LOW CARBON AMENDMENT RATES DURING ANAEROBIC SOIL DISINFESTATION (ASD) AT MODERATE SOIL TEMPERATURES DO NOT DECREASE VIABILITY OF SCLEROTINIA SCLEROTIORUM SCLEROTIA OR FUSARIUM ROOT ROT OF COMMON BEAN

Abstract

Anaerobic soil disinfestation (ASD; also termed biological soil disinfestation) is a non-chemical process which includes 1) soil incorporation of a labile carbon (C) source, 2) mulching with polyethylene film to limit gas exchange, and 3) drip irrigation to saturation of the topsoil or bedded area. A number of putative mechanisms have been proposed as contributing to control of pathogens, nematodes, and weeds during ASD treatment, although not all have been well-characterized. Mechanisms include formation of organic acids and volatile compounds during anaerobic decomposition of the added C source, biocontrol by microorganisms favored by ASD treatment, and changes in soil chemical constituents under anaerobic conditions. In Tennessee, USA, growth chamber, greenhouse, and field studies have been conducted to evaluate and optimize the ASD procedure for regional production systems and to evaluate pest, soil, and crop responses resulting from differing C source rates and properties. A growth chamber study conducted using soil temperatures typical to spring soil disinfestation treatment in this region (15 to 24°C), suggests that C amendment rates less than 1 mg C g-1 soil for ASD treatment do not consistently decrease viability of Sclerotinia sclerotiorum sclerotia or decrease incidence of endemic Fusarium root rot of common bean compared to an unamended control. Variability in measures of accumulated anaerobic soil conditions and an observed soil pH increase in ASD-treated soils are also indicative of ineffective ASD treatment at low amendment rates. Other preliminary work suggests that amendment rates may need to be as high as 4 mg C g-1 soil for effective soil disinfestation at moderate soil temperatures. Studies to determine optimal amendment rates and properties for consistent ASD treatment at moderate soil temperatures are ongoing.