Agriculture at the crossroads
The way ahead
Biomass for food, feed and fuel
Target groups and self-reliance
T.R. Preston and E. Murgueitio
The authors' address is Convenio Interinstitucional pare la Producción Pecuaria en el Valle del Río Causa (CIPAV), PO Box 7482, Cali, Colombia.
Since the inception of international aid, the goal of development projects in agriculture has been to increase productivity. Only now is it being realized that the production systems shaped by this narrow objective are not sustainable. The drawbacks are many and complex: high costs, contamination of the environment, soil erosion and animal and human stress are the consequences of modern agricultural practices. Many of these are the result of the intensification process per se. Thus, the increasing emissions of methane, perhaps the most damaging of the greenhouse gases, can be traced back to intensive rice culture and the expanding population of ruminant animals, especially in developing countries. It also appears that the effectiveness of important methane sinks, which are present in natural soil-based ecosystems, has been reduced by the burning of crop residues and heavy application of synthetic chemical fertilizers (Keller, Mitre and Stallard, 1990; Mosier et al., 1991).
Chemical contamination of water and soil is a consequence of the increased use of agrochemicals in cropping. Soil erosion in both arid and humid tropical zones is largely the result of overstocking with grazing animals. Deforestation in the Amazon and in other tropical regions of Latin America is closely linked to the expansion of cattle ranching (Murgueitio, 1990).
The industrialized countries' growing concern for animal welfare is partly a reaction to the stress caused by the intensification of housing and resource management. Consumer preference for "naturally" produced food can be partially interpreted as an expression of dissatisfaction with production systems that use an excess of additives, such as antibiotics and hormones in animals and chemicals in crop production.
The pressures to liberalize world trade predicate profound changes in agricultural production systems in industrialized countries as subsidies and tariffs are gradually withdrawn. The need to restrain the use of fossil fuels in order to combat global warming will force oil prices up which, in turn, will encourage the practice of organic agriculture and add value to biomass grown for fuel and chemical substrate.
These trends add up to an impending major crisis for agriculture in the industrialized countries. They also create a unique opportunity for the tropical regions of developing countries to capitalize on the comparative advantages inherent in their rural-based economies, including their capacity to produce year-round high yields of biomass for conversion into fuel, food and feed.
In the past, livestock production schemes in tropical developing countries were characterized more by failures than successes, largely because they attempted to transfer inappropriate (industrial) technologies, requiring expensive and often imported inputs, instead of exploiting locally available resources.
Recognition of these past errors and appreciation of the new scenarios offered by changing world climates, in both biological and economic terms, provide the rationale (Preston, 1990a) behind the hypothesis that future agricultural production systems in the tropics must be based on the following two principles:
· exploiting local comparative advantages in order to produce biomass competitively and transform it into food, feed and fuel for local consumption and sale on world markets;· ensuring that the systems selected are economically, ecologically, sociologically and ethologically sustainable.
The identification of high-yielding sustainable ecosystems must be the first step in any attempt to design new interventions. The products of such ecosystems must be able to serve as the principal inputs for integrated activities aimed at furnishing food, feed and fuel for immediate sale or consumption, while the by-products and residues should serve as inputs for livestock husbandry. This activity will then contribute to earnings by providing milk and meat, farm power and, from the recycled manure, fuel and fertilizer.
Sugar cane, trees and water plants for sustainable livestock production in the tropics
The basic technology described in this article uses sugar cane, multipurpose trees and water plants as sources of biomass to provide feed for a range of livestock species as well as fuel for the farm and household.
The preferred animal species for this technology are pigs and ducks, as they readily adapt to the "unconventional" high-moisture feed resources (mainly cane juice and water plants) and have a high meat/methane production ratio.
The data in Fig. 1 show that the most productive ecosystems are perennial crops and trees grown in the tropics. From this conclusion it is a short step to the thesis that "Sugar cane and fodder trees are the logical alternatives to cereal grains as the basis of intensive livestock production and renewable energy substrate" (Preston, 1990b).
The farming system (see Fig. 2) developed from these concepts in the Cauca Valley in Colombia supports extremely high levels of livestock production (in the order of 3 000 kg meat/ha/year) derived from environmentally protective perennial crops (sugar cane, nitrogen-fixing trees and water plants).
