Identification of specific soil properties that affect the accumulation and toxicity of ammonia to Verticillium dahliae

Abstract

The accumulation of ammonia in soil amended with meat and bone meal was previously shown to kill microsclerotia of Verticillium dahliae Kleb. This laboratory study examined to what extent cation-exchange capacity, moisture, organic carbon and nitrification, and high levels of sand and bulk density affect the accumulation of ammonia. Two soils were used as models: site B soil a loamy sand of low organic carbon content that when amended with meat and bone meal (2–2.5%) accumulates ammonia in excess of 25 mM, killing microsclerotia, and site L soil, a loam of moderate organic carbon content that does not accumulate ammonia unless amended to at least 4%. Ammonia accumulation was prevented in site B soil by addition of a muck soil that increased the organic carbon content. In site L soil, accumulation of ammonia was achieved by increasing its sand content or by preventing nitrification using the inhibitor dicyandiamide. Other factors such as exchangeable ammonium plus ammonia had similar effects for amended site B and L soils, indicating that cation-exchange reactions involving the absorption of ammonium and ammonia to soil particles are not a primary determinant of ammonia accumulation. Moisture content and density only slightly affected the accumulation of ammonia in site L soil. These findings indicate that concentrations of nitrogenous amendments required to kill V. dahliae microsclerotia can be reduced to practical levels by targeting for amendment soils having low organic carbon and high sand contents while reducing their rate of nitrification.

Keywords:

• nitrogenous amendments
• meat and bone meal
• Verticillium dahliae microsclerotia
• ammonia
• toxicity
• soil properties
• organic carbon
• nitrification
• sand