Abstract
The uptake of water from the roots of crops comes to being a physiological response of the plant to the water loss process through its stomata. Getting to know the daily transpiration rates throughout the phenological cycle allows for the application of the ideal amount of irrigation water at the right moment to maximize production with environmental protection. Since transpiration direct measurements at the field, mainly for trees in general, are to be of operational difficulty and relatively high cost we came up with a methodology that allows one to calculate the daily transpiration rates of apple trees and citrus orchards from variables of both the physical environment and the crop. The input data of the proposed model are air temperature, air relative humidity, photoperiod duration, and leaf area. Estimated transpiration rates based on the water potential gradient between the air and leaf approach were comparable in apple trees and citrus orchards. Sap flow daily values were obtained by means of the heat balance method at Bordeaux, France, and Piracicaba, SP, Brazil. All the coefficients of determination of the regression equations obtained herein were higher than 0.93. This allows one to calculate the amount of irrigation water to be applied throughout the crop growing seasons with a high precision as a function of meteorological data and crop covering density at the sites in the study.
Highlights
Valancogne and Nasr (1993) showed that when apple trees of a small height do not experience water deficiency in the soil, the sap flow determined by the heat balance method might depict very well the daily transpiration rates
The estimates of the stomachic resistance of apple tree leaves were obtained from the Equation 4, according to 12 dates selected from the years 1988 and 1989, as a function of the available data set collected at the studied site
Data of air saturation pressure deficit (De, kPa), mean air absolute temperature (T, Kelvin), mean relative humidity (RH, %), day length or photoperiod duration (N, hours), transpiration rate measured by the heat balance approach (TM, L tree-1day-1), leaf area (LA, m2) and dossel stomachic resistance (Rs, s m-1) are presented in Table 3 for the considered dates
Summary
The transpiration of crops is a variable depending on the climate, soil and plant with direct measurements at the field of operational difficulty, mainly for trees in general. Valancogne and Nasr (1993) showed that when apple trees of a small height do not experience water deficiency in the soil, the sap flow determined by the heat balance method might depict very well the daily transpiration rates. The Penman-Monteith equation has been adapted for the calculation of transpiration from leaves and is generally used for the estimation of apple trees transpiration rates The application of such equation requires meteorological data collected at the ambient of the crop in study (net radiation at the dossel level, air temperature and water vapor saturation deficit, wind speed) and assessment of crop variables, such as conductance to diffusion of water vapor through the stomata and aerodynamic conductance, which are difficult to determine (Villa Nova et al, 2002). The proposed approach dismisses the utilization of the conductance to diffusion of water vapor, aerodynamic conductance and net radiation at the dossel level and is the basis for the existing differences between water potential in the atmospheric air and within the stomachic chamber of the leaves Such a gradient is the driving-force of the transpiration process. Its utilization as a tool for the maximization of yields with a better reclamation of the water resources under drip irrigation system in orchards was tested as to its viability, taking into consideration the data of sap flow collected by Angelocci (1996) in apple trees, as well as by Marin (2000) in citrus orchards under distinct climatic conditions
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