Assessing Ammonium Lignosulfonate as a
Soil Amendment To Control Soilborne Diseases

George Lazarovits, Nader Soltani, and Kenneth Conn, Southern Crop Protection and Food Research Centre, Agriculture and Agri-Food Canada, 1391 Sandford Street, London, Ontario, Canada N5V 4T3.

Ammonium lignosulfonate (ALS), a waste byproduct of the pulp and paper industry with a high nitrogen and carbon content, can be used as a soil amendment to increase the organic matter of soils. The addition of organic materials to soils invariably alters soil microbiology, and those organisms that can utilize the energy of the organic product increase in population. Under ideal conditions, microorganisms could be increased that are either directly beneficial to plant growth or are indirectly beneficial, in that they displace detrimental organisms such as plant pathogens. Therefore, microbial populations conducive to plant health can be manipulated by "feeding" them the right substrate. We have been studying the effects of ALS on soil microbial populations and as a control of Verticillium wilt and potato scab.

Verticillium wilt is caused by the fungus Verticillium dahliae and potato scab is caused by bacteria belonging to the genus Streptomyces. Earlier studies by our lab have shown that both these pathogens are excellent models for studying the effects of soil amendments to control diseases caused by soilborne pathogens.

We set up field plots in April 1998 at a farm near Delhi, Ontario, where the potato crop in the previous year had a severe scab problem. Treatments included a control and two concentrations of ALS (0.5 and 1.0 percent v/w). Plots, 4 × 7.6 m, were set up in a completely randomized block design with three replications for each treatment. ALS was watered into each plot and rototilled to a depth of 15 cm. Weed emergence in the plots was determined four weeks later. We planted potato tubers (cv. Yukon Gold) four weeks after treatment application. From four rows of potatoes, we collected data from only the two middle rows.

All plots received the same recommended fertilizer. The effects of ALS on soil pH and microbial populations were determined. We attached bags containing V. dahliae resting structures (microsclerotia; MS) to plastic stakes and buried them in soil (2 bags/plot) immediately after applicating amendments. After four weeks, we removed the bags, plated onto a semi-selective medium and determined the percent germination of MS, and determined the Verticillium wilt incidence in mid-August. In the fall, we harvested tubers from the middle two rows of each plot and determined the yield and scab severity.

Results from our experiments showed that incorporating ALS into soil increased populations of most microorganisms. Populations gradually returned to control levels by the end of season except for the fungi, which remained higher than the control. The weed population was more than 6-fold lower in 0.5 percent ALS-treated plots than control plots. Weed numbers in 1.0 percent ALS-treated plots were even further suppressed. ALS caused a decrease in soil pH at both concentrations used by about 0.5–1 unit below untreated soils. The viability of V. dahliae microsclerotia was reduced by 40 percent with ALS treatment and the Verticillium wilt incidence in the crop, by more than 50 percent. Populations of pathogenic scab bacteria in soil were reduced by 10–100-fold after ALS application and the incidence of potato scab was reduced in all ALS treated plots. The scab severity in 0.5 percent ALS-treated plots was reduced by 6-fold compared to control plots.

We also observed a marked reduction in populations of plant pathogenic nematodes. Total yield was slightly lower in ALS-treated plots compared to the control. However, most of the tubers from the control plots were not marketable as they were severely infected with scab. In contrast, tubers from ALS-treated plots had less than 5 percent scab on their surface and most were of marketable grade. Marketable yield in 0.5 percent ALS-treated plots was more than 20-fold greater than the control plots.

Adding ALS to soil reduced populations of important fungal and bacterial soilborne pathogens, while increasing the overall microbial population by 10–100-fold. The net benefit of the changes in populations of all soil microorganisms is not yet clear, but is likely to be shown in subsequent crops. Indications are that ALS could become a component for plant disease control and an alternative to fumigants for the control of soilborne plant pathogens. In addition, ALS contributes to soil fertility and to soil structure. At the higher concentrations used, however, ALS was phytotoxic to potatoes. This phytotoxicity was non existent or transitory at rates below 0.5 percent and the plants recovered and caught up to the plants in untreated soil. Current studies are focused on finding those rates that provide disease control but do not have any phytotoxic effects. Application of ALS sooner in the season or in the fall is also being investigated as a way to avoid phtotoxicity to the crop. The use of ALS to control soilborne pathogens is under patent protection. Work is continuing toward developing ALS into a formulated product not only for managing soilborne diseases but for other agricultural uses as well.

Last Updated: April 9, 1999