during the experimental period in Cerro Azul, Misiones, Argentina
| Livestock Research for Rural Development 34 (7) 2022 | LRRD Search | LRRD Misssion | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
The aim of this study was to determine the defoliation frequency and intensity effects on biomass production and the morphology of T. diversifolia. A factorial design with two factors was used: cutting frequency, with three levels: 42, 56 and 70 days and intensity, with two levels: 50 and 70 cm, distributed in a randomized complete block design with 4 replicates. Dry matter production (DMP) per cut (g DM/plant) and accumulated DMP per cycle (g DM/plant and kg DM/ha), maximum height (cm) and number of stems were evaluated. The data were analyzed with the analysis of variance and comparison of means with Tukey test at the 1% significance level. DMP per cut and accumulated DMP were significantly higher in the treatment of 70 days and 70 cm with 240 and 856 g DM/plant respectively. Height increased significantly when the cutting frequency and intensity decreased, it ranged from 84 to 142 cm. The changes in defoliation regimes affected the DMP and morphology of T. diversifolia plants.
Keywords: cuts, height, regimes, stems, yield
In north-eastern Argentina, the predominant pastures are C4 species, with marked spring-summer-autumn growth, characterized by a rapid accumulation of biomass with high fiber content and low protein content, especially in advanced stages of growth (Rossner et al 2017). This results in the animals not getting their complete nutritional requirements during part of the year, so strategic supplementation is necessary to achieve a balanced diet (Dixon and Mayer 2021).
In this context, the alternative of incorporating forage species of higher nutritional value such as Leucaena leucocephala,Arachis pintoi, Chamaecrista rotundifolia and recently Tithonia diversifolia (Rossner et al 2017) integrated into the production system arises, which reduces the need for supplementation.
In this group of species, T. diversifolia stands out for its rapid growth and regrowth capacity after cutting or grazing and for its adaptability to various environments (Rivera et al 2021). It is a shrub native to Central America, of the Asteraceae family; it grows up to 4 meters high and in different types of soils, with acidity and low fertility conditions (Zapata et al 2016).
The forage productivity and quality is associated with plant genetics, environmental and management factors on pastures. Among these factors, the management of defoliation intensity and frequency are fundamental to maintain plant and animal production in a sustainable way (Briske and Richards 1995).
Defoliation affects the production and quality of pastures biomass through the modification of their structural and morphogenetic characteristics (Gastal and Lemaire 2015, Chapman 2016). These changes influence the ingestive behavior of animals and consequently their productive performance (Navinger and Carvalho 2009).
In 2010, T. diversifolia was introduced into Argentina and its agronomic performance was studied in Misiones, under subtropical climate and with the presence of frosts. Productive and morphological parameters were evaluated (González et al 2017, Rossner et al 2017, Corró et al 2018, Loto et al 2018); however the effect of defoliation frequency and intensity was not studied.
Due to its productive characteristics and its adaptation to acid and phosphorous-poor soils, T. diversifolia is a species of great value to increase livestock production in north-eastern Argentina. The objective of this study was to determine the defoliation frequency and intensity effects on biomass production and morphology of T. diversifolia.
The experiment was carried out at the Agricultural Experiment Station of the National Institute of Agricultural Technology, located in Cerro Azul, Misiones, Argentina at 29º, 29' south latitude, 55º west longitude and at 287 masl.
Misiones is characterized by a macro-thermal, humid and subtropical climate, Cfa type according to the Köppen classification, annual rainfall are from 1700 to 2400 mm, uniformly distributed throughout the year. The average temperature of the warmest month is 25.5ºC, while the average of the coldest month is 15ºC, with presence of frosts (Rodriguez et al 2004). The soil type was Oxic Argiudol, with moderate slopes and good drainage (Godagnone and De La Fuente 2013).
The T. diversifolia implantation was carried out with plants obtained from vegetative propagation by cuttings, 25 cm in length, extracted from the middle zone of the stems and grown in the nursery for 30 days.
The evaluation was from October 2019 to May 2020. The rainfall and temperatures registered during this period are shown in Figure 1. In the summer and autumn of 2020, the accumulated rainfall was 702 mm, which represents a decrease of 20% in relation to the historical average of summer and autumn of 877 mm.
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| Figure 1. Monthly rainfall (mm), maximum, minimum and mean temperatures (°C) during the experimental period in Cerro Azul, Misiones, Argentina |
A factorial design with two factors was used: cutting frequency, with three levels: 42, 56 and 70 days (d) and intensity, with two levels: 50 and 70 cm, distributed in a randomized complete block design with 4 replicates. Each experimental unit consisted of a 24 m² plot with 20 plants with 1-meter distance between plants and 2-meter distance between lines.
Dry matter production (DMP) per cut (g DM/plant) and accumulated DMP per cycle (g DM/plant and kg DM/ha), maximum height (cm) and number of stems of Tithonia diversifolia were evaluated.
To evaluate DMP, ten plants in the center of each experimental unit were manually cut with scissors. The harvested biomass was weighed and sub-samples were dried at 60°C for 72 hours until getting a constant weight to obtain dry matter (DM).
In relation to morphological variables, the maximum height of each individual plant was evaluated from ground level to the apex. The height of the ten plants from the center was measured with a graduated scale and the number of stems was counted.
At the beginning of the experiment, October 2019, a cutting was made to homogenize height and growth. All variables were evaluated after 42 days of the homogenization cut and during growing season. As a result, five, four and three cuts were obtained for frequencies 42, 56 and 70 days respectively.
The data were analyzed by analysis of variance and comparison of means with Tukey test at the 1% significance level to detect differences between treatments with the Info Stat program (Di Rienzo et al 2018).