1. Perennial crops and forests in the tropics are the most productive ecosystems - Les cultures et les forêts pérennes des tropiques vent les écosystèmes les plus productifs - Los cultivos perennes y los bosques en el trópico son los ecosistemas más productivos
2. Integrated mixed farming system based-on sugar cane, multipurpose trees and the recycling of wastes through biodigestors, ponds and earthworms - Système agricole mixte intégré à base de canne à sucre, d'arbres polyvalents et de recyclage de déchets grâce aux biodigesteurs, aux mares et aux vers de terre - Un sistema agrícola mixto e integrado basado en caña de azúcar, árboles pare propósitos múltiples y el reciclaje de desperdicios a través de biodigestores, estanques y lombrices de sierra
1. Performance of Pekin ducks fed sugar cane juice compared with a cereal-based (rice) diet
Performance de canards de Pékin nourris avec du jus de canne par rapport à celle de canards ayant un régime alimentaire à base de céréales (riz)
Comportamiento de patos de Pekín alimentados con jugo de caña o derivados de cereales
|
Performance |
Cereal diet |
Cane juice diet | |
|
Liveweight (kg) | |||
|
|
- Initial |
0.727 |
0.72 |
|
|
- Final |
2.75 |
2.51 |
|
Daily liveweight gain (g/day) |
52.3 |
46.0 | |
|
Feed intake (kg) | |||
|
|
- Concentrate |
6.48 |
- |
|
|
- Supplement |
- |
3.2 |
|
|
- Cane juice |
- |
17.4 |
Source: Bui Xuan Men and Vuong Van Su, 1992.
2. Productive and reproductive parameters of the flock of African hair sheep, December 1988-March 1991
Paramètres productifs et reproductifs du troupeau de moutons à poil africain, décembre 1988-mars 1991
Parámetros de producción y reproducción de un hato de ovejas africanas durante el período diciembre de 1988-marzo de 1991
|
Performance |
Mean value |
SD³ |
n4 | |
|
Liveweight (kg) |
|
|
| |
|
|
- Birth |
2.32 |
0.52 |
167 |
|
|
- Weaning |
14.90 |
2.62 |
84 |
|
Weight gain to weaning (g/day) |
106 |
33.6 |
84 | |
|
Age at weaning (days) |
129 |
45.5 |
84 | |
|
Lambing interval (days) |
284 |
85.3 |
44 | |
|
Litter size1 |
1.16 |
|
144 | |
|
Lambs born/ewe/year2 |
1.49 |
|
44 | |
|
Mortality (% all births) |
|
|
| |
|
|
- Perinatal |
5.5 |
|
|
|
|
- Birth to weaning |
10.4 |
|
|
1 Number of lambs born per parturition.
2 Mean number of lambs born per ewe per year.
3 SD = standard deviation.
4 n = sample number.
Source: Mejía et al., 1991.
3. Mean values for the feed intake of a flock of tropical hair sheep, 1 July-31 December 1990
Valeurs moyennes de la ration d'un troupeau de moutons à poil tropical, 1er juillet-31 décembre 1990
Valores medios de consumo alimenticio de un hato de ovejas africanas durante el período 1° de julio-31 de diciembre di 1990
|
Diet components |
Fresh basis |
Dry basis | |
|
Feed intake (kg/day) |
|
| |
|
|
- Gliricidia sp. |
0.777 |
9.31 |
|
|
- Sugar cane tops |
5.640 |
72.41 |
|
|
- Multinutritional block |
0.121 |
6.21 |
|
|
- Poultry litter |
0.204 |
10.61 |
|
|
- Rice polishings |
0.021 |
1.01 |
|
Total dry matter intake (kg/day)2 |
|
1.735 | |
|
Total dry matter intake (% of liveweight) |
|
4.493 | |
1 Percentage of the total diet (dry matter basis).
2 For a sheep unit (on average: 1 ewe of 25 kg and 1 lamb of 14 kg).
Source: Mejía et al., 1991.
3. Sugar cane juice supports high levels of performance in fattening pigs - Le jus de canne a sucre donne d'excellents résultats pour l'engraissement des pores - El jugo de caña da altos rendimientos en la dicta de cerdos de engorde
Source: Sarria, Solano and Preston, 1990. Data from farm trials in Colombia.
The sugar cane stalk, after removal of the tops, is fractionated into juice and bagasse, using a simple animal-powered three-roll mill. The tree foliage is separated into leaves and twigs. The cane juice is a complete replacement for cereal grains and is the basis (75 percent) of a high-quality diet for pigs (Fig. 3) and ducks (Table 1). The cane tops are fed to tropical hair sheep (Tables 2 and 3). Tree leaves and aquatic plants provide protein for both pigs and sheep (Becerra et al., 1990; Mejía et al., 1991). The bagasse and twigs are used for fuel.
