In this study, two independent experiments were carried out to determine the Si and P interaction. In the first experiment (wheat-maize experiment), first wheat and then maize were grown, and in the second experiment (maize-maize experiment), first maize and then again maize were grown. Phosphorus and Si were applied to the first plants and main and residual effects of the treatments were determined both on the first and on the second plants. Phosphorus was applied at the level of 0, 20 and 80 mg kg− 1, and Si was applied at the level of 500 mg kg− 1 from the sources of Nano-Si and Na-Si.
Characterization Of Nano-si
Figure 1 shows SEM micrograph of Nano-Si at x100.000 magnification. The strong intensity of Si, O and C was evident in EDX spectra (Fig. 2). The XRD pattern and characteristic absorption peak of Nano-Si were illustrated in Fig. 3. The Nano-Si spectra showed a broad peak in the 18–30° (2θ) range and the peak of the XRD pattern of Nano-Si at 2theta = 22.5°. Figure 4 shows the FTIR spectra of Nano-Si. At 800, 1060, and 2324 cm− 1, sharp and strong peaks were observed. The specific surface area of Nano-Si produced from rice husk was 204 m2g− 1.
Dry Weights Of Plants
In the wheat-maize experiment, the PxSi interaction was not significant. In this experiment, the dry weight of wheat increased significantly with a high P dose (Fig. 5a). In both experiments, SixP interaction was significant on dry weight of second crop (maize). The dry weight of second crop maize increased significantly with increasing P treatment, regardless of Si treatments (Fig. 5b, d). At P80 dose, the highest dry weight was obtained from Nano-Si treatment. The lowest dry weight was obtained from Na-Si treatment at P80 dose (Fig. 5b). In the maize-maize experiment, the dry weight of the first crop maize increased depending on the increasing P dose (Fig. 5c). In addition to this, the highest dry weight of the second crop (maize) was obtained from Nano-Si treatment (Fig. 5d).
Phosphorus Concentration And Content In Plants
Phosphorus x Si interaction was significant for the first crop wheat and second crop maize (Table 2). Depending on the increasing P doses, the P concentration of the first crop wheat was increased. This increase was particularly pronounced at the high P dose. Silicon treatments were effective in increasing the P concentration of plants, especially in low dose P (P20) applications. For example, while the P concentration of the plants was 0.92 g kg− 1 in the No-Si treatment at the P20 dose, this value was 1.55 g kg− 1 in Nano-Si and 1.76 g kg− 1 in the Na-Si treatment. The highest P concentration in the second plant (maize) containing Nano-Si was 2.40 kg− 1 where P was applied as P0. In the second crop maize, P concentration was increased with P20 treatments and decreased with the highest P treatment (P80) where no silicon was applied (Table 2). In Nano-Si group, the highest P concentration was obtained from P0 treatment with 2.40 g kg− 1 and the P concentrations of the plants were decreased to 1.79 and 1.98 g kg− 1 in the P20 and P80 treatments respectively. In the Na-Si group, the P concentration of the plants showed a significant increase at high P (P80) dose.
