Osvaldo Cabral

Patterns of water and heat flux across a biome gradient from tropical forest to savanna in Brazil

[1] We investigated the seasonal patterns of water vapor and sensible heat flux along a tropical biome gradient from forest to savanna. We analyzed data from a network of flux towers in Brazil that were operated within the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA). These tower sites included tropical humid and semideciduous forest, transitional forest, floodplain (with physiognomies of cerrado), and cerrado sensu stricto. The mean annual sensible heat flux at all sites ranged from 20 to 38 Wm 2 , and was generally reduced in the wet season and increased in the late dry season, coincident with seasonal variations of net radiation and soil moisture. The sites were easily divisible into two functional groups based on the seasonality of evaporation: tropical forest and savanna. At sites with an annual precipitation above 1900 mm and a dry season length less than 4 months (Manaus, Santarem and Rondonia), evaporation rates increased in the dry season, coincident with increased radiation. Evaporation rates were as high as 4.0 mm d 1 in these evergreen or semidecidous forests. In contrast, ecosystems with precipitation less than 1700 mm and a longer dry season (Mato Grosso, Tocantins

Transpiration from an Amazonian rainforest calculated from stomatal conductance measurements

Abstract A multi-layer combination equation has been used to calculate transpiration from a tropical rainforest in the central Amazon, Brazil. The five-layer formulation used through-canopy measurements of temperature and humidity deficit with leaf stomatal and boundary layer conductances scaled up to canopy layer values used a profile of canopy leaf area index derived from the literature. Net radiation input to each layer was estimated from an above canopy measurement using an extinction function and leaf area index. Transpiration calculated for hourly and daily periods in a range of seasonal conditions agreed well with those measured directly with an eddy correlation device. Four simplified forms of the transpiration calculation were also compared with the direct measurement. These simplified forms used the above-canopy or the average of the through-canopy values of weather variables and used either the average of leaf conductances multiplied by total leaf area index or the average of the layer conductances. These simplified forms of the transpiration calculation gave poorer agreement with measured transpiration.

Measurements of CO2 exchange over a woodland savanna (Cerrado Sensu stricto) in southeast Brasil

A tecnica de correlacao dos vortices turbulentos (eddy correlation) foi utilizada para se estimar a produtividade liquida do ecossistema (PLE) em uma area de Cerrado Sensu stricto, no sitio experimental da Gleba Pe de Gigante, no sudeste do Brasil. O conjunto de dados coletados incluiu tambem medidas de variaveis climatologicas e de respiracao do solo com câmaras estaticas, no periodo de 10 de Outubro de 1999 a 30 de Marco de 2002. A respiracao do solo media anual foi de 4.8 molCO2m-2s-1, com diferencas sazonais que variaram entre 2 a 8 molCO2 m-2s-1 durante a estacao seca (Abril a Agosto) e na estacao chuvosa, respectivamente, por um padrao de sensivel correlacao com a temperatura (Q10=4.9) e umidade do solo. Com base nos fluxos atmosfericos de CO2, a PLE mostrou uma variabilidade no ciclo diurno grandemente controlada pela radiacao solar, umidade e temperatura do ar. Na escala sazonal, a umidade do solo foi uma variavel de alta correlacao com a PLE, que aparentemente induziu a queda de folhedo, reducao da atividade fotossintetica e da respiracao do solo. O sinal da PLE foi negativo (sumidouro) na estacao chuvosa e no inicio da estacao seca, com taxas de -25 kgCha-1dia-1, e maximos de ate 40 kgCha-1dia-1. Na estacao seca o sinal foi positivo (emissao), o que foi revertido logo no inicio das chuvas. No fim da estacao seca, em dias de grande estresse hidrico, ainda observou-se a resposta da fotossintese na escala do ecossistema, mesmo tendo sido positiva a PLE. Paralelamente ao decorrer da estacao seca, a PLE progressivamente aumentou de 5 ate 50 kgCha-1dia-1. A soma annual da PLE mostrou-se aproximadamente balanceada, tendo sido no entanto, sob um vies de maior precisao, um pequeno mas significativo sumidouro de 0.1 0.3 tCha-1ano-1. Consideramos a hipotese de um pequeno sumidouro como possivelmente realista, dadas as restringentes correcoes impostas no calculo dos fluxos turbulentos, e algumas hipoteses favoraveis de sucessao de estagios do Cerrado, fertilizacao de CO2 atmosferico e variabilidade climatica.

Atmosphere and hydrological controls of the evapotranspiration over a floodplain forest in the Bananal Island region, Amazonia

influenced the energy exchange. Soil moisture, which was substantially depleted during the dry season, and adaptative vegetation mechanisms such as leaf senescence contributed to limit the dry season ET. Strong drainage within permeable sandy soils helped to explain the soil moisture depletion. These results suggest that the Bananal flooding area shows a different pattern in relation to the upland Amazon forests, being more similar to the savanna strictu senso areas in central Brazil. For example, seasonal ET variation was not in phase with Rn; the wet season ETwas higher than the dry season ET; and the system stored only a tiny memory of the flooding period, being sensitive to extended drought periods.

A biophysical model of Sugarcane growth

Scientists predict that global agricultural lands will expand over the next few decades due to increasing demands for food production and an exponential increase in crop‐based biofuel production. These changes in land use will greatly impact biogeochemical and biogeophysical cycles across the globe. It is therefore important to develop models that can accurately simulate the interactions between the atmosphere and important crops. In this study, we develop and validate a new process‐based sugarcane model (included as a module within the Agro‐IBIS dynamic agro‐ecosystem model) which can be applied at multiple spatial scales. At site level, the model systematically under/overestimated the daily sensible/latent heat flux (by −10.5% and 14.8%, H and λE, respectively) when compared against the micrometeorological observations from southeast Brazil. The model underestimated ET (relative bias between −10.1% and –12.5%) when compared against an agro‐meteorological field experiment from northeast Australia. At the regional level, the model accurately simulated average yield for the four largest mesoregions (clusters of municipalities) in the state of São Paulo, Brazil, over a period of 16 years, with a yield relative bias of −0.68% to 1.08%. Finally, the simulated annual average sugarcane yield over 31 years for the state of Louisiana (US) had a low relative bias (−2.67%), but exhibited a lower interannual variability than the observed yields.

