Soil Microbial Activity
Tillage and weed management practices exerted a significant influence on overall soil microbiological activity at all sampling stages (at 30 DAS after the application of herbicides and during the tasselling stage of maize). The soil microbial activity indices (SMAIs) included soil microbial biomass carbon (SMBC), microbial biomass nitrogen (SMBN), soil basal respiration (SBR), the microbial quotient (qMB) and the metabolic quotient (qCO2) (Fig. 3a, b, c, d, e and 4a, b, c, d, e). These SMAIs were significantly promoted and increased by the adoption of ZT + R(C)-ZT + R(M)-ZT + R(Sr) at both sampling stages of the crop relative to CT(C)-CT(M)-Fallow(NSr) and CT(C)-ZT(M)-ZT(Sr), but not qCO2. Among weed practices, a significant increase in SMAIs was observed with non-weeded control and the combination of chemical weed control and power + 1-hand weeding (IWM) at both sampling stages. The herbicides applied at 30 DAS to maize via chemical weed control and chemical (herbicidal) rotation resulted in a significant reduction in the SMAIs, which later increased until the tasselling stage of the crop. The qCO2 values were significantly lower in the ZT + R(C)-ZT + R(M)-ZT + R(Sr) treatment than in the CT(C)-CT(M)-Fallow (NSr) and CT(C)-ZT(M)-ZT(Sr) treatments at both stages of the crop. With respect to weed management practices, the qCO2 values were significantly lower in the non-weeded control and IWM plots than in the herbicide-treated plots. There were no significant treatment interaction effects on the SMAIs observed during either period of sampling (Fig. 3a, b, c, d, e and 4a, b, c, d, e).
At 30 DAS, for maize, the SMBC, SMBN, SBR, and qMB were significantly greater (7.52% and 26.27%, 11.01% and 28.90%, 0.64% and 17.60%, 15.15% and 15.16%, respectively) under ZT + R(C)-ZT + R(M)-ZT + R(Sr) than under CT(C)-ZT(M)-ZT(Sr) and CT(C)-CT(M)-Fallow (NSr). Among weed management options, after the application of preemergence (PE), early postemergence (EPoE) and postemergence (PoE) herbicides at 30 DAS, 21.41–21.72% and 2.93–3.23% of SMBC, 20.00-21.40% and 14.21%-15.71% of SMBN, 13.73–23.16% and 9.21–19.70% of SBR, and 8.11–21.62% and 9.09–15.91% of qMB were greater under nonweeded control and IWM, respectively, than under chemical (herbicide) rotation and chemical weed control (Fig. 3a, b, c, d, e). During the same sampling period (30 DAS), the ZT + R(C)-ZT + R(M)-ZT + R(Sr) treatment resulted in significant reductions in the qCO2 concentration compared with that in the CT(C)-ZT(M)-ZT(Sr) and CT(C)-CT(M)-Fallow(NSr) groups. There were also significant decreases of 20.24%, 32.60%, 11.23% and 24.99% in the qCO2 concentration in the non-weeded control and IWM treatment groups, respectively, compared to those in the chemical (herbicide) rotation and chemical weed control groups (Fig. 3a, b, c, d, e).
At the tasselling stage, there was an overall progressive increase in the soil microbial activity indices (SMAIs) due to the advancement of the crop. The trends in the SMAIs were similar to those observed at 30 DAS. Among all the tillage practices, ZT + R(C)-ZT + R(M)-ZT + R(Sr) had 10.92% and 26.64% SMBC, 5.53% and 19.04% SMBN, 1.88% and 9.18% SBR, and 2.27% and 13.64% qMB higher than those of CT(C)-ZT(M)-ZT(Sr) and CT(C)-CT(M)-Fallow(NSr), respectively (Fig. 4a, b, c, d, e). With respect to weed management choices, higher percentages of SMBC (10.83–16.11% and 14.46–19.54%), SMBN (11.80- 12.94% and 8.29–9.47%), SBR (5.36–9.67% and 1.58–6.06%), and qMB (9.09–15.91% and 14.89–21.28%) were observed under IWM and non-weeded control, respectively, than under chemical weed control and chemical (herbicide) rotation. During the same stage of the crop (tasselling), the trends in qCO2 were similar to those at 30 DAS, with a further significant decrease observed under ZT + R(C)-ZT + R(M)-ZT + R(Sr) relative to CT(C)-ZT(M)-ZT(Sr) and CT(C)-CT(M)-Fallow(NSr). The non-weeded control and IWM also facilitated a considerable decrease in qCO2 during crop growth compared to chemical (herbicide) rotation and chemical weed control (Fig. 4a, b, c, d, e).
