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10. Alternatives to crop residues feed resources in mixed farming systems

J. Steinbach

Department of Livestock Ecology, Tropical Sciences Centre, Justus-Liebig University, Ludwigstrasse 21, D-35390 Giessen, Germany


Abstract
Introduction
The forage potential of tropical crop production systems
Crop rotations
Fodder banks
Cover crops in plantations
Forage use of food crops
Forage production systems
Conclusions
References


Abstract

If better use is to be made of crop residues, either as basal livestock diets or by returning them to the soil, alternative feed resources must be developed. This paper examines those alternatives, concentrating mainly on the role of cultivated forages in the subsistence-oriented mixed smallholder rainfed and irrigated farming systems of the tropics and subtropics. The potential for introducing forages on cropped land is assessed, covering crop rotations, fodder banks, cover crops in plantations and the use of food crops as forages. Uncropped land may also be used to produce forages. Considerable differences in the opportunities for introducing forages in different agroecosystems and regions are found, according to such factors as available arable land per capita, the number of crops that can be grown per year, market access, labour availability and farmers' perceptions of the risks and rewards of investing in their livestock enterprises. Nevertheless, the introduction of forage crops is a promising way of promoting sustainable agriculture in the low-input systems of resource-poor farmers. More research is needed to ensure successful technology development and transfer.

Introduction

Although fibrous crop residues are important feed resources in mixed farming systems in the tropics and subtropics, many of them are characterized by low metabolizable energy and digestible protein contents, which sometimes barely cover animal maintenance requirements. In addition, the supply is frequently seasonal. To satisfy the nutrient needs of ruminant and non-ruminant livestock for the efficient production of food, fibre and power, supplementation strategies are needed. Such strategies seek to utilize all possible feed resources on the mixed farm in an optimized system.

Ruminants are by far the most important group of farm animals in developing countries. The feed resources available to them originate from rangeland, arable areas, plantations and peripheral land (such as roadsides, terrace risers, field bunds and the banks of irrigation channels). Arable areas provide fallow grazing, weeds from crop fields, forage crops and concentrates, in addition to fibrous crop residues. In plantations, the herbaceous cover crops (grasses, legumes) can be used for feeding, while fodder grasses, legumes, shrubs and trees can be grown on peripheral land. Industrial products and the byproducts of crop processing can supplement the above resources. In future, the importance of natural rangelands is likely to decrease, due to reduction in area (cropland encroachment, desertification) and reduced productivity (overgrazing). The additional nutrients needed for livestock feeding to meet the expected increase in the demand for animal products will have to come from arable land. However, it is important to realize that for most small-scale crop farmers animal production is of lower priority than crop production. This means that fodder production and feeding strategies must not reduce crop yields or make crop production more risky.

The task of this paper is to review the alternatives to fibrous crop residues as feed resources. The topics that could be discussed under this heading are legion, so I will have to limit them. Firstly, I will focus mainly on subsistence-oriented mixed smallholder rainfed and irrigated farming systems in tropical and subtropical highland, humid and subhumid, arid and semiarid ecosystems, which are deficient in production inputs due to problems of liquidity and availability (resource poverty). Secondly, I will stress cultivated fodders and place less emphasis on concentrates and industrial products, since these tend to be less accessible to smallholders. I will also use large ruminants (cattle and buffalo) as examples wherever possible, since these multipurpose (food, draught, fuel, soil fertility) species contribute more than others to the efficiency of smallholder mixed farming systems (Seré, 1994). This approach is in line with the orientation and agenda of the World Food Summit 1996, which emphasized intensified use of existing cropland. It also offers a means of meeting the considerable deficit of milk, beef and animal power in the tropics recently projected for the year 2020 by the Food and Agriculture Organization of the United Nations (FAO, 1996).

