Impact of microwave disinfestation treatments on the bacterial communities of no‐till agricultural soils

Abstract

Growing herbicide resistance has encouraged the development of new technologies for weed control. Microwave (MW) heating of soil before sowing has been shown to reduce weed establishment in no-till farming systems and substantially increases crop productivity. However, the effect of this technology on the soil microbial community in general, and on beneficial soil microbes such as ammonia oxidizers in particular, warrants further study. In order to check the effect of MW soil disinfestation treatments on the soil biota, indigenous soil microcosms were treated under a horn antenna of the MW prototype for three distinct durations. Immediately after heating (T0) and 28 days after heating (T28) the soil was collected at two penetration depths (0-5 and 5-10 cm) of MW energy to determine the bacterial community responses based on 16S rRNA amplicon sequencing and the total abundances of bacteria and ammonia oxidisers with qPCR. Although total bacteria and ammonia oxidizer abundances exhibited no response to the MW treatments, bacterial community composition differed according to the treatment durations. Community responses clustered into two categories: no effect at low heating intensities (0 and 30 s, 17-45 C) and strong effect at high heating intensities (60 and 90 s, 65-78 C). For the latter group, community richness did not recover to its preheating levels within the 4 weeks studied. Immediately after high heating intensity treatments, the relative abundance of Firmicutes increased and that of Proteobacteria decreased significantly regardless of penetration depth. The relative abundances of beneficial soil microbes (Micromonosporaceae, Kaistobacter and Bacillus) were significantly higher as soils recovered from high heating intensities compared with untreated soils at T28. Our findings suggest that although presowing MW treatments alter the soil microbial community, beneficial soil microbes exhibit faster recovery. Highlights

Development of Microwave Slow-Wave Comb Applicators for Soil Treatment at Frequencies 2.45 and 0.922 GHz (Theory, Design, and Experimental Study)

“…The temperature distribution is proportional to the square of the microwave field distribution and is determined from this squared field distribution by integration with √ , as outlined by Crank [20]: www.videleaf.com (4) The resulting temperature distribution is described by a Voigt…”

Microwave Soil Treatment and Plant Growth

“…Br. ), parthenium (Parthenium hysterophorus L.) and bellyache bush (Jatropha gossypiifolia L.) [36] Effects of microwave treatment on growth, photosynthetic pigments and some metabolites of wheat [66] Microwave seed treatment reduces hardseededness in Stylosanthes seabrana and promotes redistribution of cellular water as studied by NMR relaxation measurements [67] Effect of microwave fields on the germination period and shoot growth rate of some seeds [68] Germination of Chenopodium album in Response to Microwave Plasma Treatment [69] Work conditions for microwave applicators designed to eliminate undesired vegetation in a field [70] microwave treatment (Figure 7), Khan et al [72] demonstrated that immediately after microwave soil treatments, the relative abundance of Firmicutes increased while the relative abundance of Proteobacteria decreased significantly. They also showed that the relative abundances of beneficial soil microbes (Micromonosporaceae, Kaistobacter and Bacillus) were significantly higher, as soils recovered from high heating intensities induced by microwave soil treatment, compared with untreated soils.…”

“…This may be due to the resilience of nitrifying bacteria and archaea to microwave soil heating. Khan et al [72] showed that microwave soil treatment did not significantly affect ammonia oxidizing bacteria or ammonia oxidizing archaea. Vela et al [74] also demonstrated that nitrifying bacteria in the soil were resilient to 40 kJ cm À2 of microwave energy at the soil surface; which is 70 times higher than the energy densities used during experimental work undertaken by the current authors.…”

Editorial for the special issue on “opportunities and challenges in no‐till farming”

“…A key conclusion is that soil management practices need improvement in many NT systems to increase earthworm populations. A soil biological focus was also investigated by Khan, Jurburg, He, Brodie, & Gupta (2020), who studied the effect of microwave heating (a means to control weeds) on bacterial communities in an Australian NT soil, a Red Mesotrophic‐Haplic Dermosol (Australian soil classification). High‐temperature treatments caused irreversible damage to bacterial community richness and only heat‐resistant bacterial taxa could survive.…”