Livestock activity is one of the main uses of the land, reaching 70% of the agricultural area and 30% of the earth’s surface of the planet (Steinfeld et al. 2009). This activity, in the Latin American tropics, is characterized by low levels of productivity and profitability and by the creation of negative environmental effects.
Faced with this problem, the use of trees and shrubs, in any of the forms of silvopastoral systems, constitutes an indispensable and viable practice for animal production in the tropics (Schultze-Kraft et al. 2018), since it is developed under management principles, in which the interaction between its components favors natural processes.
Among the tree and shrub species with potential for animal feeding, Moringa oleifera is highlighted, due to its capacity for the production of high quality forage and its adaptation to tropical conditions (Padilla et al. 2014). However, the establishment of this species under commercial production conditions continues to be a limitation for its generalization.
An increasingly important practice for the propagation and establishment of tree species is the seedlings production. Queiroz (2014) points out that this alternative can be applied in the generalization of native species, and highlights that the substrate where they develop defines the seedlings growth. Mateo-Sánchez et al. (2011) refer that the substrate is one of the factors that most influences on the quality and production costs of the seedlings. Different studies show the effectiveness of the use of organic materials in substrates for the seedlings production of forest species (Salto et al. 2013) and ornamentals (Allen et al. 2017).
Despite these advances, in terms of forage tree species, there are few researchers that relate the quality of seedlings produced with the type of substrate, since this strategy has been little considered for their establishment.
Based on these conditions, the objective of this research was to study the growth and development of Moringa oleifera seedlings, produced on different substrates containing sewer sludge and bovine manure.
Materials and Methods
The research was conducted at the Institute of Agrarian Sciences from the Federal University of Minas Gerais (ICA/UFMG), in Montes Claros, MG. This facility is located at 16.2 ° south latitude and 43.87 ° west longitude, at 647.2 m o.s.l.
The substrates were made from two types of soils, sewer sludge and bovine manure, associated with the application of mineral fertilizer (table 1). A randomized block design was used, with four replications. The M. oleifera seeds were obtained from the Harmful Plants Group of ICA/UFMG.
Treatments | Soil | Sand | Bovine manure | Sewer sludge | Simple superphosphate | KCl |
---|---|---|---|---|---|---|
T1 (3:1:1:0+SS) | Loamy | x | x | - | 1 kg/m3 | - |
T2 (3:0:1:0+SS) | Sandy | - | x | - | 1 kg/m3 | - |
T3 (3:1:0:1+SS) | Loamy | x | - | x | 1 kg/m3 | - |
T4 (3:0:0:1+SS) | Sandy | - | - | x | 1 kg/m3 | - |
T5 (3:1:1:0+KCL) | Loamy | x | x | - | - | 1 kg/m3 |
T6 (3:0:1:0+KCL) | Sandy | - | x | - | - | 1 kg/m3 |
T7 (3:1:0:1+KCL) | Loamy | x | - | x | - | 1 kg/m3 |
T8 (3:0:0:1+KCL) | Sandy | - | - | x | - | 1 kg/m3 |
T9 (3:1:1:0+SS+KCL) | Loamy | x | x | - | 1 kg/m3 | 1 kg/m3 |
T10 (3:0:1:0+SS+KCL) | Sandy | - | x | - | 1 kg/m3 | 1 kg/m3 |
T11 (3:1:0:1+SS+KCL) | Loamy | x | - | x | 1 kg/m3 | 1 kg/m3 |
T12 (3:0:0:1+SS+KCL) | Sandy | - | - | x | 1 kg/m3 | 1 kg/m3 |
T13 (Control) | All volumen with comercial substrate (Bioplant) |
The dehydrated sewer sludge was collected at the Estación de Tratamiento de Esgoto (ETE) of Montes Claros, after preliminary treatment in an anaerobic reactor UASB and drying in a dehydrator to 5% humidity. The collection of bovine manure was carried out directly in the pen form ICA/UFMG experimental farm.
The sowing was carried out in rigid plastic tubes of 170 cm3, placed under shade cloth, with the capacity to retain 30% of light. A total of three to four seeds were placed in each tube, and thinning was carried out 15 d after sowing. All plants were placed in full sun, 20 d after thinning. Only one plant per tube was left and irrigation was carried out three times a day up to field capacity throughout the experiment.
