Marcelo Bortoluzzi Diaz

INFLUENCE OF SOIL PROPERTIES IN DIFFERENT MANAGEMENT SYSTEMS: ESTIMATING SOYBEAN WATER CHANGES IN THE AGRO-IBIS MODEL

AbstractThe water balance in agricultural cropping systems is dependent on the physical and hydraulic characteristics of the soil and the type of farming, both of which are sensitive to the soil management. Most models that describe the interaction between the surface and the atmosphere do not efficiently represent the physical differences across different soil management areas. In this study, the authors analyzed the dynamics of the water exchange in the agricultural version of the Integrated Biosphere Simulator (IBIS) model (Agro-IBIS) in the presence of different physical soil properties because of the different long-term soil management systems. The experimental soil properties were obtained from two management systems, no tillage (NT) and conventional tillage (CT) in a long-term experiment in southern Brazil in the soybean growing season of 2009/10. To simulate NT management, this study modified the top soil layer in the model to represent the residual layer. Moreover, a mathematical adjustment to th...

STUDY OF FILLING TECHNIQUES FOR METHANE FLOW DATA IN AN AREA OF FLOODED RICE

Studies on the emission of methane gas (CH 4 ) in agricultural ecosystems have received attention from the scientific community because it plays an important role in the greenhouse effect. Flood irrigation agriculture, such as irrigated rice, represents a considerable source of methane emissions (from 12 to 26 percent of all anthropogenic CH 4 emissions in the world). Estimates of CH 4 emissions have also been performed through the eddy covariance technique. Although this methodology makes continuous measurements of methane exchanges between the ecosystem and the atmosphere, failure to collect data can occur because the system is quite sensitive, especially in the hard weather conditions. The gap filling in the methane data are essential to obtain a daily or seasonal quantification of the emissions. In this study, different gap filling techniques are used to fill the CH 4 fluxes obtained by eddy covariance technique in an irrigated rice crop. The experimental data were obtained in Cachoeira do Sul - RS in the period from 11/20/2015 to 04/30/2016. The Look-Up Table (LUT), which consists of filling gaps using averages of flux values for periods with similar atmospheric conditions, was the technique that best close the gap in methane fluxes data.

HYSTERESIS LOOPS IN THE EVAPOTRANSPIRATION IN A PASTURE AREA IN SOUTH BRAZIL

One of the main components of water and energy balance in terrestrial ecosystems, the evapotranspiration (ET), was estimated using the eddy covariance technique. To better understand these energy transfer processes it is necessary to know how the ET responds to different meteorological variables. The main objective of this work is to investigate the hysteresis response of ET to environmental variables including air temperature (Temp), vapor pressure deficit (DPV) and net radiation (R n ) at a diel timescale for a pasture area in southern Brazil. ET presents hysteresis with DPV and Temp, responding more strongly to the vapor pressure deficit.

AN ANALYSIS OF THE SEASONALITY OF SURFACE ENERGY AND CARBON FLUXES IN AN ECOSYSTEM OF NATIVE FIELDS INSERTED IN THE PAMPA BIOME

In this study, the eddy-covariance technique was used to estimate the surface fluxes of carbon (CO2) and energy, in the latent (LE) and sensible (H) forms, over a native field ecosystem (pasture). The results show that the ecosystem in question presents a predominant seasonality in its ecological functioning, especially regarding the observations of the LE and CO2 fluxes, with carbon assimilation and evapotranspiration with maximum values during the summer. During the winter season observations point to a lower metabolic state of the ecosystem, with almost zero carbon assimilation (even a carbon source signal inversion) and the evapotranspiration rate falling to 60% of its value in the highest state metabolic activity.

VALIDATION THE PRODUCT OF EVAPOTRANSPIRATION (MOD16) FOR A CULTURE RICE IRRIGATED IN CACHOEIRA DO SUL – RS

The process of evapotranspiration (ET) is the second major component of the hydrological cycle, being connected directly with the amount of water vapor in the atmosphere. Determine the ET for large areas of irrigated rice is a limiting factor due to the high cost of equipment and skilled labor. Using data from remote sensors has been serving as an alternative technique for monitoring ET over large areas. The aim of this study is to evaluate the ET (MOD16) for a rice paddy in the Cachoeira do Sul - Brazil. The data used in this study cover the period from October 2013 to September 2014. The comparison between the ET-MODIS central pixel with the observed ET (estimated by technique Eddy Covariance) showed statistical values of RSME = 15.87, PBIAS -29.2. For the same pixels with vegetation were also extracted from the average values of ET-MODIS flow and compared with the tower, showing RSME = 14.59, PBIAS = -40.3. The biggest difference between the observed data with the MOD16 occurred during the rice cultivation that takes place between the spring/summer, not following the variability of ET.

