Água disponível em um Latossolo Vermelho argiloso e murcha fisiológica de culturas

Abstract

RESUMOPara a determinação do volume de água retido no solo e disponível às plantas, é imprescindível quantificar o teor de água do solo (TAS) na capacidade de campo (CC) e no ponto de murcha permanente (PMP). O objetivo deste trabalho foi comparar os valores do TAS na CC e no PMP determinados por distintos métodos. Utilizaram-se amostras de um Latossolo Vermelho. A CC foi obtida no campo com o método do perfil instantâneo e, no laboratório, com funis de placa porosa. O PMP foi determinado, em laboratório, como sendo o teor de água residual retida no potencial matricial de -1,5 MPa, em câmara de Richards e com medidor de potencial de ponto de orvalho WP4 PotentiaMeter. Para murcha das plantas, o TAS foi significativamente menor no método fisiológico que o determinado nas câmaras de Richards; entretanto, o teor de água do solo no PMP foi estatisticamente igual para a cultura do girassol e superior para o milho, quando comparado com aquele obtido pelo WP4. A água disponível diminuiu com o aumento na tensão para a estimativa da CC e com o método WP4, mas não diferiu do método fisiológico. Assim, o WP4 permitiu adequada estimativa do PMP e disponibilidade hídrica às plantas, em solo argiloso.Palavras-chave: capacidade de campo, ponto de murcha permanente, retenção de água no solo Available water in a clayey Oxisol and physiological wilting of crops ABSTRACT To estimate available soil water to plants it is necessary to measure field capacity (FC) and permanent wilting point (PWP). The objective of this study was to compare soil moisture at FC and PWP measured by different methods. The soil used was a tropical Oxisol (Haplorthox). The FC was measured under field conditions, using the internal drainage method and in laboratory using porous plate funnel. The PWP was quantified in laboratory as the soil moisture at -1.5 MPa matric potential measured by pressure plate apparatus (Richards chamber) and by WP4 dewpoint Potentia Meter. The physiological PWP was measured using corn and sunflower plants, when they had three leaf pairs and showed irreversible wilting. The soil moisture for PWP based on the physiological method was smaller than soil moisture measured with the pressure plate apparatus; however, soil moisture for sunflower wilting was similar while for corn it was greater than that obtained with the WP4. The available water decreased with increase in water tension considered for estimating FC and with the WP4 method, but similar to one quantified with the physiological method. Thus, the WP4 allowed for adequate estimation of PWP and available water to plants in a clay soil.

Plant-available soil water capacity: estimation methods and implications

“…Aside from the fact that Klein et al (2006) had found a lower water content at PWP with this method, the authors evaluated the physiological method of determining PWP, and found the best PWP estimate by WP4, since there was no statistical difference in the measurement of PWP by the physiological method. This reinforces the importance of the choice of the PWP estimation method, and as can be seen from the results of this work and of Klein et al (2006; for a clayey Oxisol from southern Brazil, WP4 provided the lowest results of water content at PWP, with implications for AWC estimation, as well as other applications of the parameter.…”

“…Descriptions of the process are given by Decagon Devices (2000) and Scanlon (2002). Studies showed that PWP estimated by WP4 is closer to that determined by the physiological method than to the estimate in a Richards chamber (Klein et al, 2006), reflecting a better AWC estimate by the WP4 and physiological method than by the Richards chamber.…”

“…After this procedure, all samples were also used to determine the corresponding moisture at 1500 kPa tension in the thermocouple psychrometer apparatus Dewpoint Potential Meter WP4-T (Decagon Devices, 2000), according to the method described by Klein et al (2006), and from the bulk density of each sample the corresponding θ was calculated.…”

“…As several studies showed differences between the PWP obtained by the physiological method and the estimation in the Richards chamber at 1500 kPa (Cirino & Guerra, 1994;Souza et al, 2002;Klein et al, 2006), the thermocouple psychrometer (WP4) has recently been more widely used to estimate PWP, for the possibility of obtaining soil moisture at 1500 kPa (Costa et al, 2008;Kaiser et al, 2009;Klein et al, 2006Klein et al, , 2010Lima et al, 2012). Descriptions of the process are given by Decagon Devices (2000) and Scanlon (2002).…”

“…One of the indirect methods to estimate FC is the analysis of soil samples with disturbed and undisturbed structure in the laboratory, to define a water tension corresponding to moisture at field capacity (hcc) determined in the field. In Brazil, tensions of 6, 10 and 33 kPa have been commonly attributed to the estimate of moisture at field capacity for clay soils (Ferreira & Marcos, 1983;Bernardo, 1987;Reichardt, 1988;Silva et al, 1994;Mello et al, 2002;Souza et al, 2002;Ruiz et al, 2003;Araújo et al, 2004;Klein et al, 2006). Andrade & Stone (2011) estimated the water tension corresponding to moisture at field capacity between 6.5 and 7.5 kPa for Cerrado soils, using 2,242 soil samples.…”