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Introduction
Livestock production in south-eastern Mexico is based on the use of monoculture pastures that have low levels of digestible protein and high fibre contents (Pozo-Leyva et al. 2021). The foliage of shrub and tree species has been considered, in most cases, as a nutritional alternative for the supplementation of ruminants in the tropics to improve the productive and nutritional level of the animals (Cardona et al. 2022). Mainly during periods of forage shortage, they reduce production costs and contribute to the profitability and sustainability of production systems (Pozo-Leyva et al. 2019).
A viable strategy for the integration of shrubs and trees for animal production is the implementation of silvopastoral systems (Cardona et al. 2022). These systems help to improve the productivity and quality of forage throughout the year, maintain good soil fertility due to the greater recycling of nutrients, favour high biodiversity compared to pasture monocultures, reduce heat stress of the animals and fix atmospheric nitrogen, among other benefits (Sales-Baptista et al. 2021).
In this regard, Tithonia diversifolia (Hemsl.) A. Gray. (Asteraceae), also called false sunflower or Mexican sunflower), is a shrub native to southeastern Mexico (Aboyeji et al. 2019). However, its distribution has been reported to the humid and sub-humid tropics of Central and South America (Ruiz et al. 2017). Tithonia diversifolia has been documented as an excellent alternative in ruminant feeding (Cardona et al. 2022). This is because the forage of this species contains moderate levels of fibre (30-35%) and high protein contents (14.8 to 28.8%), so it can replace up to 30% of the concentrate supplements in cattle feed without affecting production (Gutiérrez et al. 2017). One of the characteristics of forage shrub species is their high nutritional value regardless of the time of year (Ruiz et al. 2017). The dry matter digestibility can fluctuate from 72 to 85% (Gutiérrez et al. 2017) with CP concentrations of 23.5% (Vega-Granados et al. 2019). Neutral detergent fibre (NDF) is a parameter that indicates the concentration of fibres in the forage and includes cellulose, hemicellulose and lignin, and it is negatively correlated with the consumption of dry matter (Ángeles-Mayorga et al. 2022). The acid detergent fibre (ADF), while a similar measure, does not include hemicellulose and can be correlated with the digestibility of feed. The variations in the NDF and ADF contents of the forages are related to the forage species, the age of the tissue, the handling and the prevailing climatic conditions and seasons of the year (Horst et al. 2022).
One of the advantages of T. diversifolia is its rapid growth after harvest, tolerating repeated cuts throughout the year with high biomass production (Letty et al. 2021). Many farmers use T. diversifolia in forage banks for livestock feeding. However, the lack of evidence on appropriate cutting or harvest heights can cause a progressive decrease in forage production due to the reduction in the number of stem buds that limit the regrowth of new leaves (Letty et al. 2021). Likewise, it causes the depletion of plant reserves, because they mobilise reserve carbohydrates to rebuild photosynthetic tissue after harvest, grazing or seasonal loss of foliage (Navale et al. 2022). Therefore, knowing the optimal harvest height of T. diversifolia is essential for the sustainable management of this important forage plant in animal production systems in the tropics (Ruiz et al. 2017, Letty et al. 2021). Our understanding of the yield and quality of T. diversifolia biomass in forage banks under different management schemes and at different times of the year under tropical conditions is still limited. Therefore, the objective of this research was to evaluate the performance and nutritional quality of T. diversifolia forage under different cutting heights, during the dry and rainy season, in the south of the state of Quintana Roo, Mexico.
Materials and methods
Site characteristics
The experiment was carried out at the Instituto Tecnológico de la Zona Maya in Quintana Roo state, Mexico from January 2019 to January 2020 (18° 30’ N and 89° 41’ W). The area presents a warm sub-humid climate, according to Uu-Espens et al. (2019). Climatic data during the experimental period (Figure 1) was recorded daily with a WatchDog 2900ET Weather Station (Spectrum Technologies, Inc.). The mean, maximum and minimum annual temperatures and the total rainfall during this period were 26.5, 37.0, 11.0 °C and 1 009 mm, respectively.
