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

Summary

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.

Introduction

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:

• Melting of the ice cap with increased sea levels and release of the trapped gases (there is considerably more methane in the ice cap than in the atmosphere) with the need to relocate peoples from present sea level areas.
  

• Chaotic weather changes, resulting in droughts or floods and eventually massive erosion.
  

• Decreased crop yields and decreased arable land availability (the coastal and river planes are often the most fertile soils), with subsequent starvation and malnutrition.

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
	---------(kJ/m²/yr)------------
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:

• Emphasis must be given to crops which are most efficient in fixing carbon dioxide into biomass (eg: especially perennial tropical crops such as sugar cane and trees).
  

• High cost systems of food production aand other high foossil fuel dependent activities in industrial countries should be discouraged (eg: by eliminating subsidies and applying an environemental tax), since the systems used make heavy demands on fossil fuel and are often destructive of the environment.
  

• Active encouragement should be given to food production in developing countries in the tropics where there are adequate human and environmental resources, and where the production systems are much less dependent on inputs of fossil fuel.
  

• In the tropical countries, wetland rice may have to be discouraged in favour of dryland cereal production for human consumption. Cereal growing for animal consumption in tropical countries should be actively discouraged, and emphasis given to sugar cane and forage trees as the basis of intensive animal production.
  

• Wherever possible, grazing systems shoulld be gradually replaced by confinement systems and other uses for the land stimulated - such as recreational (game parks), the planting of existing grazing lands with forests (especially multipurpose trees).
  

• Crop residues should be used as animal feed or as construction material and should not be burned.
  

• A massive programme is needed to promote strategic supplementation of ruminant diets in Third World countries in order to optimise rumen function (which leads to reduced methane and carbon dioxide production) and increase the efficiency of growth and milk production. For example, in ruminants fed mainly with straw, the methane generated per unit of meat produced is of the order of 2 kg methane per kg meat; by supplementation with urea, minerals and bypass protein (Preston and Leng 1987), this be reduced to 0.36 kg methane per kg meat 0.2 tonnes annually, as a result of increased efficiency of fermentative digestion and faster growth (Table 6).
  

• Non-ruminant species (especially pigs, poultry, rabbits) and unconventional animals (eg: guinea pigs) should be promoted (using local feed resources) as meat producers while meat production from ruminants should have a lower priority.
  

• Low-cost biogas digestors should be put in place in all units where livestock are confined. This is particularly important where lack of household fuel has led to massive deforestation.
  

• Human organic food waste must be recycled as pig feed (Figueroa 1989) instead of being allowed to ferment in land fills (gives rise to methane) or incinerated (producing carbon dioxide). Sewerage from the human population should be used to produce methane and the residual nutrients recycled to the land instead of being dumped, in most cases into the sea. Large and deep lagoons covered with plastic could be used in many situations as the vehicle for recycling, with the production of methane for fuel and plant nutrients.
  

• Maximum support should be given to research and development efforts which will enable fossil-derived fuels to be replaced by biomass-derived fuels. Gasification of biomass to produce hydrogen and carbon monoxide (can be used directly as fuel or as substrates for chemical industry) would appear to be the most appropriate technology to promote.

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:

• Designing policy guidelines for Governments and International Assistance Agencies on strategies which will lead to reducing emissions of carbon dioxide and methane arising from livestock activities.
  

• Identifying, and assisting in the funding of, livestock- related projects the results from which will help to "reduce·" the "greenhouse effect".
  

• Revising some of the research programmes of the CGIAR centres to be more "environmentally friendly", for exanple re-emphasizing monogastric production from local non-cereal resources and de-emphasizing large ruminant programmes from range lands.

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:

• Establish crops which:
  

• use efficiently solar energy giving maximum yields of biomass in a sustainable system that requires minimum imported inputs;
  

• are easily fractionated into a low-fibre component which satisfies the major needs of monogastric animals (for easily digestible carbohydrate and protein) leaving a fibrous residue suitable for feeding to ruminants, for use directly as fuel or as a substrate for a chemical industry.
  

• Exploit in total confinement those animal species which use efficiently the biomass and are easy to house and manage.
  

• Recycle the animal excreta through low cost biodigestors and ponds to produce a source of fuel and organic fertiliser.

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

Conclusions

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.

References

Bolle H J, Seiler W and Bolin B 1986 Other greenhouse gases and aerosols; assessing their role for atmospheric radiative transfer. In: The Greenhouse Effect, Climatic change and Ecosystems (Editors: B Bolin, B R Doos, B Warrick and D Jager) John Wiley and Sons: New York

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

Khalil M A K and Rasmussen R A 1986 Trends of atmospheric methane: past, present and future In: Proceedings of the Symposium on CO₂ and other Greenhouse gases. Brussels, Belgium

Preston T R and Leng R A 1987 Matching Ruminant Production Systems with Available Resources in the Tropics and Subtropics. PENAMBUL Books Ltd: Armidale NSW, Australia

Preston T R 1989 Sugar cane as the basis of intensive livestock production in the tropics. In: Developing World-Agriculture (Editor: A W Speedy) Grosvenor Press International: London

World Resources Institute 1989 World Resources Institute, Washington DC