Feasibility of soil fumigation by sealing soil amended with fertilizers and crop residues containing biotoxic volatile compounds. (SA Summer 1994 (v6n3))

Summer 1994 (v6n3)

Feasibility of soil fumigation by sealing soil amended with fertilizers and crop residues containing biotoxic volatile compounds.
J.J. Stapleton and A. Gamliel
Adapted from Plant Protection Quarterly 3(3,4): 13. 1993

Editor's Note: A summary of this research, along with 18 other abstracts, appears in the recently published Cover Crops Workgroup Report. This report was compiled for the recent Workgroup meeting. For information on obtaining this report see page 15 of this newsletter. As noted above, the article originally appeared in the Plant Protection Quarterly, a publication by UC pest management specialists and advisors.

For the past 50 years farmers have been able to use synthetic chemical fumigants to disinfest soil of pest and disease organisms. These materials have been effective and easy to apply. The cost of fumigant treatments has usually been recouped through dramatically higher yield and quality of produce, healthier and longer-lived permanent crops, certification of pathogen-free nursery stock, and reduced costs of other production practices such as weed control (Chen et al., 1991).

In the current climate of strict environmental and human safety regulations, however, it appears that the era of widespread disinfestation of agricultural soils by synthetic chemical fumigants is coming to a close. Alternative methods of soil disinfestation must be developed and implemented if current levels of crop production, quality, and phytosanitary certification are to be maintained. One such method is soil solarization. Heat accumulation in solarized soil causes physical, biological, and chemical changes which normally result in greatly reduced pest and pathogen numbers and increased yield in subsequent crops. Disadvantages of solarization include dependence on favorable climatic and weather conditions, treating soil for several weeks during the growing season, lack of control of certain heat tolerant pests, and generally, decreased efficacy with increasing soil depth (Chen et al., 1991).

Another alternative for disinfesting soil is to incorporate into the soil fertilizers and plant residues that have pesticidal properties. This practice has received renewed attention, and numerous studies have shown that amending soil with various cover crops, plant residues and extracts, animal manures and composts, and inorganic fertilizers can provide some degree of pesticidal activity (Rodriguez-Kabana, 1986). Studies in which soil sealing and/or heating with plastic mulches was combined with soil amendments generally concluded that, like fumigants, levels of soil disinfestation were better than with either method alone (Brown et al., 1989; Gamliel and Stapleton, 1993a; Gamliel and Stapleton, 1993b; Ramirez-Villapudua and Munnecke, 1988; Stapleton et al., 1991).

This article summarizes recent experiments done with combinations of composts, inorganic fertilizers, or cruciferous residues and solarization with polyethylene film or liquid spray mulch to test improved pathogen control, and to determine relationships of soil heating and sealing on concentrations of biotoxic volatile compounds emanating from treated soil.

Recent Research

Solarization and fertilizers. Laboratory and field experiments in different soil types were done in 1991 and 1992 near Fresno, California, to determine the effects of organic and inorganic nitrogen sources. Commercially-composted chicken manure and inorganic ammonium-nitrogen were applied at rates equivalent to 80 kg NH4-N per hectare with and without soil solarization with clear polyethylene film. The length of the treatment was four weeks during August 1991. Measurements were taken on fungal (Pythium ultimum) and nematode (Meloidogyne incognita) pathogens in the rhizosphere and roots of lettuce (Lactuca sativa cv. Parris Island).

Solarization and crop residues or fertilizers. Another replicated field experiment was done in sandy loam soil near Fresno, in 1993 to compare the effects of amending soil with composted chicken manure (40 kg NH4-N per ha) or dried cabbage harvest residues (500 kg per ha), with and without a four-week period of soil solarization. Solarized soils were treated in July 1992, with either clear polyethylene film or black spray mulch; data were collected on the survival of P. ultimum.

Evolution of volatile compounds from amended and heated soil. Additional experiments were conducted in the laboratory to analyze evolution of volatile compounds by gas chromatography from soil amended with cabbage residues under various levels of soil heating, and to correlate the presence of these compounds with pathogen control.