Figure 1: Minimum and maximum air temperatures and rainfall at the study site; data were taken from the microclimatic station at the Instituto Tecnológico de la Zona Maya in January 2019-January 2020.
The predominant soils are Gleysols according to the Food and Agriculture Organization (IUSS Working Group WRB 2022). For the physical and chemical analysis of the soil, three random samples were taken at depths of 0-30 cm from the surface. Soil organic matter was analysed by the Walkley-Black wet digestion method, total nitrogen was analysed by the Micro-Kjeldahl procedure, and available phosphorus was analysed by the Olson extraction method. Soil potassium was determined by colourimetry, and calcium and magnesium were determined by atomic absorption spectrophotometry methods. The potentiometric method was used to analyse soil pH and electrical conductivity. The physicochemical properties of soil are presented in Table 1.
Table 1: Physical and chemical properties of the soil from the experimental plots of Tithonia diversifolia, under sub-humid tropical conditions.
| Parameter | Value |
|---|---|
| pH | 7.7 |
| Electric Conductibility (ds m−1) | 0.2 |
| Lime (%) | 46.0 |
| Clay (%) | 45.8 |
| Sand (%) | 8.2 |
| Organic material (%) | 3.7 |
| Total nitrogen (%) | 0.2 |
| Phosphorous (ppm) | 43.3 |
| Potassium (ppm) | 1875.0 |
| Calcium (ppm) | 6100.0 |
| Magnesium (ppm) | 1611.0 |
Management of experimental plots
For the establishment of the forage banks, we used T. diversifolia cuttings 2.0 to 4.0 cm in diameter, which were taken from the middle and lower portion of the stems and cut to 50 cm in length. Later, they were submerged in water with a rooting agent for 24 hours and then they were planted vertically in each plot at a depth of 20 cm from the soil surface and at a planting distance of 0.5 m between plants and 2.0 m between rows to obtain a planting density of 10 000 plants ha−1. A total of 12 10 x 10 m sampling plots were delimited, which were made up of five rows of T. diversifolia, of which only three central rows were measured to avoid the edge effect in each experimental unit. The experiment ran from January 2019 to January 2020. Before the evaluation, a standardisation harvest was performed manually in January 2019. Measurements were started in March of the same year.
Experimental design
We used a completely randomised design with a 3 x 2 factorial arrangement; the treatments consisted of evaluating three harvest heights of T. diversifolia (40, 60, 80 cm) during two seasons of the year: the dry season, which ran from May to September 2019 and the rainy season, which ranged from November 2019 to January 2020. During the experimental period, five biomass harvests were carried out with a frequency of two months at the beginning of the month. Simultaneously, the alleys were cleaned to control weeds. It should be noted that no irrigation or fertilisers were applied.
Biomass components and forage yield
After each harvesting, the total biomass (leaves, edible stems, woody stems) from each experimental unit was weighed fresh. Harvested material from each treatment (cutting) was pooled and three sub-samples (of approximately 1.0 kg each) were randomly taken. These sub-samples were divided into leaves, edible stems (< 0.5 cm diameter) and woody stems (≥ 0.5 cm diameter), which were dried at 60 °C in a forced circulation oven drier ED 400 (Binder Inc., Bohemia, NY, USA) to constant weight. Only leaves and edible stems were considered for calculating forage yield. Seasonal forage yield was obtained by adding the yield from all the harvests within the respective period.
Nutrient composition analysis
Forage sub-samples (leaves and edible stems) were ground using an electric mill IKA MF 10 (IKA Works, Inc. Wilmington, NC, USA) to a particle size of 1.0 mm and analysed for neutral detergent fibre (NDF), acid detergent fibre (ADF) and lignin, using an ANKOM A200 fibre analyser (ANKOM Technology, Macedon, NY, USA). The fraction of nitrogen (N) was estimated using a PerkinElmer 2400 Series II elemental analyser (PerkinElmer Inc., Massachusetts, USA), then converted to crude protein (CP) by the conversion factor 6.25 (Greenfield and Southgate, 1992). The organic matter (OM) and ash contents were determined by ignition at 600 °C for four hours in a muffle furnace (AOAC 2019).
