| Livestock Research for Rural Development 32 (4) 2020 | LRRD Search | LRRD Misssion | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
The low availability and fluctuating quantity and quality of forage growing in grassland, shrinking grassland area and poor management are the main causes of increased land degradation and reduced productivity of animals grazing on tropical grasslands. One sustainable way for overcoming the problems is through establishment of Leucaena leucocephala in grasslands. To generate information useful for increasing productivity of grasslands using Leucaena leucocephala, literature concerning the benefits of Leucaena grass mixture in silvopastoral system in Google Scholar, PubMed, Crossref, Scopus and Web of Science databases were searched. From those databases, characteristics of Leucaena in relation to overcoming land degradation and increasing soil fertility were elaborated and highlighted. Nutritive value of Leucaena and grasses, both in mixture and monoculture and their relations to animal production are reviewed and discussed.
Key words: forage quality, ipil-ipil, grass intercropping, land rehabilitation, livestock production, degraded land
A major constraint to increasing livestock production in tropical countries is the low availability and fluctuating quantity and quality of year round forage supply. During the wet season, forage plants grow so quickly that their dry matter yield is high but their `nutritive value only high in short term i.e when they are young and after that, their nutritive value decreased abruptly. In contrast, during the dry season, forage growth becomes slower and in the end of dry season, stops, leading to shortage of forage supply, both quantitatively and qualitatively.
To overcome these problems, some farmers give supplement to their animals with low quality agricultural by-product such as rice straw, corn stover, banana pseudo-stem etc. However in most cases, the farmers rarely give feed supplements and animals have to be grazed on overgrazed pasture or on non-conventional areas like abandoned plantation estates, river bank, forest margin, marginal lands etc.
In densely populated country like Indonesia, the low availability of forage is also attributed to poor grazing management and shrinking grassland areas as affected by high conversion rates of grassland to cropping and plantation areas, housing and industrial areas. In recent years, driven by high demands for livestock products, the farmers tend to raise the animals in grassland areas with high and constant stocking rates throughout the year that leading to overgrazing, especially during the dry season. Overgrazing impacts negatively on both grazing animals and grassland ecosystem. Animals grazing on overgrazed grassland need longer time of grazing to fulfill their needs, hence reduced growth and susceptibility to disease. Overgrazing and tree removal are the primary causes of grassland soil deterioration that result in demolition of vegetation cover, loss of surface litter, increased soil compaction and run-off, low soil nutrient availability and consequently reduced grassland productivity and even desertification (Mugerwa and Emmanuel 2014, Titterton and Bareeba 1999). Mugerwa et al (2012) noted that soil macro-nutrients (N, P and K) in overgrazed areas are usually below the critical levels required to support establishment and growth of palatable forages such as Brachiaria and Panicum species. Overgrazing also lead to invasion of non-native species and weeds (Ditomaso et al 2010) like Chromolaena odorata (Rusdy 2016). The low fertility of tropical grassland soil is also aggravated by lack of soil conservation practices and absence of application of maintenance fertilizer. According to Steinfeld et al (2006), about 20 % of global pasture and 73 % of the rangelands in the drylands have been degraded. Without any strategic action is taken, soil degradation and animal production from grassland will continue to decrease with unimaginable consequences.
One way for overcoming grassland degradation and increasing its carrying capacity is through establishment of forage tree legumes that have ability to control erosion, increasing soil fertility and have high nutritive value for livestock. Leucaena leucocephala is one of several multipurpose legume tree species that is suitable for this purpose because it has root structures that can control erosion, has high biomass potential and has high ability to fix atmospheric N2 that can increase soil fertility and nutritive value. Its high nutritive value makes Leucaena is the best forage supplement to increase animal production fed elephant grass basal diets (Rusdy 2018). Leucaena in combination with grass pasture is one of the most persistent, productive and sustainable grazing system used in north Australia (Shelton and Dalzell 2007). For these reasons, establishment of Leucaena can be a technology of choice for increasing a sustainable animal production from tropical grassland. This paper aimed to review relevant literatures concerning the effects of establishment of Leucaena in grassland area on soil erosion, soil fertility, nutritive value of forage and animal production.
