Livestock Research for Rural Development 1 (1) 1989

Citation of this paper

The greenhouse effect and its implications for world agriculture. The need for environmentally friendly development

T R Preston* and R A Leng**

*Fundación CIPAV, AA 20591, Cali, Colombia
**University of New England, Armidale NSW2351, Australia


The warming of the earth's atmosphere, due to accumulation principally of carbon dioxide and methane, promises to be the major issue of the next century. Fossil-fuel based industrial development is the major cause of the environmental imbalance; however, agricultural practices are major factors with the capacity of adding to greenhouse gases (the consequence of most modern production technologies) or reducing them by environmentally friendly development schemes. This article analyses the causes and consequences of the Agreenhouse effect and proposes remedies which are sustainable and especially appropriate for adoption on small scale family farms in tropical regions.

Key words: Environment, greenhouse effect, biomass, family farms, sugar cane, trees, integration, recycling, biodigesters, monogastrics, ruminants.


Social, anthropological, economic and political considerations have been the major determinants of Aid programmes but the growing environmental crisis due to global warming is likely to dominate many issues in the future. The greenhouse effect is the most serious issue facing the world today and which needs immediate attention by governmental and aid agencies.

The greenhouse gases

The greenhouse effect, or increasing world temperature, is clearly ascribable to the major industrial countries of the northern hemisphere as some 50% of the increased retention of energy by the atmosphere is due to the accumulation of carbon dioxide as a result of combustion of fossil fuel (Table 1 and 2).

Methane production appears to be a major issue although it only presently contributes 18% of the overall warming. It is accumulating at a fast rate and is apparently responsible for some of the depletion of the protective ozone layer. Methane arises largely from natural anaerobic ecosystems, rice paddies and ruminant animals (Table 3).

Table 1: Relative contribution of greenhouse gases to atmospheric warming (Source: World Resources Institute 1989)
Source of warming Relative contribution (%)
Carbon dioxide 49
Methane 18
CFC's 14
Nitrous oxide 6
Others 13


Table 2 Relative contribution by continent to the emissions of carbon dioxide (Source: World Resources Institute 1989)
Continent Carbon dioxide
  (10 9 tonnes)
North America 1.4
Eastern Europe 1.4
Western Europe 0.8
Asia 0.6
Pacific 0.4
Africa + Latin America 0.8


Table 3: Relative contribution by sources to global production of methane (Source: Bolle et al 1986)
Source of methane Relative
contribution (%)
Non-biological 32
Rice paddies 18
Ruminants 18
Marshes 13
Other biological 6


The rates of accumulation of methane and carbon dioxide in the atmosphere have changed dramatically in the last 10 years. Prior to this, the rise in world temperatures and composition of the atmosphere had changed little but is now in an exponential growth period (Tables 4 and 5). Undoubtedly, carbon dioxide amd methane concentrations must be stabilised in the very near future or the future of the earth is threatened.

Table 4 Trends in emission of carbon dioxide (Source: World Resources Institute)
Year Carbon dioxide emission
  (106 tonnes/yr)
1860 500
1880 1,000
1900 2,000
1920 3,500
1940 4,100
1960 5,000
1980 29,000


The developing (non-industrial) countries must insist on a decreased utilization of fossil fuels by the industrial countries. It will be essential that they also develop industrial and agricultural practices that minimise fossil fuel use and methane generation. Burning of fossil fuels is the predominant factor but deforestation and burning of forests and pastures have enormous effects also.

Likely effects of global warning

Predictions of the effects of global warming include:

The consequences of global warming are horrendous and there is need for action now. There must be a massive movement towards environmentally friendly strategies that minimise production of carabon dioxide and methane and which maximise fixation of carbon dioxide. The major responsabilities and action must be taken by the industrialized countries because they are largely to blame. However, the developing and industrializing countries must also consider the problem.

Remedial measures

Replacement of fossil fuel with fuel derived from renewable resources (solar energy), is likely to be extremely advantageous and systems should be in place when the inevitable price rises in fossil fuels are enforced by Governments as the effects of global warming become more apparent. The tropics have an enormous advantage over temperate areas as they are the places where biomass can be produced most rapidly and efficiently (Table 5).

Table 5: Biomass productivity of different ecosystems in the tropical and temperate zones (Source: Kormondy 1969)
Ecosystem Temperate Tropical
Perennial crops 125 50
Perennial forrest 80 45
Annual crops 50 30
Desert 5 -


Some of the measures that need to be implemented as quickly as possible include:

Table 6 : Effect of supplementation of a straw-based diet on methane;meat production ratio in growing cattle
  Unsupplemented Supplemented
Proportion of digested energy fermented    
to methane (%) 15 8*
Ratio methane/meat (kg/kg) 2.4 0.36**

* With urea and minerals
** With urea, minerals and bypass protein


The role of International Agencies

The International Agencies and Government and Non-government Organizations can play an important role in ensuring these policies are encouraged. The means to this end are:

Towards an environmental balance

The need is to develop the concept of integrated farming which utilizes high biomass crops for food and feed production, with minimum inputs of fuel which in itself should be derived from biomass (direct burning of crop residues and production of methane from dung in biodigestors).

