Challenging targets for future agriculture
Holger Kirchmann
a,*, Gudni Thorvaldsson
baDepartment of Soil Sciences,Swedish Uni6ersity of Agricultural Sciences,Box7014,750 07,Uppsala,Sweden bAgricultural Research Institute,Keldnaholti,112,Reykja6ik,Iceland
Received 3 September 1998; received in revised form 30 August 1999; accepted 8 November 1999
Abstract
This article points out the kinds of problems agriculture is facing, outlines and structures agricultural quality components and defined aims for them, discusses the shortcomings of organic farming, proposes some important research areas and presents an outlook. The quality components are a type of checklist of those factors that we should be aware of concerning protection of the environment, production of healthy food and the practice of good ethics. These components can be integrated into the general aims of sustainable agriculture. Many European and other countries focus on organic farming as a solution, but this approach is dangerous because it does not necessarily lead to a better environment or better food products. Concerning future agricultural research, the following issues are highly important: precision agriculture, low leaching cropping systems, management of soil biological processes and maximum recirculation. Finally, the article discusses some issues of future agriculture such as intensity, nutrient imbalances caused by regional farm specialisation, and the development of an agricultural quality assessment system. © 2000 Elsevier Science B.V. All rights reserved.
Keywords:Sustainability; Ecosystem protection; Pesticides; Water resources; Leaching; Soil fertility; Soil pollutants; Soil compaction; Trace gas emissions; Energy use; Product quality; Ethic; Biodiversity; Soil degradation; Organic farming
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1. Introduction
Agriculture is one of the oldest sources of hu-man livelihood and can be found in most parts of the world. It has developed from simple cultiva-tion to differentiated forms. In particular during the last century, mechanization, introduction of
synthetic fertilizers and pesticides, and plant breeding have increased productivity and made crop production possible on previously unculti-vated land. As a result, more humans can be fed. The population in rural areas decreased while more people settled in towns and found profes-sions within new industries. The size of farms increased and farms became more specialized be-cause economic conditions favoured this develop-ment. These changes created new kinds of problems for the environment and for society. Our challenge is to identify, analyse, evaluate and solve them.
* Corresponding author. Tel.: +46-18-672292; fax: + 46-18-672795.
E-mail addresses: [email protected] (H. Kirch-mann), [email protected] (G. Thorvaldsson)
Environmental problems in agriculture vary from one country to another. Some of them are caused by natural conditions (high native heavy metal content, drought, volcanic eruptions, etc.), others depend on agricultural practices (leaching of nutrients and pesticides etc), and some are related to human influence in other areas (air pollution). Furthermore, these causes are often interrelated. Many scientific studies of the prob-lems and their causes have been carried out. In the public debate, however, methods such as those
proposed in ‘organic agriculture’1
often outweigh the scientific solutions. It seems as if organic agriculture has become a goal in itself, EU
Regu-lation 2078/92 (EEC, 1992). In fact, however,
many environmental problems found with
con-ventional agriculture are also present with organic agriculture.
Agricultural production fulfills important needs of human beings, most importantly the produc-tion of essential nutriproduc-tional products, supplying raw materials for industrial purposes, producing bioenergy, and environmental stewardship.
The purpose of this article is to point out the kinds of problems agriculture is facing and to present important quality components of agricul-ture we should be aware of. The quality compo-nents can be integrated into the concept of sustainable agriculture. We discuss the shortcom-ings of organic farming and, finally, presents im-portant future research areas for agriculture. Hopefully, the perspective and vision presented are a sound contribution to the development of future agriculture.
2. Quality components for agriculture
In this section, the major quality components of agriculture are outlined and structured (Table 1). The quality components are aimed for character-izing the quality of agricultural production sys-tems in their wholeness and can be used as a checklist of what we should be aware of concern-ing protection of the environment, production of healthy food and the practice of good ethics. The quality components have been classified into six groups. The protection of agricultural soils is essential for maintaining the production potential and ensuring a high quality of agricultural prod-ucts. As agricultural activities affect not only the soil and agroecosystem, the protection of other biospheres, the atmosphere and groundwater must also be taken into consideration. Conserva-tive resource practices are required to achieve a long-lasting of natural resources. The quality of agricultural products is affected by a wide range of production factors and by post-harvest proce-dures. The whole chain of treatments must be taken into consideration. Agricultural manage-ment also affects whether the appearance of land-scape and countryside is attractive. Last but not least, our ethical view of nature determines how we evaluate and treat conditions. Ethics have Table 1
Quality components for agriculture, classified into six groups
Protection of agricultural soils
Soil erosion and salinization Soil fertility
Subsoil compaction Soil pollution
Protection of other biospheres,the atmosphere and groundwater
Use of pesticides
Leaching of plant nutrients Emission of trace gases
Conser6ati6e resource practices
Use of water resources Circulation of plant nutrients Energy use
Biological diversity
High quality of agricultural products
Nutritiousness Contamination Hygiene
Attracti6e landscape and countryside
Appearance of the landscape Appearance of the farm
Ethics
People Livestock Environment
Fig. 1. Integration of quality components into the overall aims of sustainable agriculture. Ethics are added as an independent but all-encompassing factor.
therefore been added as an independent but all-encompassing factor.
