Soil solarization with thin transparent polythene sheet resulted in increase in the average maximum soil temperature (Table 1).In solarized beds, highest average weekly temperature of 41.8°C was recorded at 5 cm depth followed by 38.2 and 33.6°C temperature at 10 and 15 cm soil depth, respectively in comparison to 36.4°C (5 cm), 32.6°C (10 cm) and 29.4°C (15 cm) in unsolarized nursery beds. In the present studies, maximum rise of 5.4°C in the average weekly maximum soil temperature was recorded in solarized beds at 5cm depths over unsolarized beds.
Table 1
Effect of soil solarization on soil temperature of nursery site
Duration (week) | Temperature (°C) in solarized beds | Temperature (°C) in non-solarized beds |
5 cm | 10 cm | 15cm | Overall Mean | 5 cm | 10 cm | 15cm | Overall Mean |
1 | 35.7 | 31.6 | 28.7 | 32 | 32.8 | 28.9 | 26.5 | 29.4 |
2 | 39.6 | 36.8 | 31.4 | 35.9 | 36.3 | 32.7 | 30.2 | 33.1 |
3 | 41.3 | 39.1 | 34.2 | 38.2 | 35.5 | 31.4 | 29.2 | 32.7 |
4 | 37.8 | 34.6 | 29.9 | 34.1 | 33.8 | 30.4 | 27.6 | 30.6 |
5 | 43.2 | 40.5 | 34.8 | 39.5 | 36.1 | 33.1 | 29.7 | 33.8 |
6 | 46.9 | 41.5 | 37.1 | 41.8 | 39.0 | 34.6 | 30.6 | 35.1 |
7 | 48.2 | 43.3 | 38.8 | 43.4 | 41.2 | 37.2 | 31.7 | 37.2 |
Mean | 41.8 | 38.2 | 33.6 | - | 36.4 | 32.6 | 29.4 | - |
There are number of reports from around the world which conclusively prove that soil solarization with transparent polyethylene mulch result in increase in the soil temperature. Jayaraj and Radhakrishnan (2008) reported that soil solarization with transparent polyethylene sheet for 5 weeks resulted in increase in the average soil temperature in solarized plots to the level of 46 and 36°C at 10 and 20 cm depths, respectively in comparison to 28 and 24°C in non-solarized plots at the similar depths. Khulbe (2019) reported that soil solarization with thin transparent polyethylene sheet (50 gauge) resulted in average maximum temperature of 52°C at 5 cm soil depth, which was 12.9°C higher over non-solarized beds.
Effect of soil solarisation and cauliflower leaves on the viability of the test pathogens under field conditions
In general, soil solarization with thin transparent polythene sheet reduced the viability of all the four pathogens (Tables 2, 3, 4 and 5). Treatment combination of soil solarization with transparent polyethylene mulch for 40 days with soil amendment of cauliflower leaves was found most effective in reducing the viability of Pythium ultimum, Fusarium oxysporum, Rhizoctonia solani and Sclerotium rolfsii to 5.3, 2.6, 4.6 and 3.6 per cent, respectively. Soil solarization alone with transparent polyethylene mulch for 40 days was next in efficacy with 11.0 per cent reduction of viable propagules in Pythium ultimum, 5.6 per cent reduction in Fusarium oxysporum, 9.3 per cent sclerotial reduction in Rhizoctonia solani and 7.3 per cent sclerotial reduction in Sclerotium rolfsii. Biofumigation with soil amendment of cauliflower leaves for 40 days was found least effective with 78.0, 70.3, 73.3 and 75.0 percent viability of P. ultimum, F. oxysporum, R. solani and S. rolfsii, respectively (Fig. 4,5,6,7). Duration of soil solarization also significantly affected the viability of the pathogens. Increase in duration of soil solarization from 0 to 40 days resulted in significant reduction in the viability of the pathogens. Soil depth also played a significant role in the efficacy of different treatments. Soil solarization was found more effective at upper soil layers (5 cm) soil depth than at lower (10 cm) soil depth. Triki et al. (2001) reported that soil solarization for 60 days during summer months was effective in reducing the inoculum levels of Fusarium solani from 3,000 to 450 c.f.u per gram of dry soil to a depth of 0–30 cm and inoculum levels of Pythium aphanidermatum were reduced from 1,700 and 3,000 to 0.5 and 1 propagule per gram of dry soil in the top 0–15 cm and 15–30 cm depth, respectively. Jayaraj and Radhakrishnan (2008) reported that soil solarization for 5 weeks reduced population of Pythium spp. from 56.6 (×103 CFU g − 1) to 15.6 (×103 CFU g− 1). Melero-Vara et al. (2011) also reported that soil solarization with plastic film (40µ thick) reduced the average viability of propagules of Fusarium oxysporum f.sp. dianthi by 65.0 per cent in comparison to unsolarized beds. Similar results have been reported by different workers from different parts of the world (Vannacci et al., 1993; Apodaca et al., 2002; Saremi et al., 2010).