Table 2
Total phosphorus (P), silicon (Si) and zinc (Zn) concentrations, P and Si content in wheat-maize cropping system
Treatments | P g kg− 1 | P content mg pot− 1 | Si g kg− 1 | Si content mg pot− 1 | Zn mg kg− 1 |
First Crop Wheat |
No-Si | P0 | 0.80 ± 0.05 Bb | 2.88 ± 0.35 Ac | 15.5 ± 0.58 | 55.3 ± 5.43 | 26.9 ± 1.46 |
P20 | 0.92 ± 0.04 Bb | 10.6 ± 1.08 Bb | 10.1 ± 0.71 | 117 ± 11.7 | 13.2 ± 0.71 |
P80 | 2.15 ± 0.09 Aa | 32.5 ± 1.11 Aa | 10.1 ± 0.29 | 154 ± 8.55 | 8.52 ± 0.46 |
Nano-Si | P0 | 0.87 ± 0.14 Bc | 3.11 ± 0.36 Ac | 20.1 ± 1.41 | 73.3 ± 5.02 | 61.7 ± 6.07 |
P20 | 1.55 ± 0.14 Ab | 18.0 ± 1.29 Ab | 15.8 ± 0.30 | 184 ± 14.4 | 45.6 ± 5.23 |
P80 | 2.29 ± 0.08 Aa | 33.8 ± 1.36 Aa | 14.5 ± 0.59 | 215 ± 10.4 | 33.2 ± 6.88 |
Na-Si | P0 | 1.47 ± 0.06 Ab | 5.48 ± 0.39 Ac | 22.2 ± 2.71 | 82.0 ± 7.73 | 56.2 ± 3.65 |
P20 | 1.76 ± 0.17 Ab | 21.5 ± 2.38 Ab | 16.9 ± 0.67 | 205 ± 8.88 | 34.3 ± 6.11 |
P80 | 2.40 ± 0.06 Aa | 33.6 ± 1.18 Aa | 13.3 ± 0.65 | 187 ± 7.22 | 26.1 ± 1.75 |
P mean | P0 | 1.05 ± 0.10 c | 3.83 ± 0.40 c | 19.2 ± 1.27 a | 70.2 ± 4.65c | 48.3 ± 5.10 a |
P20 | 1.41 ± 0.13 b | 16.7 ± 1.62 b | 14.3 ± 0.94 b | 169 ± 12.9 b | 31.0 ± 4.73 b |
P80 | 2.28 ± 0.05 a | 33.3 ± 0.66 a | 12.7 ± 0.63 b | 185 ± 8.83 a | 22.6 ± 3.79 c |
Si mean | No-Si | 1.29 ± 0.19 c | 15.3 ± 3.81 b | 11.9 ± 0.81 b | 109 ± 13.1 b | 16.2 ± 2.40 c |
Nano-Si | 1.57 ± 0.19 b | 18.3 ± 3.82 a | 16.8 ± 0.86 a | 157 ± 19.1 a | 46.8 ± 4.74 a |
Na-Si | 1.88 ± 0.13 a | 20.2 ± 3.57 a | 17.5 ± 1.40 a | 158 ± 16.9 a | 38.9 ± 4.43 b |
F/LSD | P | 119**/0.17 | 441**/2.04 | 27.4**/1.90 | 135**/15.5 | 27.5**/7.24 |
Si | 25.4**/0.17 | 12.1**/2.04 | 21.5**/1.90 | 28.3**/15.5 | 40.6**/7.24 |
PxSi | 4.29*/0.29 | 5.12*/3.54 | 0.95ns | 4.78ns | 0.66ns |
Treatments | Second Crop Maize |
No-Si | P0 | 1.56 ± 0.13 Bb | 15.3 ± 1.33 | 7.04 ± 0.37 | 68.8 ± 1.60 | 49.0 ± 3.68 |
P20 | 2.16 ± 0.29 Aa | 33.5 ± 4.73 | 6.62 ± 0.41 | 102 ± 5.25 | 30.5 ± 1.97 |
P80 | 1.48 ± 0.07 Ab | 32.9 ± 1.59 | 5.89 ± 0.53 | 130 ± 11.1 | 16.2 ± 0.46 |
Nano-Si | P0 | 2.40 ± 0.31 Aa | 23.7 ± 1.95 | 11.3 ± 0.42 | 114 ± 6.79 | 36.1 ± 2.37 |
P20 | 1.79 ± 0.12 ABb | 29.2 ± 3.07 | 11.6 ± 0.48 | 193 ± 8.07 | 30.4 ± 3.06 |
P80 | 1.98 ± 0.18 Aab | 44.0 ± 4.06 | 8.24 ± 0.47 | 184 ± 13.8 | 20.7 ± 6.24 |
Na-Si | P0 | 1.22 ± 0.07 Bb | 14.0 ± 0.93 | 11.0 ± 0.32 | 127 ± 8.50 | 38.7 ± 3.36 |
P20 | 1.51 ± 0.10 Bab | 21.0 ± 2.74 | 11.4 ± 0.70 | 156 ± 14.2 | 26.0 ± 2.74 |
P80 | 1.97 ± 0.32 Aa | 36.1 ± 6.35 | 10.1 ± 1.37 | 182 ± 19.8 | 16.8 ± 1.86 |
P mean | P0 | 1.72 ± 0.18 | 17.7 ± 1.51 c | 9.80 ± 0.62 a | 103 ± 27.6 b | 41.3 ± 2.36 a |
P20 | 1.80 ± 0.13 | 27.9 ± 2.45 b | 9.87 ± 0.75 a | 151 ± 27.9 a | 29.0 ± 1.51 b |
