Nilson Augusto Villa Nova

A model for the class A pan coefficient

Abstract The class A pan coefficient ( K p ) has been found to be determined by the daily wind run ( WR ), the average relative humidity ( RH ), and the fetch distance ( FD ) of the pan. While it is quite easy to measure WR and RH , FD has to be estimated. After a heavy rainfall or irrigation, FD is very large, but decreases rapidly as the field dries out. Therefore, it varies continuously. In practice, FD has been taken as a fixed distance between the pan and the border of the vegetated area. The values of K p recommended by the Food and Agriculture Organization (FAO) grossly overestimate the measured values for a tropical climate. Applying the Penman-Monteith equation to both a grass field and the pan resulted in an alternative simple model for K p which takes into consideration only the average air temperature and the grass/air resistance ratio. This ratio has been found here to vary with the wind speed, their relationship being described by a non-linear function. Bulk grass canopy resistance varied from 10 s m −1 to over 230 s m −1 , on a daily time scale, and this does not support the FAOs recommendation of a constant canopy resistance of 69 s m −1 for estimating grass reference evapotranspiration. On a daily or longer time scale the bulk grass canopy resistance does not follow the atmospheric vapour pressure deficit as well as it does on shorter time scales.

Analysis of the Priestley-Taylor parameter

Abstract Using three independent data sets, one representative of an upland rice crop grown in Campinas, Brazil, and the other two obtained in Davis, CA, for a perennial rye grass, it was shown that the variations of the Priestley-Taylor parameter α reported in the literature is well described by the fluctuations of the sensible heat flux ( H ). The results obtained show that α was linearly related to H in a positive way, either on an hourly basis or on a daily scale. The relationships found indicate that the original proposition of α = 1.26, for the potential conditions, does not represent a situation of advection.

CONSTRUÇÃO E AVALIAÇÃO DE PSICRÔMETRO ASPIRADO DE TERMOPAR

The construction of a low cost aspirated thermocouple psychrometer made of PVC tubes is described. The instrument can easily be connected to dataloggers. The aspiration is made by fans used in microcomputers and temperatures measured with cooper-constantan thermocouples. A cotton string was used to make the wet junction. Its perfomance was evaluated in comparison to an Assman aspirated psychrometer and a Vaisala Inc. capacitive higrometer, in natural and controlled environments. The results show a good agreement between measures, allowing air vapour, relative humidity, temperature and specific humidity gradients to be determined using the proposed psychrometer.

Potato potential yield based on climatic elements and cultivar characteristics

There is currently a great deal of interest in estimating crop productivity as a function of climatic elements by means of different crop weather models. An agrometeorolo gical model is presented based on carbon dioxide assimilation maximum rates for C3 plants, fraction of photosynthetically active radiation, air temperature, photoperiod duration, and crop parameters under tropical climate conditions. Such crop parameters include leaf area and harvest indexes, dry matter content of potato tubers, and crop cycles to estimate potato potential yields. Field data from observed productivity obtained with the cultivar Itarare (IAC-5986), grown under adequate soil water supply conditions at four different regions in the State of Sao Paulo (Itarare, Piracicaba, Tatui, and Sao Manuel), Brazil, were used to test the model. The results revealed an excellent performance of the agrometeorological model in study, with an underestimati on of irrigated potato productivity less than 10%.

Evapotranspiração do capim Tanzânia obtida pelo método de razão de Bowen e lisímetro de pesagem

Pasture irrigation in Brazil presented a large increasing in the recent years; however irrigation management practices have been done irrationally due to a lack of research on water use by pastures. The objectives of this research were to determine evapotranspiration of Guinea grass (Panicum maximum Jacq.) by measurements of a weighing lysimeter; to apply the energy balance method to estimate evapotranspiration of Guinea grass by means of an automated Bowen ratio system; and to compare the measured and the estimated values of evapotranspiration. The experiment was carried out in Piracicaba - SP, Brazil, between July 21, 2000 and July 15, 2001. The average evapotranspiration of Guinea grass was 4.13 mm day-1 by the energy balance method and 4.34 mm day-1 by the weighing lysimeter. It was concluded that the estimated evapotranspiration obtained by the automated Bowen ratio system can be influenced by advection and by long duration rainfalls. Despite of these constraints, there was a reasonable correlation with the measurements of a weighing lysimeter.