The relative importance of the quality compo-nents varies between countries or areas depending on the environmental and agricultural conditions. The list of quality components includes a wide range of subjects and therefore each of them can only be discussed briefly. A further and logical step is to quantify the quality components. Such quantification has not been done in this article but will be a part of future work. The question to ask is how our agriculture (organic or conventional) fits to the defined quality components.
A basic requirement for human survival is the sustainability of agriculture. The concept of sus-tainable agriculture has been discussed for several decades and has resulted in a certain consensus about four general aims (Lowrance et al., 1986; Anonymous, 1989; Allen et al., 1991; Crews et al., 1991; Christen, 1998): sufficient food and fibre production, environmental stewardship, economic viability and social justice. The quality compo-nents presented in this article can be integrated into the concept of sustainable agriculture. In Fig. 1, the main groups of quality components in Table 1 have been placed under two of the overall
aims of sustainable agriculture, sufficient food production and environmental stewardship.
2.1. Protection of soils
2.1.1. Soil erosion and salinization
Water and wind erosion are processes causing large soil losses, leading to a steady decrease of cultivated land, are among the greatest agricul-tural problems in the world (Hudson, 1985). As new soil will not be formed from bedrock within the foreseeable future, it is of vital importance and of highest priority to minimize and counter-act the processes of erosion. In addition, saliniza-tion, the accumulation of salts in the surface soils of arid and semiarid regions where annual evapo-ration is greater than leaching, is detrimental to plant growth.
of topsoil due to water erosion has affected a total of 920 million hectares, of which 3.8 million hectares are extremely degraded. The area af-fected by wind erosion amounts to 452 million hectares, of which 0.9 million hectares are ex-tremely affected, and the area affected by saliniza-tion amounts to 76 million hectares, of which 0.8 million hectares are extremely affected. A rough calculation indicates that the loss of soil nitrogen caused by water erosion is of the same order of magnitude as the use of N fertilizers in the world (FAO, 1997).
2.1.2. Soil fertility
The fertility of soils is a prerequisite for their production potential. In the long run, soil fertility can only be maintained if the output of plant nutrients through harvested products and losses in the form of leaching and gaseous emissions is compensated by an equivalent input. Otherwise, the consequence is a slow and steady depletion of the amount of plant nutrients, as shown, for example, for the highly weathered soils in coun-tries of sub-Saharan Africa (Stoorvogel et al., 1993; Smaling et al., 1996; Mugwira and Nya-mangara, 1998). In Swedish arable soils, for in-stance, ca 10% of the soils have a too low content of the plant micronutrient copper for normal plant production (Eriksson et al., 1997).
As leaching of several plant nutrients from light or acid soils can be of the same magnitude or even higher than through crop removal (Wiklander, 1970), the return of harvested plant nutrients is not sufficient to balance the reduction. Thus, recy-cling needs to be supplemented with the addition of nutrients to avoid a gradual reduction in soils with a low adsorbtive capacity and in the long-term also in heavy textured soils. Historically, nutrient exhaustion and soil erosion may have been the principal reasons why agricultural sys-tems have not been sustainable in humid and humid tropical areas (Cox and Atkins, 1979). In arid areas, as a consequence of lack of coordina-tion of watershed systems salinizacoordina-tion and nutri-ent exhaustion have been the root causes for the lack of sustainability (Cox and Atkins, 1979).
Under humid climatic conditions, all soils tend towards acidification (Russell, 1988). Thus, liming
as a measure to maintain or increase the calcium saturation on soil colloids and soil pH values is of central importance, affecting the biological activ-ity, soil structure, availability of plant nutrients, and weathering.
2.1.3. Compaction of subsoils
The mass of agricultural machinery has in-creased by a factor of 3 – 4 during recent decades and the number of field trafficking events can reach more than 10 per year (Horn, 1995). Soil compaction can therefore be considered a growing problem. In contrast to the compaction of the topsoil, subsoil compaction caused by traffic with heavy farm vehicles is so far regarded as irre-versible (Ha˚kansson and Reeder, 1994) or only slightly improvable (Horn, 1995). Compaction of the subsoil reduces water and air inflow into subsurface layers, followed by a decrease of the root growth down through the soil profile,
result-ing in lower yields and reduced nutrient
utilization.
Traditional tillage to improve subsoil condi-tions through deep plowing or ripping, sometimes combined with ameliorant addition, have often failed to provide a better structure. Massive soil loosening may not result in long-term improve-ment of the structure because the organic carbon content and microbial activity in subsoils are too low for formation of stable aggregates. It seems that stabilization of loosened particles is only possible through a combination of chemical ame-liorants, roots, organic matter and water manage-ment (Olsson et al., 1995).
