INTRODUCTION

The Brazilian floricultural sector is an important branch of agribusiness, which presents a great diversity of commercial products, with the cultivation of approximately 3,000 varieties between cut flowers, potted flowers, foliage and plants for landscaping, such as trees, shrubs and ground cover, with phytosanitary, visual and a esthetic quality (^{Junqueira and Peetz, 2017}; ^{Menegaes et al., 2022}).

Furcraea foetida (L.) Haw. (Fig. 1) is among ornamental plants which are usually intended for landscaping, with leafy shrub characteristics, which stand out for the beauty and shape of their leaves. Popularly known as giant false agave, pita, piteira, caraguatá-açu and croatá-açu, belonging to the botanical family Asparagaceae, native to coastal regions of South America, including Brazil, it is characterized as a globular subshrub with an average height of 1.5 m and average diameter of 2.0 m. Its leaves are linear-lanceolate to oblanceolate (1.0-2.0 m × 18-20 cm) arranged in a rosette, fleshy, fibrous, long, flattened, dark green in color, with an acute tip (^{Lorenzi and Souza, 1999}; ^{Lorenzi, 2013}; ^{Lopes, 2017}).

Figure 1.  Furcraea foetida (L.) Haw. A: botanical drawing adapted from Florilegius (2012), B: top view of the plant (Dutchlady, 2012) and C: side view of the plant (Navie, 2016). 

In the horticultural variety Striata, the leaves have white and green bands, and its whitish inflorescences are not very ornamental. This species multiplies easily through the numerous bulbils that form after the development of the flowers (^{Lorenziand Souza, 1999}; ^{Lorenzi, 2013}; ^{Lopes, 2017}).

Plants from the genus Furcraea are characterized by the multiplicity of economic uses, from the production of fibers for clothing, packaging, agrochemical (insecticide and fungicide) and pharmacological uses to ornamental industries (^{Lopes, 2017}; ^{Murillo-Serna et al., 2018}). The latter becomes important as long as they have a balanced nutrition, so that their beauty is fully expressed. According to ^{Menegaes et al. (2022)}, fertilizer recommendations for floriculture, in general, are scarce, requiring this form of studies, mainly for species whose leaves are the part of the plant that stand out for their beautiful and ornamental appearance. The full development of cultivated plants is the result of the interaction of genetic factors (genotype), environment and management, resulting in the phenotype. This way, the quantification of the environmental factors that affect these processes makes it possible to improve the techniques applied to production (^{Floss, 2004}; ^{Fagundes et al., 2007}).

Mineral nutrition is an important factor in agricultural crops. Nitrogen (N) is the most required mineral nutrient by plants, influencing on various plant growth and development characteristics. For some species, atmospheric N₂ is not directly utilized by plants, requiring supplementation in the form of soil fertilization (^{Epstein and Bloom, 2006}; ^{Prado, 2020}).

The high dependence of N in plant metabolism is because it participates as a constituent of chlorophyll molecules, nucleic acids, amino acids and proteins, enzymes and coenzymes, vitamins, glycoproteins, lipoproteins, pigments, among others. Thus, the absorption of mineral N will depend on the form of fertilization and its interactions in the soil-plant-atmosphere system, resulting in the use of this nutrient by the plants or even in its loss through the processes of leaching, volatilization, denitrification, among others (^{Taiz and Zeiger, 2013}; ^{Mota et al., 2015}).

During the soil fertilization process, it is observed that compounds containing nitrates (NO₃ ^-) and ammonia (N-NH₃) present great N loss by leaching and volatilization, respectively. When in pot cultivation, the dosage must be well calculated to avoid this loss. Among nitrogen fertilizers, urea becomes a source of N which is easy to handle and with high agronomic efficiency (^{Epstein and Bloom, 2006}; ^{Mota et al., 2015}).

Given the above, the objective of this work was to evaluate leaf development of F. foetida var. Striata under different nitrogen doses and sources.

MATERIALS AND METHODS

The experiment was carried out from August 2017 to September 2018, in a greenhouse of the Floriculture Sector, Department of Phytotechnics, at the Federal University of Santa Maria, in Santa Maria, Brazil (29º43' S; 53º43' W and altitude of 95 m). The climate in the region is classified as humid subtropical (Cfa), according to the Köppen-Geiger classification, with average annual rainfall of 1,769 mm, average annual temperature close to 19.2ºC and air humidity around 78.4% (^{Alvares et al., 2013}).

