Marcos V. Folegatti

A new method for estimating the leaf area index of cucumber and tomato plants

Non-destructive methods of leaf area measurement are useful for small plant populations, such as experiments with potted plants, and allow the measurement of the same plant several times during the growing period. A methodology was developed to estimate the leaf area index (LAI) of cucumber and tomato plants through the evaluation of the leaf area distribution pattern (LADP) of the plants and the relative height of the leaves in the plants. Plant and leaf height, as well as the length and width of all leaves were measured and the area of some leaves was determined by a digital area meter. The obtained regression equations were used to estimate the leaf area for all relative heights along the plant. The LADP adjusted to a quadratic model for both crops and LAI were estimated by measuring the length and width of the leaves located at the relative heights representing the mean leaf area of the plants. The LAI estimations presented high precision and accuracy when the proposed methodology was used resulting in time and effort savings and being useful for both crops.

Salt accumulation and distribution in a greenhouse soil as affected by salinity of irrigation water and leaching management

Estudaram-se os efeitos da salinidade da agua de irrigacao, fracao de lixiviacao e sua frequencia de aplicacao na salinizacao de um solo. Durante um ciclo de pepino enxertado em ambiente protegido, foram aplicadas aguas de diferentes salinidades (S1=1,54, S2=3,10 e S3=5,20 dS m-1) e duas lâminas de irrigacao associadas as suas frequencias de aplicacao (W1=1,00 ETc; W2F1=1,25 ETc em todas as irrigacoes e W2F2=1,25 ETc quando a lâmina de irrigacao acumulada em W1 alcancou 100 mm em que ETc e a evapotranspiracao da cultura). O delineamento experimental foi o de blocos casualizados em esquema fatorial 3x3 com 3 repeticoes. A salinidade do solo nas profundidades de 0,1, 0,3 e 0,5 m aumentou linearmente com a salinidade e a fracao de lixiviacao nao teve efeito independente do seu manejo. A concentracao de sais foi maior proximo a superficie do solo e na regiao compreendida entre dois gotejadores.

Water consumption of the estevia (Stevia rebaudiana (Bert.) Bertoni) crop estimated through microlysimeter

The knowledge of water requirement of crops in the different growing phases elicits higher crop yield and rational use of water resource. The aim of this work was to estimate the water consumption of stevia using two constant watertable microlysimeters. The research was conducted in San Piero a Grado, Pisa, Italy. The data were collected daily from June, 1st, to October, 22th, 2000. Reference evapotranspiration was determined by the Penman-Monteith-FAO method, in the same period. Microlysimeters watertables level were maintained at the 35 cm depth. Crop evapotranspiration for the total cicle (80 days) was 464 mm. For the most water consuming phase, crop average evapotranspiration was 5.44 mm day-1. The crop coefficient values were 1.45 for the first 25 days, 1.14 for the next period (26 to 50 days), and 1.16 for the latest period (51 to 80 days). The stevia leaf yield of the microlysimeters was 4.369 kg ha-1 and their steviosideo content 6.49%.

Class A pan coefficients (Kp) to estimate daily reference evapotranspiration (ETo)

O coeficiente do tanque classe A (Kp) tem sido empregado para se estimar a evapotranspiracao de referencia (ETo), importante componente no manejo de agua de culturas irrigadas, a partir da evaporacao do tanque Classe A (ECA). Existem diversos metodos para se determinar os valores de Kp, cuja maioria e baseada nas informacoes de velocidade do vento, umidade relativa e extensao e condicoes da area de bordadura, ao redor do tanque. Neste trabalho foram analisados os seguintes metodos de estimativa do Kp: Doorenbos & Pruitt (1977), Cuenca (1989), Snyder (1992) e Pereira et al. (1995); Raghuwanshi & Wallender (1998) e FAO/56 (Allen et al., 1998). Os valores de Kp, estimados e calculados pela relacao entre a ETo medida em lisimetro de pesagem e a ECA, foram comparados por meio de analise de regressao. O mesmo procedimento foi utilizado para se avaliar o desempenho dos diferentes metodos de determinacao do Kp na estimativa da ETo, a partir da ECA, cujos resultados mostraram que a concordância entre os valores de Kp calculados e estimados pelos diferentes metodos, foi pequena (R2< 0,2), o que resultou em estimativas de ETo com alta dispersao (R2< 0,8). Os melhores metodos de determinacao do Kp, para a estimativa da ETo, foram os de Pereira et al. (1995) e Cuenca (1989), ambos apresentando alta eficiencia. O uso de um Kp arbitrario e constante (0,71) na estimativa da ETo resultou na mesma precisao e exatidao das estimativas feitas com os valores de Kp determinados pelos metodos de Pereira e de Cuenca. O uso de um valor constante de Kp e uma opcao simples e pratica para se estimar ETo a partir da ECA, porem este valor necessita ser calibrado para cada local, sob diferentes condicoes climaticas.