Nutrient supply to livestock is one aspect of mixed farming, crop productivity another. Given rapid population growth and deteriorating soil resources, there is a general trend towards continuous cropping and reduced fallow periods in smallholder production systems, although great regional differences exist. Due to inefficient management and the use of few, if any, inputs, soils are increasingly characterized by inadequate nutrient and organic matter contents, unsatisfactory physical structure, chemical composition and biotic status, unfavourable climates (moisture and temperature) and moderate to severe problems of erosion, leaching, salinity, alkalinity or acidity. Furthermore, many cropping systems suffer from inadequate labour capacity. Using draught animals for cultivation, weeding, harvesting and transport can improve soils and crop yields as well as expand the areas cropped per farming family. I will argue that the efficient integration of crop and livestock production can solve the problems of nutrient supply, declining soil fertility and lack of animal power in mixed farming systems. The means to this end are forage production in crop rotations and as intercrops with permanent crops, and the supplementary feeding of animals with concentrates. Research on the strategic utilization of the feeds available on mixed farms will doubtless be required. The aim will be to develop new and sustainable forage systems which provide feed and maintain soil fertility.

The forage potential of tropical crop production systems


Forage production on cropped land


Forages for feeding livestock can be produced on cropped land as well as on uncropped farm or non-farm areas. Herbaceous plants (grasses and legumes) can be grown in crop rotations, on wasteland, as pioneer crops on fallow land, along roadsides, river and canal banks, on terrace risers and field bunds, and as cover crops under tree plantations. Shrubs can be planted on contour lines, along roadsides and on canal banks, or in pastures and cropping fields, while fodder trees can be used almost anywhere on the farm where excessive shading or extensive root systems will not be a problem. The primary purpose of all these forage crops is to close the nutrient gaps specific to the farming system. Broadly speaking, these are:

1. In permanent cropping systems: energy and protein deficits during the cropping season, protein deficit during the dry season.

2. In crop/fallow systems: dry-season protein deficit (fallow grazing during the rainy season).

3. In plantation systems: energy and protein deficits during the dry season (cover crop grazing during the rainy season).

4. In agropastoral systems: dry-season protein deficit (rangeland grazing during the rainy season).

The only types of system in which few deficits may occur are agroforestry systems, in which the presence of trees and shrubs integrated with the production of crops can ensure a year-round supply of forage, and irrigated systems, which have more reliable water supplies for longer periods of the year. Even in these systems, however, sporadic deficits occur.

Thus, in most mixed farming systems, a deficit in digestible crude protein is the most limiting factor affecting the quality and quantity of feed available to domestic livestock, and any forage crop development effort must address this problem. The relative share in diets of herbaceous and lignified fodder plants depends on such factors as the ecoregion, the farming system, the season, and the demand for basic and supplementary feeds. However, in most cases grasses and leguminous fortes will be more productive, while shrubs and trees will have additional ecological and economic advantages.

The ecological and economic advantages of forage production in tropical systems are several. Ecologically, forage crops may increase the primary and secondary productivity of the agroecosystem. They improve soil fertility and water harvesting (infiltration rates, water-holding capacity), suppress weeds, crop diseases and insect pests, control soil erosion and nutrient leaching by wind and water, and help balance animal diets. Economically, forage crops can raise incomes, spread risk through the increased diversity of production, improve the efficiency of crop production (particularly at low to medium input levels), and distribute the demand for labour more evenly throughout the year (draught animal use at times of peak demand, livestock management during the slack dry season).

Forage production adds another dimension to mixed farming systems. It does, of course, require additional investments in terms of land, labour and capital. The competition with food and cash crops for land and labour, the ease with which fodder crops can be integrated into the existing farming system, and the efficiency of production (ratio of inputs to outputs) will determine the adoption rates of any new technology.

Forage production on cropped land

Feed resources from cropped land include forage crops grown in crop rotations, fodder banks to cover specific protein and energy requirements, and cover crops in plantations. In addition, food crops may sometimes be used as feed for livestock.

 

Crop rotations

Crop rotations represent a vast underexploited potential for forage production in tropical developing countries. Generally, experience with their introduction through research and development projects is still limited - although more is known now than was the case 20 years ago. Since fodder crops must not reduce food or cash crop yields, land availability is a critical issue. The most obvious arable land resource is fallow land, which varies widely in extent among regions. Surprisingly, very few data exist on fallow periods and extent on a global scale (FAO, 1995). Studies conducted at local level indicate that, despite the continuing reduction in fallow periods, unmanaged fallow land may still amount to 60% or more of total arable land, even in such densely populated areas as the Malawi Lake region (Rischkowsky, 1996).