Soil Enzyme Activities
The addition of ZT + R(C)-ZT + R(M)-ZT + R(Sr) and the nonweeded control, as well as the combination of chemical weed control and power + 1 hand weeding (IWM), improved the activities of rhizosphere soil dehydrogenase (DHA), urease (SUA), alkaline and acid phosphatase (AlP and AcP), fluorescein diacetate (FDA) and β-galactosidase (β-GaA), which are involved in soil carbon (C), nitrogen (C) and phosphorus (P) cycling. This improvement in soil enzyme activity in the ZT + R(C)-ZT + R(M)-ZT + R(Sr), nonweeded control and IWM treatment groups was observed at both sampling stages, during which the activity significantly increased continuously with crop progression. Herbicides were applied at 30 DAS; after PE, EPoE, and PoE resulted in a massive decrease in the activity of the soil enzymes, which subsequently returned to their initial levels at the tasselling stage (Table 6a, b, c).
Rhizosphere soil enzyme activity at 30 DAS in maize in the CT(C)-CT(M)-Fallow (NSr) and CT(C)-ZT(M)-ZT(Sr) treatments was significantly lower than that in the ZT + R(C)-ZT + R(M)-ZT + R(Sr) treatment. The DHA, SUA, AlP, AcP, FDA, and β-GaA concentrations were 16.88% and 31.87%, 16.58% and 27.87%, 11.35% and 22.44%, 8.24% and 23.85%, and 12.35% and 19.77%, 9.44% and 16.87% greater, respectively, in the ZT + R(C)-ZT + R(M)-ZT + R(Sr) plots than in the CT(C)-ZT(M)-ZT(Sr) and CT(C)-CT(M)-Fallow (NSr) plots (Table 6a, b, c). Among the weed management options, DHA, SUA, AlP, AcP, FDA, and β-GaA had 17.76–18.68%, 30.28–31.06%, 10.24–11.79% and 25.51–26.79%, 7.37–9.29% and 18.80-20.48%, 2.41–3.81% and 21.12–22.26%, 4.31–4.88% and 24.26–24.71%, 3.89–5.18% and 24.82–25.83% greater under IWM and non-weeded control, respectively, than under chemical weed control and chemical (herbicide) rotation at the same sampling (30 DAS) (Table 6a, b, c).
At the tasselling stage, the activities of all the rhizosphere soil enzymes exhibited trends similar to those observed under the weed management options and tillage practices at 30 DAS. Enzyme activities increased significantly irrespective of the treatment, and tillage was the main factor influencing these activities. During the crop growth development period (tasselling), for DHA, SUA, AlP, AcP, FDA, and β-GaA, the percentages were 10.85% and 20.61%, 10.19% and 15.67%, 15.77% and 28.56%, 5.23% and 23.24%, 21.17% and 35.97%, and 16.71% and 32.88% greater, respectively, under ZT + R(C)-ZT + M)-ZT + R(Sr) than under CT(C)-ZT(M)-ZT(Sr) and CT(C)-CT(M)-Fallow (NSr) (Table 6a, b, c). With regard to weed management choices, for DHA, SUA, AlP, AcP, FDA, and β-GaA, 16.30-16.96% and 20.55–21.18%, 3.95–9.52% and 7.39–12.76%, 12.03–16.10% and 21.52–25.15%, 4.63–5.79% and 8.00-9.09%, 12.64–17.04% and 15.02–19.30%, 5.55–7.89% and 10.53–12.74% higher under IWM and non-weeded control, respectively, than chemical (herbicide rotation) and chemical weed control at the tasselling stage (Table 6a, b, c).