Table 2
Effect of time duration of soil solarization on the viability of Pythium ultimum
Treatment | Per cent Viability of Pythium ultimum | Overall mean |
0 days | 15 days | 30 days | 40 days |
5 cm | 10 cm | 5 cm | 10 cm | 5 cm | 10 cm | 5 cm | 10 cm |
Transparent polyethylene mulching | 100.0 (10.05) | 100.0 (10.05) | 39.33 (6.34) | 53.33 (7.37) | 24.33 (5.02) | 47.67 (6.97) | 11.00 (3.45) | 36.33 (6.10) | 51.50 (6.92) |
Transparent polyethylene mulching + soil amendment with cauliflower leaves | 100.0 (10.05) | 100.0 (10.05) | 31.00 (5.65) | 46.33 (6.88) | 21.33 (4.71) | 38.33 (6.27) | 5.33 (2.51) | 23.00 (4.89) | 45.67 (6.37) |
Soil amendment with cauliflower leaves | 100.0 (10.05) | 100.0 (10.05) | 97.67 (9.93) | 100.00 (10.05) | 88.33 (9.45) | 95.67 (9.83) | 78.00 (8.89) | 87.33 (9.40) | 93.62 (9.71) |
Control (without mulch) | 100.0 (10.05) | 100.0 (10.05) | 100.00 (10.05) | 100.00 (10.05) | 98.33 (9.97) | 100.00 (10.05) | 92.67 (9.68) | 98.00 (9.95) | 98.62 (9.98) |
Mean | 100.0 (10.05) | 100.0 (10.05) | 67.00 (7.99) | 74.92 (8.59) | 58.08 (7.29) | 70.42 (8.28) | 46.75 (6.13) | 61.17 (7.58) | - |
Figures in parentheses are square root transformed values |
CD (0.05) |
Days (0.14) |
Depth (0.10) |
Days×Depth (0.19) |
Treatment (0.14) |
Days×Treatment (0.27) |
Depth×Treatment (0.19) |
Days× Depth×Treatment (0.39) |
Table 3
Effect of time duration of soil solarization on the viability of Fusarium oxysporum
Treatment | Per cent Viability of Fusarium oxysporum | Overall mean |
0 days | 15 days | 30 days | 40 days |
5 cm | 10 cm | 5 cm | 10 cm | 5 cm | 10 cm | 5 cm | 10 cm |
Transparent polyethylene mulching | 100.0 (10.05) | 100.0 (10.05) | 25.67 (5.15) | 41.33 (6.50) | 17.67 (4.31) | 39.33 (6.35) | 5.67 (2.58) | 21.33 (4.70) | 43.88 (6.21) |
Transparent polyethylene mulching + soil amendment with cauliflower leaves | 100.0 (10.05) | 100.0 (10.05) | 20.67 (4.65) | 37.33 (6.18) | 13.67 (3.82) | 27.00 (5.29) | 2.67 (1.90) | 13.67 (3.82) | 39.36 (5.72) |
Soil amendment with cauliflower leaves | 100.0 (10.05) | 100.0 (10.05) | 93.67 (9.73) | 97.33 (9.92) | 79.33 (8.96) | 82.67 (9.14) | 70.33 (8.44) | 77.67 (8.87) | 87.63 (9.40) |
Control (without mulch) | 100.0 (10.05) | 100.0 (10.05) | 100.00 (10.05) | 100.00 (10.05) | 88.67 (9.47) | 91.67 (9.63) | 77.33 (8.85) | 83.33 (9.18) | 92.63 (9.67) |
Mean | 100.0 (10.05) | 100.0 (10.05) | 60.00 (7.40) | 69.00 (8.16) | 49.83 (6.64) | 60.17 (7.60) | 39.00 (5.44) | 49.00 (6.64) | |
Figures in parentheses are square root transformed values |
CD (0.05) |
Days (0.14) |
Depth (0.10) |
Days×Depth (0.19) |
Treatment (0.14) |
Days×Treatment (0.27) |
Depth×Treatment (0.19) |