P80 | 1.81 ± 0.13 | 37.7 ± 2.72 a | 8.09 ± 0.70 b | 166 ± 22.4 a | 20.3 ± 4.33 c |
Si mean | No-Si | 1.73 ± 0.13 ab | 27.2 ± 2.98 ab | 6.52 ± 0.27 b | 101 ± 29.2 b | 31.9 ± 4.23 |
Nano-Si | 2.04 ± 0.14 a | 32.3 ± 3.07 a | 10.4 ± 0.52 a | 164 ± 25.3 a | 29.1 ± 4.28 |
Na-Si | 1.56 ± 0.14 b | 23.7 ± 3.48 b | 10.7 ± 0.50 a | 155 ± 21.5 a | 27.2 ± 3.06 |
F/LSD | P | 0.16ns | 25.7**/5.72 | 7.45*/1.07 | 29.3**/17.4 | 13.1**/8.46 |
Si | 4.31*/0.34 | 4.86*/5.72 | 41.5**/1.07 | 32.6**/17.4 | 0.79ns |
PxSi | 4.82*/0.58 | 1.91ns | 1.44ns | 1.99ns | 1.47ns |
The values are means of four replicates ± standard errors. ns: non-significant; *: p < 0.05; **: p < 0.01. Different letters in each column represent significant difference at p < 0.05 level based on Duncan’s multiple range test. Uppercase letters are used to compare Si treatments according to P doses, and lowercase letters are used to compare P doses according to Si treatments. |
In non-silicon-treated and Nano-Si group, the P concentration of the first crop maize was relatively higher in P20 treatment than that of P0 and P80 treatment in the maize-maize experiment. On the other hand, in the Na-Si group, the P concentration of the maize plant increased with P20 treatment, but this increase was not significant and can’t be compared to P0. Additionally, the P concentration of the plants decreased with P80 treatment. The P concentration of the plants without Si in the second crop (maize) is almost the same. It was found that the P concentration of second crop (maize) increased in the Nano-Si treated group as compared to P0, but the increase was not significant, and the P concentration of maize in P80 treatment was the lowest. Compared to the control and P20 treatments, P80 treatment had the highest P concentration among the Na-Si group. When the P concentrations of both first crop maize and second crop maize are compared according to the silicon applications within P doses, it is seen that the P concentration of the maize plant is significantly higher with Nano-Si applications than the plants without Si and Na-Si applied in all P doses.
In the maize-maize experiment, the SixP interaction was significant for the first crop wheat. Phosphorus content in wheat was significantly high in P20 and P80 treatment as compared to control (no-Si treatment (Table 3). In Nano-Si treatment, P content of wheat was 173 g pot− 1 in P20 treatment and reduced to 90 g pot− 1 in P80 treatment. Both content values are significantly higher than those were obtained in the control (42.7). In Na-Si treatment, P content in wheat was significantly increased with increasing P supply. Phosphorus content of second crop (maize) was significantly increased too with the increasing level of applied P.