Statistical analysis
The biomass production data were analysed with an ANOVA model using PROC MIXED (SAS Institute Inc 2020) to examine the effect of different cutting heights, the season and their interactions. For biomass components and nutrient composition (data were square root transformed) and applied to a multivariate analysis of variance (MANOVA) using PROC GLM (SAS 2020). Where significant differences were observed, we compared the means using Tukey’s statistic (P ≤ 0.05).
Results
Biomass components
The cutting height did not show a significant effect (P > 0.05) on the proportion of fresh leaves, senescent material, tender stems, woody stems or the leaf:stem ratio of the biomass of T. diversifolia (Table 2). However, the proportion of leaves and the leaf-to-stem ratio during the dry season were higher (almost two and three times), compared to the rainy season (P < 0.05 and P < 0.01). The proportion of edible stems was two times lower (P < 0.01) during dry season compared to rainy season. The proportion of senescent material and woody stems of T. diversifolia was statistically indifferent (P > 0.05) between seasons (Table 2).
Table 2: Biomass components (%) and the leaf:stem ratio of Tithonia diversifolia at different cutting heights and during two seasons, under sub-humid
| Treatments | Leaves | Senescent material | Edible stems | Woody Stems | Leaf-to-stem ratio |
|---|---|---|---|---|---|
| Cutting heights | ns | ns | ns | ns | ns |
| 40 cm | 46.2 | 6.1 | 45.3 | 2.5 | 1.0 |
| 60 cm | 53.4 | 7.8 | 36.9 | 1.9 | 1.4 |
| 80 cm | 57.9 | 6.6 | 34.0 | 1.5 | 1.6 |
| SEM | 10.0 | 1.3 | 5.2 | 0.7 | 0.5 |
| Season | * | ns | ** | ns | ** |
| Dry | 64.5 a | 8.3 | 24.9 b | 2.3 | 2.4 a |
| Rainy | 40.6 b | 5.4 | 52.4 a | 1.6 | 0.8 b |
| SEM | 2.7 | 2.0 | 3.6 | 0.7 | 0.2 |
Means within columns followed by different letters are significantly different (Tukey’s statistic). SEM, standard error of the mean; ns, non-significant; * P < 0.05; ** P < 0.01.
Biomass yield
The average yield of forage harvested at a cutting height of 80 cm was 2 008 kg DM ha−1 harvest−1, a value that was 29 and 32% higher (P < 0.05) than the cutting heights of 40 and 60 cm, respectively (Table 3). The total biomass yield of T. diversifolia in the rainy season was slightly more than double (P < 0.01) that of the dry season (2 606 vs. 1 059 kg DM ha−1 harvest−1; Table 3). Likewise, the forage yield in the rainy season was 2 436 kg DM ha−1 harvest−1, a value that was almost three times higher (P < 0.01) than that of the dry season (Table 3).
Table 3: Mean biomass and forage yield (kg DM ha−1 harvest−1) of Tithonia diversifolia at different cutting heights and during two seasons, under sub-humid tropical conditions.
| Treatments | Total biomass | Forage |
|---|---|---|
| Cutting heights | ns | * |
| 40 cm | 1 670.2 | 1 550.6 b |
| 60 cm | 1 656.1 | 1 520.7 b |
| 80 cm | 2 170.8 | 2 007.9 a |
| SEM | 193.9 | 167.5 |
| Season | ** | ** |
| Dry | 1 058.7 b | 950.7 b |
| Rainy | 2 606.0 a | 2 435.5 a |
| SEM | 141.3 | 136.1 |
Means within rows followed by different letters are significantly different (Tukey’s statistic). SEM, standard error of the mean; ns, non-significant; * P < 0.05; ** P < 0.01.
There was a significant interaction between cutting height and the season (P < 0.01) on the forage yield of T. diversifolia (Figure 2). There was a gradual increase in forage yield with the increase in cutting height during the rainy season but the trend was different during the dry season. The highest forage yield was recorded in the rainy season and with cutting heights of 80 cm (2 999 kg DM ha−1 harvest−1), while the lowest forage yield was presented in the dry season and with a cutting height of 60 cm (823 kg DM ha−1 harvest−1; Figure 2).