It is not possible here to discuss individually all the forage crops suitable for managed fallow feed production. A fairly comprehensive list can be found on the Internet (FAO, 1994). Let us turn instead to the criteria used for selecting an appropriate crop for a given location. These criteria include the crop's ameliorative properties, nutrient production, environmental adaptation and agronomic and management requirements.

The ameliorative properties of a forage should improve upon the soil fertility restoring characteristics of the existing fallow. They relate to root depth and distribution, organic matter production, nitrogen fixation (by legumes and grasses), nutrient pumping ability (trees and shrubs), soil cover (shading, temperature reduction, erosion control) and the control of weeds, insect pests and diseases. As regards nutrient production, the important characteristics are above-ground biomass, nutrient contents (metabolizable energy, digestible crude protein, minerals and vitamins, antinutritional factors), phenological parameters (duration and timing of vegetative and generative phases), leaf: stem ratios, the efficiency of soil nutrient and water utilization, and the regeneration potential from the soil seedbank. Depending on location, tolerance to drought, frost and shade, to acid, alkaline, saline or sandy soils, to diseases and pests and to competition from weeds may be important factors affecting the crop's environmental adaptation. Finally, agronomic and management considerations include ease of cultivation, the possibility of undersowing into the proceeding food or cash crop, the fertilizer requirement, harvesting methods (grazing or cutand-carry) and their frequency, ease of eradication or ploughing for the subsequent food crop, and capacity for regeneration.

It is important to distinguish between annual and perennial forage crops, which differ in their ameliorative and productive efficiencies as well as in their management requirements. Both temporal and spatial intercropping is possible. Mixed cropping systems are easy to establish, but have distinct disadvantages due to shading and the difficulties of weed control, mechanization and harvesting. Relay cropping protects the soil and saves time, while sequential cropping allows mechanized cultivation and avoids competition from intercrops but requires more time and additional cultivation and leaves the soil unprotected for at least part of the year. Strip cropping combats erosion on slopes, but may impede mechanization. An example of the production of short-term intercrop forages is the rice farming system described by Sangakkara (1989), in which Crotalaria juncea is grown between two rice crops for 50-60 days each in February-April and August-October, yielding 3.5 and 2.9 t DM ha-1 of forage respectively. The wheat-maize system described by Badve (1991), in which sorghum or millet is combined with cowpea during the interseason between April and June, giving a combined yield of 35-40 t ha-1 of fresh matter (FM), is another example. Medium-term intercrops usually require 4 to 8 months. The best documented example is the cultivation of berseem (Trifolium alexandrinum) between October and February (23 t FM ha-1 from 1.5 cuts) or between October and April (62 t FM ha-1 from 4 cuts) in the Nile Valley, where it covers 24% of the irrigated area. Berseem can also be grown as a relay crop. Nazir et al. (1988) reported that wheat and Trifolium alexandrinum grown in multi-row strips yielded 4 t ha-1 of wheat grain and 40 t FM ha-1 of berseem in four cuts, a combination which had the highest benefit/cost ratio and yielded the greatest net income.

In spite of their undisputed ecological advantages, leys have not attracted the attention they deserve. Leys can be defined as managed fallows, and as such they fit particularly well into cropping systems in which fallow land is still available, as is the case in large parts of Africa and Latin America. Leys have a rejuvenating effect on soil structure and fertility, and are also effective in controlling crop pests. In semiarid regions, however, they may affect soil moisture negatively. The duration of leys required for adequate restoration of soil fertility has been given as 2-3 years (Powell and Mohamed-Saleem, 1987). Leys may be established by sowing grasses and/or legumes into the last food crop of the rotation, such as maize. Alternatively, they may be allowed to regenerate from soil seedbanks, as is practised with annual legumes in the Mediterranean Basin. In humid regions, planting grasses may be prohibitive because of the high labour requirement. Important criteria determining the choice of suitable species or species combinations are persistence, competitiveness and regenerative capacity (resistance to ploughing, etc). Some examples: one grass species often used is Chloris gayana (FAO, 1977); a legume recommended recently for northern Nigeria is Aeschynomene histrix (Peters, 1992); suitable grass-legume mixtures for the more humid tropics could be Cynodon nlemfuensis + Centrosema pubescens, Chloris gayana + Stylosanthes spp., Panicum maximum + Desmodium intortum or Melinis minutiflora + Pueraria phaseoloides. Ley farming is not necessarily a high-input technology, but suitable animal-drawn soil and crop-adapted cultivation implements need to be developed if this forage production system is to be widely adopted by resource-poor farmers.