Water use in a sugarcane plantation

The evapotranspiration (E) from a sugarcane plantation in the southeast Brazil was measured by the eddy‐covariance method during two consecutive cycles. These represented the second (393 days) and third year (374 days) re‐growth (ratoon). The total E in the first cycle was 829 mm, accounting for 69% of rainfall, whereas in the second cycle, it was 690 mm, despite the total rainfall (1353 mm) being 13% greater. The ratio of E to available energy, the evaporative fraction, exhibited a smaller variation between the first and second cycles: 0.58 and 0.51, respectively. The estimated interception losses were 88 and 90 mm, respectively, accounting for approximately 7% of the total rainfall. The sugarcane yield in the second cycle (61.5 ± 4.0 t ha−1) was 26% lower than the first cycle, as well as lower than the regional average for the third ratoon (76 t ha−1). The below average yield was associated with less available soil water at the beginning of the cycle, with the amount of rainfall recorded during the first 120 days of re‐growth in the second cycle being 16% of that recorded in the first (203 mm).

Método para monitorar perdas na aplicação de agrotóxicos na cultura de tomate

The available methodology for pesticide residues analysis is very expensive to be used on spraying losses studies and occupational exposure assessment during pesticide application. So, the marking of spray liquids prior to dispersion with easily detectable tracers has become widely accepted practice. The objective of this research was to evaluate a method to assessment the pesticide deposition, characterised by the use of a tracer marked spray liquid and a special sampling technique. The tracer used in this work was the copper, in a fungicide formulation, with low cost and easy atomic absorption spectrophotometric analysis. Cards of blotter-like papers were used as artificial target to catch the droplets. Cards were clipped on cotton strings at constant distances and were disposed on plants possibiliting a height stratified sampling. Cards on Petri dishes are used upon the soil. Between 59 and 76% of the spray were lost according to plant height.

Avaliação da solarização do solo para o controle de Ralstonia solanacearum

The use of soil solarization for the control of bacterial wilt, caused by Ralstonia solanacearum, was evaluated by burrowing nylon bags containing soil infested with the bacteria in plots solarized or not. Two experiments were carried out in Campinas (SP), from February to April/2001, and Piracicaba (SP), from December/2001 to February/2002. The experiments were set up in a completely randomized factorial design, with four replications, in 4 x 4 meter plots. The factors evaluated were soil solarization with a transparent plastic film 100 µm thick, period of treatment (30 and 60 days and 37 and 60 days for the first and second experiments, respectively) and, only for the second experiment, soil depth (10 and 20 cm). The soil of each nylon bag collected after the previously established solarization periods, was placed in pots where tomato (Lycopersicon esculentum) seedlings were transplanted. In the non-solarized soil, in both experiments, 43 to 100% of the tomato plants wilted. In the second experiment, 6 to 22% of the plants grown on the soil solarized for 37 days wilted. No wilted tomato plants were observed in the solarized plots of the first experiment nor in the soil solarized for 60 days, in both soil depths, of the second experiment. The results obtained indicate that soil solarization has potential for the control of R. solanacearum.

SENSIBILITY OF DISTRIBUITED BIOSPHERE-HYDROLOGICAL MODEL TO HYDRAULIC SOIL PROPERTIES FOR A SMALL BASIN OF WOODLAND SAVANNA

For modeling of hydrologic processes that occur on the scale of watersheds to characterize the availability of water in it, you need a physical model that can represents the topography, vegetation and soil characteristics. On the other hand, the variables that provide atmospheric forcing require great accuracy and models are sensitive to them mainly to rainfall, it is the main input in hydrological modeling. This study focuses on evaluation of four physical parameters of soil in hydrologic modeling in Giant Foot basin, SP, Brazil with DBHM model. The study period covers the years 2009-2014, FAO’s soil maps were used for the physical characterization of the basin, and the MODIS for vegetation data (LAI and FPAR). Domain of 500 m for spatial resolution in a basin area of 11.94 km2. Was used a basic configuration that let determine the influence of soil parameters in the water content results for the surface layer up to 1 m. It shows higher water retention in the soil to high values of the Campbell parameter, matric potential and porosity; sensitivity to hydraulic conductivity depends on the relationship with the daily accumulated rainfall.

COMPARAÇÃO DA RADIAÇÃO SOLAR GLOBAL INCIDENTE OBTIDA POR DIFERENTES FONTES DE DADOS PARA O NORTE DE SP

O objetivo deste trabalho foi comparar os dados de radiacaosolar global incidente de tres torres micrometeorologicas localizados naregiao norte do estado de Sao Paulo, com os dados disponiveis de outrasfontes: estacoes meteorologicas de superficie mais proximas e estimativasa partir de satelites (modelo GL1.2). A regressao linear entre as estimativasde radiacao do modelo GL1.2 com as observacoes na area decerrado indicou um ajuste melhor do que o obtido com a estacaometeorologica mais proxima. Esses resultados sugerem que as estimativasde radiacao do modelo GL1.2 podem ser usadas para o preenchimentode falhas de Ki medida nas torres micrometeorologicas e potencialmentecomo forcante em esquemas de superficie e modelos hidrologicosaplicados a bacias hidrograficas da regiao.