EFFECTS OF A STRAW LAYER ON THE SOIL THERMAL BEHAVIOR

The presence of crop residue on the soil surface has an impact on evaporation, water storage, soil temperature and soil heat flux. Consequently, changes the energy transfer in the soil-atmosphere system. The objective of this work is study the influence of crop residues in the soil thermal variables. It was concluded that the thermal effect of a straw layer is large, leading to surface temperature differences around 10°C. With depth increasing, the effect of straw coverage decreases, leading to a temperature difference to 4°C of 5cm depth. The most important consequence of higher temperature on bare ground is an increase of soil heat flux. In stable weather conditions, this difference can reach 29 W/m 2 .

EVAPOTRANSPIRATION ESTIMATE ON PASTURE AREA IN SANTA MARIA – RS

The eddy covariance technique was used to estimate the sensible and latent heat flux between the atmosphere and the Pampa Biome in the period from 20 November 2013 to 20 November 2014. Annual Evapotranspiration (ET) was 1021 mm, corresponding to 55% of the annual precipitation. The ET is highly correlated with the net radiation (97%). The Bowen ratio was indicated that most of the available energy was used for the evaporation. The evaporative fraction remained about average, with greater variability in the colder months.

CLASSIC CALIBRATION EQUATIONS FOR LONG WAVE RADIATION IN THE PAMPA REGION ON A CLEAR DAY

The atmospheric longwave radiation is a fundamental quantity in calculating the radiation balance at the surface. Measures of this magnitude in the gaucho Pampas region are scarce. An alternative estimate for this variable is the use of classical equations that use air temperatures and steam pressure. The objective of this study was to evaluate the performance of five equations in the estimation of the long atmospheric wave radiation for a clear day on a Pampa biome located in Santa Maria-RS. Atmospheric longwave radiation measurements taken throughout the year 2014 on the site of Santa Maria / Brazil were used to validate the performance of equations. After the radiation estimates by classical equations, an adjustment by least squares was empegando to calibrate such equations to the biome Pampa. By adjusting it noted that the equation Brutsaert (1975) was best described obsevada long wave radiation in the PAMPA region.

POST-CLOSURE OF THE ENERGY BALANCE METHOD TO EVALUATE OF THE FLUXES OF THE LAND SURFACE MODELS

In this work, an analysis of the uncertainty of energy flux resulting from post-closure methods of the energy balance: H Method, LE method and Bowen method for the data observed in native grass area of the Pampa biome, located in Santa Maria, RS, Brazil. From these three methods suggest a new one, which we call the Combined Method. This method takes into account the quality classes of eddy covariance to choose the correct method to be applied. The uncertainties of flux were obtained by the difference between the fluxes corrected by one of the post-closure methods and the raw fluxes. The maximum values of the uncertainties occur during the daytime. Regarding the combined method, the highest percentage of cases resulted in the application of correction by Bowen method, followed by the LE method and with less occurrence Method H. Thus, this method can be considered valid to evaluate the uncertainty of simulated fluxes over land surface models.

EVAPOTRANSPIRATION PARTITION FOR A MAIZE CROP

Crop transpiration is directly related to its production. Plant transpiration varies along the crop cycle and in most part of this cycle is the dominant component in evapotranspiration. There are several well-established techniques to estimate these components individually. Currently, the eddy covariance technique is widely used for measurements of evapotranspiration. However, this technique is unable to identify the flow of water between the surface and the atmosphere has its origin by evaporation from soil or plant transpiration. A new methodology based on the efficiency of water use by the plant is being used successfully. This technique determines how much water is transpired to each carbon molecule attached to the plant. This efficiency ratio is obtained by the difference of external and internal concentration on stomatal cavity of CO2 and H2O. In practice, external concentration of carbon and water is obtained from the infra-red gas analyzers used to obtain data in eddy covariance technique. In this work, the evapotranspiration for a maize crop in southern Brazil is partitioned and compared to the surface model AGRO-IBIS. Results show that the maximum development of the plant transpiration is approximately 70% of evapotranspiration.