Cícero Lopes da Silva

Coeficientes médios da equação de Angström-Prescott, radiação solar e evapotranspiração de referência em Brasília

The objective of this work was to estimate Angstrom-Prescott equation mean coefficients in Brasilia, DF, Brazil, and their effects on the calculations of global radiation (Rs) and reference crop evapotranspiration (ETo). It was used meteorological data from Embrapa Hortalicas weather station, from 1978 to 2003. The mean coefficients were determined by linear regression analysis considering monthly, annual and total periods. Using the calculated coefficients for different periods and those provided by FAO (0.25 and 0.50), Rs and ETo were estimated and their performances were evaluated. Monthly mean coefficient a varied from 0.241 to 0.345, and b from 0.430 to 0.515. Annual mean coefficients a and b were 0.278 and 0.498, and total means were 0.282 and 0.490, respectively. These coefficients did not differ from each other on radiation estimates. The month of July provided the worse estimates and performance. When using calculated Rs estimates with monthly, annual, total and FAO coefficients, estimated values of ETo did not differ from observed ones, providing excellent performance, despite the mean coefficient used. Depending on the final application, it is suggested the use of total mean coefficients due to their easiness to estimate the shortwave radiation.

Influência de variáveis climáticas e hidráulicas no desempenho da irrigação de um pivô central no oeste baiano

This work was carried out at Morenos farm, located in Barreiras, west of Bahia State, Brazil with the objective to evaluate the performance of a center pivot of irrigation, regarding the irrigation efficiency due to climatic and hydraulic variable during three periods of the year and under two lateral line rotation speeds. The three-field test was conducted, during the year 2002, in May 12 and 18; July 27 and 28; and September 28 and 29; the center pivot was operated with 100 and 50% of maximum rotation speed. The results were analyzed considering a randomized complete block design for lateral rotation speed factor, and with time factor as a split plot on lateral rotation speed. Results showed that the operating pressure at the lateral end was lower than the recommended one allowing an irrigation water depth below the average at that place. Values of irrigation efficiency were smaller than the ones recommended in the literature (80%). The irrigation depth of water was reduced from the first to the third time of evaluation, due to climatic changes. Relative humidity and specially wind speed had more influence on the application efficiency.

Drenagem interna como fator de diferenciação de Latossolos do Distrito Federal

The objective of this work was to determine the influence of soil physicohydric characteristics on Oxisols diagnostic attributes. Morphological, chemical, physical, mineralogical and physicohydric attributes were surveyed in profiles of five Latossolos Vermelhos (Rhodic Haplustox, LV) and of five Latosssolos Vermelho-Amarelos (Typic Haplustox, LVA), considered representative of this kind of Oxisols in Distrito Federal, Brazil. Besides the soil diagnostic attributes characterization, the water-table oscillation was monitored using 2.5-m depth observation wells, during one year. The studied Oxisols were considered chemically and physically similar. However, they differed as to morphological and mineralogical characterization, with the presence of concretionary horizons and goethite in the LVA. Goethite stability in this soils was influenced by the water-table oscillation. The presence of concretionry horizons in LVA caused an internal drainage deficiency, which resulted in lower saturated hydraulic conductivity and lower variation of the water-table levels. Therefore, LVA soils show lower agricultural potential than LV ones, in Distrito Federal. Oxisols physicohydric characteristics have little influence on soil diagnostic attributes, except for iron oxides mineralogy, which show increased contents of goethite in low internal drainage conditions.

