3.1 Plant height and LAI
The plant height and LAI of wheat at all the growth stages were influenced remarkably owing to the residual effect of Si and P fertilization except at 30 DAS (Table 2). Among the different P levels, the higher plant height and LAI were observed with 90 kg P2O5 ha− 1 at all the growth stages except at 30 DAS. However, this treatment was statistically similar with 60 kg P2O5 ha− 1. It could be due to more residual P availability from 90 kg P2O5 ha− 1 applied treatment in rice which reduced the immobilization of P and in turn the succeeding crop received more P from that particular treatment. Subbarao et al. [47] also reported a significant effect on plant height and LAI of wheat due to residual P applied in soybean under typic haplustert of Central India. Majeed et al. [48] reported that different levels of P had a positive influence on the growth and development of the wheat crop. Among the Si application, plant height and LAI were found higher with 120 kg Si ha− 1 which was statistically similar with 80 kg Si ha− 1. The plant height and LAI of wheat increased progressively with the advancement of crop stages. It might be because at early growth stages plant requires a small amount of Si input which was easily available from innate soil while at later stages crop requires a large amount of Si which was available from residual Si applied in the previous crop. It might also be due to the higher availability of Si from calcium silicate and its other beneficial effect like effective utilization of nutrients through the extensive root system developed by crop plants this in turn, resulted in higher growth in the wheat crop. Singh et al. [49] also observed increased plant height and LAI at all growth stages of rice due to Si application through calcium silicate. Patel et al. [34] reported the residual effect of Si on plant growth of succeeding wheat crop, and they opined increased plant growth due to increased stimulation of cell division, photosynthetic process as well as the formation of chlorophyll.
Table 2
The residual effect of P and Si application on plant height and LAI of succeeding wheat crop (pooled data of 2 years)
Treatment
|
Plant height (cm)
|
LAI
|
Grain yield
(t ha− 1)
|
30
DAS
|
60
DAS
|
90
DAS
|
Harvest
|
30
DAS
|
60
DAS
|
90
DAS
|
Phosphorus levels (kg P2O5 ha− 1)
|
0
|
26.8
|
45.6
|
76.3
|
86.0
|
0.27
|
1.78
|
3.90
|
4.81
|
30
|
27.5
|
47.9
|
78.0
|
88.0
|
0.28
|
1.84
|
4.22
|
5.24
|
60
|
29.5
|
50.6
|
82.6
|
94.4
|
0.29
|
2.24
|
4.93
|
5.78
|
90
|
29.6
|
52.1
|
83.3
|
96.1
|
0.32
|
2.34
|
5.14
|
6.01
|
SEm±
|
1.1
|
1.0
|
1.5
|
2.2
|
0.01
|
0.05
|
0.13
|
0.14
|
LSD (P = 0.05)
|
NS
|
3.0
|
4.5
|
6.4
|
NS
|
0.14
|
0.39
|
0.40
|
Silicon levels (kg Si ha− 1)
|
0
|
27.6
|
46.1
|
76.0
|
85.9
|
0.27
|
1.76
|
3.82
|
4.19
|
40
|
28.5
|
47.9
|
77.8
|
88.3
|
0.28
|
1.83
|
4.19
|
5.47
|
80
|
28.9
|
50.2
|
81.2
|
93.1
|
0.31
|
2.25
|
5.01
|
6.08
|
120
|
30.3
|
51.9
|
85.1
|
97.3
|
0.30
|
2.37
|
5.17
|
6.11
|
SEm±
|
1.1
|
1.0
|
1.5
|
2.2
|
0.01
|
0.05
|
0.13
|
0.14
|
LSD (P = 0.05)
|
NS
|
3.0
|
4.5
|
6.4
|
NS
|
0.14
|
0.39
|
0.40
|
DAS = days after sowing; NS = Non significant |
3.2 Crop Growth Indices
Data about mean CGR, RGR, and NAR were presented in Table 3. The CGR, RGR, and NAR at 30–60 DAS were found non-significant due to the application of Si and P. Among P levels at 60–90 and 90–120 DAS the maximum CGR, RGR, and NAR were obtained with 90 kg P2O5 ha− 1 and found statistically similar with 60 kg P2O5 ha− 1. The increase in CGR, RGR, and NAR might be due to an increase in dry matter accumulation with the application of P which created a favorable environment [50]. The higher values of growth parameters and yield of upland rice were recorded during the first and second years of residual P applied in Ultisols [51]. The growth of the wheat crop was improved significantly owing to the residual effect of P applied in the low-humic Andosol of Japan [52]. Among Si levels at 60–90 and 90–120 DAS higher CGR, RGR, and NAR were recorded with 120 kg Si ha− 1 and found statistically similar with 80 kg Si ha− 1. The lowest CGR, RGR, and NAR were recorded under control treatment. An increase in CGR, RGR, and NAR was attributed to the increased photosynthetic capacity of the leaves and higher dry matter accumulation with improved nutrition of the plants by Si application [34]. A higher crop growth rate was reported due to the residual effect of Si application in wetland rice under hilly and coastal regions of South India [53].
