 ± 2.48 g/kg) and T1 treatment (16.12 ± 2.24 g/kg) (Fig. 4c). Similarly, the garlic grown in 2022 had the highest concentration of nitrogen during the spring garlic stage. Among the treatment, the garlic grown under control treatment recorded the highest root concentration, which was 23.05 ± 0.33 g/kg (Fig. 4c). In 2021, the root nitrogen content of garlic under most treatments peaked at the bulb development stage. Among which, the highest root nitrogen content was recorded by the garlic under T2 treatment. In contrast, the root nitrogen contents of garlic planted in 2022 reached its peak at spring garlic stage and the highest root nitrogen content was recorded by control treatment (Fig. 4d).
In this study, the potassium content in the shoot and root of garlic plants was also quantitatively determined to explore the effect of different treatments on the potassium accumulation in garlic plants (Fig. 5). From the results, we observed that there is no significant difference between treatments except for the root potassium concentration. For the two-years study, the root potassium concentration of garlic under treatment T1 and T2 consistently higher than that of control treatment. In 2021, the root potassium concentration of garlic under treatment T1 and T2 was approximately 41% and 32% higher than those of control treatment, respectively (Fig. 5c). Similarly, in 2022, the root potassium concentration of garlic under treatment T1 and T2 was approximately 30% and 19% higher than those of control treatment, respectively (Fig. 5c).
3.5 Elemental analysis of garlic bulb
Plant Mg, Ca, Fe, B and Zn content were measured to investigate the effect of different fertilization treatments on these nutrients in garlic bulb at harvest stage (Table 3). In 2021, it was observed that the Fe content in garlic bulb under T1 and T2 treatment was significantly higher than that in the control. The accumulation of Fe in garlic bulb under T1 and T2 treatment was approximately 63% and 64% higher than that of control treatment, respectively. Meanwhile, there was no significant difference in Mg, Ca, B and Zn content among different treatments.
In 2022, the Ca content in garlic bulbs under T1 treatment was significantly higher than that in the control and T2 treatment. Contrary to the data from year 2021, the Fe content in the garlic bulb under T1 and T2 treatment was significantly lower than that in the control. The accumulation of Fe in garlic under T1 and T2 treatment was approximately 17% and 23% lower than that in the control, respectively.
Table 3
Elemental analysis of garlic bulb cultivated under different fertilization treatments. Values are means ± SE (n ≥ 3). Significant difference (P < 0.05) is indicated by different lower-case letters as determined by Duncan’s multiple range test.
Year
|
Element (mg.kg− 1)
|
Control
|
T1
|
T2
|
2021
|
Mg
|
3698.90 ± 227.83a
|
4111.22 ± 152.45a
|
4248.40 ± 322.40a
|
Ca
|
2422.80 ± 114.36b
|
2573.72 ± 57.07ab
|
2630.87 ± 131.75ab
|
Fe
|
190.12 ± 3.41b
|
310.94 ± 16.83a
|
312.00 ± 7.41a
|
B
|
11.61 ± 0.49a
|
12.62 ± 0.69a
|
13.57 ± 1.36a
|
Zn
|
11.94 ± 0.58a
|
11.14 ± 1.36a
|
10.92 ± 1.65a
|
2022
|
Mg
|
4130.73 ± 120.81a
|
3865.33 ± 139.59a
|
3887.10 ± 125.94a
|
Ca
|
2382.15 ± 110.72b
|
2737.28 ± 203.61a
|
2448.31 ± 86.43ab
|
Fe
|
196.14 ± 4.50a
|
161.93 ± 3.92b
|
150.22 ± 2.95c
|
B
|
12.82 ± 0.63a
|
13.64 ± 1.13a
|
12.89 ± 1.27a
|
Zn
|
9.90 ± 1.32a
|
8.89 ± 0.71a
|
9.26 ± 0.45a
|
Note: Mg: Magnesium; Ca: Calcium; Fe: Ferum; B: Boron; Zn: Zinc. |
3.6 Nitrogen use efficiency (NUE) in garlic under different fertilization treatments
In view of the increase in biomass and bulb fresh weight of garlic grown under T1 and T2 treatment, we calculated the nitrogen use efficiency (NUE), nitrogen absorption efficiency (NAE), physiological N use efficiency (PNUE) and nitrogen harvest index (NHI) of garlic at the harvesting stage (Table 4). In 2021, the NUE of garlic under T1 and T2 treatments increased by about 28% and 14%, respectively. Likewise, the PNUE of garlic grown under T1 and T2 treatment increased by 46% and 112%, respectively. For NHI, the garlic under T2 treatment increased by about 60%. In contrast, the NAE of the garlic under T1 and T2 treatment decreased by approximately 12% and 46%. However, the NAE and NHI of T2 treatment decreased by about 46% and 15%, respectively compared to those of control. Similarly, in 2022, the NUE of the garlic under T2 treatment increased by about 5% relative to that of control treatment. Meanwhile, the NAE of the garlic under T1 and T2 treatment increased by 46% and 92%, respectively. In contrast, the PNUE of garlic under T1 and T2 treatment decreased by about 21% and 22%, respectively. There was no significant difference in NHI among different treatment.
Table 4
Comparison of nitrogen use efficiency, nitrogen absorption efficiency, physiological N-use efficiency and nitrogen harvest index between garlic grown under different fertilization treatments. Values are means ± SE (n ≥ 3). Significant difference (P < 0.05) is indicated by different lower-case letters as determined by Duncan’s multiple range test.
|
Parameter
|
Control
|
T1
|
T2
|
2021
|
NUE (kg.kg− 1)
|
145.0 ± 2.89c
|
185.8 ± 0.83b
|
165.8 ± 2.20a
|
NAE (kg.kg− 1)
|
1.17 ± 0.05a
|
1.03 ± 0.02b
|
0.63 ± 0.01b
|
PNUE (kg.kg− 1)
|
124.39 ± 5.10c
|
181.24 ± 3.97b
|
263.75 ± 1.70a
|
NHI (%)
|
48.0 ± 0.10a
|
47.0 ± 0.10b
|
76.8 ± 0.4c
|
2022
|
NUE (kg.kg− 1)
|
201.8 ± 19.56a
|
203.5 ± 21.17a
|
210.94 ± 12.81a
|
NAE (kg.kg− 1)
|
1.06 ± 0.53a
|
1.55 ± 0.21a
|
2.04 ± 0.15b
|
PNUE (kg.kg− 1)
|
134.39 ± 4.65a
|
132.40 ± 5.34a
|
105.23 ± 13.87a
|
NHI (%)
|
46.0 ± 0.40b
|
46.0 ± 0.10b
|
47.0 ± 0.20a
|
Note: NUE: Nitrogen Use Efficiency; NAE: Nitrogen Absorption Efficiency; PNUE: Physiological N-use efficiency; NHI: Nitrogen Harvest Index. |