Tillage practices (main treatments) and weed management options interaction effects on DHA was 19.09–25.99%, 9.20-31.97%, 16.87–39.04%, SUA was 7.18–19.25%, 14.32–32.72%, 29.59–32.17% AlP was 7.34–16.98%, 13.22–22.34%, 26.37–34.90%, AcP was 16.04–22.84%, 15.02–18.57%, 27.52–28.01%, FDA was 8.71–19.76%, 21.65–28.80%, 27.41–33.96%, β-GaA was 20.87–26.22%, 26.24–28.48%, 18.21–24.62% higher under ZT + R(C)-ZT + R(M)-ZT + R(Sr) in combination with non-weeded control, CT(C)-ZT(M)-ZT(Sr) on interaction with non-weeded control, CT(C)-CT(M)-Fallow (NSr) in combination with non-weeded control over ZT + R(C)-ZT + R(M)-ZT + R(Sr) in combination with IWM and chemical weed control or chemical (herbicide) rotation, CT-ZT-ZT on interaction with IWM and chemical weed control or chemical (herbicide) rotation, CT(C)-CT(M)-Fallow(NSr) coupled with IWM and chemical weed control or herbicide rotation, respectively observed at 30 DAS of the crop (Table 6a, b, c). A progressive increase in overall rhizosphere soil enzyme activity was observed at the tasselling stage, and the treatment interaction effects (trends) on the activities of various enzymes appeared to be the same as those observed at 30 DAS, with significantly greater enzyme activity observed in the ZT + R(C)-ZT + R(M)-ZT + R(Sr) treatment in combination with the non-weeded control and IWM relative to all the other treatment combinations (Table 6a, b, c).
Table 6a Impact of tillage practices and weed management options on rhizosphere soil dehydrogenase
(µg TPF. g− 1 dry soil. day− 1) and urease (µg NH4+- N. g− 1 dry soil. 2 hr− 1) activity on two different maize plants
growth stages.
Treatment
|
Soil dehydrogenase activity
|
Soil urease activity
|
Tillage
|
WM
|
30 DAS
|
Tasselling
|
30 DAS
|
Tasselling
|
T1: CT(C)-CT(M)-Fallow (NSr)
|
W1
|
21.50
|
43.22
|
31.79
|
65.37
|
W2
|
21.90
|
48.10
|
33.00
|
68.76
|
W3
|
29.32
|
56.24
|
32.06
|
70.84
|
W4
|
35.27
|
62.81
|
46.87
|
77.00
|
T2: CT(C)-ZT(M)-ZT(Sr)
|
W1
|
27.35
|
51.67
|
34.87
|
67.47
|
W2
|
27.71
|
49.84
|
35.07
|
74.43
|
W3
|
36.50
|
66.98
|
44.41
|
78.05
|
W4
|
40.20
|
67.71
|
51.83
|
80.33
|
T3: ZT + R(C)-ZT + R(C)-ZT + R(Sr)
|
W1
|
37.00
|
63.89
|
48.03
|
79.69
|
W2
|
35.28
|
62.11
|
44.63
|
82.41
|
W3
|
38.57
|
68.01
|
51.30
|
85.99
|
W4
|
47.67
|
70.94
|
55.27
|
86.28
|
Tillage (Main plots)
|
T1: CT(C)-CT(M)-Fallow (NSr)
|
27.00
|
52.59
|
35.93
|
70.49
|
T2: CT(C)-ZT(M)-ZT(Sr)
|
32.94
|
59.05
|
41.55
|
75.07
|
T3: ZT + R(C)-ZT + R(C)-ZT + R(Sr)
|
39.63
|
66.24
|
49.81
|
83.59
|
Weed Management (Subplots)
|
W1- Chemical weed control
|
28.62
|
52.93
|
38.23
|
70.84
|
W2- chemical (herbicide) rotation
|
28.30
|
53.35
|
37.57
|
75.20
|
W3- IWM
|
34.80
|
63.74
|
42.59
|
78.29
|
W4- Non-weeded control
|
41.05
|
67.15
|
51.32
|
81.20
|
|
SE(m)±
|
CD
(P = 0.05)
|
SE(m) ±
|
CD
(P = 0.05)
|
SE(m) ±
|
CD
(P = 0.05)
|
SE(m) ±
|
CD
(P = 0.05)
|
Tillage
|
1.83
|
6.29
|
1.24
|
4.99
|
0.79
|
3.10
|
1.23
|
4.85
|
Weed Management
|
0.08
|
0.45
|
0.35
|
1.87
|
0.84
|
2.50
|
0.61
|
1.81
|
Interactions
|
W at same level of T
|
2.02
|
6.48
|
1.02
|
11.07
|
1.46
|
4.33
|
1.06
|
3.14
|
T at same level of W
|
0.31
|
1.36
|
1.00
|
11.09
|
1.49
|
4.42
|
1.54
|
4.56
|
CT = conventional tillage, ZT = zero tillage; R = crop residue retention; IWM = chemical weed control + power and 1 hand weeding; WM = weed management; C = cotton; M = maize; Sr = Sesbania rostrata; CD (P = 0.05) = critical difference at the 5% probability level; Ns = nonsignificant; SE(m) = standard error of the mean.