Table 3
The residual effect of P and Si application on plant height and LAI of succeeding wheat crop (pooled data of 2 years)
Treatment
|
CGR (g m− 2 day− 1)
|
RGR (mg g− 1 day− 1)
|
NAR (g m− 2 leaf area day− 1)
|
30–60
DAS
|
60–90
DAS
|
90–120
DAS
|
30–60
DAS
|
60–90
DAS
|
90–120 DAS
|
30–60
DAS
|
60–90
DAS
|
90–120 DAS
|
Phosphorus levels (kg P2O5 ha− 1)
|
0
|
5.41
|
10.6
|
20.9
|
70.7
|
31.4
|
25.9
|
5.04
|
3.40
|
1.87
|
30
|
5.62
|
10.7
|
21.5
|
71.5
|
32.3
|
26.2
|
5.28
|
3.50
|
1.98
|
60
|
5.77
|
11.1
|
22.7
|
71.6
|
33.0
|
27.1
|
5.31
|
3.93
|
2.08
|
90
|
5.78
|
11.9
|
24.1
|
72.0
|
34.4
|
29.7
|
5.66
|
4.20
|
2.15
|
SEm±
|
0.14
|
0.3
|
0.6
|
0.8
|
0.7
|
0.9
|
0.30
|
0.16
|
0.09
|
LSD (P = 0.05)
|
NS
|
0.8
|
1.7
|
NS
|
2.1
|
2.7
|
NS
|
0.45
|
0.25
|
Silicon levels (kg Si ha− 1)
|
0
|
5.48
|
10.6
|
21.5
|
70.7
|
31.8
|
25.8
|
4.96
|
3.34
|
1.79
|
40
|
5.70
|
10.9
|
21.4
|
71.5
|
32.3
|
26.2
|
5.25
|
3.41
|
1.97
|
80
|
5.83
|
11.0
|
22.5
|
71.6
|
32.8
|
27.4
|
5.52
|
4.03
|
2.11
|
120
|
5.74
|
11.8
|
23.9
|
72.0
|
34.2
|
29.5
|
5.57
|
4.25
|
2.21
|
SEm±
|
0.14
|
0.3
|
0.6
|
0.8
|
0.7
|
0.9
|
0.30
|
0.16
|
0.09
|
LSD (P = 0.05)
|
NS
|
0.8
|
1.7
|
NS
|
2.1
|
2.7
|
NS
|
0.45
|
0.25
|
DAS = days after sowing; NS = Non significant |
3.3 Grain Yield
The grain yield of wheat was significantly influenced due to the residual effect P and Si applied in the preceding rice crop (Table 2). The residual effect of 120 kg Si and 90 kg P2O5 ha− 1 significantly improved the grain yield of the succeeding wheat crop by 24–45%. The higher grain yield was received with 90 kg P2O5 ha− 1 and found statistically similar with 60 kg P2O5 ha− 1. The crop performed better under this treatment because residual P was released gradually and continuously throughout the whole crop growth cycle. According to Rehman et al. [54], as compared to other nutrients, plant recovery of applied P fertilizer is relatively poor, with just 10–20 percent of applied P fertilizer accessible to the present crop and the remainder available to succeeding crops [51]. Phosphate fertilizers can have long-term residual impacts on following crops, and the amount of soil P progressively rises as residues build, contributing more to the P pool accessible to developing plants [55]. Among Si levels, maximum grain yield was recorded with 120 kg Si ha− 1 and found statistically similar with 80 kg Si ha− 1. A