Days× Depth×Treatment (0.39) |
Table 4
Effect of time duration of soil solarization on the viability of Rhizoctonia solani
Treatment | Per cent Viability of Rhizoctonia solani | Overall mean |
0 days | 15 days | 30 days | 40 days |
5 cm | 10 cm | 5 cm | 10 cm | 5 cm | 10 cm | 5 cm | 10 cm |
Transparent polyethylene mulching | 100.0 (10.05) | 100.0 (10.05) | 30.00 (5.56) | 44.67 (6.75) | 20.67 (4.64) | 40.33 (6.43) | 9.33 (3.20) | 26.67 (5.23) | 46.46 (6.49) |
Transparent polyethylene mulching + soil amendment with cauliflower leaves | 100.0 (10.05) | 100.0 (10.05) | 25.33 (5.12) | 37.67 (6.20) | 13.67 (3.82) | 31.00 (5.65) | 4.67 (2.37) | 16.33 (4.14) | 41.08 (5.92) |
Soil amendment with cauliflower leaves | 100.0 (10.05) | 100.0 (10.05) | 94.67 (9.78) | 97.67 (9.93) | 82.33 (9.13) | 86.00 (9.33) | 73.33 (8.62) | 80.67 (9.04) | 89.33 (9.49) |
Control (without mulch) | 100.0 (10.05) | 100.0 (10.05) | 100.00 (10.05) | 100.00 (10.05) | 93.67 (9.73) | 98.33 (9.97) | 83.33 (9.18) | 90.67 (9.57) | 95.75 (9.83) |
Mean | 100.0 (10.05) | 100.0 (10.05) | 62.50 (7.63) | 70.00 (8.23) | 52.58 (6.83) | 63.92 (7.84) | 42.67 (5.85) | 53.58 (7.00) | |
Figures in parentheses are square root transformed values |
CD (0.05) |
Days (0.13) |
Depth (0.09) |
Days×Depth (0.19) |
Treatment (0.13) |
Days×Treatment (0.26) |
Depth×Treatment (0.19) |
Days× Depth×Treatment (0.37) |
Table 5
Effect of time duration of soil solarization on the viability of Sclerotium rolfsii
Treatment | Per cent Viability of Sclerotium rolfsii | Overall mean |
0 days | 15 days | 30 days | 40 days |
5 cm | 10 cm | 5 cm | 10 cm | 5 cm | 10 cm | 5 cm | 10 cm |
Transparent polyethylene mulching | 100.0 (10.05) | 100.0 (10.05) | 34.00 (5.90) | 48.33 (7.02) | 22.67 (4.85) | 43.33 (6.65) | 7.33 (2.87) | 29.67 (5.53) | 48.17 (6.62) |
Transparent polyethylene mulching + soil amendment with cauliflower leaves | 100.0 (10.05) | 100.0 (10.05) | 27.33 (5.32) | 38.67 (6.29) | 18.33 (4.39) | 29.67 (5.53) | 3.67 (2.16) | 18.67 (4.42) | 42.04 (6.03) |
Soil amendment with cauliflower leaves | 100.0 (10.05) | 100.0 (10.05) | 95.67 (9.83) | 98.33 (9.97) | 81.33 (9.07) | 87.67 (9.42) | 75.00 (8.72) | 83.33 (9.18) | 90.17 (9.54) |
Control (without mulch) | 100.0 (10.05) | 100.0 (10.05) | 100.00 (10.05) | 100.00 (10.05) | 95.00 (9.80) | 97.67 (9.93) | 80.33 (9.02) | 94.33 (9.76) | 95.92 (9.84) |
Mean | 100.0 (10.05) | 100.0 (10.05) | 64.25 (7.78) | 71.33 (8.33) | 54.33 (7.03) | 64.59 (7.88) | 41.59 (5.69) | 56.50 (7.22) | |
Figures in parentheses are square root transformed values |
CD (0.05) |
Days (0.13) |
Depth (0.09) |
Days×Depth (0.19) |
Treatment (0.13) |
Days×Treatment (0.27) |