 

Fodder banks

Although crop rotations have the greatest potential for increasing forage production in smallholder settings in both the tropics and subtropics, other options do exist. On cultivated land, these options consist of fodder banks and, in tree and shrub plantations, the use of cover crops.

The purpose of fodder banks is to supplement livestock fed from natural pasture or with crop residues with additional protein and/or energy. On sloping land, fodder banks may also serve to control erosion. Banks intended to supply protein can be produced using herbaceous legumes or shrubs and trees. Besides protein yield, selection criteria include phenological characteristics, competitiveness with weeds, regeneration potential and the maintenance of an adequate soil seedbank. Many suitable species have been identified by institutions such as the International Livestock Centre for Africa (ILCA), the International Center for Agricultural Research in the Dry Areas (ICARDA) and the Centro Internacional de Agricultura Tropical (CIAT): Centrosema brasilianum stays green in the dry season, Chamaecrista rotundifolia regenerates quickly after the first rains, while Stylosanthes guianensis is a useful dry-season forage. However, many of the species tested exhibit poor persistence if not weeded regularly, or have low productivity (Peters, 1992). Leguminous forage shrubs and trees occur in great diversity (Gutteridge and Shelton, 1994), and are used extensively as multipurpose species providing the farmer with forage, fuel and more fertile soils. Desirable characteristics are high leaf production and good nutrient content, resistance to ratoon cropping, coppicing ability and fuelwood yield. Typical species used are Leucaena leucocephala, Gliricidia septum, Sesbania grandiflora, Calliandra calothyrsus and Acacia albida. Banks designed to increase the supply of energy normally consist of highly productive grasses (e.g. Pennisetum purpureum, Andropogon gayanus) or energy crops such as sugarcane (Saccharum officinarum). The three-strata forage system developed in India combines the energy grass hybrid Napier with leguminous forage shrubs and trees, such as L. leucocephala (Gill and Tripathi, 1991; Patel et al., 1992) or Casuarina equisetifolia (Mathew et al., 1992), that have high dry-matter and crude protein yields. However, this system suffers from high labour requirements, while the shading effect can reduce ground cover and fodder productivity by 35-50% up to 10 m from the tree row (Purl et al., 1994).

 

Cover crops in plantations

Cover crops in plantations are also multipurpose. Besides producing fodder they assist in weed control, maintain or improve soil fertility and control erosion. Forage production is an efficient way of using cover crops in young and relatively open plantations, where the light is sufficient to satisfy the high light requirements for photosynthesis characteristic of most tropical forage crops. In a young rubber plantation in Indonesia, Siagian and Sumarmadji (1992) harvested around 25-48 t DM ha-1 year-1 from Panicum maximum, Pennisetum purpureum and Paspalum dilatatum, with no harmful effect on seedling growth. Jayasundara and Marasinghe (1989) described a model in which an old (40 years) coconut plantation (156 palm trees ha-1) was undercropped with 2500 Leucaena shrubs and a ground cover of Brachiaria miliiformis and Pueraria phaseoloides. The total forage yield was 22.5 t DM ha-1 year-1, which translated into marked gains in milk production and liveweight by grazing cows. Soil fertility improved and fertilizer costs were cut by 70%, while the yield of coconuts rose by 11%. Weeding requirements decreased. It is obvious from these examples that fodder production can be combined with plantation agriculture to the benefit of both the cash crop and the subsidiary livestock enterprise. However, inappropriate grazing management may damage the plantation crop, especially while young.