strong positive linear relationship was observed between grain yield and Si application (R2 = 0.8430, P < 0.05, Fig. 3). This result was mainly justified by higher number of spike m− 2 and filled grains spike− 1. The significantly higher wheat grain yield was recorded due to the residual effect of Si applied in rice crops [34]. The improvement in yield could be attributable to enhancement in growth and yield attributes as a result of higher photosynthetic efficiency following Si treatment, or it could be due to an improvement in root growth and increased P availability as a result of Si application [36].
3.4 Soil Enzyme Activity
3.4.1 Dehydrogenase Activity (DHA)
The P and Si fertilization had tremendous impact on DHA at 60 DAS & harvest over the control (Table 4). The residual effect of 120 kg Si and 90 kg P2O5 ha− 1 increased the dehydrogenase activity by 17.2% over control. With 60 kg P2O5 ha− 1, the highest soil DHA at 60 DAS (247.3 g TPF g− 1 day− 1) and harvest (116.8 g TPF g− 1 day− 1) were attained, and 90 kg P2O5 ha− 1 was found to be equivalent. The increased availability of leftover P from the previous crop created favorable habitat for soil-dwelling microorganisms [56]. When compared to 60 DAS, DHA levels in all treatments decreased considerably after crop harvest. DHA levels may have dropped since wheat is nutrient-feeder-crop, and numerous organic chemicals produced in the rhizosphere have decreased since wheat harvest. According to Kumari et al. [57], treatment with a soil application of P increased DHA. The addition of P to soil may impact microbial growth and enzyme activity, potentially resulting in a rise in biochemical process rates in the soil environment. The maximum soil DHA at 60 DAS (249.2 g TPF g− 1 day− 1) and harvest (118.3 g TPF g− 1 day− 1) were observed with 80 kg Si ha− 1, which was shown to be comparable to 120 kg Si ha− 1. In the control treatment of Si and P, the lowest levels of soil DHA were obtained. The activity of dehydrogenase was considerably increased when K-silicate was applied [58]. In the faba bean rhizosphere, fertilization of K-silicate promotes above and below ground growth of the plant, leading to increased microbial biomass and, indirectly, improve the soil enzymatic activities [59–60]. Furthermore, K-silicate may increase the availability of N which eventually improves soil enzyme activity [61–62].