Aspectos quantitativos e qualitativos do grão de trigo influenciados por nitrogênio e lâminas de água

A field experiment was carried out in a Red-Yellow Latosol in 2009 in order to assess the effects of different doses of nitrogen fertilization and water depth and their interaction on the grain yield and quality of wheat BRS 254. The experimental design was a completely randomized block with split plot on water level and four replications. Nitrogen doses in the plot were: 20, 50, 100, 200, and 400 kg ha-1. In the split plot water depths were: 120, 264, 342 and 392 mm. Mean yield and the majority of its components differed significantly with water depth and nitrogen dose. The exception occurred on the number of grains per spikelet which was not affected by nitrogen level. Minimum and maximum yield were 1,135 kg ha-1 and 5,209 kg ha-1, respectively for 120 mm and 50 kg ha-1 of N; and 392 mm and 200 kg ha-1 of N. In all of them, the highest yields were achieved by nitrogen doses over 220 kg ha-1. Crude protein content was significantly affected by water and nitrogen level interaction. The hectoliter mass, the strength of gluten and the falling number were significantly affected by water level. Water depths lower than 365 mm provided hectoliter weight below 78 kg hL-1. On the other hand water depths higher than 340 mm provided falling number below 250 s, suggesting caution on wheat agrossystems water management.

Comparação da evapotranspiração real simulada e observada em uma bacia hidrográfica em condições naturais de cerrado

The main objectives of this research were: (i) to simulate actual evapotranspiration in a small watershed under natural conditions of Brazilian Savannah during a year, between 08/04/98 and 08/03/99; (ii) to compare observed and simulated values of actual evapotranspiration, runoff and water depth stored in the soil. Using the water balance equation, the actual evapotranspiration (830.53 mm) was computed. During the year, twenty-one intermediate measurements were made in order to use the water balance method for short time intervals. Simulated and measured values of the actual evapotranspiration and the water flow did not have a good correlation. On the other hand, simulated values of the quantity of water stored in the soil to a one meter depth presented results very similar to the measured ones. During the driest period of the year, in spite of the high values of reference evapotranspiration, the actual evapotranspiration presented small values because of the lack of available water to evapotranspirate.

Variáveis climáticas e o desempenho de um pivô central, em Cristalina Goiás

This research aimed to evaluate center pivot performance as a function of wind speed (VV), relative humidity of air (UR) and mean air temperature (T) and establish a stochastic model to estimate application efficiency as a function of these independent variables. Data were collected, during the morning and the afternoon period, and during three times of the year (August, 12 and 13; September, 22 and 23; and October, 27 and 28, 2005), considering two speeds of outer driver unit (50 and 100%). A randomized block design was used for factor speed of outer driver with factor time of the year as a split plot of factor speed, and considering period of the day as replication. The mean pressure head at the end of the lateral was 137.3 kPa and close to the value predicted by the dealer of 127.5 kPa. The average water depths applied were 12 and 5.7 mm for 50 and 100% speed, respectively. Calculated Christiansens uniformity coefficient (CUC) provided values considered in literature as standard. Average water depths collected in the morning period were greater than the ones collected in the afternoon. VV, T and UR independent variables influenced significantly water application efficiency values.

Caracterização das vazões em uma pequena bacia hidrográfica do Distrito Federal, Brasil

No Brasil, a regiao do Distrito Federal e caracterizada pela presenca de corregos e pequenos rios, o que torna importante a caracterizacao das vazoes em microbacias. Utilizando uma serie de 13 anos provenientes da microbacia do corrego da Capetinga, foram analisadas: a estacionariedade de parâmetros hidrologicos; as distribuicoes estatisticas que melhor representam a vazao; a aplicacao de series curtas versus series medias no calculo de vazoes; e a necessidade de pedido de outorga para o uso da agua, de acordo com a legislacao vigente. As distribuicoes Lognormal 3 e Pearson 3 foram as que melhor representaram a serie de vazoes maximas, enquanto que Logpearson 3 foi a distribuicao mais indicada para a vazao minima. A precipitacao total anual, a vazao media de longa duracao e a vazao minima apresentaram series estacionarias, diferentemente da vazao maxima instantânea. O uso de series curtas para o calculo de vazoes na microbacia estudada nao se mostrou adequado, ja que gerou a superestimativa das vazoes minimas e a subestimativa das vazoes maximas. De acordo com a legislacao, captacoes no corrego Capetinga exigem pedidos de outorga a agencia reguladora, apesar de a vazao minima apresentar baixa magnitude, o que reflete no baixo potencial de exploracao do corrego.