Table 6
b: Impact of tillage practices and weed management options on rhizosphere soil acid and alkaline phosphatase activity (µg. p-Nitrophenol. g− 1 dry soil. hr− 1) at two different maize growth stages.
Treatment
|
Acid phosphatase activity
|
Alkaline phosphatase activity
|
Tillage
|
WM
|
30 DAS
|
Tasselling
|
30 DAS
|
Tasselling
|
T1: CT(C)-CT(M)-Fallow (NSr)
|
W1
|
45.54
|
122.75
|
117.18
|
221.05
|
W2
|
46.14
|
123.12
|
120.63
|
226.27
|
W3
|
45.85
|
129.64
|
132.52
|
241.76
|
W4
|
63.26
|
130.51
|
179.99
|
251.70
|
T2: CT(C)-ZT(M)-ZT(Sr)
|
W1
|
56.42
|
148.85
|
143.27
|
260.44
|
W2
|
57.35
|
153.19
|
146.79
|
277.31
|
W3
|
58.88
|
157.89
|
160.09
|
275.21
|
W4
|
69.29
|
164.89
|
184.48
|
296.25
|
T3: ZT + R(C)-ZT + R(C)-ZT + R(Sr)
|
W1
|
63.17
|
162.56
|
176.55
|
306.33
|
W2
|
59.25
|
152.59
|
160.50
|
300.42
|
W3
|
64.47
|
167.72
|
179.13
|
337.04
|
W4
|
76.79
|
176.40
|
193.32
|
373.14
|
Tillage (Main plots)
|
T1: CT(C)-CT(M)-Fallow (NSr)
|
50.20
|
126.51
|
137.58
|
235.20
|
T2: CT(C)-ZT(M)-ZT(Sr)
|
60.49
|
156.20
|
157.25
|
277.30
|
T3: ZT + R(C)-ZT + R(C)-ZT + R(Sr)
|
65.92
|
164.82
|
177.38
|
329.23
|
Weed Management (Subplots)
|
W1- Chemical weed control
|
55.04
|
144.72
|
145.66
|
262.61
|
W2- chemical (herbicide) rotation
|
54.25
|
142.97
|
142.64
|
268.00
|
W3- IWM
|
56.40
|
151.75
|
157.25
|
284.67
|
W4- Non-weeded control
|
69.78
|
157.27
|
179.38
|
307.03
|
|
SE(m)±
|
CD
(P = 0.05)
|
SE(m) ±
|
CD
(P = 0.05)
|
SE(m) ±
|
CD
(P = 0.05)
|
SE(m) ±
|
CD
(P = 0.05)
|
Tillage
|
0.80
|
3.15
|
2.34
|
9.18
|
3.06
|
12.02
|
6.38
|
25.04
|
Weed Management
|
0.66
|
1.96
|
1.43
|
4.24
|
3.07
|
9.13
|
4.56
|
13.56
|
Interactions
|
W at same level of T
|
1.14
|
3.39
|
2.47
|
7.35
|
5.32
|
15.81
|
7.9
|
23.48
|
T at same level of W
|
1.27
|
3.78
|
3.17
|
9.42
|
5.53
|
16.44
|
9.36
|
27.79
|
CT = conventional tillage, ZT = zero tillage; R = crop residue retention; IWM = chemical weed control + power and 1 hand weeding; WM = weed management; C = cotton; M = maize; Sr = Sesbania rostrata; CD (P = 0.05) = critical difference at the 5% probability level; SE(m) = standard error of the mean.
Table 6
c: Impact of tillage practices and weed management options on rhizosphere soil fluorescein diacetate (µg. fluorescein. g− 1 dry soil.3 h−1) and β-galactosidase (nmol p-nitrophenol. g− 1 dry soil. hr− 1) activity at two different maize growth stages.