Table 4
Residual effect of P and Si application on soil enzyme activities of succeeding wheat crop (pooled data of 2 years)
Treatment
|
DHA
(µg TPF g− 1 day− 1)
|
MBC
(µg g− 1)
|
FDA
(µg Fluorescein g− 1 hr− 1)
|
APA
(µg p-nitrophenol g− 1 h− 1)
|
60 DAS
|
Harvest
|
60 DAS
|
Harvest
|
60 DAS
|
Harvest
|
60 DAS
|
Harvest
|
Phosphorus levels (kg P2O5 ha− 1)
|
0
|
199.9
|
98.5
|
163.5
|
143.1
|
2.91
|
1.20
|
50.9
|
21.3
|
30
|
217.7
|
107.5
|
179.0
|
162.6
|
3.03
|
1.42
|
57.8
|
23.8
|
60
|
247.3
|
116.8
|
223.8
|
191.7
|
3.28
|
1.61
|
69.2
|
36.8
|
90
|
235.2
|
112.1
|
214.7
|
180.3
|
3.23
|
1.54
|
73.8
|
39.9
|
SEm±
|
11.1
|
2.8
|
6.0
|
6.2
|
0.09
|
0.04
|
2.25
|
1.55
|
LSD (P = 0.05)
|
32.0
|
8.2
|
17.3
|
17.8
|
0.25
|
0.11
|
6.49
|
4.47
|
Silicon levels (kg Si ha− 1)
|
0
|
201.0
|
96.9
|
163.5
|
131.2
|
2.85
|
1.35
|
54.7
|
24.4
|
40
|
215.3
|
105.3
|
177.8
|
140.9
|
3.05
|
1.39
|
59.0
|
25.3
|
80
|
249.2
|
118.3
|
226.6
|
209.5
|
3.31
|
1.55
|
66.7
|
36.0
|
120
|
234.7
|
114.5
|
213.0
|
196.1
|
3.25
|
1.49
|
71.2
|
36.2
|
SEm±
|
11.1
|
2.8
|
6.0
|
6.2
|
0.09
|
0.04
|
2.25
|
1.55
|
LSD (P = 0.05)
|
32.0
|
8.2
|
17.3
|
17.8
|
0.25
|
0.11
|
6.49
|
4.47
|
DHA = dehydrogenase activity; MBC = microbial biomass carbon; FDA = fluorescein diacetate activity; APA = Alkaline phosphatase activity |
3.4.2 Microbial Biomass Carbon (MBC)
Soil microbial biomass, a living component of soil organic matter, functions as a labile reservoir for plant-available N, P, and S and acts as a transformation agent for both added and native organic matter [63]. The data about MBC recorded at 60 DAS and at harvest also showed similar trends as observed in the case of soil DHA (Table 4). The residual effect of 120 kg Si and 90 kg P2O5 ha− 1 increased the SMBC by 33.5% as compared to the control. The maximum MBC was observed with 60 kg P2O5 ha− 1 at both stages and found statistically similar with 90 kg P2O5 ha− 1. The value of MBC decreased in all treatments after the crop was harvested, compared to 60 DAS, which might be attributed to decreased root activity after harvest. The residual P enhanced the growth of crop and vegetation subsequently resulted in increased soil organic matter (SOM) content. The soluble C compounds from SOM consequently induced MBC [64]. Microbial biomass is a minor component of SOM, yet it is critical for nutrient cycling and SOM stability [65]. In the case of Si fertilization highest MBC was recorded with 80 kg Si ha− 1 at both stages and found statistically similar with 120 kg Si ha− 1. Control treatment of Si and P recorded the lowest values of MBC during both years. Das et al. [66] reported that application of Si fertilizer (steel slag) enhanced MBC and soil enzyme activities of rice in Korea which might be due to improved growth of microbes and subsequently SOM resulted in higher MBC.
3.4.3 Alkaline Phosphatase Activity (APA)
The residual effect of Si and P application accomplished in the previous crop showed significant influence on APA at 60 DAS and harvest stages (Table 4). The residual effect of 120 kg Si and 90 kg P2O5 ha− 1 increased the APA by 37.5% over control. Soil APA was higher at 60 DAS and declined at harvesting. The maximum values of APA at 60 DAS and harvest were recorded with residual 90 kg P2O5 ha− 1 and found statistically similar with 60 kg P2O5 ha− 1. Due to increased microbial populations in the rhizosphere and the excretion of plant root enzymes, Sarapatka et al. [67] found that residual P enhanced APA in the rhizosphere. Phosphatases are secreted by plant roots and can cause the hydrolysis of some organic phosphates [68]. The lowest values of APA were recorded with the control treatment. Among Si levels, maximum APA at 60 DAS and at harvest was recorded with residual 120 kg Si ha− 1 and found at par with 80 kg Si ha− 1. Applied Si, on the other hand, increased the activity of APA in soil, resulting in more plant-available P via phosphorylation for improved rice plant growth and development, according to Guo et al. [69]. External application of Si may result in the greater synthesis of root exudates and enhanced microbial activity in the rhizosphere zone, explaining the positive connection between Si and APA [70].
