Application of solar-heated water for soil solarization

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W. I. Abu-Gharbieh, W. I. H. Saleh, and L. Al-Banna

Professor, Assistant Professor, and Research Assistant, respectively, Faculty of Agriculture, University of Jordan, Amman, Jordan.

This research was supported by the Deanship of Research at the University of Jordan

Abstract

This experiment was conducted in a plastic house in the Jordan Valley, to investigate the effectiveness of combining soil solarization (SS) for 11 weeks using black plastic tarping, with the application of a single treatment of solar-heated water (75-90°C). The experiment comprised seven treatments; soil solarization alone (S); S in combination with hot water at the beginning (SH1) or at the end (SH2) of the solarization period; hot water alone at the beginning (H1) or at the end (H2) of SS period; and two controls, either wet (COO) or dry (CD)

The results indicated that soil temperature at 10cm depth increased by 3-6°C over the control when black plastic tarping alone was used, while the combined treatments with hot water increased soil temperature by 8-14°C over tarping (maximum temperature reached 56°C). Generally, S. SH1 and SH2 reduced root galling of tomato, the number of J2 of Meloidogyne javanica and free living nematodes in the soil, as compared to the other treatments. The same treatments also reduced propagules of Fusarium spp., but caused an increase of Aspergillus spp. Growth responses of tomato also appeared generally better than the hot water alone or control treatments.

Results of SH1 and SH2 were not significantly different, indicating that under the conditions of the experiment, hot water treatment did not add significantly to the effect of the solarization treatment alone. Also, results indicated that application of hot water at the beginning of SS was more effective than prior to planting.

Introduction

Soil solarization as an efficient soil disinfestation method can only be used when climate is suitable and soil is crop-free for at least one month (912). The effect of combining solarization using black plastic tarping and solar-heated water treatment, to reduce the needed crop-free period and to improve soil heating, was investigated over two years in the Jordan Valley. In the first year (1987/1988) Saleh et al. (13) indicated possibilities for using hot water and black plastic tarping for effective control of soilborne pathogens. In 1988/1989, an experiment was carried out in a plastic greenhouse in Jordan Valley that included application of hot water treatments alone or in combination with black plastic tarping. The purpose was to confirm findings of 1988 and to further improve soil heating.

Materials and Methods

During the 1988/1989 season, an experiment was conducted in a plastic house in the Jordan Valley, consisting of seven treatments as follows: in the first three treatments, plots were solarized with black plastic tarping (60 mm) and included solarization alone (S), in combination with solar-heated water at the beginning of the solarization period (SH1) on 7/30/88, or at the end of the solarization period (SH2) on 9/27188. Two other treatments consisted of the addition of solar-heated water either at the beginning (H1) or at the end (H2) of the solarization period. The SS period commenced in 7/19/88 and ended in 10/12188. The experiment also included two control treatments (neither with black plastic tarping nor application of solar-heated water) that served as either wet (COO) or dry (CD) controls. The experimental plots of all treatments were 7m long x 1m wide, each, and were replicated five times in a randomized complete block design.

Irrigation during the solarization period was done weekly at the rate of 20 1/m² soil. The application of hot water (75-80°C) was done using a domestic solar heater of the thermocyphon type.

Each plot treated with solar-heated water received a single treatment of 25 1/m² through the drip irrigation system. Soil temperatures were recorded at 10 cm depth using type thermocouple 'T' connected to a computerized recorder.

At the end of the solarization period 10/12/88 plots were planted with seedlings of the tomato cultivar Claudia Raf.Cultural practices were done as needed to maintain good plant growth. Soil sampling was done four times during the experimental period; before and at the end of solarization period in 10/12/88; and in the middle (12124/88) and at termination (5123189) of the growing season. Soil samples were used to assay the number of J2 larve of the root-knot nematodes, Meloidogyne javanica (Treub) Chitwood, free-living nematodes (5), and to estimate fungal numbers (Fusarium & Aspergillus spp.) per g oven dry soil (7). Plant samples were taken in the middle of the growing season (4 plants/plot) and at termination of the experiment (8 plants/plots) to determine foliage weight, root weight and root galling index. Root galling was evaluated using a 0-4 scale, where 0=no galling, 1=1-25 percent, 2=26 percent-50 percent,3=51-75 percent,4=76-100 percent of the root system galled (5). Plant height was measured 40 days after planting. Number and weight of tomato fruit harvested from each plot were recorded.

