Variability of water balance components in a coffee crop in Brazil

Abstract

Establishing field water balances is difficult and costly, the variability of their components being the major problem to obtain reliable results. This component variability is presented herein for a coffee crop grown in the Southern Hemisphere, on a tropical soil with 10% slope. It was observed that: rainfall has to be measured with an appropriate number of replicates; irrigation can introduce great variability into calculations; evapotranspiration, calculated as a remainder of the water balance equation, has exceedingly high coefficients of variation; the soil water storage component is the major contributor in error propagation calculations to estimate evapotranspiration; and that runoff can be satisfactorily controlled on the 10% slope through crop management practices. Key words: component variability, rainfall, evapotranspiration, soil water storage VARIABILIDADE DOS COMPONENTES DO BALANÇO HÍDRICO DE UMA CULTURA DE CAFÉ NO BRASILRESUMO: O estabelecimento de balanços hídricos no campo é difícil e dispendioso, sendo a variabilidade de seus componentes o maior problema para se obter resultados confiáveis. Esta variabilidade dos componentes é aqui apresentada para uma cultura de café desenvolvida no hemisfério sul, em um solo tropical com 10% de declividade. Foi observado que a chuva deve ser medida com número apropriado de repetições; a irrigação pode introduzir grande variabilidade dos cálculos; a evapotranspiração calculada a partir da equação do balanço hídrico tem coeficientes de variação muito altos; o componente armazenamento de água no solo é o que mais contribui na propagação dos erros; e que a enxurrada pode ser satisfatoriamente controlada nesse declive de 10% por meio de práticas de manejo. Palavras-chave: variabilidade dos componentes, chuva, evapotranspiração, armazenamento de água

Armazenagem de água e produtividade de meloeiro irrigado por gotejamento, com a superfície do solo coberta e desnuda

“…Valores elevados de coeficiente de variação são comumente citados na literatura que aborda o estudo dos componentes do balanço de água no solo (Reichardt et al, 1993;Villagra et al, 1995;Silva et al, 2006) e refletem a variabilidade espacial natural que os solos apresentam. Villagra et al (1995) ressaltam que em períodos em que os valores de armazenagem inicial e final são semelhantes, a variação de armazenagem se aproxima de zero, e altos valores de coeficiente de variação podem ser observados.…”

Fertilizer 15N balance in a coffee cropping system: a case study in Brazil

“…The climatic conditions that prevailed during the experimental period (Figure 3), expressed in terms of air temperature (T air ), rainfall (P), potential crop evapotranspiration (Et c ) evaluated according to the method of Penman-Monteith (Allen et al, 1998) and actual evapotranspiration (ER) estimated from water balances (Silva et al, 2006), did not deviate very much from the long-term behavior for Piracicaba (Villa Nova, 1989). Total rainfall during the first and second years, 1,342.9 and 1,118.9 mm, respectively, were somewhat above and below the long-term average of 1,247 mm and did not induce water stress to plants during vegetative growth, fruit development and maturation.…”

“…Hence, during the first year, 68.9 % of the fertilizer N was absorbed by the plant (C 1 to C 12 ) which represents a very high fertilizer use efficiency, due mainly to: (1) appropriate timing of fertilizer, applied before the coffee plant growth rate started to decrease (Fenilli et al, 2007b); (2) the mode of N fertilization, applied split in four, below the plant canopy, available to roots of the surface soil layer kept moist by the mulch; (3) the choice of ammonium sulfate as N source, with a low volatilization potential; and (4) the favorable soil-water regime throughout the year and at times of fertilizer application (Silva et al, 2006). In other situations, reports show lower recoveries, e.g.…”

“…To observe the N dynamics in the soil profile, complete water balances were established every 14 days (Silva et al, 2006) aiming at an evaluation of periods of water excess during which drainage might occur and, as a consequence, N would be leached from the soil profile. The instantaneous leaching N flux densities q N (kg m -2 day -1 ) were estimated from the product of the water drainage flux densities q w (L m -2 day -1 ) and the total-N (NO 3 + NH 4 ) concentration C N (kg L -1 ) (Kutílek & Nielsen, 1994):…”

Modelling air temperature for the state of São Paulo, Brazil

“…Examples of methods are traditional hand-interpolated isopleths (Burrough & McDonnell, 1998), and computational techniques involving spatial Thiessen polygon interpolators, inverse distance weighting, cubic splining, trend surface analysis, thin plate splines (Hutchinson, 1991;Lennon & Turner, 1995;Saveliev et al, 1998;Felicísimo-Pérez et al, 2001), Kriging (Dingman et al, 1988;Bigg, 1991;Philips et al, 1992) or co- Kriging (Goovaerts, 2000) are frequently used. Multiple regression analysis is another method widely used to compute the distribution of climatic variables from discrete data (Collins & Bolstad, 1996;Goodale et al, 1998;Ninyerola, 2000;Ninyerola et al, 2000;Lennon & Turner, 1995;Valeriano & Picini, 2000;Silva et al, 2006).…”