The physical and chemical analyzes of the prepared substrates and the control (table 2) was carried out in the solid waste laboratory of ICA/UFMG, according to the Embrapa (1997) methodology. The pH, electrical conductivity (EC), moisture retention capacity (MRC), particle density (PD) and apparent density (AD) were evaluated; in addition, the total porosity (TP) was estimated.
Treatments | Attributes of substrates | ||||
---|---|---|---|---|---|
Chemicals | Physicals | ||||
pH | EC (µs/cm) | MRC (ml/g) | AD (g/cm³) | TP (%) | |
3:1:1:0+SS | 6.1 | 335.03 | 0.57 | 1.35 | 44.16 |
3:0:1:0+SS | 6.8 | 313.23 | 0.50 | 1.41 | 39.61 |
3:1:0:1+SS | 5.3 | 465.07 | 0.53 | 1.31 | 44.61 |
3:0:0:1+SS | 5.2 | 457.80 | 0.45 | 1.39 | 44.12 |
3:1:1:0+KCL | 6.1 | 501.53 | 0.53 | 1.27 | 48.74 |
3:0:1:0+KCL | 7.0 | 513.47 | 0.50 | 1.39 | 42.05 |
3:1:0:1+KCL | 5.7 | 456.30 | 0.50 | 1.36 | 44.36 |
3:0:0:1+KCL | 5.6 | 431.13 | 0.48 | 1.44 | 38.46 |
3:1:1:0+SS+KCL | 6.9 | 545.93 | 0.55 | 1.29 | 47.15 |
3:0:1:0+SS+KCL | 7.1 | 519.10 | 0.50 | 1.43 | 42.07 |
3:1:0:1+SS+KCL | 5.8 | 571.43 | 0.50 | 1.32 | 46.37 |
3:0:0:1+SS+KCL | 5.5 | 558.40 | 0.45 | 1.42 | 42.77 |
Control | 5.7 | 500.00 | 0.77 | 0.36 | 69.37 |
In the plants, after sowing and during 22 d, the emergence speed index (ESI) was determined in each experimental unit, according to the methodology proposed by Maguire (1962). At the time of transplantation to the field, 60 d after sowing, physiological observations were made with the use of a portable meter LI-6400 (Li-Cor Inc., Nebrasca, USA). The third full leaf from the apex to the base was used and the liquid photosynthesis rate per unit of leaf area (A), the stomatal conductance to water vapor (gs), the transpiratory rate of the leaf (E) and the temperature were determined.
The plant height (H) was determined with a millimeter ruler, measuring the stem from its base at the substrate level to the plant apex. The stem diameter (D) was calculated at the substrate level with the help of a vernier, with 0.05 mm precision. The number of branches and leaves per plant, total dry matter production (TDMP), dry matter production of the aerial part (DMPAP), root dry matter weight (RDMW), root volume and Dickson's quality index (Dickson et al. 1960) were also determined.
The leaves, stems and roots were weighed on a precision balance to obtain the fresh mass. Before weighing, the roots were washed in a low pressure water basin. sieves of 5 mm were used to avoid losses and later they were dried with a paper towel. The dry mass of leaves, stems, and roots was determined after drying in an oven at 65°C until reaching constant weight.
For the statistical processing of the information, the InfoStat program, version 1 (Di Rienzo et al. 2001) was used. The data were tested for normality (Shapirio and Wilk 1965) and homogeneity (Levene 1960). The counting indicators were transformed according to X0.5 and the percentage indicators according to arcsine of (X/100)0.5. Analysis of variance was performed and, when necessary, the Scott-Knott test was applied at 5% probability for means comparison. A Pearson correlation analysis was also performed between the substrates attributes and the ESI.
Results and Discussion
The ESI was higher (5.86) in the treatment with Bioplant commercial substrate, and it differed P <0.001 from the rest (table 3). The combination of organic sources with the type of soil defined the ESI, with the highest values for the proportions 3:1:1:0+SS, 3:1:0:1+SS and 3:1:1:0+ KCL. The use of sewer sludge and the application of KCL in loamy soils had a negative impact (0.13) on the ESI of M. oleifera.
Treatments | ESI | Treatments | ESI |
---|---|---|---|
3:1:1:0+SS | 2.78b | 3:0:0:1+KCL | 1.02c |
3:0:1:0+SS | 1.20c | 3:1:1:0+SS+KCL | 2.18c |
3:1:0:1+SS | 2.80b | 3:0:1:0+SS+KCL | - |
3:0:0:1+SS | 0.97c | 3:1:0:1+SS+KCL | 1.69c |
3:1:1:0+KCL | 3.27b | 3:0:0:1+SS+KCL | 1.52c |
3:0:1:0+KCL | - | Control | 5.86a |
3:1:0:1+KCL | 0.13c | Significance | P<0.0001 |
abc Means with different superscripts in the same row differ from the Scott-Knott test at 5%
-Indicates that no emergency occurred.