2.1.4. Soil pollution
There is an on-going accumulation of heavy metals in European agricultural soils through at-mospheric deposition, certain organic wastes and phosphorus fertilizers. For instance, the average atmospheric deposition of cadmium in Sweden
amounts to 1.1 g Cd ha−1 per year, whereas
removal through leaching and crops is assessed at
0.7 g Cd ha−1per year (Andersson, 1992). As soil
functions (Giller et al., 1998; Johansson et al., 1998). Soil microorganisms are considered as the most suitable rapid indicator for changes in soil quality (Visser and Parkinsson, 1992). Although there is an absence of consensus on metal limits for soils (McGrath et al., 1994), it is wise to restrict the rate of metal accumulation in arable soil. Other metals conventionally not determined in soil, for example, silver, rhodium, tungsten, etc., need also to be considered in the future.
Application of agrochemicals and sewage
sludge and atmospheric deposition of organic compounds on soils and crops means a contami-nation with anthropogenic chemicals (Jones, 1991; Beck et al., 1995). For example, the content of polynuclear aromatic hydrocarbons in the arable soils of Western Europe has increased 4-fold over the last century (Jones et al., 1989), whereas the content of polychlorinated biphenyl reached a maximum during the late 1960s and since then there has been a dramatic reduction to concentra-tions similar to those of the early 1940s (Alcock et al., 1993). In addition, veterinary medicines end-ing up in animal wastes and sewage sludge are transferred to soil.
Long-term monitoring of organic compounds in soil has shown that a small fraction remained undecomposed (Calderbank, 1989). One main rea-son is that organic compounds can be sorbed in microsites within the soil matrix not available for microrganisms (Bergstro¨m and Stenstro¨m, 1998). The declining availability of organic compounds to soil microorganisms means a decrease of toxic-ity of organic chemicals with time (Alexander, 1995). Still, with respect to the enormous amounts of organic chemicals produced, the protection of soils against pollution is of greatest environmental and public interest.
2.2. Protection of other biospheres, the atmosphere and groundwater
2.2.1. Use of pesticides
Pesticides are a powerful tool and of great importance for agricultural production. Applied on arable land, they are transported through wind drift to adjacent areas, leached to surface- and groundwater (Kreuger, 1998) and are distributed
over large areas through volatilization followed by deposition (Siebers et al., 1994; Lode et al., 1995). Use of pesticides in agriculture will lead to their occurrence in other environments. To guar-antee minimal negative side-effects in ecosystems other than the soil-plant system, pesticides, whether natural or synthetic, should have no or low toxicity, except for the target organisms. There seems to be a great potential to develop microbially-derived pesticides, which are effective, reliable and have a low environmental risk (Mar-rone, 1999). In addition, new application tech-niques, for example precision band spraying (Giles and Slaughter, 1997), can reduce the dose, which can be a very effective way to minimize transport and emission but also to avoid a build-up of resistance of target organisms (Powles et al., 1997).
2.2.2. Leaching of plant nutrients
Eutrophication of water bodies through nitrate and phosphorus is caused by inflow of nutrient-rich groundwater, surface water and sewage (Owen and Ju¨rgens-Geschwind, 1986; Armstrong and Burt, 1993). In particular, the transfer of nitrate from farming systems to groundwater is a major environmental concern on the agricultural agenda (Nitrate Directive, 1991; National Re-search Council, 1993). Thus, the maintenance of a high water quality through good agricultural practices is of highest priority.
It seems that in German agriculture an excess of farm manure is the main reason for the nitrate problem (Van der Ploeg et al., 1997). The same is true for the Netherlands (Spiertz, 1991) and prob-ably also in countries with similar conditions. The application rate of manure often exceeds the need of the crop, which is ultimately caused by an unbalanced ratio between the number of livestock on farms and the number of hectares used for production. Furthermore, the nutrient use effi-ciency of animal wastes is lower than from inor-ganic fertilizers (Kirchmann, 1985).
Primarily, excessive use of plant nutrients must be avoided, which does not mean that no inten-sive agriculture can be practised. A historical
per-spective on nitrogen leaching in Swedish
the middle of the 19th century was approximately the same as today (Hoffmann, 1999). The reasons were (i) large areas of fallow; (ii) poor nitrogen utilization by crops (pests, insects, unfavourable chemical and physical conditions) and (iii) en-hanced mineralization from newly cultivated land. One solution to the groundwater pollution problem is to outline principles in national agri-cultural policies regarding livestock density. In Sweden, regulations concerning livestock density, storage capacity and spreading of animal wastes came into force in 1995 (Lantbruksstyreslen, 1990). Furthermore, low-leaching cropping sys-tems are needed to control nutrient concentra-tions in percolating soil water and to limit total outflows from arable land. In tropical low-input agriculture, however, not primarily nutrient man-agement but erosion control is necessary to im-prove surface waters (Lal and Stewart, 1994).