3.4.4 Fluorescein Diacetate Activity (FDA)
The data showed that FDA was significantly influenced by levels of Si and P at 60 DAS and harvest (Table 4). The residual effect of 120 kg Si and 90 kg P2O5 ha− 1 increased the FDA by 12.4% over control. FDA activity was higher at 60 DAs and declined at harvesting. The maximum value of FDA was recorded with 60 kg P2O5 ha− 1 at 60 DAS and at harvest. The lower FDA was observed with control treatment. Kumawat et al. [71] recorded the highest values of FDA with 100% recommended dose of P under maize-wheat cropping system in semi-arid agro-ecology of Northern India. FDA was found to be greater in rhizospheric soil than in non-rhizospheric soil. This might be because microbial communities in the rhizosphere have higher oxidative functional activity than bulk soil. According to Yang et al. [72], this increased oxidative functional activity might be attributed to the higher carbon supplies in the rhizosphere soil, which are thought to be the driving force for microbial activity and density. Among Si applications, maximum FDA at 60 DAS and harvest was obtained with residual 80 kg Si ha− 1 and found statistically similar with 120 kg Si ha− 1. The lowest FDA was obtained with control treatment during both years. FDA was recorded at its maximum (2.96 g fluorescein g− 1 h− 1) in soil treated with SiO2, according to Kukreti et al. [73]. Increased enzyme activity in treated soil might be linked to an increase in the microbial population. The findings show that applying Si to soil might help improve plant and soil health by increasing microbial population and enzyme activity.
3.5 N Concentration and Uptake
The N concentration and uptake both in grain and straw were significantly influenced by residual Si and P. The residual Si and P improved the N concentration in grain and straw by 13.2 and 32.3%, respectively, over control (Table 5). The higher N concentration in grain (2.04%) and straw (0.65%) was recorded with residual 90 kg P2O5 ha− 1 and found statistically similar with 60 kg P2O5 ha− 1. A similar trend was also found with N uptake both in grain and straw. The maximum N uptake by grain (125.6 kg ha− 1), straw (55.4 kg ha− 1), and total uptake (181 kg ha− 1) was recorded with residual 90 kg P2O5 ha− 1 (Table 6). Residual P increased the growth of free-living bacteria which secrete certain growth-promoting hormones such as IAA, GA, and cytokinin, responsible for promoting vegetative growth and root development which eventually increased N uptake and concentration in wheat. Singh and Ahlawat [74] found that increasing rates of applied P in wheat up to 80 kg P2O5 ha− 1 resulted in a significant increase in N (159.8 kg ha− 1) uptake as compared to lower levels. Among Si applications, the maximum N concentration in grain (2.07%) and straw (0.62%) was recorded with a residual 120 kg Si ha− 1. A similar trend was also found with N uptake both in grain and straw. The maximum N uptake by grain (129 kg ha− 1), straw (52.2 kg ha− 1), and total uptake (181.1 kg ha− 1) was recorded with a residual 120 kg Si ha− 1. A strong positive linear relationship was observed between Si and N uptake (R2 = 0.8611, P < 0.05, Fig. 4). Residual Si increased the N concentrations in the flag leaves of white oat [75]. This result can be a consequence of improved root growth and N uptake as reported by [76]. Higher NPK uptake in grain was observed when faba bean were treated with K-silicate in Egypt [58].
