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Title: Alteration of the soil environment to maximize Meloidogyne incognita suppression by an alkaline-stabilized biosolid amendment

item Zasada, Inga

Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2008
Publication Date: 10/31/2008
Citation: Zasada, I.A., Tenuta, M. 2008. Alteration of the soil environment to maximize Meloidogyne incognita suppression by an alkaline-stabilized biosolid amendment. Applied Soil Ecology. 40:309-317.

Interpretive Summary: Plant-parasitic nematodes are microscopic worms that attack plants and cause ten billion dollars in crop losses annually in the United States. Farmers face an enormous problem because they lack safe and effective ways of reducing the numbers of nematodes in soils. One approach being pursued by researchers developing safe and effective methods of nematode management is the use of biosolids, i.e., materials produced from biological wastes. In this study, conditions that influence the ability of a biosolid product to control plant-parasitic nematodes were identified. The biosolid product evaluated, called N-Viro Soil, is formed from municipal sewage treatment wastes that have been freed of human disease organisms through a sanitization and stabilization process. Following N-Viro Soil application, scientists monitored plant-parasitic nematode death and changes in soil chemistry under different conditions. Nematode death was closely associated with the production of the toxic nitrogen compound ammonia in soil, and high soil temperature, low soil moisture and covering the soil with plastic increased the concentration of ammonia in soil. These results are significant because they identify conditions that can be manipulated to improve the ability of N-Viro Soil to kill nematodes. This research will be used by scientists developing new methods for improving the ability of biosolids to reduce nematode numbers in agricultural fields.

Technical Abstract: The ability to identify and manipulate environmental factors conducive for nematode suppression by organic amendments is essential. The impact that soil temperature and moisture, an additional source of nitrogen, and simulated tarping had on the ability of an alkaline-stabilize biosolid amendment (N-Viro Soil; NVS) to suppress Meloidogyne incognita was evaluated. A M. incognita-infested loamy sand was amended with 2% (dry w/w) NVS plus urea (0.25 g/L dry soil) and incubated for 5 days at different temperatures (21, 26 and 31º C), moistures (25, 50 and 75% of water holding capacity (WHC) in an open or closed incubation environment. Soils were also amended with NVS or urea (additional nitrogen source), alone or in combination. Soil solution pH and ammonia (NH3) concentration (mM) were measured at 0, 3 and 5 days after amendment, and M. incognita reproduction on cucumber (eggs/L dry soil) was assessed. In all experiments soil solution pH increased rapidly after NVS amendment to approximately 10.5 under all factors; by the end of the experiments soil solution pH had decreased to 8.5 to 9.0 in NVS-amended soil. NVS plus urea amended to soil resulted in greater M. incognita suppression than either alone, and compared to an unamended control. This suppression was related to maximum and cumulative NH3 measured in soil over a 5-day period. Nematode suppression was not related to soil solution pH. For the tested factors (temperature, moisture, open vs. closed), M. incognita suppression was always greater in NVS plus urea-amended soil compared to the unamended controls, regardless of the tested factor. Differences within the factors were observed for NH3 dynamics in soil solution over time. High temperature (31º C), low percentage of WHC (25%), and closed incubation resulted in at least twice as much NH3 being accumulated in soil, to levels above 100 mM NH3. Reduced rates of NVS could be applied if combined with a labile source of nitrogen (urea) to promote the rapid production of NH3 under alkaline conditions. The ability of NVS to suppress M. incognita could also be improved by amending dry soils and increasing soil temperatures through tarping.