The results correspond to the experimental period, from October 2019 to May 2020. A significant interaction was detected between frequency and intensity factors in DMP per cut and accumulated DMP, so the results are presented by combined treatment (Figure 2).
DMP per cut and accumulated DMP was significantly higher for 70 d and 70 cm treatment. DMP per cut was significantly lower for 42 d and 50 cm treatment.
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| Figure 2.
Dry matter production (DMP) per cut and accumulated DMP (g DM /plant) for
Tithonia diversifolia treatments. The different letters indicate significant differences between production means (p <0.01) |
Regarding accumulated DMP per hectare in kg DM /ha, there was a significant interaction between frequency and intensity (Figure 3). DMP per hectare was higher for the frequency of 70 d and 70 cm of cutting intensity and significantly lower for the frequency of 42 d in both intensities and 56 d and 50 cm treatment, which is consistent with the results of accumulated DMP per plant.
 |
| Figure 3.
Accumulated dry matter production per hectare (kg DM /ha) for
Tithonia diversifolia treatments. The different letters indicate significant differences between production means (p <0.01) |
In relation to the maximum height of the plant, there was a significant interaction between factors and height increased significantly when frequency and intensity of cutting decreased (Figure 4).
 |
| Figure 4.
Maximum plant height of Tithonia diversifolia. The different
letters indicate significant differences between means (p <0.01) |
DMP per cut presented a significant relationship with the plant height, indicating that the height variable largely explains the response in production per plant (Figure 5).
 |
| Figure 5.
Production per plant (g DM /plant) in relation to plant height (cm) in all Tithonia diversifolia treatments |
Regarding the number of stems, no significant interaction was detected between factors and there were significant differences between treatments. The number of stems was 42.2 (AB), 41.7 (B) and 46 (A) for the frequencies of 42, 56 and 70 cutting days respectively and decreased significantly when cutting intensity increased of 45.9 (A) and 41 (B) for 70 and 50 cm of height respectively.
The highest DMP per cut and accumulated obtained in the low frequency and low intensity of defoliation is expected because longer rest period favors the occurrence of compensatory responses, like the relative growth rate increase, the reallocation of growth from elsewhere in the plant and the activation and proliferation of meristems (Ferraro and Oesterheld 2002).
Also low intensity leaves more residual leaf area and intact meristems that stimulates regrowth (Briske and Richards 1995, Chapman 2016). Contrarily, severe defoliation leaves fewer residues and suppresses root production (Wilson et al 2021), which limits the water and nutrients absorption, affecting above-ground growth.
DMP results per cut were lower than those of Londoño et al (2019) at 50 d and 30 cm of cutting height and Guatusmal et al (2020) at 60 d and 20 cm of cutting height who obtained 220 and 250 g DM /plant on average respectively, in Colombia, which could be due to chemical fertilization and higher planting density used in these works.
The range of accumulated DMP values obtained was from 360.2 to 856.1 g DM /plant, which is lower than that cited by Corró et al (2018) in north-eastern Argentina, where they obtained 1614 g DM /plant and by Lugo et al (2012) with 1730 g DM/plant with a frequency of 60 d in Venezuela.
It was also observed that there were no significant differences in accumulated DMP between the 56 d -70 cm and 70 d -50 cm treatment, which indicates that similar DMP can be obtained with less rest period if low defoliation intensity is used.
Regarding DMP per hectare, the results obtained matches those of Partey (2011) at 100 cm of intensity, Pereira et al (2018) at 56 d of frequency, Ruiz et al (2012) and Alonso et al (2015) at a frequency of 60 days in the rainy season with 3, 4, 1.7 and 2.3 t /ha of DMP respectively. However, the results of this study are lower than those of Guatusmal et al (2020) and Londoño et al (2019) with 11 and 22 t /ha respectively, with fertilization and higher planting density in Colombia.
According to Pereira et al (2018) the optimal defoliation frequency for T. diversifolia is 56 days in north-eastern Argentina and according to Partey (2011) in Ghana and Lugo et al. (2012) in Venezuela is 60 days, due to the greater amount of forage produced in kg DM /ha and the quality obtained associated with its chemical composition (crude protein and fiber).
The maximum plant height varied from 84.3 to 142.9 cm for all treatments, which are similar values to those of Alonso et al (2015) in Cuba and Corró et al (2018) in north-eastern Argentina with 142 and 144 cm at 60 d of cutting respectively, but less than those obtained by González et al (2017) with 250 cm in T. diversifolia in the shade.
In general, the height varies significantly and responds to frequency and intensity of defoliation, and it presents higher values with lower defoliation frequencies and intensities.
Regarding the significant relationship between DMP per cut with plant height, some authors found similar responses to those obtained in this work. Agustoni Pais et al (2008) in Lolium perenne pastures obtained R²=0.995 and Gaytán Valencia et al (2019) in Medicago sativa obtained R² = 0.83. This suggests the potential use of the plant height as a tool for grazing management (Alvarenga et al 2020).
The higher stems number obtained in the low defoliation intensity could be due to the existence of more intact meristems that stimulates stems production. The values obtained match those found by Guatusmal et al (2020) of 42 stems and are higher than those found by Loto et al (2018) and Londoño et al (2019) of 19 and 21 stems per plant respectively, this could be due to the higher planting density used by the authors, which generally reduces the number of stems per plant, as cited by Castillo et al (2016).
We thank the National Institute of Agricultural Technology for allowing and facilitating this experiment and Alfredo Zakowicz, Fernando Fernandéz and Federico Corró for their valuable help.
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