A completely randomized experimental design was used, in a 3×3+1 factorial scheme (doses, sources and additional treatment), the doses were 100, 200 and 300 mg L^-1; the nitrogen sources presented different percentages of nitrogen (N): calcium nitrate (CaNO₃ with 15.5% N), ammonium nitrate (NH₄NO₃ with 34.0% N) and urea (CH₄N₂O with 42.0% N); plus the additional treatment (control: no treatment); with six repetitions. Each experimental unit consisted of a vase containing a F. foetida seedling.

The seedlings were obtained from the bulbils of mother plants from the Floriculture Sector itself. The well-developed seedlings, containing five leaves (16.4 × 6.3 cm), after 60 days of propagation, were transplanted into 8 L plastic pots in black color, containing Arenic Dystrophic Red Argisol soil. The soil was collected at a depth of 20 cm, and the chemical analysis report of the soil before cultivation, carried out at the UFSM Soil Laboratory, presented the following characteristics: clay 26%; organic matter 2.2%; water pH (1:1) 5.9; SMP index 6.1; CTC efet. 8.9; CTC pH 7, 10.6; base saturation 80.5%; zero Al saturation; Ca 6.3 cmol_c dm^-3; Mg 5.8 cmol_c dm^-3; S 12.3 mg dm^-3; P-Mehlich 52.8 mg dm^-3; K 219 mg dm^-3; Cu 1.75 mg dm^-3; Zn 3.58 mg dm^-3; B 0.1 mg dm^-3.

The nitrogen fertilizations were divided into five times, the first fertilization occurred on the day of transplanting the seedlings into the pots and the others took place with an interval of 75 d, with the fertilizations on days: 0, 75, 150, 225 and 300 days after transplanting (DAT). Leaf development is understood by the average number of leaves (live and senescent) per branch by the method of counting, width and length of leaves using a millimeter rule, every 30 DAT, according to leaf emission based on figure 2. Irrigation was carried out via drip tape every 2 d.

Source: ^{Menegaes et al. (2016)}

Figure 2. Schematic representation of the leaf emission of F. foetida in the form of a rosette in front view (A), top view (B) and factors for calculating the leaf area (C) in which W: leaf width and L: leaf length. 

Total leaf area (AF) was determined using the methodology described by ^{INRA (1970)}, expressed in the Equation LA=∑1nW*C*k, in which: W: leaf width; L: leaf length; n: number of total leaves; k: correction factor calculated from the angular coefficient of the linear equation between leaf width and length by the methodology of ^{Moraes et al. (2013)}, k=0.664.

The results were statistically evaluated by means of analysis of variance (ANOVA), with the individual effects of treatments by regression (P<0.05) as a function of the period during the 390-d experiment, being carried out with the aid of the SISVAR software (^{Ferreira, 2014}).

RESULTS AND DISCUSSION

It was observed that the variables of total number of leaves and expansion of F. foetida leaf length and width (Fig. 3) were similar for all doses and sources of nitrogen fertilization. During the evaluations, 390 DAT, it was observed that the overall average number was 10.4 leaves/plant.

Figure 3. Evolution of the number of leaves (live and senescent) of F. foetida var. Striata cultivated under different nitrogen doses and sources. 

Foliar emission averages were, for all treatments, 5.5; 6.8; 8.1; 9.0; 9.9; 10.8; 11.1; 11.6; 11.4; 12.5; 12.5; 13.0 and 13.3 leaves for 30; 60; 90; 120; 150; 180; 210; 240; 270; 300; 330; 360 and 390 DAT, in that order. Throughout the experiment, averages of 10.0; 9.7; 9.9; 10.3; 10.1; 11.0; 11.0; 10.1; 10.8 and 11.2 leaves issued for the control treatments (additional one); 100; 200 and 300 mg L^-1 calcium nitrate, 100; 200 and 300 mg L^-1 ammonium nitrate and 100; 200 and 300 mg L^-1 urea, respectively.

It was observed that between 30 to 210 DAT there was an increase in the curve for leaf emission, whereas from 330 DAT onwards there was a tendency to stabilize and maintain the number of leaves. Only after 210 DAT did leaf senescence begin with an average of 1.5; 1.5; 2.2; 2.2; 1.6; 1.1 and 1.1 leaves in all treatments for 210; 240; 270; 300; 330; 360 and 390 DAT, in that order. This indicates that F. foetida plants have high leaf durability, an important factor for ornamental plants intended for landscaping. Therefore, leaf persistence for long periods helps the plant to preserve its shape and plasticity without major changes. According to ^{Menegaes et al. (2022)}, ornamental plants should maintain beauty, shapes and plasticity in the garden, forming a harmonic visual set.