Table 5
Residual effect of P and Si application on nutrient concentration and NHI of succeeding wheat crop (Pooled data of 2 years)
Treatment
|
Nutrient concentration (%)
|
N
|
P
|
K
|
Si
|
Grain
|
Straw
|
Grain
|
Straw
|
Grain
|
Straw
|
Grain
|
Straw
|
Phosphorus levels (kg P2O5 ha− 1)
|
0
|
1.83
|
0.47
|
0.33
|
0.15
|
0.35
|
1.25
|
0.91
|
1.35
|
30
|
1.86
|
0.55
|
0.42
|
0.17
|
0.47
|
1.35
|
1.06
|
1.56
|
60
|
2.03
|
0.57
|
0.47
|
0.20
|
0.52
|
1.60
|
1.21
|
1.75
|
90
|
2.04
|
0.65
|
0.49
|
0.20
|
0.57
|
1.62
|
1.21
|
1.83
|
SEm±
|
0.06
|
0.03
|
0.02
|
0.01
|
0.02
|
0.05
|
0.02
|
0.07
|
LSD (P = 0.05)
|
0.17
|
0.09
|
0.04
|
0.02
|
0.07
|
0.15
|
0.07
|
0.19
|
Silicon levels (kg Si ha− 1)
|
0
|
1.80
|
0.49
|
0.35
|
0.16
|
0.38
|
1.30
|
0.87
|
1.35
|
40
|
1.87
|
0.56
|
0.41
|
0.17
|
0.47
|
1.42
|
1.09
|
1.55
|
80
|
2.02
|
0.56
|
0.46
|
0.18
|
0.52
|
1.55
|
1.21
|
1.75
|
120
|
2.07
|
0.62
|
0.50
|
0.20
|
0.54
|
1.56
|
1.21
|
1.85
|
SEm±
|
0.06
|
0.03
|
0.02
|
0.01
|
0.02
|
0.05
|
0.02
|
0.07
|
LSD (P = 0.05)
|
0.17
|
0.09
|
0.04
|
0.02
|
0.07
|
0.15
|
0.07
|
0.19
|
Table 6
Residual effect of P and Si application on nutrient uptake (Si, N, P and K) of succeeding wheat crop (Pooled data of 2 years)
Treatment
|
N uptake
(kg ha− 1)
|
P uptake
(kg ha− 1)
|
K uptake
(kg ha− 1)
|
Si uptake
(kg ha− 1)
|
Grain Straw Total
|
Grain Straw Total
|
Grain Straw Total
|
Grain Straw Total
|
Phosphorus levels (kg P2O5 ha− 1)
|
0
|
88.8
|
30.6
|
119.4
|
17.0
|
10.0
|
26.9
|
17.6
|
83.9
|
101.4
|
44.9
|
90.6
|
135.5
|
30
|
97.8
|
42.2
|
140.1
|
22.3
|
12.5
|
34.8
|
25.0
|
103.3
|
128.3
|
56.1
|
116.6
|
172.6
|
60
|
119.7
|
49.5
|
169.2
|
27.7
|
16.9
|
44.6
|
31.0
|
138.3
|
169.3
|
70.2
|
151.1
|
221.3
|
90
|
125.6
|
55.4
|
181.0
|
30.3
|
17.3
|
47.6
|
35.3
|
141.1
|
176.4
|
74.4
|
159.7
|
234.1
|
SEm±
|
5.5
|
2.4
|
5.4
|
1.3
|
0.6
|
1.3
|
1.8
|
4.7
|
5.6
|
1.9
|
5.9
|
6.4
|
LSD (P = 0.05)
|
15.9
|
6.9
|
15.7
|
3.7
|
1.7
|
3.8
|
5.2
|
13.7
|
16.2
|
5.4
|
17.1
|
18.6
|
Silicon levels (kg Si ha− 1)
|
0
|
75.5
|
34.1
|
109.6
|
15.2
|
11.3
|
26.5
|
16.6
|
91.2
|
107.8
|
36.9
|
93.5
|
130.4
|
40
|
102.4
|
44.2
|
146.5
|
22.8
|
13.7
|
36.5
|
26.5
|
114.4
|
140.8
|
60.0
|
123.5
|
183.5
|
80
|
125.2
|
47.2
|
172.4
|
28.2
|
15.3
|
43.6
|
32.0
|
128.8
|
160.8
|
73.9
|
145.5
|
219.4
|
120
|
128.9
|
52.2
|
181.1
|
31.0
|
16.4
|
47.4
|
33.8
|
132.1
|
165.9
|
74.8
|
155.5
|
230.3
|
SEm±
|
5.5
|
2.4
|
5.4
|
1.3
|
0.6
|
1.3
|
1.8
|
4.7
|
5.6
|
1.9
|
5.9
|
6.4
|
LSD (P = 0.05)
|
15.9
|
6.9
|
15.7
|
3.7
|
1.7
|
3.8
|
5.2
|
13.7
|
16.2
|
5.4
|
17.1
|
18.6
|
DAS = days after sowing; NS = Non significant |
3.6 P Concentration and Uptake
P concentration and uptake by wheat were presented in Table 4. Residual Si and P significantly improved the grain and straw content of P by 45 and 29%, respectively, over control (Table 5). The maximum concentration of P in grain (0.49%) and straw (0.20%) was recorded with residual 90 kg P2O5 ha− 1 and found at par with 60 kg P2O5 ha− 1. P uptake by wheat grain and straw has also shown a similar pattern. The maximum P uptake in grain (30.3 kg ha− 1), straw (17.3 kg ha− 1), and total uptake (47.6 kg ha− 1) were recorded with residual 90 kg P2O5 ha− 1 (Table 6). It might be due to the residual effect of P applied in rice which might gradually contribute to wheat. Mehdi et al. [77] observed an increase