Leucaena is a tropical tree legume plant that has been used worldwide to control land degradation and maintain or increase soil fertility. Its ability to control land degradation is attributed to its extensive, dense rooting and depth of penetration that could provide superrficial as well as deep-seated soil erosion control (Osman et al 2008). Its aggressive taproot system helps break up compacted subsoil layers, improving penetration of water into the deep soil and allows Leucaena can grow in dry conditions because of its ability to extract water from the deep soil strata that is not accessible to most herbaceous plants such as grasses (Anonymous 2019). Its lateral roots that grow horizontally and profusely make Leucaena can control run off and soil erosion (Saifuddin and Normaniza 2016). Leucaena also aids in recycling leached essential nutrients, including P and K from the subsoil to the soil surface (Otsyina and Dwozela 1995). Leucaena can grow on steep slopes and in marginal lands with long dry season, making it a prime plant for restoring forest cover, watersheds and grasslands (Anonymous, 2019). Being a drought-tolerant species, Leucaena also has higher water use efficiency compared with draught resistant native grasses like Cenchrus ciliaris (Dalzell et al 2006).
The other important benefit of Leucaena is its ability to associate symbiotically with N2-fixing bacteria to fix atmospheric N2 and use the fixed N for its growth and other plants. Estimates of N fixed by Leucaena varied from 110 kg/ha/yr (Hogbert and Kvarnstrom (1982) to 584 kg/yr (Nutman 1976). When intercropped with grasses, the N fixed can be transferred to the grass. On average, up to 21% N in grass growing with Leucaena could be derived from biologically fixed N (Jayasundara et al 1997). Successfully nodulated Leucaena can produce more sufficient nitrogen for its own needs and intercropping with companion grass maximizes pasture production because the grass can utilize excess fixed N to enhance its growth and creates strong ground cover, which helps prevent soil erosion and control weeds (Shelton and Dalzell 2007).
N fixed by legume can be transferred to soil and grasses through animal excreta, legume litter decomposition and direct transfer, but transfer of fixed N to the soil and grass predominantly occurs through decomposition of legume litter-fall and livestock excreta (Dubeux et al 2007, Vendramini et al 2014). In grassland area where the animals can not reach Leucaena leaves, litter-fall is the major pathway of nutrient cycling, however when animals can access Leucaena leaves, excreta which is comprised of urine and dung is the major pathway of nutrient cycling (Apolinario et al 2015).
Leucaena litter buried in the soil at 15 cm depth had high decomposition rates. By the end of 12th week, Leucaena lost 75.9% of its dry matter; higher compared with Senna siamea and Albizia lebbeck which lost 45.2 and 43.3% of dry matter, respectively (Gaisie et al 2016). Among all Leucaena litter components, leaf litter contributes more nutrients, especially N than other litter components. The high biomass production, N content and decomposability of Leucaena leaves indicates its greater potential for use as green manure (Mwiinga et al 1994).
About 70 to 90% of nutrients ingested by ruminants return via excreta, however, while litter is more evenly distributed in grassland, distribution of nutrient cycling via excreta is not uniform (Vendramini et al 2014) as animals tend to concentrate excreta on small areas of grassland, mostly under shade, inside the barnyard and near water point (Hayness and Williams 1993). Thus, a greater proportion of excreta return occurs in in those areas and tend to cause reduced soil fertility in other grassland areas.
Although less evenly distributed, however, nutrient cycling via excreta is faster than litter-fall because much more nutrients in excreta have been converted to plant available form during digestion. Because of this reason, nutrients voided via excreta will be easier to lost compared to litter-fall. As high grazing pressure lead to greater proportion of nutrients return via excreta (Dubeux et al. 2007), increasing stocking rate without increasing pasture primary productivity will lead to land degradation and reduced pasture productivity (Boddey et al 2004). By establishing Leucaena with large proportion in grassland area which also provides shade for livestock, it will likely bring benefits in uniformity of nutrients distribution by animals.
Litter fall affects soil physical and chemical properties. A significant increase of soil pH, organic carbon, total N, available P and exchangeable Ca and Mg occur after incorporating of Leucaena pruning in the soil (Majule 2006). Leucaena grass pasture that had been grown for 20 years accumulated organic carbon and total N at rates exceeding those of adjacent native grass by 267 and 16.7 kg/ha/yr, respectively (Radrizzani et al 2011). With increasing relative proportion of Leucaena in mixture with teak, total soil N and available P content of soil increased as the proportion of Leucaena increased to 50% (Kumar et al 1998).