 

Forage use of food crops


Forage production on uncropped land
Utilization
Constraints and research needs
Concentrates


Finally, cultivated land produces food crops, which can be used for feed either in their entirety - if in excess of human requirements or if harvesting for food is considered not worthwhile because of inadequate yields - or in part (leaves, vines). Examples are cassava and banana leaves, groundnut and sweet potato vines, and pigeonpea forage, all of which have high levels of digestible protein (Dixon and Egan, 1987). In Pakistan, surplus maize plants are harvested continuously during the growing season and fed to cattle. In Mauritius, whole sugarcane or sugarcane tops are used for ruminant feeding, while cassava tubers and leaves are valuable sources of energy and protein respectively for both non-ruminant and ruminant species. In Syria, drought-affected barley is leased out to the Bedouin for direct grazing by sheep. The potential for increasing forage supplies from such sources is considerable, having as yet been only partially realized. For instance, in Indonesia only 3% of cassava leaves and 7% of sugarcane tops are used for feeding livestock (Winugroho, 1996).

Forage production on uncropped land

Depending on farm size, topography, hydrology and infrastructure, uncropped areas may occupy a considerable proportion of total farm land. These areas roadsides, irrigation channel banks, contour bunds, terrace risers, shelter belts, live fences, ponds and waste lands - can be used for intensive feed production and erosion control. Suitable plants are grasses, such as Napier or sugarcane, for energy production, leguminous shrubs and trees as fodder banks for protein, or water hyacinths (Eichhornia crassipes) in ponds.

Utilization

The aim, in feeding livestock, is to provide the animals with a balanced diet through out the year, with sufficient nutrients to perform as required in terms of milk production, liveweight gain, reproduction and draught work. Where fibrous crop residues provide the basic ration, they must be supplemented quantitatively and qualitatively throughout the different seasons of the year.

The efficiency with which forage resources are used depends on the type of stock as well as on feeding practices. The most efficient conversion of green forages is achieved by dairy cows. However, where cultivation work has top priority, the supplementation of draught oxen may, at least seasonally, be more viable economically. Maximum overall efficiency may be obtained by using multipurpose cows for milk, meat and draught production, but work performance and feed efficiency may be poorer in females than in males (Cole, 1996) and there may be cultural or religious barriers against using cows for draught.

The forages grown should be fed fresh to the animals, since conservation as hay or silage has given disappointing results in the tropics, particularly in smallholder situations. Whether in situ grazing or confinement feeding is practiced depends on the crop production system and the importance attached to manure. Where forage resources are derived from intercropping, a cut-and-carry system with stall or kraal feeding is preferable, since it prevents damage to field or plantation crops. Such systems also facilitate the collection of manure required for fuel or fertilizer. However, they require more feed, as an estimated 15-35% of production is wasted (Boodoo, 1991) and a higher labour input in feeding. Leys, three-strata-forage systems and mature plantations can be grazed ad libitum or for a limited time daily, the animals being herded or tethered. Results from the literature on the relative advantages of continuous or rotational grazing are the subject of controversy. However, the cutting or grazing frequency should be sufficiently high to provide the animals with an adequate diet of digestible nutrients.

The establishment of forage calendars for particular cropping systems and environments is a useful way of ensuring that the feed demand of existing livestock populations can be met and of adjusting the nutrient balance at different seasons. Seasonal deficits in certain classes of stock can be covered by redirecting resources. For instance, supplementing grass-fed lambs and dairy cows with Leucaena leucocephala leaves improved their nitrogen retention and milk yield respectively (Mtenga and Shoo, 1990; Munga et al., 1992).

In cut-and-carry systems, forage is often collected and fed by women and children. The effects on the workload of these groups should always be considered when seeking to optimize forage production and utilization. Since women are often entitled to the income from milk sales, they can benefit greatly from improvements in the feeding of dairy cattle.

Constraints and research needs

Despite the technical options just described, the forage production potential of smallholder mixed farms in the tropics remains largely untapped. For several reasons, the adoption rates of fodder production technologies are poor. This is not simply because extension services are under-resourced and ineffective, but also because of a wide range of real or imagined constraints including increased labour and capital requirements, land shortage (particularly in Asia), poor soil moisture, lack of a market for livestock products (especially milk) and the higher returns to food crops. Traditional rules governing access may also prevent adoption, since in many societies fodder for livestock is considered common property. Improvements may create a heightened potential for conflict, especially if previously communal resources are suddenly privatized. Sometimes the ameliorating properties of forage crops described above are not well understood and appreciated by resource poor farmers.