of P concentration in grain, straw, and their uptake in the wheat crop in all the P treatments except control. Rice plants responded to P fertilizer applied at the start of the trial, according to [52]. Rice dry matter and P uptake were higher in NPK soil than in NK soil, in contrast to wheat. This suggests that the residual P fertilizer in the soil was absorbed by the rice. Among Si applications, maximum P content in grain (0.50%) and straw (0.20 %) were obtained with 120 kg Si ha− 1. However, this treatment was found at par with 80 kg Si ha− 1. A similar trend was obtained with P uptake in grain, straw, and total uptake. The maximum P uptake by grain (31 kg ha− 1), straw (16.4 kg ha− 1), and total uptake (47.4 kg ha− 1) was recorded with a residual 120 kg Si ha− 1. A strong positive linear relationship was observed between Si and P uptake (R2 = 0.9031, P < 0.05, Fig. 4). It could be owing to increased root development and soil P availability with Si application decreased soil P-retention capacity, and higher P solubility, all of which lead to increased phosphatic fertilizer efficiency [78]. P uptake is affected by silicon application; higher yields are more likely to be associated with lower manganese (Mn) toxicity, especially when the P/Mn and P/Fe ratios rise with increasing Si application [79].
3.7 K Concentration and Uptake
The K concentration and uptake both in grain and straw and total uptake by wheat crop were significantly affected by residual Si and P. Residual Si and P significantly improved the grain and straw content of K by 56 and 24.8%, respectively, over control. The maximum K concentration in grain (0.57%) and straw (1.62%) were obtained with 90 kg P2O5 ha− 1 (Table 5). A similar trend was also followed in the case of K uptake both in grain and straw and total uptake. K uptake in grain (35.3 kg ha− 1), straw (141.1 kg ha− 1), and total uptake (176.4 kg ha− 1) were recorded with residual 90 kg P2O5 ha− 1 (Table 6). However, this treatment was found at par with 60 kg P2O5 ha− 1. When compared to other P levels, Sharma et al. [80] found that applying 60 kg P2O5 ha− 1 boosted K uptake considerably in wheat. They claimed that enhanced soil K availability could be related to organic acids generated from solubilizing K from K-bearing minerals, which could have improved K concentration and uptake in plants. With respect to Si levels, higher K concentration in grain (0.54%) and straw (1.56%) were recorded with 120 kg Si ha− 1. This treatment was found at par with 80 kg Si ha− 1. A similar trend was obtained with K uptake and total uptake. The maximum K uptake by grain (33.8 kg ha− 1), straw (132.1 kg ha− 1), and total uptake (165.9 kg ha− 1) of K was recorded with a residual 120 kg Si ha− 1. A strong positive linear relationship was observed between Si and P uptake (R2 = 0.8754, P < 0.05, Fig. 4). Pati et al. [6] found that Si treatment had a favorable effect on rice K concentration and absorption. This has been connected to cell wall silicification. The increase in absorption was mostly attributable to an increase in grain and straw concentration as well as increased yield. According to Chanchareonsook et al. [81], using NPK fertilizer in combination with Si considerably enhanced rice total N, P, and K uptake. According to Singh et al. [25], applying Si to rice boosted K uptake.