Results

The weekly average of maximum soil temperatures under black plastic tarping at 10 cm depth ranged from 41-48°C during the solarization period. This corresponded to an increase of 3-6°C and 2-5°C over the non-solarized wet and dry soil, respectively. The application of hot water alone, or in combination with solarization at the beginning of the solarization period increased soil temperature at 10 cm depth to 53°C for 5 and 9 hours, respectively. The corresponding increase at the end of the solarization period was 9-14°C for about 7 hours.

Higher soil temperatures effectively reduced soilborne pathogens and improved plant growth and yield responses. The population of J2 larvae of M. javanica was not detectable before and after solarization. The population of J2 larvae was also very low in the middle of the growing season, while at termination, numbers were higher in the CD and H2 treatments, but significantly reduced in all other treatments (Table 1). The root galling index showed no significant differences among treatments in the middle of the season while at termination (S) alone or in combination with heated water (SH1 and SH2) and H1 alone showed significantly lower values than all other treatments (Table 1). At the end of the polarization period and in midseason, numbers of free-living nematodes were lower in the S. SH1, SH2 and CD treatments than H1, H2, and CW treatments.

Significantly lower numbers of Fusarium propagules were found at the end of the solarization period in the S,SH1, and SH2 than in either control treatment. H1 and H2 were not significantly different from all other treatments. Contrary to effects on Fusarium, numbers of propagules of Aspergillus were significantly higher in S and SH1 than in H2 and the control treatments, while the later treatments did not differ from SH2 and H1. Results of the Aspergillus assay at the end of season were identical to those recorded at the end of the solarization period (Table 2).

The S. SH1, SH2 and H1 treatments significantly increased foliage weight of tomato as compared to the H2 and control treatments at termination time (Table 3). Plant height measured 40 days after planting was significantly increased in the S. SH1 and SH2, over all other treatments (Table 3). Although no significant differences were found among treatments in yield (Table 3), the application of hot water at the beginning of the solarization period combined with solarization gave the highest yield (20 percent increase over the wet control).

Discussion

Katan (9) stated that transparent, not black, polyethylene film should be used for solarization, because it transmits most of the solar radiation into the soil; and that mulching should be carried out during the period of maximum temperature and intense solar radiation. However, results using black plastic tarping in this experiment and other research carried out in Jordan (1, 4) indicated that soil temperature at 10 cm depth was increased between 3-6°C in this experiment and by about 2°C and 7°C respectively, in other experiments (1). Application of solar-heated water in combination with black plastic tarping raised the soil temperature to nearly 55°C for several hours, which was about 8-14°C higher than in soil with black plastic tarping alone and about 4-6° C higher than in soil tarped with transparent plastic.

With application of hot water treatment, it is important to raise soil temperature to only slightly above the temperature lethal to the pathogen, so as to allow many saprophytes to survive the treatment (2, 3). Results from this investigation showed that combined treatments, as well as black plastic alone, reduced numbers of Fusarium propagules while numbers of Aspergillus spp. were increased. Such results were also found by Al-Asa'd (1) and Barakat (4) using black plastic tarping, and by Bollen (6) and Katan et al. (8,9) using transparent sheets.

Populations of M. lavanica J2 were at about the same level in plots with solarization alone and in the combined treatments. Root galling, however, was lower in the combined treatment than with solarization alone. Concerning crop growth, plants grew higher in the combined treatments, while the highest yield was obtained when hot water at the beginning of the solarization period was combined with solarization using black plastic covers. Tomato yields were not different between the solarized alone and that of the combined treatments. However, the significance of this treatment might be more apparent under heavier soil infestations with soilborne pathogens, and possibly under lower soil temperatures. In another test (unpublished), carried out by the authors in the same season in a soil heavily infested with M. javanica application of solar-heated water combined with soil solarization using black plastic tarping, significantly reduced the number of J2 larvae in the soil as compared to the solarization treatment alone.

Results also indicated that application of hot water a few days after soil tarping (H1 and SH1) was more effective than application of hot water near the end of the solarization period (H2 and SH2), i.e. very close to planting time.

References

1. Al-Asa'd, M. A. 1983. Effect of solarization on soilborne fungi and nematodes in the Central Jordan Valley. M. S. Thesis, Univ. of Jordan. 74 pp.

2. Baker, K. F. 1962. Principles of heat treatment of soil and planting material. J. Aus. Inst. Agric. Sci. 28, 118-26.

3. Baker, K. F. & C. M. Olsen. 1964. Effect of selective heat treatment of soil on root pathogens. Abstracts, Tenth Int. Bot. Congr., p. 73.

