RESUMEN

BACKGROUND: The recent studies of the variations in the atmospheric column-averaged CO2 concentration ([Formula: see text]) above croplands and forests show a negative correlation between [Formula: see text]and Sun Induced Chlorophyll Fluorescence (SIF) and confirmed that photosynthesis is the main regulator of the terrestrial uptake for atmospheric CO2. The remote sensing techniques in this context are very important to observe this relation, however, there is still a time gap in orbital data, since the observation is not daily. Here we analyzed the effects of several variables related to the photosynthetic capacity of vegetation on [Formula: see text] above São Paulo state during the period from 2015 to 2019 and propose a daily model to estimate the natural changes in atmospheric CO2. RESULTS: The data retrieved from the Orbiting Carbon Observatory-2 (OCO-2), NASA-POWER and Application for Extracting and Exploring Analysis Ready Samples (AppEEARS) show that Global Radiation (Qg), Sun Induced Chlorophyll Fluorescence (SIF) and, Relative Humidity (RH) are the most significant factors for predicting the annual [Formula: see text] cycle. The daily model of [Formula: see text] estimated from Qg and RH predicts daily [Formula: see text] with root mean squared error of 0.47 ppm (the coefficient of determination is equal to 0.44, p < 0.01). CONCLUSION: The obtained results imply that a significant part of daily [Formula: see text] variations could be explained by meteorological factors and that further research should be done to quantify the effects of the atmospheric transport and anthropogenic emissions.

RESUMEN

Production, transport, and emission of CO2 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 CO2 emission (FCO2), 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 FCO2, 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 FCO2. 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 FCO2 and Msoil were high on days 229 and 230 due to precipitations in the study area. The relationship between FCO2 and Msoil was positive in all the assessed management, and about 60% of FCO2 variation over the study period could be explained by soil water content variation.

Asunto(s)

RESUMEN

The optimization of conservationist production systems, whose goal is to increase carbon stocks and reduce greenhouse gas emissions, is considered one of the greatest challenges faced by agriculture nowadays. Therefore, this study aimed to assess the variation of soil CO2 emission (FCO2) and its relationship with soil attributes under long-term no-tillage systems with different successions of summer and winter crop sequences. Treatments consisted of combinations of three summer and two winter crop sequences. Summer sequences were maize monocrop (MM), soybean monocrop (SS), and soybean-maize intercrop (SM), while winter crops were crotalaria and maize. FCO2 showed no difference among summer sequences (p > 0.05). For winter crops, however, the soil under crotalaria crop residues presented higher FCO2 values (1.03 ±â€¯0.027 µmol m-2 s-1) when compared to that under maize crop residues (0.94 ±â€¯0.027 µmol m-2 s-1). Soil moisture presented the greatest influence on the temporal variation of FCO2, being correlated in the summer sequences MM (r = 0.79; p < 0.0001) and SS (r = 0.70; p = 0.002), as well as in the winter crops crotalaria (r = 0.78; p < 0.0001) and maize (r = 0.66; p = 0.005). In the Oxisol under no-tillage for >14 years, the spatial variation of FCO2 was explained by the soil physical attributes total porosity, macroporosity, microporosity, and soil temperature. The soil under crotalaria crop residues as a winter crop had an improvement in soil physical attributes, leading to a more aerated environment and hence a higher CO2 production process. However, the winter crops crotalaria (38.65 ±â€¯0.08 Mg ha-1) and maize (38.14 ±â€¯0.09 Mg ha-1) also provided a higher carbon stock on this tropical soil. Maize monocrop (41.13 ±â€¯0.11 Mg ha-1) as a summer crop under no-tillage system also promoted higher carbon stocks on this tropical soil. A strategy to optimize no-tillage systems in terms of FCO2 reduction and increase in soil carbon stock is related to the adoption of crop cultivation that includes legumes and grasses under intercropping and succession. Therefore, our results suggested that the summer sequences used in this study might contribute to reducing FCO2 and that both winter crops influenced the increased soil carbon stock.

Asunto(s)