There is, in addition, a more pervasive lack of knowledge on the land resources (fallow land, uncropped areas) available for forage production in different parts of the world, on the effects of forage crops and draught animal use on crop yields, and on the complementarily of available feed resources and the optimum structure of feeding calendars for specific situations. Too little is known about indigenous knowledge of local resources - their potential and how best to manage them. Research on sustainable fodder production should be intensified, with the aim of developing strategies to close the feed gap and improve soil fertility in smallholder farming systems. Priority topics for participatory on-farm or (where necessary) station-based research are: (i) low-input means of improving soil fertility and food/fodder crop productivity; (ii) the soil fertility effects of various forage systems (leys, intercropping); (iii) the collection and characterization of forage species; (iv) the evaluation of locally adapted indigenous species; (v) environmental impact assessment (EIA) and economic analysis of intensified forage production; and (vi) socioeconomic studies on indigenous knowledge and problem awareness, labour requirements, gender issues and technology adoption.

In addition, the strategies for technology transfer need overhauling. Participatory on-farm and/or farmer-managed research are promising vehicles for the transfer of improved and locally adapted technologies. They need to be more widely adopted at national level. For technology transfer to succeed, new practices and technologies need to be developed that are adapted to the location and the farmer's goals, manageable within his or her resources, ecologically beneficial, economically viable and socially acceptable.

Concentrates

Most of the feed resources commonly referred to as concentrates can be used equally as human food and animal feed. In a time of food shortages, concentrate feeding to livestock may be ethically questionable. For instance, in the Lake Region of Malawi the food grain supply lasts only for 7 to 9 months of the year, and a surplus for feeding to cattle does not exist (Rischkowsky, 1996). However, in specific situations there may be advantages in supplementing the basic roughage diet with limited amounts of concentrate feeds with a higher nutrient density. Seasonal and location-specific nutrient deficits (protein, energy, minerals) may occur in roughages and crop residues. Animals have only limited nutrient pools, and all classes of livestock need balanced diets with a certain minimum nutrient density for growth, lactation or work. Balancing the diet and increasing the nutrient density will, at least theoretically, increase the intake of fibrous crop residues, raise secondary productivity and improve feed conversion. As a consequence, pollution of air, soil and water resources per unit animal product will be reduced.

There is a wide range of energy- or protein-rich supplements that are useful for animal feeding. These are cereal and grain legumes, roots and tubers as feed grain substitutes, industrial crop by-products, such as milling residues (bran), molasses, brewery grains and oilseed cakes, slaughter and milk processing byproducts, industrial supplements (minerals, vitamins, urea), compound feeds and food wastes. After satisfying human needs, non-ruminant production systems (poultry, pigs, fish) should probably take priority in the use of concentrates. Among ruminants, the use of concentrate feeds is most efficient for milk production by cattle, buffalo, goats and sheep. However, concentrates have also been used for smallholder cattle fattening in Malawi, for lamb fattening near Aleppo, Syria, and in draught animal feeding. Cole (1996) demonstrated that supplementing N'dama cattle fed on Guinea grass with 1 kg day-1 of maize meal decreased heat stress by 20% and increased work output by 33%.

Since resource-poor farmers have only limited financial resources, their own farms must be the main source of any concentrated feeds they use. Commonly used by such farmers are cereals, grain legumes, brans, roots and tubers, sugarcane juice, palm oil, copra and household wastes. Market access to commercially available feeds is much more restricted for logistical as well as financial reasons.

Frequently, the theoretical benefits of concentrate feeding are not realized in practice. Economic viability is threatened by poor input: output ratios. More research is required in the areas of on-farm feeding trials, the physiological effects of supplementing fibrous forages, the identification of antinutritional factors, rumen microbes and the complementary effects of supplementation.

Industrially produced feeds such as urea blocks, mineral mixtures and compound feeds are rarely used by resource-poor farmers, who find them unaffordable and only periodically available.

Forage production systems


Rainfed systems
Irrigated systems


Seré (1994) identified 11 tropical livestock production systems based on grassland, mixed farming or landlessness. Only the mixed farming systems integrating crop and livestock production are relevant here. The six crop/livestock systems of this kind were classified according to three major climatic zones and to the main source of soil moisture - rainfall or irrigation (Table 10.1). A further subdivision of climatic zones into subhumid and semiarid (as distinct from merely humid and arid) and for tropical and subtropical systems might have been desirable.

