Abstract
Efficacy of anaerobic soil disinfestation (ASD) for soilborne plant pathogen suppression is strongly influenced by soil environment and organic amendment attributes. At the same time, these factors influence soil nutrient availability, crop nutrition, and crop performance, but published information on ASD amendment property effects, including carbon to nitrogen (C:N) ratio and C substrate bioavailability, on crop performance and soil nutrient availability is limited. We evaluated ASD amendment effects on soil N availability, crop N status, and solanaceous crop performance in a series of trials: (1) greenhouse/growth chamber study of amendments (primarily molasses/soybean hulls and wheat bran) formulated at 10:1, 20:1, 30:1 and 40:1 C:N ratios (4 mg C gâ1 soil), (2) field study with molasses/soybean hull-based amendments at equivalent C:N ratios/C rates (3) on-farm study with molasses/soybean hull-based amendments (4 mg C gâ1 soil) compared to grower-standard control, and (4) field study of labile to recalcitrant amendment substrates at 30:1 C:N ratio (~3.4 mg C gâ1 soil). ASD amendment C:N ratio strongly influenced soil inorganic N and the lowest (10:1) ratio was associated with highest soil inorganic N at ASD treatment termination in both trials 1 and 2, which often persisted into the cropping phase. Accordingly, the lowest amendment C:N ratio was also associated with the highest biomass (trail 1), leaf tissue N (trial 2), and crop yield (trials 1, 2) among treatments, even with application of recommended fertigation rates to all treatments in the field study. In trial 3, ASD treatment induced higher soil inorganic N and crop yield than the control, but no differences were observed in plant tissue N. In trial 4, more decomposable ASD substrates reduced soil inorganic N at ASD treatment termination, with the highest soil inorganic N associated with the most recalcitrant amendment, but there was no effect on crop yield. ASD amendment C:N ratio, and to a lesser extent, amendment decomposability, exert a strong influence soil inorganic N and crop performance. Optimization of ASD treatments for disease management will require simultaneous optimization of crop nutrition practices to facilitate more holistic, less confounded assessment of crop performance and to facilitate recommendations for grower adoption.
Highlights
Anaerobic, or biological, or reductive soil disinfestation has emerged as a biologically-based alternative to soil fumigation for suppression of soil borne pests (Shrestha et al, 2016)
In this study we evaluate the importance of anaerobic soil disinfestation (ASD) amendment properties, including C:N ratio, C rate and substrate decomposability on soil/crop nitrogen and crop performance under environmental conditions typical to the southeastern USA
The ASD treatment was conducted in an environmental growth chamber (ECG, Chagrin Falls, OH, USA) at 25âŚC for 14 h and 15âŚC for 10 h to simulate soil temperature regimes in relevant production regions during spring in Tennessee and similar warm-temperate to subtropical production regions
Summary
Biological, or reductive soil disinfestation has emerged as a biologically-based alternative to soil fumigation for suppression of soil borne pests (Shrestha et al, 2016). Comprehensive studies and reviews of ASD (Rosskopf et al, 2005; Shennan et al, 2014; Strauss and Kluepfel, 2015) have shown that ASD is a versatile technique that can be adapted regionally by using varying types of locallyavailable organic amendments to control various soil borne pathogens and plant-parasitic nematodes, and with effects on weed pests. Application of organic amendments can improve soil physical and chemical properties of soil leading to ASD treatment impacts on vegetable and fruit yield (Butler et al, 2014a). Existing published work tends to be limited in scope because it was generally not designed to evaluate mechanistic impacts of varying ASD amendment properties on soil/crop nutrients and crop performance
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