Undoubtedly the environmental crisis arising from global warming or the commonly called “greenhouse effect” must develop as a major issue in the near future and it will inevitably influence aid programs.
Global warming, attributable to the accumulation of gases in the atmosphere will have enormous repercussions on agriculture. Inevitable changes in sea levels, climate and temperature are forecasted with repercussion for both plant and animal agriculture.
The patterns of change are being modelled and predicted but our present level of knowledge suggests that these models will invariably be wide of the mark. Global warming is likely to reduce world food production perhaps largely through the disruption that will occur through changing climate.
The conclusions are universally that the world will suffer and therefore attempts must be made to ameliorate the rapidly increasing levels of gases in the atmosphere (see IPCC report 1990).
The relative contribution of various gases to global warming is shown in Figure 7.1, the changing CO2 or CH4 levels in the atmosphere in Figures 7.2 and 7.3.
Figure 7.1: Relative contribution (%) of greenhouse gases to atmospheric warming (Source: World Resources Institute)
Figure 7.2: Trends in emissions of CO2 (Source: World Resources Institute)
Figure 7.3: Trends in atmospheric methane accumulation (Khalil & Rasmussen, 1986)
Clearly CO2 production from fossil fuel sources is the major contributor and a reduction in fossil fuel combustion is required, coupled with increased capacity for long term carbon dioxide uptake (e.g. reduced tree felling and increased tree planting).
Global methane production must also be curbed. The source of atmosphere methane are shown in Figure 7.4. Ruminants contribute a significant amount (18% of the total) of the world production of methane and are targeted as a source which is one of the few easily manipulated (see IPCC report 1990).
As discussed in this report the levels of ruminant production on roughage based diets are in general well below that possible from the available resources and often between 10 and 30% of the genetic potential of the animal species. The reasons for low productivity is complex but it has been argued that the poor feed base which provides an imbalanced nutrition is by far the greatest limitation (see Leng 1990).
Figure 7.4: Relative contribution of biological resources to the global production of CH4 in the atmosphere (Bolle et al., 1986)
Figure 7.5: (A) The effects of improving the efficiency of rumen fermentative activity on methane production/kg of digestible energy consumed (B) The production of methane/kg gain in supplemented cattle (feed conversion efficiency (FCR) 9:1) or unsupplemented cattle (FCR=40:1) fed straw based diets (after Saadullah, 1984)
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Methane is produced in the pre-gastric fermentative digestion of ruminants at a rate which varies between 8 and 17% of the digestible energy consumed (see Leng, 1982, 1990).
A ruminant that grows slowly matures over say 5 years, as against the potential of finishing it at between 12–18 months, may produce up to 4 times the amount of methane per unit of product (see Figure 7.5).
The numbers of ruminants in the world and their location is shown in Table 7.1. Potentially any technology which improves the efficiency of conversion of feed into livestock products lowers the number of animals required to produce meat, milk, wool and other products. The reduction in numbers that can potentially be achieved can have a significant effect on methane emissions.
Lowered numbers of animals will also feed back on available land requirements for livestock production allowing greater emphasis on alternative use of pasture lands including tree crop production.
Table 7.1: Estimates of methane emissions from animals (adapted from Crutzen et al., 1986)
| Animal type and regions | World Population (x 106) | CH4 Prod. (kg/hd/year) | Total CH4 (Tg)** |
| Cattle; developed countries | 573 | 55 | 31.8 |
| Cattle; developing countries * | 653 | 35 | 22.8 |
| Buffaloes | 142 | 50 | 6.2 |
| Sheep; developed countries | 400 | 8 | 3.2 |
| Sheep; developing countries and Australia | 738 | 5 | 3.7 |
| Goats | 476 | 5 | 2.4 |
| Camels | 17 | 58 | 1.0 |
| Pigs; developed countries | 329 | 1.5 | 0.5 |
| Pigs; developing countries | 445 | 1.0 | 0.4 |
| Horses | 64 | 18 | 1.2 |
| Mules, Asses | 54 | 10 | 0.5 |
| Humans | 4670 | 0.05 | 0.3 |
| Wild ruminants and large herbivores | 100–500 | 1–50 | 2–6 |
| TOTAL |
Biotechnology, feeding, management and breeding can be combined to improve animal production and could potentially increase animal production to the extent that in the developing countries (which contain approximately half the livestock in the world) it may be possible to reduce methane generation by up to 60% from the same product (see Leng, 1990). Similar reductions in methane emissions from ruminants in developed countries can also be achieved where the production systems are also often inefficient.
One of the major reasons for the development of livestock production in cropping systems in developing countries is to utilise crop residues, thus, eliminating waste and optimising the use of the total biomass produced within the small farm system for the benefit of the small farmer. The small farmer has often a requirement for draught power with animal production as a secondary consideration.
Integrated crop and livestock production systems are highly efficient; potentially crop residues are used as livestock feed; the waste products (e.g. faeces and urine) are fed into biogass digestors and the effluent used to fertilise ponds for aquatic plant/algae production, with fish farming as the terminal activity. These systems are very worthwhile pursuing as a means of providing nutrients/fuel for the family, minimising fossil fuel combustion and methane generation and, thus, reducing environmental pollution (Preston, 1990).
The array of integrated systems that could be developed is large. They all have as a central core a basic flow of nutrients through a number of systems. At each of these steps research can be brought to bear to optimise the partitioning of the available biomass into food, fuel and residues (see Figure 7.6). The environmental attributes of such systems are that methane emissions into the atmosphere and fossil fuel use are minimised. In addition the efficient and almost total harnessing of the energy from high producing crops reduces the land areas required per unit of product (see Preston, 1990). The problems are the necessary high level management that must be exerted by the small farmer, which can often be beyond his presently developed skills.
Figure 7.6: Flow diagram showing the potential recycling of feed and faeces biomass from crop residues
Figure 7.7: An example of an integrated farming system based on sugar cane and forage trees fractionated to provide feed for pigs and poultry (the juice and tree leaves), sheep (the cane tops and tree leaves), fuel for the family (bagasse and firewood) and litter for sheep and earthworms (bagasse), with recycling of excreta through biodigesters to provide fuel (biogas) and fertiliser (the effluent) for water plants in ponds and for the crops (Preston, 1990)
A complete discussion of these systems is beyond the scope of this document but two examples are:—
the use of aquatic plants/algaes grown on biodigested effluent for protein production for feeding to pigs and ruminants particularly in the humid tropics and
the farming of suitable fish in biogass digesta fluids.
A system incorporating these aspects is currently being investigated and developed by T.R. Preston in Colombia (see Preston, 1990) (and Figure 7.7).
