Abstract
International collaboration on agronomy projects often requires the shipment of soil samples between countries to conduct analyses. However, quarantine regulations in numerous countries restrict the importing of soil samples unless they are sterilized, or analysis is carried out only in quarantine facilities, which greatly increases cost. Yet, sterilization is only an option if it does not change the soil properties. There is conflicting information about the effect of irradiation on soil chemical properties. To assess the effect of gamma irradiation on some soil chemical properties, one hundred randomly selected air-dried (40 °C) soil samples were split into two samples. One sample was left untreated and the other sample was irradiated with 50 kGy as prescribed by Australian biosecurity regulations. Commonly measured agronomic soil chemical properties were then measured and results from the non-irradiated samples were compared to the irradiated samples. The results show no effect of irradiation on soil cation exchange capacity, exchangeable cations, total carbon and nitrogen content, and DTPA-extractable Zn. Small (<5%) but statistically significant effects of irradiation were observed for pH (1:5 water), electric conductivity (EC1:5), DTPA-extractable Cu, Fe and Mn, and Colwell P. The irradiation effects on Fe were greater in the topsoil than subsoil. Considering that irradiation-induced changes to soil chemical properties were below 5%, gamma irradiation can be considered a suitable method to sterilize air-dried soil to meet import requirements, without affecting the interpretation of soil fertility reports.
Highlights
International collaboration between agronomists and soil scientists often requires the movement of soil samples across countries or continents to conduct soil analyses
There were no significant differences between irradiated and non-irradiated air-dry soil samples with respect to the total soil carbon, total soil nitrogen, exchangeable Ca, K, Mg, Na, the cation exchange capacity (CEC), and DTPA-extractable Zn (Table 1)
For Fe, the irradiation effect differed between topsoil and subsoil samples (p = 0.0174), but irradiation-induced changes in the other parameters were not significantly affected by soil type, horizons or textures
Summary
International collaboration between agronomists and soil scientists often requires the movement of soil samples across countries or continents to conduct soil analyses. Quarantine regulations in countries such as Australia, Canada, New Zealand, Singapore and the USA prescribe that imported soil either needs to be sterilized or used only in quarantine approved facilities. The administrative costs and management burden associated with the analysis of samples in quarantine-approved laboratory facilities have more than doubled in recent years, compared to non-quarantine samples. It would be beneficial if samples could be sterilized instead, as these samples are no longer subject to quarantine and can be analyzed in non-quarantine laboratories. A prerequisite is that sterilization of soil does not change the soil properties under investigation
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