Climate behavior

During the experimental period, changes in the climatic variables that affected the behavior of Moringa oleifera forage banks were observed. The pre-conditions for cuts 1, 2 and 5 were more favorable, which could benefit the production of forage and the leaf: stem ratio. A slight increase in temperature was observed in the seasons of less precipitation, but this perhaps had the greatest relevance in the performance of the species (figure 1).

The behavior of the relative humidity and solar radiation were relatively constant. However, a slight increase in solar radiation was observed in the last two cuts (figure 2).

Source: Elaborated by the authors

Figure 1. The behavior of precipitation and temperatures (maximum, average and minimum), during the evaluation period of the Moringa oleifera forage bank in Casanare, Colombia. 

Source: Elaborated by the authors

Figure 2. The behavior of the relative humidity and solar radiation during the evaluation of the Moringa oleifera forage banks in Casanare, Colombia. 

Effect on soil quality

A change was found in the initial contents of some minerals in the soil (table 1). Despite the short evaluation time, increases in mineral contents were observed where the M. oleifera forage bank was established. The tendency was to improve the chemical conditions of the soil, increase the bases and enhance its availability to the plants.

Table 1. Soil nutrient content variation before (initial) and after 16 months of the establishment of the Moringa oleifera forage bank, department of Casanare, Colombia 

Source: Elaborated by the authors

om: Organic matter; oc: Organic carbon

Furthermore, there was an increase in om, oc, saturable bases and higher water retention capacity in the soil, essential aspects for forage production and adaptation to extreme climatic conditions, agreeing with what was found by Seddaiua et al. (2013) and Rodríguez (2011).

This variation can be explained by the cycling of nutrients carried out by tree species, as these recover nutrients and water from deep soil profiles and places them on top of the ground through litter. These interactions can explain the differences in the initial and final soil conditions. The effect of these systems and their contribution to the recovery and improvement of degraded soils is clear. Vallejo et al. (2012) argue that the entry of organic matter that comes from trees provides substrates for soil microorganisms, increasing their activity and the populations that participate in nutrient recycling.

In this study, the initial condition of the macrofauna in the soil was null (no type of organisms were observed), so the presence of the arboreal species contributed, in the short term, to recover the biological characteristics of the soil (figure 3). In the plots of M. oleifera, the presence of different families of macrofauna (Lumbricidae, Termitidae, Chilopoda, and Scarabaeidae), which have ecological functions in the soil such as pore formation, humification, and mineralization of organic matter was observed. This increase in the macrofauna could also explain the increase of some minerals in the soil, since the micro, meso and edaphic macrofauna contribute to nutrient release, leaving them available for plants. Moreover, this also agrees with Rousseau, Fonteb, Téllez, Van der Hoek and Lavellea (2013) and Sánchez (2007), who found a greater abundance of macrofauna in systems with forage trees. Further, Noguera, Reyes and Mendieta (2017) reported a higher number of individuals and families in M. oleifera plantations with no chemical management compared to conventional management systems.

Source: Elaborated by the authors

Figure 3. Macrofauna abundance (number of individuals) in the soil of Moringa oleifera forage banks, including a control treatment (initial) that reflects the initial condition of the soil in Casanare, Colombia. 

Production of green fodder anddry matter

The production of edible biomass by forage tree species is influenced by multiple factors, such as climatic conditions, planting density, cutting frequency, cutting height, among others. Under management practices, the forage bank showed an average gf production of 98 t/ha/year and 21.6 t/ ha/year of dm. Statistical differences (p = 0.0084) were found in dm production with higher leaf production (table 2).

Table 2. Average green forage (gf) and dry matter (dm) production per plant fraction of Moringa oleifera in forage banks in the department of Casanare, Colombia 

Source: Elaborated by the authors

The production of gf per cut in this study was higher t/ha/cut and 2.93 t/ha/cut; meanwhile Valarezo compared to what has been previously reported by and Ochoa (2013) reported values of 9.33 t/ha/year Díaz (2013), who found productions between 2.48 and 2.04 t/ha/year of gf and dm, respectively.

Moreover, Jarquín and Jarquín (2003) found fresh matter yield values of 81.03 t/ha/year and dm values of 14.44 t/ha/year, due to the higher plant recovery time, as these suffered fewer cuts per year. On the other hand, Padilla, Fraga, Scull, Tuero and Sarduy (2014) found an average dm yield of 2.83 t/ha/cut, similar to what was found in this study, and contrary to what was found by Espinoza and Sevilla (2010), who obtained much higher gf yields (119.2 t/ha/year), which can be attributed to the use of fertilization.

Likewise, Zheng, Zhang and Wu (2016) show fresh matter and dm productions ranging from 43 to 76.4 t/ha/cut and from 1.66 to 12.85 t/ha/cut, respectively, i.e., much higher values compared to those found in this study. These results can be explained by the higher planting densities and, in some treatments, by the lower cutting frequencies used by these authors. The dm yields of M. oleifera vary from 2.6 to 34.0 t/ha/cut depending on the planting density (Foidl et al., 1999, cited by ^{Pérez, Sánchez, Armengol, & Reyes, 2010}). Ledea, Rosell, Benítez, Arias and Pérez (2018) documented much higher dm productions to those found in this study (4.2 t//ha/cut and 3.3 t/ha/cut for leaves and stems, respectively), differences that in production can be attributed to the application of organic fertilization and irrigation.