Although many tropical grasses have high dry matter yield potential but generally they have low crude protein contents and high levels of NDF and ADF that associated with limiting nutrient intake and digestibility by animals (Amiri et al 2012). In contrast, many forage tree legumes like Leucaena is capable of producing high quantities of dry matter of 40.29 tons/ha (Aminah and Wong 2004) with high quality (crude protein 21.5%, NDF 38.7% and ADF 22.4% of dry matter) (Phesatcha and Wanapat 2016). Compared with many other legume trees, Leucaena is more suitable used as silvopasture plants because it has highest dry matter yield potential and provided the best nutritional value of all legumes studied (Gama et al 2014).
Introduction of Leucaena into pastures improves quantity and quality of associated grass. De Oleivera et al (2017) reported that dry matter yields of Leucaena elephant grass mixture were higher than that of sole elephant grass or sole Leucaena but crude protein contents of sole Leucaena were higher than those of sole elephant grass or Leucaena elephant grass mixture. Biomass yield and N accumulation of Leucaena growing along with Cenchrus ciliaris were also higher than grass monoculture (Rao and Giller 1993). Crude protein and organic matter contents of Panicum maximum and Brachiaria brizantha increased when they were intercropped with Leucaena but their NDF increased when the grasses were grown in monocultures. (Aldaya-Navarro et al 2017).
Digestibility of Leucaena - grass mixture also is higher than grass monoculture. .In vitro dry matter digestibility ofLeucaena Ischaemum aristratum was higher (60.8%) than Ischaemum monoculture (52.5%) (Aregheore et al 2004). Also, dry matter digestibility of Leucaena associated with Panicum maximum was 60.64%, higher than monoculture of Panicum maximum (43.52%) (Hippolite et al 2019).
Intercropping of Leucaena with grass contributes to increased intake and growth by animals compared with feeding the same grass as monoculture. Animals fed mixture of Leucaena and Megathyrsus maximus had higher intakes of crude protein, calcium, fat and lower NDF and ADF intakes than those fed M. maximus monoculture (Cuartas et al 2015). Inclusion of Leucaena at 24 % level in growing heifers fed basal diet of Cynodon plectostachyus increased dry matter intake from 2,02 to 2,47% DM of animal live weight (Molina et al 2016). Daily dry matter intake of goats fed basal diets of Panicum maximum plus 100g maize bran (control) was 229 g but increased to 339 g when the control diets_were supplemented with Leucaena (Saha et al 2008). The higher digestibility and intake of Leucaena grass mixture over grass monoculture could be attributed to the lower ADF and NDF contents of intercrops over grass monoculture, respectively.
With basal diet of fresh elephant grass cv.Taiwan, increasing levels of Leucaena leaves increased crude protein intake and N excretion by heifers linearly up to 80% Leucaena level, but optimum levels of Leucaena incorporation was 40 60% of the ration DM (Pineiro-Vazquez et al 2017). This is in line with Aregheore (2002) that in goats fed Panicum maximum basal diets, Leucaena leaves could be fed up to 40% level with improved dry matter intake, growth rate and nutrient utilization.
Supplementation with Leucaena at higher levels seems is not good for feed efficiency by animals. Aregheore et al (2004) reported that in goats fed basal diet of Ischaemum aristratum, increasing Leucaena leaves from 0%, 20%, 50% to 80% of total daily allowance increased voluntary intake and live weight gain by goats linearly with incremental Leucaena supplementation levels, but there was a decline in growth rate at 80% Leucaena level. High intakes of Leucaena might cause imbalance of diet due to high intake of crude protein relative to lower intake of fermentable energy which in turn lead to low efficiency of microbial protein synthesis in the rumen (Casmamiglia et al 2010).
Intake of grass Leucaena pasture is higher when it is supplemented with fermentable energy sources. Intake of ME and milk yield of cows grazing on Leucaena - Cynodon nlemfuensis pasture and supplemented with grain sorghum was higher (161 MJ/d and 14.5 kg/cow/d, respectively) than monoculture of C. nlemfuensis plus concentrate (131 MJ/d and 13.5 kg/cow/d, respectively) (Bottini-Lucardo et al 2016)
Because of higher of nutritive value, digestibility and intake of animals fed mixture of Leucaena grass, more milk and meat are generally produced from intercrop plants compared with grass monoculture.