2.2.3. Emission of climatic trace gases
The agricultural contribution to an increase of climatic trace gases in the atmosphere is through emissions of methane from ruminants and rice wetlands, emissions of nitrous oxides during the process of nitrification and denitrification in soil, and production of carbon dioxide through decom-position of soil organic matter. However, the role of agricultural soils to act as a source or sink for climatic trace gases and the impact of agricultural practices as a key to control emissions has so far only been briefly examined concerning methane and nitrous oxides (Mosier et al., 1991; Willison et al., 1995; Hu¨tsch, 1998), whereas carbon se-questration in agricultural soils has gained consid-erable interest due to a global political agreement on emissions of carbon dioxide (Kyoto protocol). A wanted aim is to decrease emissions of trace gases from agriculture, and furthermore to use agricultural soils as an effective absorber and sink for these gases.
2.3. Conser6ati6e resource practices
2.3.1. Use of water resources
Water is one of the basic elements for agricul-ture and a shortage of water decreases plant pro-duction or even makes cultivation impossible.
Water shortage is the major reason for desertifica-tion (Steen, 1998a). In most arid and semi-arid regions of the world (mainly Third World coun-tries), precipitation is too low to produce crops that will provide self-sufficiency for the calculated population of four billion who will be living in these regions within the next 25 years (Greenland et al., 1997). Rainfall patterns are characterized by short and intensive downpours followed by long droughts. Under such conditions, methods that make the best use of each rainfall through collection, storage and directing run-off water to agricultural crops are a prerequisite for survival.
As every ton of dry plant biomass requires
200 – 500 m3 of water (Marschner, 1995), the use
of water in dry areas for production of low-value staple food in the long term is doubtful. Although there is no alternative today, a change is desirable and even necessary: water should preferably be used to support a biomass of high economic value. Low value biomass should be produced where there is plenty of water and high value biomass should consequently increase its role in
areas of water scarcity (Falkenmark and
Lundqvist, 1998; Steen, 1998b). Construction of both small collection units, as well as dams and larger water reservoirs, seems to a prerequisite for agricultural production in these regions. Waster must be pipelined, stored in cisterns and contain-ers or covered smaller dams to be spread with drip irrigation alongside the plant rows with the pipes laying on the ground or laid in the ground (Samad et al., 1992; Clemings, 1996). Extensive grazing of dry areas should be abandoned in favour of more stationary feeding systems.
2.3.2. Circulation of plant nutrients
Animal husbandry and human food consump-tion are accompanied by the producconsump-tion of wastes. It is a challenge to recycle these wastes to arable land in a proper way, both to compensate for the removal of plant nutrients in harvest and to eliminate the risk caused by deposited wastes. However, if large amounts of wastes are applied to soil, this may also cause environmental pollu-tion (Juste and Mench, 1992).
farm) with the consequence of a surplus of animal wastes in relation to the farming area. The imbal-ance between the amount of animal wastes pro-duced and the arable land available for their recirculation results in a highly enriched soil nu-trient concentration (Leinweber et al., 1994) and groundwater pollution due to too high application rates on the soil (Liebhardt et al., 1979; Evans et al., 1984). This is an environmental hazard and results in wasteful use of plant nutrients (Mengel, 1998). As about 80% of the nutrients from fodder end up in animal wastes, a balanced distribution of animal manure on farm areas is the most important step to establish effective circulation of plant nutrients.
The presently open plant nutrient cycle between rural and urban areas may become more closed, if plant nutrients of all municipal organic wastes can be used in agricultural production (Lammel and Kirchmann, 1995). However, pollution of wastes with heavy metals and a range of organic com-pounds have so far been a main problem (Jacobs et al., 1987; Mininni and Santori, 1987; Witter, 1996).
Removal of plant nutrients is highest in systems without livestock as no manure is produced on the farm. In systems with livestock, there is nor-mally a recirculation of nutrients through animal wastes but there are also significant losses, first of all of nitrogen, from the waste materials (Jarvis, 1993; Bussink and Oenema, 1998).
Despite a highly improved recirculation of wastes of agricultural origin, recirculation is not sufficient to maintain soil fertility because of leaching and gaseous emissions of plant nutrients from soil and wastes, removal of nutrients through pet animal wastes, dead pets and removal through dead humans. Thus, cropping systems relying on circulation of wastes of agricultural origin only will result in negative plant nutrient balances. However, an assessment of phosphorus flows in Swedish society indicate that the recycling of P is greater than removal including leaching because both mineral fodder additives containing P end up in animal manure as well as detergents containing P in sewage sludge (Kirchmann, 1998). However, soils under pastoral agriculture are an exception and their nitrogen levels can be
maintained, if pastures include leguminous crops, which can contribute substantial amounts of N, up to 400 kg ha-1yr-1, through biological fixation
(Ledgard and Steele, 1992).