Depth×Treatment (0.19) |
Days× Depth×Treatment (0.38) |
Effect of time duration of soil solarisation and cauliflower leaves on potential of the pathogens to cause the disease in tomato, chili and capsicum
With the increase in the duration of soil solarization from 15 to 40 days at 5cm soil depth, the potential of the pathogens to cause the disease reduced significantly as the incidence of the damping-off reduced from 63.3 to 16.6 per cent in tomato, 66.6 to 20.0 per cent in chilli and 70.0 to 23.3 per cent in capsicum (Table 6). However, as the soil depth increased from 5 to 10 cm, there was comparatively less effect on the potential of the pathogens to cause damping-off. At 10 cm soil depth, the incidence of the damping-off reduced from 70.0 to 23.3 per cent in tomato, 73.3 to 30.0 per cent in chilli and 76.6 to 26.6 percent in capsicum.
Table 6
Effect of time duration of soil solarization on potential of the pathogens to cause the disease in tomato, chili and capsicum
Crops | Disease incidence (%) |
15 days | 30 days | 40 days | Mean |
5 cm | 10 cm | 5 cm | 10 cm | 5 cm | 10 cm |
Tomato | 63.33 (52.75) | 70.00 (56.98) | 43.33 (41.14) | 53.33 (46.90) | 16.67 (23.85) | 23.33 (28.27) | 45.00 (41.65) |
Chilli | 66.67 (54.76) | 73.33 (58.98) | 40.00 (39.13) | 56.67 (48.83) | 20.00 (26.06) | 30.00 (32.98) | 47.78 (43.46) |
Capsicum | 70.00 (56.98) | 76.67 (61.20) | 46.67 (43.06) | 50.00 (44.98) | 23.33 (28.77) | 26.67 (30.98) | 48.89 (44.33) |
Mean | 66.67 (54.83) | 73.33 (59.05) | 43.33 (41.11) | 53.33 (46.90) | 20.00 (26.23) | 26.67 (30.75) | |
Figures in parentheses are arc since transformed |
CD (0.05) |
Days (3.41) |
Depth (2.79) |
Days×Depth NS |
Treatment NS |
Days×Treatment NS |
Depth×Treatment NS |
Potential of the damping-off pathogens reduced more at lower depths (5 cm) than at 10 cm depth because at lower depths more heat is generated which has sub-lethal effects and also different fungal antagonists affect the viability and potential of the pathogens. Viable propagules surviving after soil solarizaion may possess lower inoculum potential and shorter longevity due to slower germination or growth; reduces number and length of mycelia germinating from multi-cellular propagules, reduced capacity to produce enzymes, ruptures in cell membranes and leakage of nutrients from cells (Katan, 1981; Smith, 1923). Sundarum (1986) suggested a reduced cell membrane function due to the presence of low-melting-point unsaturated lipids in cell membranes. Heat inactivation of respiratory enzymes was also found as a further cause for thermal decline of soil-borne microorganisms (Brock 1978; Sundarum, 1986).