Treatment
|
Fluorescein di-acetate activity
|
β-galactosidase activity
|
Tillage
|
WM
|
30 DAS
|
Tasselling
|
30 DAS
|
Tasselling
|
T1: CT(C)-CT(M)-Fallow (NSr)
|
W1
|
118.91
|
149.97
|
118.25
|
152.92
|
W2
|
130.70
|
172.35
|
120.58
|
159.79
|
W3
|
120.94
|
186.95
|
128.31
|
168.79
|
W4
|
180.06
|
190.21
|
156.88
|
187.71
|
T2: CT(C)-ZT(M)-ZT(Sr)
|
W1
|
132.83
|
199.73
|
128.74
|
192.67
|
W2
|
135.92
|
204.54
|
129.38
|
206.47
|
W3
|
146.18
|
220.52
|
132.76
|
210.06
|
W4
|
186.57
|
236.42
|
180.00
|
221.15
|
T3: ZT + R(C)-ZT + R(C)-ZT + R(Sr)
|
W1
|
169.96
|
240.19
|
148.76
|
243.49
|
W2
|
152.56
|
244.31
|
140.50
|
237.73
|
W3
|
173.57
|
303.62
|
150.70
|
249.57
|
W4
|
190.14
|
304.35
|
190.44
|
266.22
|
Tillage (Main plots)
|
T1: CT(C)-CT(M)-Fallow (NSr)
|
137.65
|
174.87
|
131.01
|
167.30
|
T2: CT(C)-ZT(M)-ZT(Sr)
|
150.38
|
215.30
|
142.72
|
207.59
|
T3: ZT + R(C)-ZT + R(C)-ZT + R(Sr)
|
171.56
|
273.12
|
157.60
|
249.25
|
Weed Management (Subplots)
|
W1- Chemical weed control
|
140.57
|
196.63
|
131.92
|
196.36
|
W2- chemical (herbicide) rotation
|
139.73
|
207.07
|
130.15
|
201.33
|
W3- IWM
|
146.90
|
237.03
|
137.26
|
213.17
|
W4- Non-weeded control
|
185.59
|
243.66
|
175.48
|
225.03
|
|
SE(m)±
|
CD
(P = 0.05)
|
SE(m) ±
|
CD
(P = 0.05)
|
SE(m) ±
|
CD
(P = 0.05)
|
SE(m) ±
|
CD
(P = 0.05)
|
Tillage
|
2.88
|
11.30
|
4.17
|
16.38
|
0.96
|
3.76
|
3.01
|
11.82
|
Weed Management
|
3.02
|
8.97
|
4.37
|
12.97
|
1.62
|
4.81
|
3.08
|
9.14
|
Interactions
|
W at same level of T
|
5.23
|
15.53
|
7.56
|
22.46
|
2.80
|
8.33
|
5.33
|
15.84
|
T at same level of W
|
5.36
|
15.94
|
7.76
|
23.07
|
2.61
|
7.75
|
5.51
|
16.38
|
CT = conventional tillage, ZT = zero tillage; R = crop residue retention; IWM = chemical weed control + power and 1 hand weeding; WM = weed management; C = cotton; M = maize; Sr = Sesbania rostrata; CD (P = 0.05) = critical difference at the 5% probability level; SE(m) = standard error of the mean.
Microbial population
Rhizosphere soil microbial and rhizoplane fungal counts were significantly influenced by different tillage practices and weed management practices, and the interaction effects of the tillage and weed management practices on the soil microbial and rhizoplane fungal populations were significant at both sampling stages (30 DAS and tasselling) (Table 7a and b).
The spraying of the herbicides either in rotation or repeatedly every other year, such as preemergence (PE), early postemergence (EPoE) and postemergence (PoE), at 30 DAS suppressed the growth and population of the microorganisms. Among all weed management options, at 30 DAS, the rhizosphere soils of Azotobacter (Azot), Azospirillum (Azosp), and total fungal (TF) and total fungal (RF) rhizoplane populations were 0.44–0.66% and 3.62–3.84%, 1.40–1.63% and 4.51–4.74%, 0.47-070% and 3.63–3.85%, 1.79–2.04% and 6.55–6.80% greater under IWM and nonweeded control, respectively, than under chemical weed control and chemical (herbicide) rotation (Table 7a, and b). In terms of all the different tillage systems, the rhizosphere soil Azot, Azosp, TF, and rhizoplane TF populations were 1.51% and 2.81%, 1.60% and 3.43%, 1.61% and 2.75%, and 3.69% and 6.39% greater under ZT + R(C)-ZT + R(M)-ZT + R(Sr) than under CT(C)-ZT(M)-ZT(Sr) and CT(C)-CT(M)-Fallow (NSr), respectively, at 30 DAS (Table 7a, and b). The population of rhizosphere soil microorganisms and rhizoplane total fungi (TF) increased significantly during the tasselling period of the crop in all the treatments, and tillage was the principal factor influencing the progressive increase in the microbial population. At that growth stage, for maize crops (tasselling), the populations of rhizosphere soil Azot, Azosp, TF, and rhizoplane TF were 1.20% and 1.80%, 1.21% and 2.23%, 2.38% and 4.75%, and 3.12 and 4.45% greater, respectively, in the ZT + R(C)-ZT + R(M)-ZT + R(Sr) treatment than in the CT(C)-ZT(M)-ZT(Sr) and CT(C)-CT(M)-Fallow (NSr) treatments (Table 7a, and b). A significant difference with a continuous increase in the overall microbial population was observed for all weed management options, possibly due to microorganism recovery from herbicidal injury at tasselling. The patterns of the growth of both the rhizosphere soil and rhizoplane microbial counts at that crop growth stage (tasselling) resembled the trends observed at 30 DAS.