2.3.3. Energy use
The energy demand of agricultural production, expressed in relation to the total national energy consumption (Stout et al., 1979; Smil, 1992), ranges from 1.8 to 2.8% in developed countries, 5.3% in the Far East and 6.4% in the oil-rich Near
East. The energy use for crop production is B
20% of the total energy quantity of the crop, including direct and indirect inputs, and about 80% of the energy in crops is captured solar energy (Pimentel, 1992). Jansson and Siman (1978) calculated the approximate energy input as
14.5 GJ ha−1 in Swedish agriculture and the
output through crops as 65 GJ ha−1. Feeding
reduced the energy in food to 10 GJ ha-1. Thus,
crop production has a positive energy balance, whereas the transformation of crops into animal products results in a net negative energy balance. It is desirable to reduce the demand for energy by increasing the productivity of agriculture and using fuels more efficiently. Analysis of energy flows will help to identify the most energy-de-manding processes on individual farms. Decisions based on such analyses should help to improve the use of energy sources. Biofuels produced in agriculture can reduce the use of fossil fuels to some extent. For example, the agricultural area has to be increased by 25% for biofuels to be able to provide the energy quantity used in agriculture in Sweden (Naturva˚rdsverket, 1997).
2.3.4. Biological di6ersity
a variety of species mixed with cultivated crops in the field. Indeed, meadows and pastures are com-posed of such high richness in species that Scandi-navian agroecosystems have a greater diversity than forest ecosystems. Grazing (or cutting) of these areas with no nutrient input is a prerequisite to maintaining the richness of species. In practice, grazing farm animals are of ultimate importance for their conservation.
The genetic resources of cultivated crop species seem to be best protected by systematic collection and storage in gene banks, which is also partly true for the genetic resources of livestock. However, the conservation of biodiversity in ecosystems other than agriculture is an impor-tant task for the sustainability of modern agricul-ture (Swanson, 1997). Genetic diversity is a well-recognized factor to enhance agricultural produc-tion.
2.4. High quality of agricultural products
Genetic and environmental factors affect the quality of crops (Nilsson, 1984). Concerning envi-ronmental factors, soils should enable the produc-tion of nutritious crops that do not contain critical levels of toxic metals or environmental pollutants. Cultivation techniques are needed that minimize plant diseases and the presence of un-wanted fungi and insects as well as pesticide residues. These factors are discussed in other sections.
Organic wastes and irrigation water used in plant production must not contain disease-carry-ing bacteria and viruses. Handldisease-carry-ing of agricultural products must ensure that no unwanted sub-stances, either natural or industrial, can pollute the products. The whole production process must be hygienic and clean. As the handling process includes other factors such as storage, transport and industrial refinement, the topic is not dis-cussed in more detail.
2.5. Attracti6e countryside
Agriculture has a great effect on the appearance of the countryside as it keeps the landscape
‘open’. Farms should be tidy and fit into the landscape. The appearance of farms gives the product an image. It may be hard to convince consumers of the quality of a product if the aesthetic of the farm does not support it. Each farm should express robustness, care, attractive-ness and environmental adaptation.
2.6. Ethics
2.6.1. Human relationships towards nature
Human relationships towards nature are ruled by an ethical code, which has varied throughout history and cultural epochs. The ethical code, however, is deeply conditioned by beliefs about ourselves and our relation to nature. Elmore (1996) summarizes four principally different views on our relationship towards nature.
2.6.1.1. The geocentric 6iew. Precedence of the ecosystem over human interests: the good of the ecosystem is more important than human life and welfare, people are the problem.
2.6.1.2. The acentric 6iew. Everything is one and part of the same essence with no major distinction between species and things. Coequality of all cre-ation. This was the view of some American Indi-ans, as manifested in pantheism, New Age philosophy, and often seen in science.
2.6.1.3. The anthropocentric 6iew. People believe that they are above nature and have no higher authority to hold them accountable for their treatment of the ecosystem.
2.6.1.4.The theocentric6iew. Theocentrists believe that a higher authority (God) than people or the ecosystem exists. He has entrusted man the stew-ardship of his creation (Genesis 1:26, 1:28; 2:15). Christianity is theocentric, as are other religions based on the Old Testament.
2.6.2. Agricultural issues
Concerning agriculture, three different ethical issues can be distinguished: (i) the conditions of the people living and working on the farms; (ii) the livestock husbandry and (iii) the impact of cultivation on the environment.
The circumstances for earning one’s livelihood from agriculture have to be such that working and social conditions as well as benefits are attrac-tive. Humans are obliged to show kindness and respect to livestock as well as being morally
re-sponsible for their health and well-being
(Hansson, 1996; Nilsson, 1996). Humans should treat their environment in such a way that it is sustainable and can continue to give mankind joy, food and other products.
3. The shortcomings of organic farming
When the environmental problems in agricul-ture came into spotlight, different forms of or-ganic farming had been practiced in Europe for several decades. These farming methods were quickly presented as a solution for most of the problems agriculture is facing. In this section, we point out the inability of organic farming methods to solve some of the major environmental problems.
3.1. A brief history
Although some environmental problems were already identified as a result of the industrializa-tion of societies in the 19th century, the break-through of broad environmental consciousness took place in the 1960s. New research orienta-tions, national and multinational environmental protection agencies, and environmental interest organizations were founded. Within agriculture several organizations, sharing a prejudiced view of nature, biodynamic and organic-biological, pro-moted their agricultural methods as a solution to the environmental problems.