3.8 Si Concentration and Uptake
Si concentration and uptake were significantly influenced by residual Si and P. Residual Si and P significantly improved the grain and straw content of K by 35.5 and 36.2%, respectively, over control. Among P applications, the maximum value of Si concentration in grain (1.21%) and straw (1.83 %) was received with 90 kg P2O5 ha− 1 (Table 5). A similar trend was also obtained with Si uptake in grain and straw and the total uptake. Si uptake in grain (74.4 kg ha− 1), straw (159.7 kg ha− 1), and total uptake (234.1 kg ha− 1) were recorded with residual 90 kg P2O5 ha− 1 (Table 6). The amount of silicon in the stem sheath, water-soluble silicon in the soil, soil phosphatase activity, and available P in the soil were all influenced by P fertilizer. This could be owing to the synergistic effects of P and Si fertilizers, which had a significant impact on the Si and total P concentrations in the stem sheath. Previously, similar findings relating Si content in various plant sections were also documented [82]. Among the residual Si, the highest Si concentration in grain (1.21%) and Straw (1.85%) was recorded with 120 kg Si ha− 1. However, this treatment was found at par with a residual 80 kg Si ha− 1. A similar trend was also recorded with Si uptake in grain & straw and the total uptake. Si uptake in grain (74.8 kg ha− 1), straw (155.5 kg ha− 1), and total uptake (203.3 kg ha− 1) were recorded with a residual 120 kg Si ha− 1. The biomass Si content measured at tillering ranged from 1.28 to 1.48 per cent, according to [83]. The Si content of biomass ranged from 0.93 to 1.21 percent at harvest. From tillering until harvest, the Si content of biomass declined steadily, owing to the “dilution effect” as plant growth increased, as well as Si translocation to the grain. Pooja et al. [14] also reported enhanced NPK and Si content at harvest in grain and straw and nutrient uptake by the wheat crop in Si applied treatments over control. This enhanced Si uptake could be attributed to an increase in Si supply, which boosted Si availability to the root system [84–85], allowing the plant to absorb more Si from the soil [28]. The amount of Si applied and Si uptake in above-ground biomass had a strong positive linear relationship (P 0.05, R2 = 0.8471, Fig. 5).
3.9 PCA and Correlation Study
In the present study, PCA comprises two principal components (PC1 and PC2) which explain ~ 15 and 55% of the total variation for nutrient uptake, enzyme activities, growth, and yield, respectively with various treatment combinations (Fig. 6). The correlation range of 1 to -1 was represented by an angle of 0 or 180°, respectively. The PCA biplot can be explained by the positioning of the treatment group and group of measures attributes. The superimposition of the individual plot for treatments on variable plots showed that 60 and 90 kg P2O5 with increasing use of Si improved nutrient uptake, soil enzymes such as FDA and APA along with greater growth and yield of aerobic rice. The correlation study among different variables explained that other than DHA and MBC interaction among plant height, LAI and NAR showed a positive correlation (Fig. 7). Similarly, grain yield was positively correlated with growth, enzymes (except DHA and MBC), and nutrient uptake at p ≤ 0.01.