When studying the initial growth of different trees in the nursery stage, Noguera-Talavera et al. (2014) showed that M. oleifera began its emergence on the sixth day after sowing, without differing from the rest of the species, and reached the best performance of this indicator between the seventh and the ninth day, which coincides with what was observed in this research.
The physical-chemical characteristics of the used substrates can explain the performance of this indicator, since they showed a high and significant correlation with the ESI (table 4). The negative correlation and apparent density show that this indicator can limit the emergence of this forage tree.
The physico-chemical characteristics of the substrates show higher moisture retention capacity (MRC) in the commercial substrate (table 2), which could favor the imbibition of water in the seed and its germination. The use of sand, when loamy soil was used in the preparation of the substrates, had a direct impact on its moisture retention capacity, by showing a performance similar to the commercial substrate.
The reduction of the osmotic potential of the substrates, when different sources of organic matter and chemical fertilization strategies are used, could be another cause of the ESI obtained. In this regard, Da Silva et al. (2019) report that the osmotic potential of the substrate affects the availability of water absorbed by the seeds, which interferes with their germination.
Among the characteristics of substrates, porosity is of vital importance. The retention of water (micropores) and aeration (macropores) depend on it, and it has a direct influence on the development of the root system and the plant as a whole (Castillo et al. 2013). Substrates made from coconut powder, sisal wastes and loamy red and dystrophic yellow soils, showed total porosity similar to that observed in this study, with values between 40 and 60%, which favors the development of the plant (Lacerda et al. 2006).
The type of soil used in the preparation of substrates defined their apparent density. This indicator in the elaborated substrates was high, and always higher than what Pire and Pereira (2003) refer to when evaluating organic substrates, composed of rice husk and sugarcane bagasse. In the substrates that contained sandy soil it varied between 1.39 and 1.44 g/cm3, with values higher than those made with loamy soils. The lowest apparent density (0.36 g/cm3) was recorded in the commercial substrate Bioplant.
The structural characteristics of the materials used in the preparation of the substrates may respond to the differences found in this study. Alvardo and Solano (2002) report that the size of the particles is related to the MRC and the AD, since the presence of very small particles reduces the total porosity and increases the amount of retained water, due to the increase in micropores; it also makes it possible to reduce the porosity occupied by air, when reducing the volume of the voids between particles or macropores, which are the largest.
The use of organic sources (sewer sludge and bovine manure) marked the acidity of substrates (table 2). The lowest values (5.21 and 5.80) were found in those made with sewer sludge. When using bovine manure as a source of organic matter, the pH was raised to values between 6.10 and 7.13. According to Silva et al. (2013), the increase in pH can be derived from processes that occur in the substrates, such as the reduction of the resulting H + activity, the mineralization of the organic forms of nitrogen, as well as the denitrification and decarboxylation of fatty acids, among others.
The mineral fertilization characterized the electrical conductivity of the substrates, with values higher than the control in the treatments that combined the application of simple superphosphate and potassium chloride. High values of electrical conductivity can show the existence of unfavorable conditions in the environment for the nutrition of the plant, since the excess of salts in the root zone can harm the germination, emergence, development and productivity of the plants.
The physiological indicators of M. oleiferea seedlings, 60 d after sowing, were similar in all treatments and showed values between 5.86-9.73 (µmol m-2 s-1) of liquid photosynthetic rate (A); 0.02-0.13 (mol m-2 s-1) of stomatal conductance (gs) and 1.04-1.76 (µmol CO2 mmol H2O-1) of efficiency in the use of water (E). Leaf temperature ranged between 27.5 and 31.6 (°C).
The morphological characterization of M oleifera species showed that in the elaborated substrates, higher plant height, higher stem diameter and more leaves were reached, although some of them did not significantly differ with respect to the commercial substrate Bioplant (table 5). However, root growth, expressed by root volume, and Dickson's quality index, reached the highest values in the control treatment.