One theory of organic farming, biodynamic farming, which is part of a comprehensive philos-ophy called anthroposphilos-ophy, was presented by Steiner in 1924. Its aim was not to solve
environ-mental problems but to introduce a form of pro-duction for high food quality capturing ‘cosmic forces’. Biodynamic and other forms of organic agriculture exclude easily soluble inorganic fertil-izers and synthetic pesticides on principle (KRAV, 1999).
3.2. Con6entional 6ersus organic agriculture
Most problems that occur in conventional agri-culture may also be present in organic farming, such as erosion, nitrogen leaching, ammonia volatilization from animal wastes, high levels of native soil cadmium, accumulation of trace metals in soil, and subsoil compaction caused by farm machinery. Organic farming methods do not offer solutions to many of these problems.
For example, the exclusion of easily soluble inorganic fertilizer does not necessarily imply less leaching or less eutrophication. On the contrary, leaching of total N from soil receiving animal manure, either composted or anaerobically stored, can be much higher than from inorganic fertilizer applied at the same N rate if measured over several years (Bergstro¨m and Kirchmann, 1999). Green manuring can also cause high nitrate leach-ing losses, as shown in several investigations (Cameron and Wild, 1984; Bonde and Rosswall, 1987; Linde´n and Wallgren, 1993). From an envi-ronmental point of view, it does not matter whether the nutrients come from inorganic or organic sources. What matters is when, how and in what quantity plant nutrients are available to crops, i.e. if the nutrient supply is in synchrony with the demand of the crop (Myers et al., 1997). However, the release of nutrients from organic manures is very often not synchronized with crop uptake, mineralization can take place at times when no crops are present, and as a result organic manures can cause high nitrate leaching losses.
addition of peat, rock powder and calcium salts, is rather small. Storing animal manure anaerobi-cally has resulted in significantly lower ammonia losses than composting (Kirchmann and Lund-vall, 1998). Composting, however, is a prerequi-site in biodynamics and a preferred method in organic farming in general. Means to reduce am-monia losses from manure and slurry have been proposed in national agricultural programmes (Gustavsson, 1998) and not organic farming organisations.
There are strong indications that the cadmium content of soils is increasing not only through fertilization but also deposition. In Sweden the cadmium content of wheat grain has signifi-cantly increased during the period 1916 – 1980 (Kjellstro¨m et al., 1975; Andersson and Binge-fors, 1985). Andersson (1981) found that the re-moval of cadmium by leaching was negligible compared to the supply by precipitation. To re-duce the cadmium supply through inorganic fer-tilizers in Sweden, the manufacturing process for phosphorus fertilizer has been changed, remov-ing most of the cadmium. Through this process, the concentration of cadmium in soluble
phos-phorus fertilizers has been reduced to B5 mg
Cd kg−1
P (Hydro Agri, 1998). In contrast, in organic farming, fertilization with raw phos-phates can lead to a much higher application of cadmium.
Crop quality is put forward as an important argument for organic farming (Koepf et al., 1976; Dlouhy´, 1981). Crop quality depends on the plant nutrient status in the soil, the dynam-ics of nutrient release, weather conditions during growth, damage caused by pests, toxic com-pounds produced by the crops themselves and the adherent microflora, contamination with pes-ticides and pollutants, and the post-harvest treatment. Several investigations have clearly shown that the type of fertilization, contrary to the principle of organic farming, does not affect plant quality (Hansen, 1981; Evers, 1989a,b,c)
whereas the intensity of fertilization does
(Hogstad et al., 1997). Thus, crop quality is not dependent on the principal difference between inorganic fertilization and organic manuring.
Furthermore, considerable variation in crop
quality can be found between farms regardless of whether they are using conventional or or-ganic methods. This division into ‘oror-ganic’ and ‘conventional’ agriculture loses sight of the prin-cipal factors concerning crop quality and envi-ronmentally friendly agriculture.
In contrast to conventional agriculture, or-ganic farming without purchase of feed may re-sult in a nutrient depletion of soils (Nolte and Werner, 1994). Through the import of feeding stuff to farms, which means a net input of nutri-ents, depletion is normally avoided (Kaffka and Koepf, 1989; Fowler et al., 1993; Granstedt, 1995). As the feeding stuff may be produced
elsewhere with inorganic fertilizers, organic
farming indirectly depends on the soil fertility of
conventional farming. However, regulations
about the amount of conventionally grown feed-ing stuff to be used in organic farmfeed-ing differ between countries.
Side-effects caused by synthetic pesticides and drug feeding are not found in organic farming, a positive result. However, the exclusion of pesti-cides may result in increased concentrations of secondary plant metabolites and of mycotoxins of field fungi. Eltun (1996) reported higher con-centrations of deoxynivalenol and nivalenol in grain samples from organic than from conven-tional farming. Furthermore, in the same experi-ment no pesticide residues were found in grain samples grown conventionally. Thus, the exclu-sion of pesticides does not necessarily mean that crop products do not contain unwanted sub-stances.