Results and Discussion

Solarization and fertilizers. Preplant incorporation of ammonium phosphate fertilizer or composted chicken manure slightly reduced galling of lettuce roots by M. incognita (3-24%); solarization was more effective (74% reduction). Ammonium phosphate combined with solarization was no better than solarization alone, but compost plus solarization reduced nematode galling to undetectable levels (figure 1). With regard to P. ultimum, incorporating fertilizer or compost alone reduced propagule numbers in lettuce rhizosphere by 0 to 25 percent; solarization alone reduced their number by 80 to 100 percent. Due to the high activity of solarization, combination with soil amendments did not give increased control (figure 1).

Solarization and crop residues or fertilizers. In this experiment, neither soil amendment had a fungicidal effect when used alone. Solarization with polyethylene film or spray mulch, on the other hand, was very effective, resulting in reduction of fungal propagules ranging from 82 to 100 percent. No interaction was found between soil amendments and solarization.

Evolution of volatile compounds from amended and heated soil. Relative concentrations of several volatile compounds emanating from cabbage-amended soil were increased by soil heating. These compounds included various alcohols, aldehydes, isothiocyanates, and sulfides. Others (e.g., CO₂) were generally higher in nonheated soil. The levels of isothiocyanates and aldehydes generated in heated soil were significantly correlated with reduced propagule numbers of P. ultimum. Both soil heating and amendment with cabbage residue and chicken compost increased the lethal effect on P. ultimum.

Summary

Results of these experiments indicate that sealing animal and plant residues containing biotoxic volatile compounds into soil and using materials such as polyethylene film and spray mulch can provide at least partial soil disinfestation, especially when combined with soil heating. Under present laws, use of these soil amendments, even when intended for pesticidal activity, do not carry regulatory requirements when the materials are produced on-farm. However, additional research will be necessary to develop guidelines for optimal usage. As interest and experimental results increase, it may be possible to develop "customized" soil amendments. which will have greater activity on specific pest organisms found in particular fields. Crop managers will require more intensive soil sampling to identify and enumerate threshold levels of soilborne pests as the broad spectrum fumigants become unavailable.

Figure 1. Field effect of soil solarization, chicken compost , and ammonium phosphate fertilizer on (A) galling of leaf lettuce (Lactuca sativa cv. Parris Island) by Meloidogyne inognita, and (B) numbers of Pythium ultimum in the rhizophere if lettuce plants. Columns tended by different letters are different (P<=0.05) according to factorial ANOVA.

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References

Brown, J.E., M.G. Patterson and M.C. Osborn. 1989. Effects of clear plastic solarization and chicken manure on weed control. Proc. Natl. Agr. Plastics Congr. 21:76-29.

Chen, Y., A. Gamliel, J .J. Stapleton and T. Aviad. 1991. Chemical, physical, and microbial changes related to plant growth In disinfested soils. In: Catan, J. and J.E. DeVay (eds.) Soil Solarization. CRC Press, Boca Raton. pp. 103-129.

Gamliel, A. and J.J. Stapleton. 1993a. Characterization of antifungal volatile compounds evolved from solarized soil amended with cabbage residues. Phytopathology 83:899-905.

Gamliel, A. and JJ. Stapleton. 1993b. Effect of chicken compost or ammonium phosphate and solarization on pathogen control, rhizosphere microorganisms, and lettuce growth. Plant Disease 77:886-891.

Rodriguez-Kabana, R 1986. Organic and inorganic nitrogen amendments to soil as nematode suppressants. J. Nematology 18:129-135.

Ramirez-Villapudua, J. and D.E. Munnecke.1988. Effect of solar heating and soil amendments of cruciferous residues on Fusarium oxysporum f. sp. conglutinans and other organisms. Phytopathology 78:289-295.

Stapleton, J.J., J.E. DeVay and B. Lear 1991. Simulated and Held effects of ammonia-based fertility and soil solarization on pathogen survival, soil fertility and crop growth. In: DeVay, J.E. et al. (eds.) Soil Solarization. Plant Production and Protection Paper 109, UN Food and Agriculture Organization, Rome. pp. 331-342.

Acknowledgments

The authors thank R.A. Duncan, S.T. Koike, D.M. May, C.M. Schaefer, and H. Yunis for technical assistance; Petoseed, inc., Foster Farms, and Trical, Inc. for provision of vegetable seed, chicken compost, and plastic mulch film, respectively; and we gratefully acknowledge BASF Corp., and the UC Statewide IPM Project for financial support.

For more information write to: J. Stapleton, University of California, Kearney Agricultural Center, Parlier, CA 93648.

Contributed by J.J. Stapleton

(DEC.520)

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