Figure 2: Mean forage yield per harvest of Tithonia diversifolia at different cutting heights and during two seasons, under sub-humid tropical conditions; error bars represent the standard error of the mean; means labelled by different letters are significantly different (Tukey’s statistic, P ≤ 0.05).
On the other hand, the cutting height of 80 cm showed the greatest (P < 0.05) cumulative yield of the T. diversifolia forage (10 066 kg DM ha−1 year−1), followed by the cutting heights of 40 and 60 cm, with values of 8 228 and 7 728 kg DM ha−1 year−1, respectively (Figure 3).
Nutrient composition
The crude protein contents of T. diversifolia forage harvested at cutting heights of 40 and 60 cm showed an increase of 8.4 and 10.9% (P < 0.05), compared to the height of 80 cm. However, the forage harvested to 80 cm from the ground level showed the highest acid detergent fibre. The content of neutral detergent fibre, lignin, ash and organic matter of T. diversifolia forage were statistically indifferent (P > 0.05) between cutting heights (Table 4).
Table 4: Nutrient composition (%) of forage from Tithonia diversifolia at different cutting heights during two seasons, under sub-humid tropical conditions.
| Treatments | CP | NDF | ADF | Lig | Ash | OM |
|---|---|---|---|---|---|---|
| Cutting heights | * | ns | * | ns | ns | ns |
| 40 cm | 21.9 a | 44.6 | 26.7 b | 3.2 | 12.9 | 87.1 |
| 60 cm | 22.4 a | 43.0 | 26.4 b | 3.4 | 13.4 | 86.6 |
| 80 cm | 20.2 b | 44.0 | 27.5 a | 3.4 | 14.1 | 85.9 |
| SEM | 0.6 | 0.6 | 0.3 | 0.2 | 0.4 | 0.4 |
| Season | ** | ** | ** | * | * | * |
| Dry | 17.0 b | 47.9 a | 29.1 a | 3.6 a | 14.9 a | 85.1 b |
| Rainy | 26.0 a | 39.9 b | 24.7 b | 3.2 b | 12.0 b | 88.0 a |
| SEM | 0.5 | 0.5 | 0.1 | 0.1 | 0.3 | 0.3 |
Means within rows followed by different letters are significantly different (Tukey’s statistic). CP, crude protein; NDF, neutral detergent fibre; ADF, acid detergent fibre; Lig, lignin; OM, organic matter; SEM, standard error of the mean; ns, non-significant; ** P < 0.05; ** P < 0.01
The CP content varied significantly between the season of the year (17% in the dry season and 26% in the rainy season). The OM contents of T. diversifolia forage in the rainy season were 3.4% higher than that of the dry season (P < 0.01). The contents of neutral detergent fibre, acid detergent fibre, lignin and ash were higher during the dry season, since they had increases of 20.0, 17.8, 12.5, 24.2%, respectively, compared to the rainy season (Table 4).
There were interactions between cutting height and the season (P < 0.01) on CP, NDF and ADF content of the T. diversifolia forage (Figure 4). The highest CP content was recorded in the rainy season and with a cutting height of 60 cm (28.3%), while the lowest CP contents were found in the dry season regardless of the heights of cut with values ranging from 16.5 to 17.9% (Figure 4).
Figure 4: Crude protein, neutral detergent fibre and acid detergent fibre (%) of forage from Tithonia diversifolia at different cutting heights and during two seasons, under sub-humid tropical conditions; error bars represent the standard error of the mean; means labelled by different letters are significantly different (Tukey’s statistic, P ≤ 0.050).
The higher NDF contents of T. diversifolia forage were recorded in the dry season and with cutting heights of 40, 60 and 80 cm (48.8, 48.3 and 46.5%, respectively), while the lowest NDF content was found during the rainy season and with a cutting height of 60 cm (with a value of 37.7%, Figure 4). Similarly, the greatest ADF contents of T. diversifolia forage were recorded in the dry season and with cutting heights of 80 cm (29.4%), while the lowest ADF content was observed in the rainy season and with a cutting height of 60 cm with a value of 23.5% (Figure 4).
