Abstract
The present work aimed to investigate the effects of mechanical impedance of wax layer (wax discs were installed 0.1 m deep) on root system deepening of citrus seedlings growing in columns with sand and nutrient solution. Two planting systems were evaluated: direct seeding (DS) and planting of seedlings (PS) (plants obtained from seed germination in tubes). Two experiments were carried out in a sequence: first to investigate the wax layer resistance levels (0.14 to 2.7 MPa) on root system penetration and two planting systems (DS and PS). The second evaluated the root and plant development of the two planting systems and two resistance of wax layer to root penetration: control (0.14 MPa) and a strong wax layer (1.06 MPa). The experimental design was randomized blocks, the first experiment in a 2 × 4 factorial scheme with 4 replications and the second a 2 × 2 factorial scheme with 6 replications. Resistance level ≥ 1.52 MPa (60% hard wax and 40% soft wax) completely limited root penetration in the artificial strong layer. The presence of strong wax disc reduced the citrus root system in both planting systems. PS was associated with greater root and shoot vigor, indicating that, in soils with good physical structure and porosity or allowing root deepening beyond the cohesive layer, this planting system is fully adequate, despite the possible benefit of not cutting the pivoting root in direct sowing.
Highlights
The low yield of citrus orchards on Coastal Tablelands of Northeast Brazil, the second largest producing region of the country (IBGE, 2015), is mainly attributed to seasonal rainfall and presence of cohesive soils (Rezende et al, 2015)
The practice of sowing the rootstock in the definitive site (DS) for later grafting in the field has been performed as a technical option for citrus growers, in order to minimize the agricultural limitations of the Coastal Tablelands (Rezende, 2013), aiming at favoring root system deepening, since the taproot grows free and intact, and maintenance of good water status in the plants in the driest periods of the year (Rezende et al, 2015)
This experiment tested the effect of two levels of mechanical impedance of wax disc on ‘Rangpur Santa Cruz’ lime growing in the same system of Experiment 1: 0.14 and 1.06 MPa, respectively corresponding to 10% and 50% hard wax concentrations combined with the soft wax
Summary
The low yield of citrus orchards on Coastal Tablelands of Northeast Brazil, the second largest producing region of the country (IBGE, 2015), is mainly attributed to seasonal rainfall and presence of cohesive soils (Rezende et al, 2015). The practice of sowing the rootstock in the definitive site (DS) for later grafting in the field has been performed as a technical option for citrus growers, in order to minimize the agricultural limitations of the Coastal Tablelands (Rezende, 2013), aiming at favoring root system deepening, since the taproot grows free and intact, and maintenance of good water status in the plants in the driest periods of the year (Rezende et al, 2015). It is criticized as a risky practice that exposes very young plants to biotic stress as citrus variegated chlorosis (CVC). The present study aimed to investigate, based on cultivation system adapted from Coelho Filho et al (2013) and mechanical impedance layer simulations by Clark et al (2000), and Whalley et al (2013), the effects of the presence of physical impedance on the root architecture of citrus, considering two planting systems (direct sowing and planting of seedlings)
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