Table 3
Total phosphorus (P), silicon (Si) and zinc (Zn) concentrations, P and Si content in maize-maize cropping system
Treatments | P g kg− 1 | P content mg pot− 1 | Si g kg− 1 | Si content mg pot− 1 | Zn mg kg− 1 |
First Crop Maize |
No-Si | P0 | 0.90 ± 0.07 Bc | 12.1 ± 1.32 Bb | 8.20 ± 0.63 Ba | 110 ± 9.20 Bb | 78.4 ± 2.81 |
P20 | 2.19 ± 0.13 Ba | 116 ± 16.0 Ba | 6.21 ± 0.89 Ba | 328 ± 61.5 Ba | 24.5 ± 1.13 |
P80 | 1.42 ± 0.14 Ab | 101 ± 10.2 Aa | 4.04 ± 1.01 Bb | 287 ± 71.2 Ba | 13.6 ± 1.27 |
Nano-Si | P0 | 1.47 ± 0.22 Ab | 42.7 ± 4.34 Ac | 12.3 ± 0.23 Aa | 367 ± 34.8 Ac | 94.1 ± 10.4 |
P20 | 2.61 ± 0.19 Aa | 173 ± 11.7 Aa | 7.92 ± 0.57 ABb | 527 ± 34.4 Ab | 33.5 ± 3.15 |
P80 | 1.14 ± 0.04 ABb | 90.0 ± 4.23 Ab | 8.64 ± 0.62 Ab | 685 ± 58.6 Aa | 20.5 ± 2.65 |
Na-Si | P0 | 0.96 ± 0.05 Bab | 18.3 ± 1.51 Bb | 10.8 ± 0.67 Aa | 204 ± 13.8 Bb | 73.3 ± 3.03 |
P20 | 1.29 ± 0.10 Ca | 73.5 ± 2.66 Ca | 9.99 ± 1.12 Ab | 580 ± 75.9 Aa | 27.0 ± 2.31 |
P80 | 0.88 ± 0.07 Bb | 54.0 ± 4.27 Ba | 4.97 ± 0.59 Bb | 310 ± 46.2 Bb | 21.6 ± 0.78 |
P mean | P0 | 1.11 ± 0.11 b | 24.4 ± 4.24 c | 10.4 ± 0.58 a | 227 ± 34.1 b | 81.9 ± 4.30 a |
P20 | 2.03 ± 0.18 a | 121 ± 13.8 a | 8.04 ± 0.66 b | 478 ± 45.2 a | 28.3 ± 1.67 b |
P80 | 1.14 ± 0.08 b | 81.5 ± 6.99 b | 5.88 ± 0.72 c | 427 ± 63.3 a | 18.6 ± 1.41 c |
Si mean | Si- | 1.50 ± 0.17 b | 76.2 ± 14.9 b | 6.15 ± 0.68 b | 241 ± 40.3 c | 38.8 ± 8.60 b |
Nano-Si | 1.74 ± 0.21 a | 102 ± 16.8 a | 9.61 ± 0.63 a | 526 ± 45.4 a | 49.4 ± 10.2 a |
Na-Si | 1.04 ± 0.07 c | 48.6 ± 7.07 c | 8.58 ± 0.89 a | 365 ± 54.8 b | 40.6 ± 7.09 b |
F/LSD | P | 50.0**/0.21 | 114**/13.2 | 27.6**/1.25 | 20.8**/84.4 | 209**/6.85 |
Si | 23.2**/0.21 | 35.0**/13.2 | 17.0**/1.25 | 24.1**/84.4 | 5.70*/6.85 |
PxSi | 7.67**/0.37 | 9.90**/22.9 | 3.82*/2.17 | 4.60*/146 | 1.89ns |
Treatments | Second Crop Maize |
No-Si | P0 | 1.24 ± 0.10 Ba | 13.4 ± 0.67 | 7.14 ± 0.69 Ba | 78.5 ± 6.91 | 45.8 ± 1.21 |
P20 | 1.45 ± 0.14 Ba | 26.1 ± 2.36 | 6.49 ± 0.99 Bab | 117 ± 17.5 | 21.7 ± 2.36 |
P80 | 1.51 ± 0.12 Aa | 38.5 ± 3.89 | 4.79 ± 0.55 Bb | 122 ± 14.4 | 17.7 ± 0.70 |
Nano-Si | P0 | 2.23 ± 0.11 Aab | 24.1 ± 1.87 | 11.8 ± 0.83 Aa | 129 ± 15.8 | 48.3 ± 3.86 |