Discussion
Biomass components
Our results showed that harvest height and the season are important factors that affect forage yield and the nutritional quality of T. diversifolia plant. The effect of harvest height on the biomass recovery and nutrient composition of forage shrub species has been poorly documented in south-eastern Mexico. A study by Ramos-Trejo et al. (2015), in eastern Yucatán, showed that the cutting height (40, 80 and 120 cm) at harvesting intervals of 45 and 60 days did not influence the leaf-to-stem ratio of the biomass of Moringa oleifera Lam., in forage banks. In addition, Ramos-Trejo et al. (2016) reported that the composition of leaves, stems and the leaf-stem relationship of Gliricidia sepium in forage banks did not differ with harvest heights of 45 and 90 cm. The results of these two investigations did not coincide with this experiment because the cutting height significantly affected the crude protein content of T. diversifolia forage in our study.
For their part, these results differ from the report made by Bacab-Pérez et al. (2012), who documented that the cutting height affected the length of the Leucaena leucocephala stem. However, in the case of the Panimum maximum grass, this behaviour was not reflected. These differences could be caused because the woody plants have low apical dominance, contributing to the early regeneration of foliar biomass. The response to cutting height could be different depending upon the species and/or the forage variety (Casanova-Lugo et al. 2014). Similarly, Senarathne et al. (2018) documented that an increase in the frequency of harvest increases the total foliage biomass yield of T. diversifolia and decreases the woody part of the biomass, while a decrease in the harvest frequency increased the woody biomass fraction and decreased the edible stems and foliage biomass.
The seasonal differences for the proportion of leaves and the leaf:stem ratio observed in this study may be attributed to the higher water availability compared to the dry season, which allowed a greater elongation of the edible stems and consequently, a greater proportion of them. Unlike the dry season where plants use more resources to form leaves, and therefore a better leaf: stem ratio (Horst et al. 2022). In addition, shrubs and trees in tropical livestock systems invest more in belowground components during the dry season compared to rainy seasons (Morales-Ruiz et al. 2020).
Another factor that could have intervened in this process was the temperature and the photoperiod since the temperatures registered at the beginning of the dry season (21 °C) were lower than those that were registered in the rainy season (23 °C). According to a study carried out by Navale et al. (2022), the decrease in temperatures coupled with a shorter photoperiod favours flowering and the transport of carbohydrates in plants. This can favour the elongation of stems and the formation of flowers at the expense of the formation of leaves. This goes hand in hand with the flowering and seed production period of T. diversifolia, which coincides with October-November. In this type of study, the comparison of results with previous research is usually complex, since the results may differ depending on the methodology used, the age of the plant, the cutting height, the planting density and the agrometeorological characteristics of the study site (Senarathne et al. 2018).
Biomass yield
In our research, the best forage yield was obtained with height of 80 cm. The highest forage yields of M. oleifera (1 912 kg DM ha−1 harvest−1), were recorded at heights of 40 cm, compared to heights of 80 and 120 cm in South-eastern Mexico (Ramos-Trejo et al. 2015). In contrast, the forage yield of G. sepium with harvest heights of 45 and 90 cm were similar in the same region (Ramos-Trejo et al. 2016).
In Columbian Andes, T. diversifolia harvested at cutting heights of 10 and 50 cm and Sambucus nigra L. with cutting heights of 30 and 50 cm, the cutting height did not affect the biomass yield (Guatusmal-Gelpud et al. 2020). In addition to the cutting height, other factors influence the forage yield of woody species, such as climatic conditions, soil types, water and nutrient availability. The reduction of forage leaves and stems in the dry season in our study is consistent with that found by Cabezas y Sánchez (2008) who showed that the low contents of macronutrients affected plant growth as nitrogen deficiency lowered the heights, stem growth, size and thickness of leaves of Passiflora mollissima plants. There are studies in other parts of the world showing that nutrient limitation in the soil during the dry season can affect biomass production (Letty et al. 2021).
