Antonio Roberto Pereira

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.

An analysis of the criticism of thornthwaite's equation for estimating potential evapotranspiration

Abstract Thornthwaites approach for estimating potential evapotranspiration has been reviewed and an analysis of the criticism of its suitability was performed. An investigation of published data and results indicates that Thornthwaites equation is not appropriate for estimating oasis evapotranspiration, a condition of advection of dry hot air to a moist vegetated area. The analysis also showed that such a simple method is reliable if appropriate care is taken with the fetch necessary to obtain the potential rate condition. Several examples were used to check Thornthwaites proposal and it was concluded that the method should not be avoided, as has been suggested, neither for irrigation scheduling nor for climatic classification and crop zoning.

Um simulador dinâmico do crescimento de uma cultura de cana-de-açúcar

Este trabalho descreve a primeira versao de um simulador matematico-fisiologico do crescimento diario de uma cultura de cana-de-acucar (SIMCANA) em resposta as condicoes do ambiente durante a estacao de crescimento. SIMCANA resume a maior parte das informacoes disponiveis concernentes aos processos fisiologicos da cultura de cana-de-acucar. Esta sua versao nao inclui os processos degerminacao e florescimento, havendo necessidade de especificar as condicoes da cultura no primeiro dia de simulacao. Em funcao das condicoes diarias de radiacao solar global, temperatura maxima e minima, umidade relativa do ar, SIMCANA calcula as taxas de fotossintese, respiracao e crescimento da cultura, as taxas de senescencia das folhas e raizes, a massa seca das folhas, colmos e raizes, e o indice de area foliar. Embora varias relacoes empiricas tenham sido usadas, SIMCANA parece ser capaz de simular o crescimento da cultura de cana-de-acucar.

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%.

Toxicidade de produtos fitossanitários utilizados na cultura do cafeeiro a larvas de Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae) e efeitos sobre as fases subseqüentes do desenvolvimento do predador

The objective was to evaluate the selectivity of pesticides used in coffee crops to larvae of Chrysoperla externa (Hagen) and their effects on the subsequent developmental stages of the predator. The treatments in g a.i./L of water were: 1 - endosulfan (Thiodan 350 CE - 1.75), 2 - chlorpyrifos (Lorsban 480 CE - 1.2), 3 - betacyfluthrin (Turbo 50 CE - 0.013), 4 - sulphur (Kumulus 800 PM - 4.0), 5 - azocyclotin (Peropal 250 PM - 0.31), 6 - copper oxichloride (Cuprogarb 500 PM - 5.0) and 7 - control (water). The products were sprayed on first, second and third-instar larvae using a Potters tower. The larvae were individualized in glass tubes and maintained at 25 ± 2oC, RH of 70 ± 10% and 12h photophase. The toxicity of the pesticides was calculated based in their total effect (E) and classified according to recommendations of IOBC. Chlorpyrifos and betacyfluthrin were harmful to first-instar larvae (E > 99%). Endosulfan, sulphur, azocyclotin and copper oxichloride were harmless to first-instar larvae and the others were selective. Chlorpyrifos was also toxic to second and third-instar larvae, and the other compounds were selective (E < 30%). None of the pesticides affected the duration and survival rate of pupae or the sex ratio of the adults originated from treated larvae. Endosulfan, sulphur, azocyclotin and copper oxichloride were harmless to the larval stage of C. externa and did not affect the subsequent stages, so that they can be recommended in IPM programs for the coffee crop.

Relações radiométricas de uma cultura de cana-de-açucar

Durante o periodo de maximo indice de area foliar de uma cultura de cana-de-acucar, cv. NA56-79, os coeficientes de reflexao, transmissao e absorcao da radiacao solar incidente variaram em funcao do ângulo de incidencia dos raios solares e da faixa espectral considerada. A radiacao fotossinteticamente ativa (PAR) foi sempre menos refletida e transmitida e mais absorvida que a radiacao do infravermelho proximo (NIR). Em geral, para as fracoes consideradas, obtiveram-se as seguintes relacoes radiometricas: (1) radiacao disponivel, NPAR = 1,2 NNIR; (2) radiacao refletida, RPAR = 0,1 RNIR; (3) radiacao transmitida, TPAR = 0,2 TNIR; (4) radiacao absorvida, APAR = 1,6 ANIR.

Solar radiation regime in three cassava (Manihot esculenta Crantz) canopies

Abstract For solar elevation greater than 20° and clear sky conditions, the near infrared (NIR) and photosynthetically-active radiation (PAR) were, respectively, 0.54 and 0.46 of the incoming solar radiation. During the period of maximum leaf area index (LAI), plant structure had no apparent effect upon the crop reflection, transmission and absorption coefficients which were, however, functions of solar elevation. NIR was always more reflected and transmitted but less absorbed than PAR regardless of the plant structure. For the wavebands considered the following radiometric relations were, in general, obtained: (1) incoming radiation, IPAR = 0.85 INIR; (2) reflected radiation, RPAR = 0.07 RNIR; (3) net solar radiation, NPAR = 1.29 NNIR; (4) transmitted radiation, TPAR = 0.5 TNIR.

Estimativa da área foliar em milharal

In a single cross corn hybrid experiment it was tested the use of a Leaf Area Factor, obtained in one replication, in estimating the leaf area per plant of the other replications. It was used the corn hybrids HS1227 (flint) and HS7777 (dent) grown at the densities of 42,000 and 84,000 plants per hectare. There was no statistical difference between the observed and the estimated values. The standard error of the estimation, in all cases, was lower than 10%.

Calibration and test of the cropgro-dry bean model for edaphoclimatic conditions in the savanas of Central Brazil

Simulation models are important tools for the analysis of cultivated systems to estimate the performance of crops in different environments. The CROPGRO- model (DSSAT) was calibrated and validated using Carioca bean (Phaseolus vulgaris L.) to estimate yield and the development of the crop, sown in three row spacings (0.4, 0.5, and 0.6 m) and two fertilization rates (300 and 500 kg ha-1 of 4-30-16 N-P-K), in Santo Antonio de Goias, GO, Brazil. To calibrate the model a combination of the genetic coefficients that characterize the phenology and morphology of the dry bean crop was used to obtain the best possible fit between predicted and observed anthesis and physiological maturity dates, leaf area index (LAI), total dry matter (TDM), yield components, and grain yield for the 0.6 m row spacing. To test the model the experimental records of the 0.4 and 0.5 m row spacings were used. In both, calibration and test, the performance of the model was evaluated plotting observed and predicted values of LAI and TDM versus time, using the r2, and the agreement index (d) as statistical criteria. In relation to yield and yield components the percent difference between the observed and predicted data was calculated. The model appeared to be adequate to simulate phenology, grain yield and yield components for the Carioca bean cultivar, related to different levels of fertilization and row spacing, either during calibration or the testing phase. During the test, the grain yield was overestimated by less than 15.4%, indicating a potential use for the calibrated model in assessing climatic risks in this region.