P20 | 2.54 ± 0.07 Aa | 43.6 ± 1.71 | 7.82 ± 0.30 Bb | 135 ± 4.91 | 26.2 ± 0.75 |
P80 | 1.90 ± 0.14 Ab | 44.1 ± 6.74 | 6.96 ± 0.38 Ab | 158 ± 8.27 | 18.6 ± 0.40 |
Na-Si | P0 | 1.25 ± 0.05 Bb | 13.6 ± 1.01 | 10.1 ± 0.26 Aab | 109 ± 4.60 | 46.2 ± 0.89 |
P20 | 1.63 ± 0.23 Bab | 24.1 ± 3.50 | 10.8 ± 0.34 Aa | 160 ± 5.09 | 24.8 ± 1.52 |
P80 | 1.87 ± 0.18 Aa | 35.9 ± 3.28 | 8.63 ± 0.62 Ab | 168 ± 16.8 | 20.7 ± 0.68 |
P mean | P0 | 1.56 ± 0.18 b | 17.9 ± 1.64 c | 9.68 ± 0.67a | 106 ± 8.27 b | 46.8 ± 1.29 a |
P20 | 1.87 ± 0.17 a | 31.3 ± 2.98 b | 8.37 ± 0.64 b | 137 ± 7.82 a | 24.3 ± 1.04 b |
P80 | 1.76 ± 0.09 ab | 39.5 ± 2.75 a | 6.79 ± 0.55 c | 150 ± 9.29 a | 19.0 ± 0.49 c |
Si mean | No-Si | 1.40 ± 0.07 b | 26.1 ± 3.36 b | 6.14 ± 0.50 b | 106 ± 9.21 b | 28.4 ± 3.84 |
Nano-Si | 2.22 ± 0.10 a | 37.3 ± 3.55 a | 8.86 ± 0.70 a | 141 ± 6.77 a | 31.1 ± 3.98 |
Na-Si | 1.58 ± 0.12 b | 24.5 ± 3.12 b | 9.84 ± 0.35 a | 146 ± 9.59 a | 30.6 ± 3.43 |
F/LSD | P | 3.57*/0.23 | 35.8**/5.50 | 17.4**/1.01 | 11.2**/19.6 | 221**/2.86 |
Si | 30.0**/0.23 | 13.5**/5.50 | 30.5**/1.01 | 10.4**/19.6 | 2.00ns |
PxSi | 4.02*/0.40 | 1.13ns | 4.34*/1.75 | 1.08ns | 0.59ns |
The values are means of four replicates ± standard errors. ns: non-significant; *: p < 0.05; **: p < 0.01. Different letters in each column represent significant difference at p < 0.05 level based on Duncan’s multiple range test. Uppercase letters are used to compare Si treatments according to P doses, and lowercase letters are used to compare P doses according to Si treatments. |
In the maize-maize experiment, the P content of maize increased with increasing P dose in all Si treatments (Table 3). Regardless of the Si treatments, the P content of the second crop maize increased significantly. While the P content of the maize plant was 32.3 mg pot− 1 in the Nano-Si application, this value was mg pot− 1 in the Na-Si treatment. When Si treatments were compared according to P doses, the highest P concentrations and content were obtained from the highest Nano-Si treatment at all P doses in both first and second crop maize.
