Abstract
ABSTRACT The knowledge on soil water dynamics is the basis of crop water management. The soil water balance (SWB) method is used for this purpose. However, its application in cactus may lead to misinterpretation in water efficiency analysis, since it does not consider the amount of water retained in the plant (WRP). This study aimed to evaluate SWB applicability, hydrodynamic changes and water efficiency of forage cactus clones under irrigation. The clones ‘Orelha de Elefante Mexicana’ (OEM), ‘IPA Sertânia’ (IPA) and ‘Miúda’ (MIU) were submitted to irrigation depths (2.5, 5.0 and 7.5 mm) and frequencies (7, 14 and 28 days), in Serra Talhada, PE, Brazil, between March 2012 and August 2013. The SWB was applied, by adding the WRP in the estimate of the effective actual evapotranspiration (ETrEF). The water efficiency indicators were calculated. The actual evapotranspiration on SWB (ETrSWB) overestimated ETrEF and, like other SWB components, it was affected by the factors irrigation depth, frequency and clone. The clone OEM is the most efficient, due to the use of the WRP, while MIU leads to highest gross economic returns for sale of cladodes as seed. As conclusion, the application of the soil water balance method in areas cultivated with cactus species must be accompanied by WRP.
Highlights
Despite its complexity, the soil water balance (SWB) has satisfactory results in the analysis of water dynamics in the cultivation of C3 and C4 plants (Ghiberto et al, 2011; Evett et al, 2012)
The soil water balance (SWB) has satisfactory results in the analysis of water dynamics in the cultivation of C3 and C4 plants (Ghiberto et al, 2011; Evett et al, 2012). In cactus species, such as forage cactus, which has high moisture content in the cladodes (85 to 90%), the SWB method may lead to misinterpretation in the estimate of the actual crop evapotranspiration (ETr), since it does not consider the amount of water retained by the plant (WRP), which occurs in the parenchyma aquifer and in the large vacuoles (Taiz & Zeiger, 2009)
The evapotranspiração real efetiva (ETrEF) varies among forage cactus clones due to their morphological differences (Silva et al, 2015a), which alter the capacity of water accumulation in the canopy and, water use efficiency (Pinheiro et al, 2014; Silva et al, 2015b)
Summary
The soil water balance (SWB) has satisfactory results in the analysis of water dynamics in the cultivation of C3 and C4 plants (Ghiberto et al, 2011; Evett et al, 2012). The knowledge on forage cactus ETrEFwill allow a better understanding about the process of water transfer to the atmosphere and will refine the analysis of water use efficiency, i.e., of the capacity of conversion of water into biomass production and the economic water productivity, which represents the gross profitability, both as a function of crop evapotranspiration (Pereira et al, 2012). Water use efficiency indicators allow to analyze the productive response of the plants in order to identify favorable cultivation conditions. They assist in the selection of cultivars more tolerant to water stress, in water management and in the analysis of effectiveness of irrigation systems (Araya et al, 2011; Pereira et al, 2012)
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