During the initial stage of crop development (30 DAS), the interaction effects of the various treatments (tillage and weed management) on the rhizosphere soil Azotobacter (Azot) were 1.91–3.39%, 3.62–4.26%, and 3.88–4.31%; Azospirillum (Azosp) counts were 2.90–4.24%, 2.71–4.30%, and 4.32–6.36%; total fungal (TF) counts were 2.68–4.25%, 2.51–3.20%, and 3.89–4.35%; rhizoplane total fungal (TF) counts were 2.64–3.84%, 3.41–7.56%, and 8.33–9.31%; and the results were superior to those of the ZT + R(C)-ZT + R(Sr) treatment in combination with the non-weeded control, CT(C)-ZT(M)-ZT(Sr) combined with the non-weeded control, and CT(C)-CT(M)-Fallow (NSr) coupled with the non-weeded control over the ZT + R(C)-ZT + R(M)-ZT + R(Sr) At the tasselling stage of the crop, all microbial counts increased further, regardless of the treatment combination. Among all the treatment interactions, at tasselling of maize, ZT + R(C)-ZT + R(M)-ZT + R(Sr) in combination with the unweeded control had a significantly greater rhizosphere soil microbial and rhizoplane fungal population, which was closely and statistically followed by the interaction of ZT + R(C)-ZT + R(M)-ZT + R(Sr) and IWM in comparison with all the other treatment combinations (Table 7a and b).
The fungal population observations indicated that the rhizosphere soil fungal counts were greater than the rhizoplane fungal counts during both sampling periods (30 DAS and tasselling) in the maize crop (Table 7a and b).
Table 7
a: Impact of tillage practices and weed management options on rhizosphere soil Azotobacter and Azospirillum populations (log CFU g− 1 soil) at two different maize growth stages.
Treatment
|
Azotobacter population
|
Azospirillum population
|
Tillage
|
WM
|
30 DAS
|
Tasselling
|
30 DAS
|
Tasselling
|
T1: CT(C)-CT(M)-Fallow (NSr)
|
W1
|
4.44
|
4.89
|
4.12
|
4.79
|
W2
|
4.46
|
4.91
|
4.13
|
4.81
|
W3
|
4.45
|
4.92
|
4.21
|
4.85
|
W4
|
4.64
|
4.93
|
4.40
|
4.86
|
T2: CT(C)-ZT(M)-ZT(Sr)
|
W1
|
4.50
|
4.94
|
4.23
|
4.87
|
W2
|
4.51
|
4.95
|
4.24
|
4.88
|
W3
|
4.53
|
4.96
|
4.30
|
4.89
|
W4
|
4.70
|
4.98
|
4.42
|
4.89
|
T3: ZT + R(C)-ZT + R(C)-ZT + R(Sr)
|
W1
|
4.62
|
5.01
|
4.34
|
4.90
|
W2
|
4.56
|
5.03
|
4.29
|
4.93
|
W3
|
4.63
|
5.05
|
4.35
|
4.95
|
W4
|
4.72
|
5.08
|
4.48
|
4.99
|
Tillage (Main plots)
|
T1: CT(C)-CT(M)-Fallow (NSr)
|
4.50
|
4.91
|
4.22
|
4.83
|
T2: CT(C)-ZT(M)-ZT(Sr)
|
4.56
|
4.94
|
4.30
|
4.88
|
T3: ZT + R(C)-ZT + R(C)-ZT + R(Sr)
|
4.63
|
5.00
|
4.37
|
4.94
|
Weed Management (Subplots)
|
W1- Chemical weed control
|
4.52
|
4.91
|
4.23
|
4.85
|
W2- chemical (herbicide) rotation
|
4.51
|
4.94
|
4.22
|
4.87
|
W3- IWM
|
4.54
|
4.95
|
4.29
|
4.89
|
W4- Non-weeded control
|
4.69
|
5.00
|
4.43
|
4.91
|
|
SE(m)±
|
CD
(P = 0.05)
|
SE(m) ±
|
CD
(P = 0.05)
|
SE(m) ±
|
CD
(P = 0.05)
|
SE(m) ±
|
CD
(P = 0.05)
|
Tillage
|
0.004
|
0.015
|
0.004
|
0.014
|
0.004
|
0.016
|
0.003
|
0.012
|
Weed Management
|
0.003
|
0.008
|
0.001
|
0.002
|
0.003
|
0.010
|
0.001
|
0.003
|
Interactions
|
W at same level of T
|
0.005
|
0.014
|
0.001
|
0.004
|
0.006
|
0.017
|
0.002
|
0.005
|
T at same level of W
|
0.006
|
0.016
|
0.004
|
0.011
|
0.006
|
0.019
|
0.003
|
0.010
|
CT = conventional tillage, ZT = zero tillage; R = crop residue retention; IWM = chemical weed control + power and 1 hand weeding; WM = weed management; C = cotton; M = maize; Sr = Sesbania rostrata; CD (P = 0.05) = critical difference at the 5% probability level; SE(m) = standard error of the mean.