Silicon Concentration And Content Of Plants
In the wheat-maize experiment, the Si concentration of both first crop wheat and second crop maize decreased with increased P supply (Table 2). On the other hand, the Si concentration of the plants increased significantly with the application of Si. In the maize and maize experiment, the PxSi interaction was significant (Table 3). In general, the Si concentration of plants decreased with P application, and this decrease was especially greater in high P (P80) treatment. When we compared the Si concentration in plants with the Si treatments according to the P doses, it is seen that the Nano-Si and Na-Si treatments of the plants were higher at each P dose as compared to no-Si treatment.
In the wheat-maize experiment, the Si content of wheat significantly increased with increasing P supply (Table 2). Silicon content in wheat and maize increased with increasing P dose. Although there was no difference between the Si sources, the Si content of both wheat and maize plants increased significantly with the Si treatment as compared to the control.
In the maize-maize experiment, the Si content of the first crop (maize) significantly increased with increasing Si in Na-Si and Nano-Si treatments (Table 3). Silicon content of first crop (maize) was significantly higher in P20 treatment than in control and P80 in Na-Si treatment. There was no significant difference between the Si sources, the Si content of the second crop (maize) increased significantly with the increasing P supply and Si treatment as compared to the control.
Zinc Concentration Of Plants
In both experiments, Increasing P treatments caused a significant decrease in Zn concentration in both first and second crops (Tables 2 and 3). On the other hand, while the Zn concentration was 16.2 mg kg− 1 in plants not treated with Si, it rose to 46.8 mg kg− 1 with Nano-Si and to 38.9 mg kg− 1 with Na-Si. Nano-Si treatments in maize-maize experiments significantly increased Zn concentrations in the first maize compared to the no-Si treatments.
Anthocyanin Concentration In Plants
Anthocyanin concentration of the first crop (wheat & maize) in the wheat-maize experiment was not significantly changed depending on Si and P treatments (Fig. 6a,b). On the other hand, in the maize-maize experiment, anthocyanin concentrations changed depending on the treatments (Fig. 6c,d). In the first crop (maize), anthocyanin concentrations significantly reduced by increasing the P and Si treatments. Again, Si treatments, especially Nano-Si, decreased the anthocyanin concentration. In the second crop (maize), anthocyanin concentrations significantly reduced by increasing the P levels.
Plant Available P Concentrations In The Soil
Plant available P concentrations in the soils were determined at the end of each experiment. In the wheat-maize experiment, the plant available P concentration in the soils after first crop (wheat) increased with increasing the P supply (Fig. 7a,b). Plant available P concentration in the soil after second crop (maize) was increased with the increasing P supply. In the maize-maize experiment, the plant available soil P was increased with the increasing the P dose (Fig. 7c,d). After the second crop (maize), the plant-available P concentration in the soil was higher with Si applications than the control. In both experiments, the available P concentrations in the soil decreased significantly after the second plant. Even after the second trial, the plant available P concentration in the soils was below the critical limit 8 mg kg− 1.
Plant Available Silicon Concentrations In The Soil
Plant available Si concentrations in the soil were determined at the end of each experiment. In the wheat-maize experiment, Si concentrations were increased with P80 treatment as compared to control soils of first crop (wheat). Silicon treatments increased plant available Si concentrations both in wheat and maize soils (Fig. 8a, b). Silicon x P interactions was significant in the maize-maize experiment. Plant available Si concentrations were increased as compared to control and P20 treatments in the first crop (maize). While the plant-available Si concentrations did not change in no-Si and Nano-Si treatments, the plant-available Si content in soils decreased with increasing doses of P in Nano-Si treatment. In the maize-maize experiment, when the available Si concentrations of the soils are compared according to the P doses, it is understood that the highest Si concentrations are significantly increased in Si applications compared to the control (Fig. 8c, d).