The area for housing and outdoor movement of farm animals has received more attention in organic than in conventional agriculture. This
concern is positive and space requirements
3.3. Philosophy of life or scientific thinking?
In order to understand today%s organic farming
movement, it may be useful to know that the highly influential form of organic agriculture, bio-dynamic farming (Steiner, 1975), had its roots in a philosophy of life and not in the agricultural sciences (Kirchmann, 1994). A common attitude within the organic movement is that nature and natural products are good, whereas man-made chemicals are bad, or at least not as good as natural ones. This way of thinking may also ex-plain why man-made fertilizers and synthetic pes-ticides are excluded.
Although there is no reason to believe that nature is only good, as exemplified in agriculture by crop failures, plant or animal diseases, and the effects of natural disasters, this romantic way of thinking is widespread. The forces of nature are fantastic and filled with still unknown secrets, but at the same time the results of natural activity may be ‘bad’. That is why natural conditions cannot be the only guideline for an ethical code about inter-actions between humans and nature. We have to define an ethical code which takes into account the full truth, and it is our responsibility to do so.
As indicated above, views and beliefs originat-ing from a philosophy of life are the drivoriginat-ing force behind organic farming. People should have free choice concerning religion or a philosophy of life and a strong ethical foundation is very important, but placing philosophical ideas above scientific thinking, especially if they contradict scientific results, leads to severe communication problems. For example, to demand the exclusion of synthetic fertilizers shifts matters of science into the field of dogma (Jansson, 1971). The fundamental ques-tion, why plant nutrients should be added in organic forms or as untreated minerals only, has never been proved.
One reason for the increase in organic agricul-ture in many countries in Europe today is our need to solve environmental problems. In such situa-tions, we often tend to accept appealing solutions. Furthermore, intensive propaganda by representa-tives of organic farming movements has had a strong influence on public opinion, politicians, and scientists.
4. Relevant research areas
This section describes some research areas that are important for the development of our future agriculture. One may keep in mind that this selec-tion is highly affected by the environmental condi-tions we live in and our personal knowledge.
4.1. Precision agriculture
Precision agriculture is a discipline that aims to increase efficiency in the management of agricul-ture. It is the development of new technologies, modification of old ones and integration of moni-toring and computing at farm level to achieve a particular goal (Blackmore, 1994).
For example, the spatial variability of plant nutrients in fields affects the efficiency of nutrients added and thereby yield. Thus, techniques for recording variations within fields and the software to support the farmer when making decisions need to be developed. Prediction of mineralizable N in soils through combination of extraction methods with model simulation is one desirable way (Appel and Mengel, 1998). This will enable plant nutrients to be applied according to the nutrient status of the soil and the growing crop. Such precise appli-cation will optimize the utilization of manure and fertilizers and will help to increase yields and improve crop quality. Also, a spatially selective application of pesticides will help to reduce the amount of chemicals used (Stafford and Miller, 1993). Furthermore, methods to assess the N status of growing crops, for example via chloro-phyll concentration in the tissue, are needed to avoid overfertilization with nitrogen and the re-sulting impact on N leaching.
4.2. Low leaching cropping systems
4.2.1. Co6er crops
survive winter conditions. Mineralization of plant nutrients during decay should synchronize with the uptake of nutrients by the following crop.
4.2.2. Perennial cereals
In some parts of the world the risk of erosion is so high that a permanent vegetative cover is es-sential. Perennial cereals enable the production of grains in areas that are otherwise not possible. Development of such species seems to be a mean-ingful task (Pimm, 1997).
4.3. Acti6e management of soil biological processes
4.3.1. Decomposition and synchronization
Decomposition processes in soil are comprised of the humification of fresh litter and the break-down of humus. Measures that enable a more efficient carbon stabilization of fresh litter can enable an increase in carbon sequestration in soil. Speeding up the breakdown of mineralizable N during crop growth will result in better synchro-nization between release and uptake. Slowing down the breakdown of mineralizable N during
autumn and winter may help to conserve
nutrients.
4.3.2. Climatic trace gas emissions
Soil biological processes are linked to the trace
gas composition of the atmosphere. Reduced CO2
emission from soil and the use of the land as a
sink for excess CO2 can help to counteract an
increase in the atmosphere. It is most likely that emissions of nitrous oxides from soils as well as methane oxidation can also be controlled. An understanding of regulating factors and knowl-edge of the effect of different cultivation tech-niques may enable us to actively manage soil biological processes.
4.4. Maximum circulation of plant nutrients
4.4.1. Animal wastes
A balanced distribution of animal manure on farm areas is the most important step to establish effective circulation of plant nutrients. Further-more, the development of new methods to handle
and store solid animal manures on farms that enable nutrient conservation are desirable.
4.4.2. Food and urban wastes
Development of new or supplemental industrial systems for utilization of plant nutrients in munic-ipal wastes is needed in order to enable recycling without contamination by environmental pollu-tants. Waste products need to be transported over longer distances to avoid too high nutrient levels in arable soils in the circumference of cities and towns. Methods that enable long-distance circula-tion are desirable.