4. Barakat, R.M. 1987. Comparison of effect of different colours of polyethylene tarping on soilborne pathogens, M.Sc.Thesis, Univ. of Jordan, 82 pp.

5. Barker, K. R. 1985. Nematode extraction and bioassays, Pages 19-38 In: An Advance treatise on Meloidogyne, Vol. II. Methodology: K. R. Baker, C.C. Carter and J. N. Sasser, eds, North Carolina State University. 223 pp.

6. Bollen, G. J. 1974. Fungal recolonization of heat treated glasshouse soils. Agro-Ecosystem 1: 139-155.

7. Grossan, D. F. 1967. Selective isolation of soil microorganisms by means of differential media. Page 19 - 21,In: Sourcebook of Laboratory Exercises in Plant Pathology. American Phytopathological Society, San Francisco and London. 379 pp.

8. Katan, J., Greenberger, A., Alon, H., and A. Grinstein. 1976. Solar heating by polyethylene mulching for the control of disease caused by soilborne pathogens. Phytopathology 66: 683-688.

9. Katan, J. 1980. Solar pasturizaiton of soils for disease control, status and prospects. Plant Disease 64:450 - 454.

10. Katan, J. 1981. Solar heating (solarization) of soil for control of soilborne pests. Ann. Rev. Phytopathol. 19:211-236.

11. Pullman, G.S., J.E. DeVay, R.H. Garber, and A.R. Weinhold 1979. Control of soilborne fungal pathogens by plastic tarping of soil. In: Soilborne Plant Pathogens. B. Schippers and W. Gams, eds. Academic Press, New York. pp. 696.

12. Pullman, G. S., J. E. DeVay, C. L. Elmore, and W. H. Hart 1984. Soil solarization: a nonchemical method for controlling diseases and pests. Cooperative Extension, Univ. of California, Division of Agriculture and Natural Resources, Leaflet 21377. Davis, CA.

13. Saleh, H., W. I. Abu-Gharbieh, and L. Al-Banna. 1989. Augmentation of soil solarization effects by application of solar-heated water. Nematologia Mediterranea (in press).

Table 1. Effect of soil solarization and application of solar heated water on root-knot (Meloidogyne javanica) and free-living nematodes

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1S= Solarized with black polyethylene alone; SH1= same as S but with solar heated water at the beginning of the solarization period; SH2= same as S but with solar heated water at the end of the solarization period; H1= solar heated water at the beginning and H2 at the end of the period; and CW= wet and CD= day controls without black plastic tarping.

2 J2 of Meloidogyne javanica population/100cc soil at (a)= 72 days after planting; (b)= at termination.

3 Root galling index 04; 0=no galling, 1=1-25 percent, 2=26-50, 3=51-75 percent, 4=76- 100 percent of the root system galled at (a)= 72 days after planting and (b)= at crop harvest.

4 Free-living nematode population/100cc soil at (a)= before solarization; (b)= at the end of solarization period; (c)= 72 days after planting, (d)= at crop harvest.

5 Numbers in each column followed by the same letter are not significantly different (P= 0.05).

Table 2. Effect of soil solarization and application of solar heated water on numbers of propagules of Fusarium and Aspergillus spp.

1S= Solarized with black polyethylene alone; SH1= same as S but with solar heated water at the beginning of the solarization period; SH2= same as S but with solar heated water at the end of the solarization period; H1= solar heated water at the beginning and H2 at the end of the period; and CW= wet and CD= day controls without black plastic tarping.

2 Average number of propagules of fungi/g oven dry soil at (a)= the end of solarization period; (b)= 72 days after planting; (c)= at crop harvest.

3 Numbers in each column followed by the same letter are not significantly different (P= 0.05).

Table 3. Effect of soil solarization and/or application of solar heated water on plant growth and yield parameters

1S= Solarized with black polyethylene alone; SH1= same as S but with solar heated water at the beginning of the solarization period; SH2= same as S but with solar heated water at the end of the solarization period; H1= solar heated water at the beginning and H2 at the end of the period; and CW= wet and CD= day controls without black plastic tarping.

2 Average wt. of foliage & root (g/plant) (a)= 72 days after planting (4 plants/replicate), (b)= at crop harvest (8 plants/replicate).

3 Plant height (cm/plant) 40 days after planting.

4 Yield was recorded as average number & weight (kg) of fruit/replicate.

5 Numbers in each column followed by the same letter are not significantly different (P= 0.05).

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