Calibração da Reflectometria no Domínio do Tempo (TDR) para a estimativa da concentração da solução no solo

Time Domain Reflectometry (TDR) is a reliable method for in-situ measurements of the humidity and the solution concentration at the same soil volume. Accurate interpretation of electrical conductivity (and soil humidity) measurements may require a specific calibration curve. The primary goal of this work was to establish a calibration procedure for using TDR to estimate potassium nitrate concentrations (KNO3) in soil solution. An equation relating the electrical conductivity measured by TDR and KNO3 concentration was established enabling the use of TDR technique to estimate soil water content and nitrate concentration for efficient fertigation management.

Spatial and temporal characterization of water and solute distribution patterns

The use of drip irrigation and marginal water is growing rapidly in some areas, highlighting the need to develop sound fertigation practices that combine environmental and crop production concerns. In this study the spatial and temporal water and solute distribution patterns are characterized to underpin fertirrigation design and management systems. Time domain reflectometry (TDR) probes were used to monitor the distributions of potassium nitrate (KNO3) and water from drippers discharging at a constant flow rate of 4 L h-1 in soil-filled containers. In the interactions between the different profiles, a gradient distribution of the solution in the soil was observed, with greater storage of solution close to the dripper, which decreased gradually as it approached the wetting front. To reduce leaching of fertigated ions, the frequent application of small amounts of solution during irrigation is recommended.

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.

Evapotranspiration and crop coefficient of cucumber in greenhouse

The evapotranspiration (ETc) and crop coefficient (Kc) of cucumber in a greenhouse were determined during the winter-spring season in Piracicaba, SP, Brazil. Crop was irrigated with water of three different levels of salinity: S1 = 1.5, S2 = 3.1 and S3 = 5.2 dS m-1. Electrical conductivity of S1 was obtained only by addition of fertilizers, as fertigation was used, and the S2 and S3 levels in addition to fertilizers received magnesium sulphate, calcium chloride and sodium chloride. Cucumber seedlings, cv. Hokushin, were grafted on squash, transplanted on beds in double rows and directed vertically with a single stem. Irrigation was performed when soil matric potential reached -30 kPa, which was determined by the mean matric potential at 0.15 and 0.30 m depths, and the depth of irrigation was calculated from a reduced-evaporation pan. A randomized block design was adopted with three replications. The ETc and Kc were found to reduce linearly by the salinity of the irrigation water with reduction in ETc of 4.6% for unit increase of salinity. Due to the reduced evapotranspiration in saline treatments, deep percolation was increased by saline water and corresponded to 4, 7 and 17% of the total applied water in S1, S2 and S3, respectively. Measured Kc values for S1 were very close to the estimated values thus the combined use of tensiometers and evaporation pan was found to be adequate for irrigation management in greenhouse.

Doses de N e K no tomateiro sob estresse salino: III. Produção e qualidade de frutos

The application of high doses of fertilizers could increase the tolerance of crops to salts by reducing the nutritional imbalance caused by salinity. In order to test this hypothesis, a study was conducted to evaluate the production and quality of tomato fruits, hybrid Facundo, irrigated with saline water, under different doses of N and K. The work was conducted in a greenhouse and the treatments were composed of the combination of three levels of N (7.5, 15.0 and 22.5 g per plant of N) and three levels of K (8, 16 and 24 g per plant of K2O) applied through drip fertigation, in the 3 x 3 factorial design, with five replications. Also the salts sodium chloride and calcium chloride were also added to irrigation water for obtaining an electrical conductivity of the irrigation water of 9.5 dS m-1. Effects of the treatments were not verified on the production components (yield, size and mean weight of fruits) nor on some parameters of the quality of the fruits (concentration of nutrients, soluble solids and titratable acidity), the concentration of K increased and the ratio Na/K reduced in the fruits with increasing dose of K. It was concluded that the application of high doses of N and K did not contribute to the increase the tolerance of tomato to salinity.

Estudo exploratório do uso da vinhaça ao longo do tempo: I. Características do solo

The aim of this study was to accomplish an exploratory study of the stillage in the areas with sugarcane, through a comparative and systematic analysis. The present work was conducted in the company USACIGA - Sugar, Alcohol and Electric Power S.A. located at Gaucha, northwest Parana state. Treatments constituted of areas cultivated with sugarcane and submitted to different times of stillage application, respectively 1, 2, 3, 4, 12 and 20 years, and a reference area, without application. In all the studied areas trenches of 1 m3 were opened, geo referenced in 340 m of altitude for accomplishment of the soil classification and sample collection. The evaluations were performed of the density, soil particle density, organic carbon, cation exchange capacity (CEC), total porosity, soil water moisture for the sugarcane, besides the relationships among K, Ca, Mg and V%. The results indicated that the stillage application contributed to the organic carbon and potassium increase in the soil and that the sugarcane productivity presented a direct relationship with the ratio of potassium adsorption increase in the soil.