The pigs and sheep are confined and their excrete recycled through plastic-bag biogas digesters, ponds (for aquatic plants) and earthworms. These downstream elements complement the system, providing additional household fuel, protein for the livestock and organic fertilizer and humus for the crops. Moreover, soil erosion, which is a serious problem in tropical grazing systems, is avoided.
The biomass subsystem
Sugar cane varieties, chosen for high biomass yield, are planted at twice the normal density in row widths of 75 cm, vis-à-vis industrial sugar production. The stalks and tops are harvested for animal feed at 12-month intervals. The dead leaves (trash) are left on the soil as mulch. The interface between the decaying mulch and the soil is where a symbiotic combination of bacteria and fungi (Patriquin, 1982) fix up to 100 kg N/ha/year. It should be noted that, in most countries, in industrial sugar production both the tops and trash are burned to facilitate harvesting. Apart from the waste of a valuable resource, this practice pollutes the environment.
At least three multipurpose tree species are now being used commercially to produce feed protein (leaves) and fuel (branches): Gliricidia septum, Trichantera gigantea and Erythrina fusca. The two former species adapt to a wide range of soil types and elevations (up to 1 800 m above sea level). The niche for which these species are not suitable (heavy clay soils with a high water-table) is the ideal habitat for Erythrina fusca. Leucaena is not recommended because of its high cost of harvesting in cut-and-carry systems. Both Gliricidia sp. and Trichantera sp. are planted at densities of 20 000 plants/ha, the former from seed and the latter from cuttings. A lower density (1 000 plants/ha) is recommended for Erythrina sp. which can be established from seed or stakes.
Two ha of sugar cane are estimated to have an annual yield of 240 tonnes of stalk which, fractionated in a three-roll mill, produces 120 tonnes of juice and 120 tonnes of bagasse (816 MJ of fuel energy). G. septum and/or T. gigantea, planted on 0.14 ha, yield an annual 8.2 tonnes of edible foliage which is fed to the sheep.
The pig and duck subsystem
The technologies for feeding pigs sugar cane juice were developed in Mexico (Mena, 1981), the Dominican Republic (Fermin et al., 1984) and Colombia (Fig. 3). The feeding system for ducks was developed in Viet Nam (Table 1). One pig fattened from 25 to 90 kg of liveweight consumes 1 200 kg of cane juice, 53 kg of whole soybean grain and 560 kg of fresh azolla water fern (Azolla filiculoides). It also produces 0.5 kg of methane.
A duck fattened on cane juice from brooding (700 g of liveweight at 21 days of age) to 2.5 kg of liveweight consumes about 18 l juice (20° Brix) and 3.2 kg of supplement.
Assuming that 1 200 ducks (four batches of 300) are to be fattened, they will consume 21 600 l of juice and the remaining 98 400 l from a total of 120 000 l will fatten 80 pigs.
The sheep subsystem
Two ha of sugar cane also produce 60 tonnes of tops. The cane tops, together with the gliricidia foliage, are sufficient to provide the basic diet for 29 African hair sheep (adult ewes), one ram and their progeny. In addition, the sheep consume 1 280 kg of molasses-urea blocks, 2 160 kg poultry litter and 222 kg rice polishings, inputs which must be purchased. The annual lambing rate is 1.9 (the average litter size is 1.22 with 1.53 parturitions per year) and the weaning rate is 1.7. With an average growth rate of 100 g/day up to weaning and 80 g/day from weaning to a slaughter liveweight of 25 kg, the lambs are sold at 255 days of age. Annual sales of liveweight are 972 kg. Annual methane production from the sheep is estimated to be 100 kg.
The biodigestor and pond subsystem
The cost of materials (tubular polythene sheet and accessories) needed to construct a biodigestor that will supply a family of six in cooking fuel is about US$100. The ponds that receive the effluent are also used to grow water ferns (Azolla filiculoides) which can provide up to 50 percent of the protein needs for the final growth stage of pigs, i.e. from 50 to 90 kg of liveweight. At any one time, a farm has about 30 pigs, requiring 240 kg of azolla daily. This quantity can be produced from a pond surface area of 1 500 m² (Becerra, 1991).
