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Using the crop water stress index in irrigation scheduling in apple orchards on southern Romania

Author(s): Cristian Paltineanu | Emil Chitu | Nicolae Tanasescu

Journal: Scientific Papers of the Research Institute for Fruit Growing Pitesti, Romania
ISSN 1584-2231

Volume: XXIV;
Start page: 126;
Date: 2008;
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Keywords: Leaf temperature | irrigation application | irrigation depth

Water is a limiting factor in many countries because of decreasing quality and supplies. The trend in climate evolution toward aridization has also been observed in Romania. The apple (Malus domestica) is one of the most widely cultivated temperate climate fruit-trees in Romania, particularly in hilly regions. With increasing interest in commercial production of apples, physiological responses to factors limiting growth and yield need to be studied. The soil in the experimental plots at Pitesti-Maracineni, southern Romania, is loamytextured, with a clay (less than 0.002 mm particle diameter) content of 30 – 35 % g g-1 throughout the 0 – 1 m depth profile. Soil bulk density has ranged from 1.40 to 1.49 g cm-3 and total soil porosity from 44 to 48 %. The land slope is from 0 to 2 % and the water table varies between 4 and 6 m depth. The climate conditions at the experimental site are characterized by a mean annual temperature (1967 – 2007) of 9.6 °C and a mean annual precipitation of 671 mm. not uniformly distributed across the year. The experiment was carried out during two growing seasons (2006 and 2007), in an apple orchard 12 years old, with Idared cultivar grafted on M9 rootstock. There were fully-irrigated (FI), half-irrigated (HI) and control, non-irrigated treatments (NI). Trees are spaced 3.6 m between the rows and 1.5 m in the row giving 1852 trees ha-1. Canopy temperature was measured using an infrared thermometer X2955L-Crop Trak Infrared Thermometer. Spectrum Technologies, Inc., with a built-in laser pointer to identify target areas, to calculate the components of the CWSI and to assess the crop response to water stress periods during the warmest months of the growing season. The lower base line of CWSI, as a correlation between the crop and air temperature difference versus the vapor pressure deficit for apple under the soil and climate conditions of Pitesti- Maracineni, Romania, has a highly significant regression equation. The CWSI mainly ranged between 0.10 and 0.80. Irrigation applications were usually carried out in this experiment at CWSI values from 0.20 to 0.50. Soil moisture content varied with time, usually between field capacity (FC) and wilting point (WP) in the research treatments during the months of maximum interest in irrigation application: July and August. There were significant differences for fruit yield between the irrigation treatments studied and the control. The FI treatments gave higher yields than the HI ones, but the difference was not significant for the conditions of experiment. This could have a major importance in the case of the global warming when water resources would be less. Significant differences in the weight of individual fruits were observed between the FI treatments and NI. So, one of the most important advantages of irrigation here is, in addition to fruit yield, greater fruit weight. Further studies are needed to find relationships between the CWSI and various soil variables, like the moisture content or matric potential.
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