I will now attempt to apply the principles presented in the first part of this paper to these six production systems, which will first be characterized in slightly greater detail.

Rainfed systems

Tropical and Subtropical Mountain Areas

These areas are found in the Andean region, in eastern Africa and in the southern Himalayas. They have high population pressure and low land availability. Poor soils are a frequent problem, and growing seasons vary greatly with altitude, latitude and amount of rainfall. Farm sizes permit all types of forage production in sub-Saharan Africa and in Central and South America, but the limited arable land available in Asia (0.3 ha person-1) does not permit ley farming. Poor infrastructure frequently hampers market access and the purchase of inputs. Multipurpose cattle production systems, mostly based on stall feeding, to satisfy the subsistence and growing market demand for milk and beef and to provide manure and draught power for crop cultivation appear to be the best way forward.

Table 10.1. The forage potential of tropical production systems1.



Forage source

Production system

Rainfed agriculture

Irrigated agriculture

Mountain

Humid

Arid

Mountain

Humid

Arid

Field crop rotations:


Ley farming

+

+

+

-

-

-


Annual intercrops

+

+

+

?

-

-

Fodder banks:








Protein

+

+

+

+

+

+


Energy

+

+

-

+

+

+

Plantations:


Cover crops

+

+

-

-

-

+

Uncropped land:


Herbaceous/tree forage

+

+

+

+

+

+

Supplements:


Farm-grown

+

+

+

+

+

+


Purchased

?

?

?

?

?

?

1 Potential depends greatly on population density, the availability of arable land, the degree of market integration and farmers' incomes.

Source: Seré (1994).

Humid and Subhumid Tropics and Subtropics

Here, too, human population density tends to be fairly high, with available arable land ranging from 0.2 (Asia) to 1.0 (Latin America) ha person-1. The opportunity to grow two crops a year reduces the pressure somewhat. Soil fertility is generally poor, requiring ameliorative treatment. Again, all the types of forage production described above are possible in sub-Saharan Africa and Latin America, but in Asia the shortage of cropland generally prohibits the use of ley systems and annual forage crops. Multipurpose cattle, buffalo and goat production systems are possible, in addition to the flourishing non-ruminant sector found in Asia and, increasingly, other regions too. Near large cities, specialized smallholder dairy production systems may be found (e.g. around Bombay).

Arid and Semiarid Tropics and Subtropics

These zones are found mainly in Asia, sub-Saharan Africa and West Asia-North Africa. The main climatic constraints are the lack of soil moisture and the short growing season. The situation is further aggravated by the shortage of cropland in many areas (e.g. in Kano State, Nigeria). However, natural grasslands, which are often closely associated with these cropping systems, meet a high proportion of the nutrient requirements of livestock during the short rainy season. Ley farming is possible in sub-Saharan Africa and in most of West Asia-North Africa. Fodder banks for protein supplementation can be established on uncropped land, and supplementation with concentrates is widespread. Multipurpose cattle, buffalo, camels and sheep/goat production systems prevail.

Irrigated systems

Tropical and Subtropical Mountain Areas

These are typically found on the southern slopes of the Himalayas. They are characterized by extremely high population pressure. Terraced rice production dominates, with two crops possible annually. Due to deforestation these areas are increasingly threatened by devastating droughts and floods. Seasonal forage crops and forage production from uncropped land are promising options here. Stall-fed cattle or buffalo milk production systems combined with draught animal use offer an efficient path for integrating crop and animal production.

Humid and Subhumid Tropics and Subtropics

These are the rice production systems of Southeast Asia. With an average of only 0.16 ha person-1 of arable land, these regions are among the most densely populated in the world. However, two or three crops can be grown each year. With respect to forage production, the regions' plentiful supplies of crop residues need to be supplemented with green forage from seasonal intercrops and from fodder banks, and with foliage from leguminous shrubs and trees, grown on uncropped field bunds, roadsides and channel banks. Livestock production systems focus on dairy cattle, milch buffalo and pigs and poultry, as well as on aquaculture and silkworms. For the major domestic species, feeding has to follow a cut-and-carry or zero-grazing system so as to avoid damage to crops. Only in mature plantations is free or tethered grazing possible.