The table mean values are in log CFU g -1 soil from log transformation of exponential (103) values from CFU g-1 soil (oven dry basis) taken from plate counts.
Table 7
b: Impact of tillage practices and weed management options on the total fungal population of the rhizosphere soil and rhizoplane at two different maize growth stages.
Treatment
|
Rhizosphere soil total fungal population (log CFU g− 1 soil)
|
Rhizoplane total fungal
Population (log CFU g− 1 roots)
|
Tillage
|
WM
|
30 DAS
|
Tasselling
|
30 DAS
|
Tasselling
|
T1: CT(C)-CT(M)-Fallow (NSr)
|
W1
|
4.18
|
4.38
|
3.70
|
4.21
|
W2
|
4.20
|
4.39
|
3.71
|
4.24
|
W3
|
4.19
|
4.42
|
3.74
|
4.30
|
W4
|
4.37
|
4.45
|
4.08
|
4.39
|
T2: CT(C)-ZT(M)-ZT(Sr)
|
W1
|
4.24
|
4.46
|
3.79
|
4.31
|
W2
|
4.25
|
4.49
|
3.81
|
4.32
|
W3
|
4.27
|
4.51
|
3.96
|
4.35
|
W4
|
4.38
|
4.61
|
4.10
|
4.41
|
T3: ZT + R(C)-ZT + R(C)-ZT + R(Sr)
|
W1
|
4.34
|
4.60
|
4.05
|
4.43
|
W2
|
4.28
|
4.61
|
4.01
|
4.45
|
W3
|
4.35
|
4.64
|
4.06
|
4.49
|
W4
|
4.47
|
4.68
|
4.17
|
4.58
|
Tillage (Main plots)
|
T1: CT(C)-CT(M)-Fallow (NSr)
|
4.24
|
4.41
|
3.81
|
4.29
|
T2: CT(C)-ZT(M)-ZT(Sr)
|
4.29
|
4.52
|
3.92
|
4.35
|
T3: ZT + R(C)-ZT + R(C)-ZT + R(Sr)
|
4.36
|
4.63
|
4.07
|
4.49
|
Weed Management (Subplots)
|
W1- Chemical weed control
|
4.25
|
4.48
|
3.85
|
4.32
|
W2- chemical (herbicide) rotation
|
4.24
|
4.50
|
3.84
|
4.34
|
W3- IWM
|
4.27
|
4.52
|
3.92
|
4.38
|
W4- Non-weeded control
|
4.41
|
4.59
|
4.12
|
4.46
|
|
SE(m)±
|
CD
(P = 0.05)
|
SE(m) ±
|
CD
(P = 0.05)
|
SE(m) ±
|
CD
(P = 0.05)
|
SE(m) ±
|
CD
(P = 0.05)
|
Tillage
|
0.003
|
0.014
|
0.006
|
0.024
|
0.007
|
0.029
|
0.005
|
0.022
|
Weed Management
|
0.003
|
0.007
|
0.001
|
0.004
|
0.004
|
0.013
|
0.002
|
0.006
|
Interactions
|
W at same level of T
|
0.004
|
0.013
|
0.003
|
0.008
|
0.008
|
0.023
|
0.003
|
0.010
|
T at same level of W
|
0.005
|
0.015
|
0.007
|
0.019
|
0.010
|
0.030
|
0.006
|
0.018
|
CT = conventional tillage, ZT = zero tillage; R = crop residue retention; IWM = chemical weed control + power and 1 hand weeding; WM = weed management; C = cotton; M = maize; Sr = Sesbania rostrata; CD (P = 0.05) = critical difference at the 5% probability level; SE(m) = standard error of the mean.