Leucaena grass intercropping had positive effects on milk yield in dairy goats and dairy cows. In Venezuela, with an additional 2 h of browsing Leucaena in addition to pasture (Cenchrus ciliaris) feeding, crossbred Saanen-Anglo Nubian goats yielded 0.84 kg/day milk compared with 0.55 kg/day for goats fed on Cenchrus ciliaris alone (Clavero and Razz 2003). In Brazil, intercropping of Leucaena and Brachiaria decumbens increased milk yield of dairy cows from 9.5 (grass monoculture) to 10.4 litres/cow/day (Paciullo et al 2014). Also, in Thailand, average milk production was higher (13.6 kg/hd/d) in cows strip grazed on Leucaena - Brachiaria ruziziensis pasture than grazed on Brachiaria ruziziensis pasture only (11.9 kg/hd/d) (Tudsri et al 2001).
Mixture of Leucaena and grasses also increased growth performance in goats. Average daily gain, fetal development, and birth weight of goats raised on Leucaena improved grasses (Eragrostis curvula and Panicum maximum) mixture were higher than those raised on natural pasture. (Akingbade et al 2000). Goats fed on mixtures of Leucaena and Panicum maximum also produced more gain (25.4 g/day) compared with those fed Panicum grass only (15.9 g/day) (Saha er al 2008).
Animals growth grazing on Leucaena improved grasses pasture is higher than Leucaena natural grass pasture or natural grass pasture only Cattle grazing on Leucaena natural grass pasture with stocking rate of 0.7 head/ha gained 0.56 kg/head/day but those grazing on natural grasses with the same stocking rate gained only 0.25 kg/head/day (Jones 1994) while steer grazing on Leucaena cv Tarramba Brachiaria decumbens pasture in Papua New Guinea gained 0.65 kg day-1 but those grazing on Brachiaria decumbens only gained 0.48 kg day-1 (Galgal et al 2000).
In northern Australia, Leucaena - grasses pastures were the most productive, profitable, and sustainable beef production systems (Shelton and Dalzell 2007). The benefits of using Leucaena-grass pasture systems was increased animal production up to 4 times due to a combination of greater weight gain, increased carrying capacity and longevity of pastures, potential to intensify production and escalating land prices Those authors noted that in Central Queensland, steers grazing onCenchrus ciliaris, Chloris gayana and Panicum maximum pastures gained only 140 to 190 kg/yr; but steers grazing on those grasses mixed with Leucaena gained 250 to 300 kg/yr. These values are close to that reported by Lemcke (2019) at Douglas Daly area Australia that cattle grazed on Leucaena - grass pastures gained 190 - 240 kg/head/year at stocking rates of 1.25 yearlings/ha. This is about 30-40 kg/head higher than animals raised on pure grass paddocks. In Africa, increasing Leucaena levels from 0 to 30 g/kg BW0.75 increased daily gain of cattle fed elephant grass basal diet from 0.54 to 0.85 kg/day (Abdulrazak et al 1996).
Although intercropping Leucaena with grasses has positive effect on milk yield and gain of animals, supplementation with fermentable carbohydrate sources is needed to increase animal production. Cynodon nlemfuensis Leucaena pastures produced low microbial protein biomass while Cynodon nlemfuensis Leucaena molasses produced higher microbial protein biomass (Estrada-Lievano et al 2009). Goats fed on Leucaena - grass of Tifton 85, Andropogon and Panicum maximum mixtures and supplemented with ground maize at 0.5, 0.9 and 1.3% of body weight resulted in reduced grazing time and increased rumination. Besides, it influences feeding behavior and had a favorable effect on daily gain (17.9 to 67.3 g/day) (De-Carvalho et al 2017). With Leucaena as basal diet, supplementation with rice bran at 34% of diet increased body weight gain of cattle from 0.42 to 0.61 kg/day (Quiley et al 2009)
Besides attributed to high nutritive value. increased animal production from Leucaena based pasture also been attributed to presence of condensed tannin in Leucaena, which can protect crude protein from ruminal degradation and increasing its bypass into the intestine where it is digested and absorbed. This is in line with Saha et al 2008) that goats fed on Panicum maximum hay and supplemented with Leucaena leaves (tannin 4.39%) retained more N (3.5 g/day) than control treatment (Panicum maximum hay) with tannin content of 1.94%.
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Received 15 February 2020; Accepted 18 February 2020; Published 1 April 2020