Estimativa do coeficiente de cultura do cafeeiro em função de variáveis climatológicas e fitotécnicas

Estimativas do Coeficiente de Cultura do CafeeiroRESUMOCom base em pesquisa realizada no cafezal do Departamento de Producao Vegetal da ESALQ,Universidade de Sao Paulo, utilizando a cultivar Mundo Novo IAC 388-17, enxertada na cultivar ApoataIAC 2258, plantada no espacamento de 2,5 m x 1,0 m (4.000 plantas.ha

Método alternativo para cálculo da temperatura base de gramíneas forrageiras

The assessment of the temperature below which plant growth ceases, known as base temperature (Tb) is key in for establishing the potential yield of a plant resource at a given location, and for quantifying the fitness of a given crop for a given production system. Whereas this is widely recognized, it is especially true in the case of perennial crops such as many of the forage species. This present study was aimed at developing, evaluating, and proposing a new methodological approach for the calculation of the Tb of forage crops, using both temperature and daylength, as a climatic variable named photothermal unit (PU). By using two regrowth cycles and their respective amounts of forage accumulated, the value of Tb can be calculated if the proportion between harvested yields and accumulated PUs of both regrowth cycles are the same. Yield data from two forage grass species, elephantgrass (Pennisetum purpureum Schum. cv. Napier) and Florico stargrass (Cynodon nlemfuensis Vanderyst var. nlemfuensis), from two field trials were used to test the proposed approach. Calculated Tb values were 15 and 12°C for elephantgrass and stargrass, respectively. These values are consistent with those generated by the classic method and reported in the literature.

Radiação solar disponível em Manaus (AM) e sua relação com a duração do brilho solar

Medidas de radiacao solar global, ao nivel do solo (Og), foram realizadas na sede do INPA em Manaus-AM, com um piranometro Eppley no periodo de 1977 a 1979. Foi estudada a correlacao entre a radiacao solar global e a insolacao. O resultado obtido foi Og = Qo (0,26 + 0,49 n/N). Sao apresentados tambem os valores diarios de radiacao e de insolacao. O valor medio diario de radiacao solar encontrado para o periodo foi de 373 cal. cm-2 dia-1.

Estimation of the potential evapotranspiration by a simplified penman method

The numerous methods for calculating the potential or reference evapotranspiration (ETo or ETP) almost always do for a 24-hour period, including values of climatic parameters throughout the nocturnal period (daily averages). These results have a nil effect on transpiration, constituting the main evaporative demand process in cases of localized irrigation. The aim of the current manuscript was to come up with a model rather simplified for the calculation of diurnal daily ETo. It deals with an alternative approach based on the theoretical background of the Penman method without having to consider values of aerodynamic conductance of latent and sensible heat fluxes, as well as data of wind speed and relative humidity of the air. The comparison between the diurnal values of ETo measured in weighing lysimeters with elevated precision and estimated by either the Penman-Monteith method or the Simplified-Penman approach in study also points out a fairly consistent agreement among the potential demand calculation criteria. The Simplified-Penman approach was a feasible alternative to estimate ETo under the local meteorological conditions of two field trials. With the availability of the input data required, such a method could be employed in other climatic regions for scheduling irrigation.

Base temperature and heat units for leaf flushing emission and growth ofHevea brasiliensis Muell. Arg.

In this study we determined the base temperature and Heat units for leaf flushing initiation and growth of RRIM-600 and GT1Hevea clones. The minimum base temperature was found to be approximately 16° C for leaf flushing emission and 19° C for shoot growth in terms of height. Approximately 420 degree days at 16° C as base temperature is required for successive leaf flushing initiation. Linear equations with correlation coefficients above 0.95 allow an estimation of the height increase from the accumulated degree days, corrected or otherwise for photoperiod. The highest correlation coefficients demonstrated a positive effect of the photoperiod among the factors influencing the shoot growth.In this study we determined the base temperature and Heat units for leaf flushing initiation and growth of RRIM-600 and GT1Hevea clones. The minimum base temperature was found to be approximately 16° C for leaf flushing emission and 19° C for shoot growth in terms of height. Approximately 420 degree days at 16° C as base temperature is required for successive leaf flushing initiation. Linear equations with correlation coefficients above 0.95 allow an estimation of the height increase from the accumulated degree days, corrected or otherwise for photoperiod. The highest correlation coefficients demonstrated a positive effect of the photoperiod among the factors influencing the shoot growth.