The climatic conditions possibly influenced the productive behavior of M. oleifera, since there were marked periods of lower (cuts 3 and 4) and higher (cuts 1, 2 and 5) precipitation. The productions of gf and dm showed statistical differences (p < 0.0001), finding higher values in cuts preceded by abundant rains; conversely, production was reduced significantly in dry periods (table 3). Despite these climatic conditions, the species produced fodder, which makes it a fodder resource with potential for adaptation strategies to climate change, since, under the same climatic conditions, the grass species have less tolerance to these conditions.

Table 3. Green forage and dry matter (t/ha/cut) biomass production of the entire plant and each fraction (leaf and stem) of Moringa oleifera in forage banks subjected to five cutting session, in the department of Casanare, Colombia 

Source: Elaborated by the authors

Precipitation measured during a cutting session: cut 1 = 230 mm; cut 2 = 121 mm; cut 3 = 0 mm; cut 4 = 39 mm; cut 5 = 323 mm.

Padilla et al. (2014) found a similar dm production per cut and affirm that the production in each cut remained stable, attributing the stability to the production of M. oleifera biomass. On the contrary, in this study, considerable differences were observed in production between lower and higher precipitation periods. These results agree with what was reported by Zheng et al. (2016), who evaluated the behavior of the species in drought and rainfall periods, finding a similar behavior to what was found in the current study, although with higher gf and dm production in each season.

Forage production, even in times of drought, can be explained by its thickened tap root system, which allows storing nutrients, water and growth hormones (^{Casanova et al., 2018}).

Nutritional quality of the entire plant and its fractions (leaf and stem)

Table 4 shows the nutritional quality of the entire plant of M. oleifera and its fractions. The nutritional quality of the entire plant was acceptable, especially the percentage of cp, as this species has the potential for animal feed in ecosystems where forage species usually have low cp levels.

Leaves were the plant fraction with the best nutritional quality, presenting higher levels of cp, ivdmd and me, and lower levels of ndf and adf, nutritional characteristics that favor a better use by animals.

Table 4. Nutritional quality of the entire plant and each fraction (leaf and stem) of Moringa oleifera in forage banks, in the department of Casanare, Colombia 

Source: Elaborated by the authors

dm: Dry matter; cp: Crude protein; ivdmd: In vitro dry matter digestibility; me: metabolizable energy; ndf: Neutral detergent fiber; adf: Acid detergent fiber; ±: Standard deviation.

Likewise, Padilla et al. (2014) reported similar cp levels to those found in this study during the rainy season, but with percentages higher than 20.8 % in the dry season, meanwhile Díaz (2013), García et al. (2008) and Valarezo and Ochoa (2013), found cp percentages of 22.8 %, 26.6 %, and 22.1 % to 25.5 %, respectively, which can be explained by the nitrogen fertilization they used. Méndez et al. (2018) found 22.8 % and 24.0 % of cp in rainy and not very rainy seasons without fertilization.

Some papers report lower levels of ndf for the entire plant compared to those found in this study. For example, Méndez et al. (2018) report 39.2 %, Díaz (2013) found 41%, and Meza, Olivares, Gutiérrez, Bernal and Aranda (2014) obtained 43.7 % to 50.6 %; meanwhile, Padilla et al. (2014) found similar levels in the entire plant during the rainy season (60.80 %, 56.44 %, and 58.76 %) and lower levels in times of drought (55.3 %, 52.19 %, and 52.95 %).

The adf reported by Meza et al. (2014) was higher compared to what was found in this work, i.e., 35.3 % and 42.4 %, just as what Padilla et al. (2014) found, indicating that in the rainy season, the adf values were 45.89 %, 44.47 % and 44.90 %, meanwhile in the dry season, they documented levels of 38.48 %, 38.68 %, and 32.21 %. Diaz (2013), on the contrary, reported lower levels (27.84 %) than those found in this work, although they used nitrogen fertilization; likewise, Méndez et al. (2018) found lower levels but without fertilization or irrigation (22.5 %).

The leaf: stem ratio in forage plants is a valuable indicator since the most substantial amount of nutrients is concentrated in the leaves; therefore, higher production of this fraction (better ratio) has positive effects on animal production systems, by providing higher amounts of nutrients. The leaf: stem ratio in this study was on average 1.4:1, finding statistical differences (p < 0.0001) between cuts, possibly due to climatic conditions (table 5). In the fourth cut the relation is negative, possibly because the plants suffered a prolonged drought period, and as a homeostatic mechanism in the face of water stress, it stimulates the fall of leaves to reduce water losses. Besides, in the third cut, despite corresponding to a period in which there was no precipitation (drought), the leaf: stem ratio was not affected in comparison to the rainy season. The higher resistance that the arboreal species show in dry periods can explain the above, due to the length of their roots that allows them to explore greater depths of the soil, taking water from deeper profiles, in comparison with herbaceous species.

Table 5. Percentage of each fraction of the plant and leaf: stem ratio of Moringa oleifera plants in forage banks subjected to five cutting sessions, department of Casanare, Colombia 

Source: Elaborated by the authors

Precipitation: cut 1 = 230 mm; cut 2 = 121 mm; cut 3 = 0 mm; cut 4 = 39 mm; cut 5 = 323 mm.

Meza et al. (2014) report leaf: stem ratios from 1.7: 1 to 2.4: 1, and attribute the reduction in the ratio to climatic factors such as temperature, as it decreases at higher temperatures. Padilla et al. (2014) did not find differences in the number of leaves/plant when cuts were made at different heights. Conversely, Ledea et al. (2018) found statistical differences in the percentage of leaves (62.7 %) and stems (37.3 %), with higher leaf production compared to what was found in this study.

In the holistic analysis of the system, the loss of leaves should be understood as a positive aspect, since it is a mechanism through which the recycling of nutrients is favored, and it contributes to recover or maintain soil properties.