Arid and Semiarid Tropics and Subtropics

Irrigated production systems within these climatic zones refer mainly to the widely distributed oasis and river floodplain systems of Asia and Africa, where available arable land ranges from 0.18 to 2.68 ha person-1. Typical examples are the Tozeur and Turfan oases and the Nile or Huanghe valleys of North Africa and Central Asia, the fadamas (depressions) along the Niger River in West Africa, and similar systems on the coast of Peru. The high insolation rates mean that, given adequate amounts of water, primary above-ground productivity is high and two crops can be grown annually. Forage options include seasonal rotation crops, undercropping in date palm plantations, and the use of spent, slightly saline irrigation water to produce salt-tolerant shrubs (e.g. Atriplex spp.) or trees (e.g. Casuarina spp., Tamarix spp.) on uncropped land. Dairy cattle, camels and small ruminants can be kept, under a largely zero-grazing system with supplementary grazing and browsing in the adjacent rangland or steppe areas. Fish and waterfowl may be raised where open water bodies exist.

Conclusions

Underused land resources suitable for various types of fodder production can be identified in most agroecosystems, although such land differs markedly in quantity and quality from region to region. It is important to harness these resources to balance nutrient deficits in feeding systems based on fibrous crop residues, to improve the fertility of cropland and to generate additional income for resource-poor farmers by integrating crop and livestock production. In addition, there is probably still a large pool of underexploited domesticated and wild forage germplasm with varying phonological characteristics and a wide range of ecological adaptations and nutrient productivities. This plant biodiversity should be used to advantage while it is still there.

The assumption underlying this paper is that suitable forage crops can increase soil fertility to such an extent that subsequent food crop yields compensate for the loss in area cropped.

Consequently, the integration of forage production into tropical and subtropical food cropping systems is a promising way of promoting sustainable, low-input agriculture. In addition, producing forage as a pioneer crop on wastelands can allow the return of such land to food crop production. In Europe, these technologies were developed 200 years ago and have been practiced successfully for more than a century. Temporarily out of favour as high-input monocropping systems came in after 1945, they are now being re-introduced into temperate agriculture through the organic farming movement. While there may be a need for adaptation to tropical conditions, there are good prospects for success in this climatic zone as well.

However, the integration of forage crops and livestock into food cropping systems requires a holistic approach, taking into account the systems' ecological, economic and social characteristics and the priority attached to different crop and livestock components by the farmers themselves. Shortages of both land and capital dictate systems that rely as much as possible on multipurpose crops and livestock. Although complex, these integrated systems are also less risk-prone and hence more sustainable not only ecologically but also economically than monocropping systems.

Compared with the potential of green feed production from arable and wasteland, the other options discussed - concentrate feeding from own farm or commercial sources - are less important. Concentrate feeding will only be widely adopted if farmers' economic circumstances and improved availability permit.

Obviously, there are still large gaps in our knowledge on how tropical production systems function and how they can be improved through the introduction of forage production. More research is necessary. The priority topics are as follows:

1. The extent of available land resources (fallow, uncropped land, wasteland) in target regions.

2. The collection and evaluation of indigenous forage species, including studies on their adaptation and productivity, their contribution to annual and seasonal nutrient requirements and their effects on soil fertility and subsequent food crop yields.

3. The development of crop rotations (fey farming, intercropping) adapted to specific locations; their contributions to forage production, soil fertility and farm income; environmental impact assessment (EIA).

4. Strategic feed utilization studies on selected combinations of forages with food crop residues and concentrates, and the development of feeding calendars.

5. Socioeconomic studies on resource-poor farmers, assessing their awareness of the problems caused by continuous food cropping, their willingness to try out new solutions, and their adoption of improved forage technologies.

These studies should be carried out as local on-farm research with strong farmer participation, with national research groups taking responsibility and international research institutions providing guidance and support where necessary. The aim is to achieve results that can be turned into a set of recommentations and technologies for a fully fledged technology transfer effort involving non-government organizations (NGOs) alongside conventional government extension services. Efforts of this kind should, at last, lead to significant rates of adoption by the resource-poor farmers of the tropics, who are so greatly in need of improved standards of living through more sustainable forms of agriculture.

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