This approach is being actively promoted in Colombia (Preston and Solarte 1989). The system seeks to reverse the Greenhouse effect by emphasising carbon dioxide fixing crops (sugar cane and trees), meat production from monogastric animals using local resources, simple biogas technology, and use of biomass as combined sources of feed and fuel, thus reducing dependency on fossil fuels.

The principles of the system are:

The cropping systems are based around sugar cane as the main biomass source, complemented with forage trees and aquatic plants. Pigs, hair sheep, and a mule (or multi-purpose cow) are the principal animal species, complemented with ducks and earth worms.

The farm has an area of 2 ha of which 1 ha is in sugar cane, 0.5 ha in forage trees, and 200 m5 in ponds for Azolla and fish. The sugar cane is separated into tops and stalk, and the stalk further fractionated into juice and bagasse using an animal-powered (mule or horse) cane mill. The juice provides the basal feed for an annual intake of 40 pigs (3 successive lots of 13-14) and is complemented with the Azolla (50 kg are harvested daily, providing 50 g protein for each of 13 pigs), leaves from the forage tree Trichantera gigantea (16 kg of leaves amonmg 13 pigs supplies 50 g/protein/pig/day) and 250 g daily of either a commercial protein supplement (40% protein) or soybean meal (to provide the remaining 100 g/ protein/pig/ daily). Thirteen sheep and their progeny are fed on the cane tops complemented with the foliage from Gliricidia sepium, multinutritional blocks and a mixture (9:1) of poultry litter and rice polishings. The mule is fed on the bagasse from the cane supplemented with a multinutritional block and gliricidia foliage. The remainder of the bagasse is used as litter for the sheep, as fuel and for aerobic composting with earth worms. The equipment comprises the animal-powered cane mill, a pedal-powered (adapted from a bicycle) forage chopper and assorted tools.

Assuming a sugar cane yield of 80 tonnes/ha/year of stalks and 20 tonnes of tops, the expected annual output of animal product is 40 x 90 kg = 3.600 kg of pig liveweight (from 40 tonnes of cane juice) and 26 x 25 kg of lamb liveweight (from the 20 tonnes of cane tops). Assuming average world prices of US$1.50/kg liveweight for both pig and lamb liveweight then total income from the animal unit will be US$6,375. From this must be deducted: the cost of the weaner pigs (40 x 30 kg liveweight x US$1.75 = US$2,100 ) and their protein supplement (40 x 100d x 0.25 kg = 1.000 kg x US$500); the cost of the block (347 kg x US$0.15) and the poultry litter (424 kg x US$0.05) and rice polishings (47 kg x US$0.2); leaving a net margin of US$3,347.

Equally important as the economic feasibility of the system is the balance of meat to methane. Total meat output (40 x 90 kg x 0.8 = 2.880 kg for pigs and 26 x 25 kg x 0.5 = 325 kg for sheep) of 3.205 kg is associated with the production of 186 kg methane. The 13 sheep and their progeny eat each day a total of 22 kg dry matter (400MJ) which gives rise to 400 x 0.065 = 26MJ/day methane = 170 kg/year of methane; the 40 pigs (each fed for 100 days) are expected to produce 16 kg of methane (a methane production rate of 1.5 kg methane/pig/year is estimated for this species). The ratio of methane to meat is thus:

0.058kg methane per kg meat

By contrast, a steer grazing unsupplemented tropical pastures requires 4 years to reach slaughter weight of 450 kg with a meat yield of 225 kg. It will consume at least 8600 kg of dry matter in the process which fermented in the rumen will give rise to 190 kg of methane, a ratio of:

0.80 kg methane per kg meat


Fossil-fuel based industrial development is the major cause of the environmental imbalance; however, agricultural practices are major factors with the capacity of adding to greenhouse gases (the consequence of most modern production technologies) or reducing them by environmentally friendly ecodevelopment. An example of this latter approach is given, designed specifally for tropical zones, the widespread adoption of which will help to close the production-utilization gap for carbon dioxide with a more than tenfold reduction in emission of methane per unit meat production, compared with traditional tropical systems based exclusively on cattle ranching. Such technologies are sustainable and especially appropriate for adoption on small scale family farms in tropical regions.


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Figueroa Vilda 1989 Feeding systems based on sugar cane In: Integration of livestock with crops in response to increasing population pressure on available resources (Editor: T R Preston and M Rosales). CTA:Wageningen

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World Resources Institute 1989 World Resources Institute, Washington DC