It has been reported that one of the limiting factors for forage production is the low rainfall season (Navale et al. 2022), which is consistent with the results of this research. On the other hand, studies carried out on G. ulmifolia and L. leucocephala in tropical forage banks did not show a negative effect on forage yield during the dry season (Casanova-Lugo et al. 2014). This reflects a greater tolerance to drought by G. ulmifolia and L. leucocephala, compared to T. diversifolia. In the Colombian Andes, Guatusmal-Gelpud et al. (2020), reported a cumulative yield of T. diversifolia of 24 600 and 23 850 kg DM ha−1 year−1, for cutting heights of 10 and 50 cm, values higher than that we found in this study with heights of 60 cm (7 727.6 kg DM ha−1 year−1). Differences in edaphoclimatic conditions, the planting density, the age of the plants and the management can explain the differences in forage yield.
Nutrient composition
In this study, we observed that the cutting height influenced the CP and ADF content of the T. diversifolia forage. This may be related to the regrowth capacity of the plant, since at taller cutting heights (80 cm), they maintain higher residual biomass and, consequently, a higher proportion of buds, which contributed to improving the quality of forage (Letty et al. 2021). Another factor that influences the nutrient composition of T. diversifolia forage is seasonality. For example, we observed that the total carbohydrate contents were higher during the rainy season while structural fractions of the carbohydrates were higher during the dry season (Gutiérrez et al. 2017). This implies that the easily digestible (labile) fractions of the carbohydrates were higher during the rainy season favouring the digestibility of the forage. During the rainy season, there was a greater mobilisation of resources in the plant due to the greater availability of water for growth and development (Navale et al. 2022). The above favoured the quality of the forage with an increase in CP and OM and lower concentrations of NDF, ADF and ash. This was consistent with those proposed by Cediel-Devia et al. (2020), who likewise reported that seasonality intervened in the concentration of CP, NDF and ADF of T. diversifolia forage. Such an increase in CP is favoured in the rainy season (Senarathne et al. 2018). In addition, the leaf biomass of T. diversifolia also increases with increasing rainfall (Uu-Espens et al. 2019).
The quality of the forage depends on the reserves of the plant for the development of morpho-structural parts like branches and stems; in turn, the concentrated reserves of these components favour the foliar concentrations of sugars, proteins and minerals after regrowth (Gutiérrez et al. 2017). Nevertheless, Ramírez (2018) documented that for T. diversifolia grown in low levels of nitrogen fertilisation, the production of dry forage, leaf content and protein production increased by applying N. However, Botero-Lodoño et al. (2019) mentioned that the DM contents decrease with increasing fertilisation levels and that the CP and ash contents increase. Cabezas y Sánchez (2008) showed that the deficiency of N and K in the soil presents a reduction in biomass of 50%, which affects the size of leaves. Tithonia diversifolia forage has a high CP content compared to traditional tropical grasses (7% CP and dry matter digestibility of 38%). In addition, they maintain CP concentrations higher than 17% throughout the year, which corresponds to excellent quality forage for feeding ruminants and backyard animals (Vega-Granados et al. 2019).
In this sense, the NDF and ADF values reported in this study were lower than those commonly reported for tropical grasses (Gutiérrez et al. 2017), highlighting the superior quality of T. diversifolia forage as a forage alternative to replace or reduce the amounts of commercial concentrates for animal feeding. Pastures have a higher concentration of structural tissues (like cellulose, hemicellulose and lignin) and a lower concentration of CP compared to the foliage of trees and shrubs, which provides them with an advantage in terms of digestibility, forage consumption and a favourable effect on animal production and performance (Horst et al. 2022).
Conclusions
We obtained the highest cumulative forage yield of T. diversifolia plant to a cutting height of 80 cm and demonstrated that harvest height influenced forage quality in terms of crude protein and acid detergent fibre contents. The proportions of leaves, edible stems and the leaf:stem ratio are favoured during the rainy season. The height of 80 cm showed the highest average forage yields during the rainy season. The nutritional quality of the T. diversifolia forage was influenced by the cutting height and the season of the year. The cutting height of 80 cm showed the best quality of the forage throughout the year under the edaphoclimatic and management conditions reported in this research. The results are useful for animal farmers to manage livestock systems in terms of forage production and quality during different seasons of the year.