5. Outlook
5.1. Intensi6e agricultural production — en6ironmental pollution?
The production of food has to increase as the global human population will increase by about two billion during the next 25 years (Greenland et al., 1997). Thus, intensive production seems abso-lutely necessary to guarantee that production will be able to keep pace with population growth. The critical question is whether it will be possible to increase production without an increase or even a lowering of emissions.
In general, emissions from arable land increase with more intensive fertilization. Nitrate leaching, for example, increased slightly with higher fertil-ization intensity and first at an excessive supply of N fertilizer, leaching reached very high and unsat-isfactory levels (Bergstro¨m and Brink, 1986). A slight increase in emissions at higher intensity has to be distinguished from the very high emissions due to excessive use.
leaching of N in organic farming, for example, amounted to 5.5 kg N per ton of cereals but to 4.2 kg N per ton for cereals conventionally farmed in the south of Sweden. This result, that emissions per unit of yield are not lower in low- or medium-intensive cropping systems, needs to be taken into consideration when evaluating the environmental impact from cropping systems. Addiscott (1995) pointed out that low-intensive crop production is least sustainable, whereas high-intensive use of arable land is most sustainable, in accordance with the theory of thermodynamics.
Furthermore, with high yields per area, more food can be produced and more land can be saved for other uses. This is most important in countries with limited land resources and a high population density. Still, a high degree of knowledge is essen-tial for intensive agriculture to be able to utilize the means of production in a highly efficient way and avoid misuse of resources, overfertilization and any negative effects on the environment.
5.2. Nutrient imbalances
Regional specialisation of farms has resulted in production that is most often much greater than the need of the immediate market. Agricultural products are transported long distances, both crops used for human consumption and fodder concentrates for animal husbandry, which means a net removal and no return of harvested nutri-ents. On the other hand, a large import of feeding stuff to farms contributes to an excessive supply at a local or even regional level. This more or less open plant nutrient cycle causes nutrient imbal-ances. Examples of long distance transport across countries are also common. For example, concen-trates may be produced on land in developing countries where rain forests were cut and soils
may degrade through erosion and nutrient
depletion.
We need tools to prevent and overcome the negative impacts of this development. Specialisa-tion of single farms need not necessarily have a negative impact on the environment — for exam-ple, an excess of manure can be distributed within acceptable areas to adjacent farms — but special-isation of farms in a whole region carrying out the
same production will have a negative impact. Thus, we need to question the development of one-sided, regional agricultural production.
Farm specialisation of regions has been highly influenced by the climate, soil properties and eco-nomic conditions and it may be difficult to reintroduce mixed farming, i.e. a combination of animal and crop husbandry. Although mixed farming is a straight-forward solution to avoid imbalances, this form of farming may put the farm’s economy at risk. Economic implementa-tions to favour mixed farming may be one possi-bility. Another measure to prevent a further increase in animal density is to limit the number of farm animals kept in relation to the arable land available regionally.
One probable way to affect farming in the future is through analysis and classification of agricultural production and environmental stew-ardship on individual farms. This analysis, to-gether with an assessment system (see below), may stimulate favourable farming development. If properly designed and well founded, a quality assessment system for agriculture can be a driving instrument to be used for legislative implementa-tion of guidelines.
5.3. A quality assessment system for agriculture
A range of quality assessment systems such as for forest landscape, groundwater, lakes and wa-tercourses, coasts and seas, contaminated sites and agricultural landscape have been published by the Swedish Environmental Protection Agency (Naturva˚rdsverket, 1999). The assessment systems were designed as a tool to evaluate the situation. Each assessment system contains a selection of variables which were chosen because of their vital importance for the functioning of each ecosystem. The classification of variables, expressed on a scale of 1-5, involved two aspects: (i) an appraisal of whether the recorded state may have an ad-verse effect on the environment or human health, and (ii) an appraisal of the extent to which the recorded state deviates from a ‘comparative value’.
envi-ronment, the status of selected properties and the efficiency of production must be taken into ac-count. The quality components outlined in this paper can be useful for a structural outline. A
comprehensive quality assessment system,
combining different aspects of production and environmental stewardship, can be a very power-ful tool to direct development towards environ-mentally sound and sustainable cropping systems. The use of such an assessment system may favour agricultural production in certain areas and question it in others. Within a country, this assessment may lead to setting aside agricultural land. However, as food production is a funda-mental need for humans, most nations are inter-ested in producing their own food to some extent. The result could be that agricultural land used in one country could be set aside in another. Where to actually carry out agriculture is therefore also a political decision.
6. Conclusions
On a global scale, we need to increase food production and at the same time ensure the qual-ity of agricultural soils and of the surrounding environment. This article has presented a list of quality components to combine the goals of sufficient food production and environmental stewardship. An awareness and application of these quality components is useful to gain an overview of the conditions of agriculture and they are also considered as guidelines for agricultural research and development. Innovation, creative solutions and discoveries based on natural sci-ences will be helpful in the development of sus-tainable agriculture, but not methods based on dogmatism.
Acknowledgements
We would like to thank the Swedish Environ-mental Protection Agency and the Agricultural Research Institute in Iceland for their financial support.
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