In figure 4, it was verified that the average leaf length of F. foetida was favored by the increase in nitrogen doses in relation to the control (additional) treatment, which at 390 DAT presented an average leaf length of 34.9 cm, in relation to the other treatments that presented averages of 35.5; 37.6; 35.2; 35.1; 39.1; 37.6; 37.4; 37.5 and 39.0 cm for treatments of 100; 200 and 300 mg L^-1 calcium nitrate, 100; 200 and 300 mg L^-1 ammonium nitrate and 100; 200 and 300 mg L^-1 urea, respectively.

Figure 4. Evolution of leaf length and width of F. foetida var. Striata cultivated in different nitrogen doses and sources. 

It was observed that the leaf width of F. foetida showed little variation over the 390 DAT evaluations (Fig. 4), regardless of the doses and nitrogen sources offered as fertilizer for the plants, obtaining averages of 1.5; 1.6; 2.0; 2.4; 2.8; 3.2; 4.1; 4.8; 4.9; 5.1; 5.6; 6.0 and 6.3 cm at 30; 60; 90; 120; 150; 180; 210; 240; 270; 300; 330; 360 and 390 DAT, in that order.

According to ^{Lopes (2017)}, F. foetida presents leaf length and width between 1.0-2.0 m and 18-20 cm, respectively, when the plant is adult. However, in our experiment, F. foetida was cultivated in an 8 L pot, at 390 DAT, with averages of 36.9 cm in length and 6.3 cm in leaf width. This can be attributed to the fertilization adopted in this experiment.

The results for total leaf area were observed, being similar for all doses and sources of nitrogen fertilization (Fig. 5), varying according to the evolution of the leaf area, for all treatments of 62.0; 75.8; 90.6; 106.8; 132.9; 162.4; 197.7; 229.4; 233.6; 273.4; 300.4; 299.2 and 309.9 cm² at 30; 60; 90; 120; 150; 180; 210; 240; 270; 300; 330; 360 and 390 DAT, in that order. The treatments obtained averages of 263.3; 249.2; 296.3; 304.2; 268.6; 340.7; 375.8; 320.1; 367.4 and 313.0 cm² at 390 DAT; in control, 100; 200 and 300 mg L^-1 calcium nitrate, 100; 200 and 300 mg L^-1 ammonium nitrate and 100; 200 and 300 mg L^-1 urea, respectively.

Figure 5. Total leaf area of F. foetida var. Striata cultivated in different nitrogen doses and sources. 

According to ^{Mainardi et al. (2004)} and ^{Taiz and Zeiger (2013)}, the leaf area of a plant is related to the emission of new leaves, with a direct correlation between the forms of fertilization and light intensity, thus favoring the fixation of energy as by-products for photosynthesis. ^{Menegaes et al. (2016)} found that the increase in leaf area of chrysanthemum (Dendranthema grandiflora Tzelev) cv. Snowdon is favored by light intensity (long days).

It should also be noted that these values are within acceptable averages for F. foetida at this age, another point to consider is that this species is very rustic and well adapted to the region under study and that the different doses of nitrogen fertilization were very close and, therefore, there was no significant difference for the variables mentioned above.

^{Freitas et al. (2010)}, studying nitrogen fertilization (nitrate and ammonium) in anthurium (Anthurium andraeanum Linden.), observed results that are similar to ours for the number of leaves. The same authors also clarify that the prominence of anthurium as an ornamental plant is due to the exuberant foliage, information which is likewise accepted for F. foetida. Therefore, adequate nitrogen nutrition is important to avoid an imbalance in the synthesis of phytohormones, which can lead to accelerated growth due to N retention in the plant, however, the deficiency of this nutrient anticipates leaf senescence.

Also, ^{Santos et al. (2015)}, evaluating the effect of N doses on the vegetative development and nutrient content in leaves of bromeliads Nidularium fulgens Lem., found that there was an increase in plant height when increasing doses of nitrogen were applied. An important point to highlight in relation to nitrogen fertilization is moderation in the applied doses. According to ^{Camargo et al. (2008)}, it is necessary to be careful with high N fertilizations in order not to reduce the production of flowers in soils with high fertility, as shown by the results of their experiment with aster (Aster ericoides L.).

CONCLUSION

The different nitrogen doses and sources studied in this experiment favored the quality of leaf development of giant F. foetida var. Striata, grown in pots for 390 days after transplanting the seedlings. The ornamental characteristics of shape and plasticity were maintained throughout the cultivation, with averages of 10.4 leaves/plant, 36.9 cm in leaf length and 6.3 cm in leaf width.