The earthworm subsystem
This subsystem is still in the development stage (Cruz, Preston and Speedy, 1989); nevertheless, preliminary results are encouraging. From 1 m³ of cattle manure, over one year the production of California red worms was 6 kg (211 g of protein) (Rodriguez and Salazar, 1991). Fresh worms have proved to be an excellent complement to the azolla. The combination of the two feeds (50:50 protein basis) has been used successfully to replace 50 percent of the soybean meal in a cane juice diet for fattening chickens (Rodríguez and Salazar, 1991). Ducks consume azolla even more readily than chickens and it can therefore be expected that similar rates of substitution of the protein supplement can be achieved. Research to demonstrate this is currently in progress.
4. Estimated inputs and outputs of an integrated mixed farming system
Estimations de la consommation et des productions d'un système agricole mixte intégré
Estimación de los egresos e ingresos de un sistema agrícola integrado mixto
|
Subsystem |
Inputs |
Outputs1 |
|
Biomass |
· 2 ha sugar cane |
· 60 tonnes (816 GJ) bagasse (fuel) |
|
|
· 0.14 ha Gliricidia sepium |
|
|
Pig fattening |
· 80 weaner pigs at 25 kg |
· 7 200 kg pig liveweight |
|
|
· 4 240 kg supplement |
· 40 kg methane |
|
Duck fattening |
· 1 200 ducklings at 0.7 kg |
· 3 000 kg duck liveweight |
|
|
· 3 840 kg supplement |
· 12 kg methane |
|
Sheep rearing and fattening |
· 29 ewes, 1 ram |
· 972 kg lamb liveweight |
|
|
· 1 280 kg MUB2 |
· 100 kg methane |
|
|
· 2 160 kg poultry litter |
|
|
|
· 222 kg rice polishings |
|
|
Net liveweight/ha |
|
· 4 160 kg |
|
Methane: meat (liveweight) ratio |
|
· 0.017 |
1 Saleable liveweight, fuel and methane.
2 MUB = molasses-urea blocks.
Productivity
The overall level of livestock productivity using sugar cane is high (Table 4). In addition, there is a considerable quantity of biomass (consisting of bagasse) which is a potential source of farm-based energy (Preston and Echavarria, 1991). Even if the sugar cane yield were no higher than the world average (about 55 tonnes/ha/year), the livestock output would still be more than 2 000 kg of liveweight/ha/year.
Sustainability
The system as a whole is environmentally friendly and sustainable, building on the concepts of ecodevelopment and self-reliance. Almost all needs are farm-grown with a minimum of fossil fuel-derived inputs, and a surplus of biomass energy is provided. Based on estimates taken from Crutzen, Aselman and Seiler (1986), it is calculated that the pig/duck and sheep units will produce, respectively, 52 and 100 kg of methane per year. This results in a methane:meat ratio of 0.017, compared with an average of 0.75 for pastoral systems.
Agrochemicals are not used: biodigestor effluent, manure from the sheep and humus from the earthworms supply all the required plant nutrients. Dead leaves from the cane and trees form a continuous mulch over the soil surface, thereby improving fertility, fixing atmospheric nitrogen (Patriquin, 1982), probably oxidizing atmospheric methane (Keller, Mitre and Stallard, 1990; Mosier et al., 1991) and certainly preventing erosion.
The system is directed at, and has the greatest impact on, resource-poor farmers whose family members may all be provided employment. It is not a package, but rather a series of subsystems which can be introduced independently. The innovative feature of the system is that it is integrated in such a way as to maximize utilization of available natural resources and minimize inputs. The technologies themselves are not innovative. All are known and have been applied commercially in other contexts. Many farmers in Colombia are introducing or using either some or all of the elements that make up this integrated farming system. FAO-assisted projects to transfer the technology are-under way in the Philippines (TCP/PIII/8954) and Viet Nam (TCP/VIE/8954) while others are being planned for El Salvador, Barbados and Trinidad and Tobago. Elements of the technology are already being applied on a large scale in Cuba (Figueroa, personal communication) and are in the development phase in Mexico (Alvarez, personal communication) and Honduras (Esnaola, personal communication).
The "self-reliant" feature of the technology is that it has given a comparative advantage to small, as opposed to large-scale, producers by virtue of using farm-produced resources derived from a rational and sustainable exploitation of the natural riches of the tropical environment - solar energy, soil, water, biological diversity and people.
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