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

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-stabilized 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−1) NVS plus urea (0.25 g L−1 dry soil) and incubated for 5 days at different temperatures (21, 26 and 31 °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−1 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 8.5-9.0 in NVS-amended soil. NVS plus urea amended to soil resulted in greater M. incognita suppression than either alone, or 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 (31 °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. Temperature appeared to have increased urea hydrolysis and combined with the high pH resulting from NVS amendment liberated NH3 + NH4+ from added urea accumulated as NH3 in soil. 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 manipulation of the soil environment through irrigation and/or tarping.