poster - International Conference of Agricultural Engineering

influenced by environmental conditions, especially by temperature and water vapor
saturation. Under identical conditions, the differences in transpiration may indicate stomatic
mechanism with greater or lesser efficiency, leading to the water savings by the plant.
The efficiency in water use can be understood as an efficient evolutionary mechanism
by which the plant acquires more elasticity to deal with possible water deficits (LIMA, 1995).
The tolerance of seedlings of forest species for water deficits is determined by several
factors and it can be temporarily modified by nutrition and water management. Regarding the
seedlings of plants in the nursery, the hardening stage, the final period of the production, it is
of great importance for the adjustment of the plants to field conditions and the way to adapt
them is based on the application of one or more types of stress. Silva (1998) reports that, in
the specific case of Brazil, the most important ones are water and nutritional stress. Both
cause morphological and physiological changes that interfere with the ability to resist to the
harsh conditions of the field, therefore affecting their quality.
The hardening of the seedling through the handling of fertilization is based on the
application of fertigation solutions with low N/K ratio in the range of 1/3 to 1/5 (HIGASHI &
SILVEIRA, 2004). Increasing the concentration of K fertilization on hardening is due to their
functions in the plant. The potassium cation is the most abundant cytoplasm and in
conjunction with the accompanying anion has the largest contribution to the osmotic potential
of cells and plant tissues (MARSCHNER, 1995), protein synthesis and maintenance of their
stability, membrane permeability in the control of pH (MALAVOLTA al., 1997), activation of
many enzymes and transport of sugars in the phloem (COLL et al., 1992), the mechanism of
opening and closing of stomata (COLL et al., 1992 ; MALAVOLTA et al., 1997), increased
plant resistance to drought and frost due to the increased water retention (SILVEIRA &
MALAVOLTA, 2000).
The levels of potassium, as suggested by some authors, for the nutrient solution
applied daily as fertigation during the hardening phase are: 220 mg L-1 (SILVEIRA et al.,
2001), 249 mg L-1 (D'AVILA et al., 2011). However, studies are needed to verify the
influence of fertigation parceling on the hardening of the seedlings. Thus, this study aimed to
verify the effect of the concentration of potassium in the nutrient solution on the transpiration
of seedlings in three Eucalyptus species.
2. Material and methods
The study was conducted in the Nursery Forestry Seedling Research, Faculty of
Agronomic Sciences of UNESP, Botucatu, Sao Paulo - Brazil, located at the coordinates
22º 51' 22'' south latitude and 48° 26' 0'' West longitude, at an altitude of 810m and I Cwa
type climate, Köppen classification of Wilhelm and average annual rainfall of 1524 mm. The
experiment was carried out from December to March, 2009.
The seeds of Eucalyptus grandis were derived from clonal seedling orchard F1
generation and Eucalyptus urophylla from a seed orchard of F4 generation. The cuttings of
the hybrid Eucalyptus grandis x Eucalyptus urophylla were purchased from a commercial
nursery. We used tubes with a volume capacity of 50cm³, filled with commercial substrate,
decomposed pine bark and expanded vermiculite fertilized with 300 mg of FTE BR 12
("fritted Trace Elements") per m 3 .
The seedlings remained for about 40 days in the greenhouse and 15 days in the shade
house. Subsequently, the seedlings were transferred to a plastic covered greenhouse, where
fertigation started.