The table mean values are in log CFU g-1 soil/roots from log transformation of exponential (103) values from CFU g-1 soil (oven dry basis)/roots taken from plate counts.
Fungal Diversity
Sub-culturing of the fungi from the culture plates was performed prior to sequencing to purify the fungal strains, as depicted in Fig. 5, and agarose gel electrophoresis images of total deoxyribonucleic acid (DNA) and polymerase chain reaction (PCR) products of the 18s rRNa gene are shown in Fig. 6a, b and c. The fungi were identified based on nucleotide sequence homology of the 18 s rRNA gene are presented in Table 8. The results of 18S rRNA gene sequencing indicated that Talaromyces flavus var. flavus (5-PJTSAU-KNIGHT-23) was identified under the T3: ZT + R(C)-ZT + R(M)-ZT + R(Sr) and W3: IWM combinations (T3W3) and T2: CT(C)-ZT(M)-ZT(Sr) on interaction with IWM (T2W3). The other species of rhizosphere soil fungal and rhizoplane fungal isolates, viz., Aspergillus niger, Penicillium limosum, Aspergillus terreus, Apiospora serenensis, Zasmidium cellare, and Ochraceocephala foeniculi, were identified under the T1: CT(C)-CT(M)-Fallow (NSr), T2: CT(C)-ZT(M)-ZT(Sr) and T3: ZT + R(C)-ZT + R(M)-ZT + R(Sr) tillage (main treatments) in combination with the W1: chemical weed control, W2: chemical (herbicide) rotation and W4: non-weeded control (sub-treatments) (Table 8). The isolate ID (8-PJTSAU-KNIGHT), which was isolated abundantly from the rhizoplane zone across all the tillage and weed management treatments, was identified as Penicillium limosum. Phylogenetic tree(s) of all the 8 identified fungal species and multiple sequence alignments (MSAs) of the data are included in the supplementary data.
Table 8
Impact of tillage and weed management practices on fungal diversity at the tasselling stage of winter maize.
Rhizosphere soil fungal microbe (s)
|
S.NO
|
Isolate ID
|
Treatment combination
|
Fungal name
|
Identity
(%)
|
Accession
numbers
|
1
|
1-PJTSAU-KNIGHT-23
|
T1W1
|
Aspergillus niger
|
100.00%
|
PP177339
|
1-PJTSAU-KNIGHT-23
|
T1W2
|
Aspergillus niger
|
1-PJTSAU-KNIGHT-23
|
T1W4
|
Aspergillus niger
|
2
|
2-PJTSAU-KNIGHT-23
|
T1W3
|
Aspergillus niger
|
100.00%
|
PP177340
|
3
|
3-PJTSAU-KNIGHT-23
|
T2W1
|
Aspergillus terrus
|
99.33%
|
PP177341
|
4
|
4-PJTSAU-KNIGHT-23
|
T2W2
|
Apiospora serenensis
|
98.47%
|
PP177342
|
4-PJTSAU-KNIGHT-23
|
T3W2
|
5
|
5-PJTSAU-KNIGHT-23
|
T2W3
|
Taloromyces flavus var. flavus
|
99.63%
|
PP177343
|
5-PJTSAU-KNIGHT-23
|
T3W3
|
6
|
6-PJTSAU-KNIGHT-23
|
T2W4
|
Zasmidium cellare
|
100.00%
|
PP177344
|
7
|
7-PJTSAU-KNIGHT-23
|
T3W1
|
Penicillium limosum
|
99.88%
|
PP177345
|
7-PJTSAU-KNIGHT-23
|
T3W4
|
Rhizoplane fungal microbe (s)
|
8
|
8-PJTSAU-KNIGHT-23
|
Abundant in all T & W combinations
|
Ochraceocephala foeniculi
|
96.55%
|
PP177346
|
Main treatments: T
1 = CT(C)-CT(M)-Fallow (N
Sr); T
2 = CT(C)-ZT(M)-ZT(
Sr); T
3 = ZT + R(C)-ZT + R(M)-ZT + R(
Sr);
Sub-treatments: W
1 = chemical weed control; W
2 = chemical (herbicide) rotation; W
3 = chemical weed control and power + 1 hand weeding; W
4 = non-weeded control. T = Tillage; W = Weed Management, CT = Conventional Tillage, ZT = Zero Tillage; C = Cotton; M = Maize;
Sr =
Sesbania rostrata.