Ratio of CO2 and O2 as index for categorising soil biological activity in sugarcane areas under contrasting straw management regimes

Abstract

This study was developed in a sugarcane area under contrasting management regimes defined by mechanical green harvesting (GH) and burning harvesting (BH) to test the hypotheses that the ratio of carbon dioxide (CO2) and oxygen (O2), known as the apparent respiratory quotient (ARQ), can be used to categorise soil biological activity. The study aimed to (i) examine the profile and relationship between the CO2 flux (FCO2) and the O2 flux (FO2) in a sugarcane area under mechanical harvesting with straw burning (BH) and mechanical harvesting with maintenance of straw (GH), considering soil moisture; (ii) and suggest the use of ARQ as an index for categorising the biological activity of soils. Our results showed consistently lower FCO2 for soil moisture in the range of 6.0–8.6% for both management regimes. The soil moisture increments triggered a decrease in FO2 and an increase in FCO2 and ARQ. The FCO2 and FO2 were positively correlated under BH. The BH yielded a cumulative CO2 emission of 53.68% higher than for GH. Overall, our findings revealed that soil moisture affected the O2 uptake and CO2 emission profile of soil, limiting O2 uptake and increasing CO2 releases for water-filled porosity below 70%. The GH management system, which incorporates sugarcane residues into the superficial layer of the soil, can help protect against soil erosion. The ARQ can be used as an index to categorise biological activity in soil, where ARQ values close to 1 can be considered a reflection of aerobic activity with balance between CO2 production and O2 consumption.

CO2 emission and its relation to soil temperature, moisture, and O2 absorption in the reforested areas of Cerrado biome, Central Brazil

“…A synergy exists between both respirations, and they compete for the availability of nutrients and O 2 (Ben-Noah and Friedman 2018). Doran and Parkin (1984) and Almeida et al (2018) also reported RQ > 1 values after rainfall events and increased soil water content. However, the RQ > 1 values observed in this study were not associated with rainfall events Table 7.…”

“…The soil FO 2 rate (dO 2 /dt) was calculated via linear interpolation of the concentration values as a function of time, taking into account the atmospheric pressure, temperature, and volume of the gas trapped in the chamber by using FO 2 (Smagin et al 2016;Almeida et al 2018) as follows:…”

“…In addition, Dilly (2001) reported that RQ values close to 1 indicate that both CO 2 evolution in soil and O 2 absorption may be reliably used for the estimation of microbial biomass. Almeida et al (2018) reported the use of FO 2 as an index for categorising the source of FCO 2 respiration.…”

“…Kursar (1989) reported that SR includes microbial decomposition of litter, root exudates, and dead roots as well as respiration by roots and root symbionts. However, many factors influence these processes, including soil water content and temperature; physical and chemical soil attributes such as humification index (H LIFS ) of SOM, the C:N ratio of organic material, and solar radiation; topography; and FO 2 (La Scala et al 2000;Panosso et al 2008;de Brito et al 2009;Panosso et al 2011;Bicalho et al 2014;Moitinho et al 2015;Almeida et al 2018). On a global scale, SR rates change seasonally and are positively correlated with mean annual precipitation and annual air temperatures (Raich and Schlesinger 1992).…”

“…Soil CO 2 emission can be used as a bioindicator of soil C dynamics; the ratio between FCO 2 and FO 2 (respiration quotient, RQ) is another means of describing and categorising microbial activities (Angert et al 2014). The RQ can be used as an index to categorise soil biological activity: RQ values close to 1 reveal aerobic activity, with a balance between CO 2 production and O 2 consumption (Almeida et al 2018). Thus, the determination of FO 2 , which is driven by aerobic microbial activity, is imperative to understand the relationships of CO 2 emissions in tropical environments (Stern et al 1999).…”