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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 (C[O.sub.2]) and oxygen ([O.sub.2]), 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 C[O.sub.2] flux (FC[O.sub.2]) and the [O.sub.2] flux (F[O.sub.2]) 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 FC[O.sub.2] for soil moisture in the range of 6.0-8.6% for both management regimes. The soil moisture increments triggered a decrease in F[O.sub.2] and an increase in FC[O.sub.2] and ARQ. The FC[O.sub.2] and F[O.sub.2] were positively correlated under BH. The BH yielded a cumulative C[O.sub.2] emission of 53.68% higher than for GH. Overall, our findings revealed that soil moisture affected the [O.sub.2] uptake and C[O.sub.2] emission profile of soil, limiting [O.sub.2] uptake and increasing C[O.sub.2] 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 C[O.sub.2] production and [O.sub.2] consumption. Additional keywords: C[O.sub.2] emission, sugarcane straw management, [O.sub.2] uptake, respiratory quotient, soil biological activity., Introduction Measurements of oxygen flux (F[O.sub.2]) in soils are related to the metabolic status of microorganisms and carbon accumulation or loss, especially in environments where these processes are driven by [...]

Soil CO2 emission (FCO2) in agricultural areas results from the interaction of different factors such as climate and soil conditions. Our objective was to investigate the spatiotemporal variation of FCO2, temperature (Tsoil), moisture (Msoil) and air‐filled pore space (AFPS), as well as their interactions, during the sugarcane field reform. The study was conducted on a 90 × 90 m sampling grid with 100 points at 10 m spacings. Ten assessments of FCO2, Tsoil and Msoil were carried out at each point over a 28‐day period. The greatest mean values of FCO2 (0.74 g m−2 hr−1) and Msoil (31.7%) were obtained on Julian day 276, 2013, being associated with precipitation events at the study site. Also, the smallest values of AFPS (19.17%) and Tsoil (20.90°C) were observed on the same day. The spatial variability of FCO2, Tsoil, Msoil and AFPS was best described by an adjusted spherical model, although an exponential model better fitted some results. The spatial pattern of all soil attributes showed little temporal persistency, indicating a high complexity for FCO2 during precipitation. Correlation maps assisted in identifying regions where Msoil and AFPS better controlled the emission process and where Tsoil was important. A major challenge for world agriculture is to increase the efficiency of conventional soil management practices. We highlight the importance of the spatial pattern of soil properties that directly influence the CO2 emission dynamics. Future mitigation actions should involve less intense tillage and ensure homogeneous applications of soil inputs, thereby reducing production costs and the contribution of these activities to CO2 emissions during the sugarcane field reform. [ABSTRACT FROM AUTHOR]

CO 2 production in soil is the result of biological processes, such as the decomposition of organic matter and the respiration of roots and soil organisms. It also depends on the physical, chemical and biological properties and their interactions. Such properties exhibit variability in space and time, which provides a high degree of complexity on soil CO 2 emission (FCO 2 ). However few studies discuss the spatial and temporal component of FCO 2 , jointly. The objective of this study was to characterize the spatial and temporal variability of FCO 2 and its relationship to the edaphoclimatic properties of the soil in sugarcane fields. The LI-8100 system, which monitors changes in CO 2 concentrations within a portable chamber, was used to assess the FCO 2 . The CO 2 flux measurements, soil temperature (0–20 cm, thermometer of LI-8100) and soil water content (0–12 cm, TDR device) were evaluated concomitantly. Overall, the mean values for FCO 2 , soil temperature and soil water content were 2.8 μmol m −2 s −1 , 19.48 °C and 17.20 m 3 m −3 , respectively. The FCO 2 was positively correlated with the soil organic matter content (SOM) ( r = 0.67, p < 0.001), the air-filled porosity (AFP) ( r = 0.71, p < 0.001) and the available phosphorus ( r = 0.28, p < 0.05) but negatively correlated with the soil C/N ratio ( r = −0.75, p < 0.001) and soil water content ( r = −0.29, p < 0.05). The air-filled porosity was the last property added to the multiple regression model and explained 77% of the spatial variability in soil CO 2 emission. The largest temporal variations in CO 2 emissions over the study period were explained by changes in soil water content, especially after rainfall. Spatially, the CO 2 emission is modeled by chemical (organic matter and soil C/N ratio) and physical (air-filled porosity) soil properties which are associated to production and transport of CO 2 in soil. [ABSTRACT FROM AUTHOR]

Production, transport, and emission of CO 2 from soil to the atmosphere are directly influenced by soil temperature and moisture conditions, exhibiting a high variability over time due to the influence of climate events and soil management practices. Thus, this study aimed to investigate the effect of summer and off-season crop residues on the temporal variation of soil CO 2 emission (FCO 2), soil temperature (Tsoil), and soil moisture (Msoil) under a no-till system that has been managed with the same crop arrangement for >16 years. The experiment was conducted in strips with three replications. Treatments consisted of summer crop sequences maize monoculture, soybean monoculture, and soybean-maize rotation, as well as off-season crops maize, millet, pigeon pea, grain sorghum, and crotalaria. Sixteen assessments of FCO 2 , Tsoil, and Msoil were carried out over 51 days. A significant effect of the interaction between time and summer crop sequences (F = 1.44; p = 0.02) and between time and off-season crops (F = 2.26; p < 0.01) was observed for FCO 2. Moreover, a triple interaction was observed between summer crop sequences, off-season crops, and time for Msoil (F = 1.83; p < 0.01) and Tsoil (F = 1.32; p = 0.01). The values of FCO 2 and Msoil were high on days 229 and 230 due to precipitations in the study area. The relationship between FCO 2 and Msoil was positive in all the assessed management, and about 60% of FCO 2 variation over the study period could be explained by soil water content variation. Unlabelled Image • Soil moisture is responsible for governing the temporal variation of soil CO 2 emissions in a tropical soil under no-till system for more than 16 years. • The temporal variation of soil CO 2 emission under no-till system tends to remain stable until precipitation events occur. • The type of crop cover chosen to compose the no-till system determines the temporal variation of soil CO 2 emission. • Soil moisture can explain soil CO 2 emission variation by more than 50% in areas with crotalaria, pigeon pea, and grain sorghum as winter crop. [ABSTRACT FROM AUTHOR]