Treatments | Plant height, cm | Stem diameter, mm | Number of leaves/plant | Volume of root/plant, cm3 | DQI |
---|---|---|---|---|---|
3:1:1:0+SS | 12.69a | 3.20b | 4.45b (19.83) | 4.45b | 0.22b |
3:0:1:0+SS | 12.93a | 3.19b | 4.93a (24.28) | 4.80b | 0.32b |
3:1:0:1+SS | 13.92a | 3.71a | 4.80a (23.30) | 4.31b | 0.29b |
3:0:0:1+SS | 12.35a | 3.44b | 4.53b (20.90) | 3.30b | 0.26b |
3:1:1:0+KCL | 11.86b | 3.32b | 4.25b (18.05) | 3.90b | 0.27b |
3:0:1:0+KCL | - | - | - | - | - |
3:1:0:1+KCL | 13.95a | 3.73a | 4.63a (21.14) | 5.70b | 0.36b |
3:0:0:1+KCL | 13.52a | 5.59a | 4.28b (18.38) | 4.78b | 0.26b |
3:1:1:0+SS+KCL | 11.12b | 3.33b | 4.43b (16.65) | 3.90b | 0.25b |
3:0:1:0+SS+KCL | - | - | - | - | - |
3:1:0:1+SS+KCL | 12.96a | 3.74a | 5.08a (25.93) | 3.60b | 0.26b |
3:0:0:1+SS+KCL | 12.26a | 3.59a | 4.25b (18.13) | 3.80b | 0.19b |
Control (Bioplant) | 10.05b | 3.28b | 3.85c (14.95) | 8.25a | 0.56a |
SE ± | 0.71* | 0.12** | 0.14*** | 0.61*** | 0.03*** |
Significance | P<0.0143 | P<0.0077 | P<0.0001 | P<0.0002 | P<0.0001 |
abc Means with different superscripts in the same row differ from the Scott-Knott test at 5%
* P<0.05 ** P<0.01 *** P<0.001
-Indicates that no emergency occurred
These results show that the quality of the produced seedlings directly depends on the development reached by the seedlings, in which the dry matter of different organs (leaves-stems-roots) necessarily intervenes. The simple use of morphological indicators, such as the plant height and the stem diameter, without taking into account their relation (H index or slenderness index) can lead to defining erroneous times of seedlings use for this species. Sallesses et al. (2015) state that the slenderness in the seedlings production from Eucalyptus species should be less than two so that the plant is balanced. According to Luna (2019), the recommended values of this indicator should be high and depend on the species.
Paiva and Gomes (2012) pointed out multiple morphological characteristics to evaluate the seedlings quality of forest species, and highlighted among them the plant height and its diameter due to its easy measurement. However, as could be observed in this research, these indicators are not always going to be directly related to the best quality of seedlings, since it is necessary to take into account the interdependence that exists between root development and the development of the aerial part of the plant, as reported by Close et al. (2010).
The Dickson quality index (DQI) is the most accepted indicator to evaluate the quality of the seedlings produced in nurseries, since it expresses the balance of the mass distribution and the robustness of the seedlings (Cobas et al. 2015). However, the number of plants used for its calculation is lower than that used in other indices, when considering the total dry weight of the plant, the dry weight of the aerial part and the root dry weight. Aguirre et al. (2018) obtained DQI in M. oleifera higher than those of this research, when they studied the effect of the substrate on the seedlings quality of five forest species. This result could be influenced by the type of soil used in both researchers. However, in this study, the DQI values for the elaborated substrates show that they are of medium quality (Rueda et al. 2014).
In this analysis, another element to consider is related to the effect that root volume can cause on the morphological attributes of nursed plants. Table 5 shows that the commercial substrate Bioplant did not always show the highest values for the morphological indicators studied, but it did show the highest root volume and the highest quality index of seedlings. This result can be directly related to the response mechanisms developed by plants to a variation in the availability of resources. In this case, of substrate nutrients, because they tend to modify the biomass distribution patterns (Camargo and Rodríguez 2006).
According to Lagoute et al. (2009), the supply of photoassimilates and different growth regulators are interrelated with the root volume, since the aerial biomass depends on the root biomass for the mechanical anchoring of the plant to the soil (substrate), the absorption of water and nutrients and the production of hormones.
From the analysis performed, it is concluded that the use of sewer sludge and bovine manure in substrates for the production of M. oleifera seedlings constitutes an appropriate alternative with results similar to those obtained with the commercial substrate Bioplant. It is recommended to carry out economic feasibility studies to assess its inclusion in the commercial production of substrates.