A dynamic balance between plants, animals, and the surrounding environment comprises an ecosystem. The impact of humans, as an integral part of most ecosystems, must be taken into account when managing the system’s health. For healthy functioning and sustainability, an ecosystem’s living members must be in balance with the non-living elements.
WHAT IS AN AGROECOSYSTEM?
A model for the functioning of an Agricultural system, with all inputs and outputs. An ecosystem is as small as a set of microbial interactions that take place on the surface of roots, or as large as the globe. An agroecosystem may be at the level of the individual plant-soil-microorganism system, at the level of crops or herds of domesticated animals, at the level of farms or agricultural landscapes, or at the level of entire agricultural economies.
The simplified agricultural ecosystems that humans create have relatively few species of plants and animals, primarily only the one type of crop plant or animal that the farmer wants to grow. And, especially in conventional farming systems, just about any other species that dares to enter the field or barn is considered “the enemy” and liable to be exterminated by poisons. Agricultural ecosystems are designed by humans and are based on a long chain of experience and experiments.
Future agricultural success depends on our ability to make use of Earth’s natural resources without permanently damaging or depleting them. As a result of increasing population demands and poor agriculture practices, natural and managed ecosystems face growing threats from:
* Plant or animal diseases
* Uncontrolled fires
* Increased human activity
Agroecosystems differ from natural ecosystems in several fundamental ways.
First, the energy that drives all autotrophic ecosystems, including agroecosystems is either directly or indirectly derived from solar energy. However, the energy input to agroecosystems includes not only natural energy (sunlight) but also processed energy (fossil fuels) as well as human and animal labour.
Second, biodiversity in agroecosystems is generally reduced by human management in order to channel as much energy and nutrient flow as possible into a few domesticated species.
Finally, evolution is largely, but not entirely, through artificial selection where
commercially desirable phenotypic traits are increased through breeding programs and genetic engineering.
WHY AGROECOSYSTEMS?
The soil on conventional farms has often been nearly sterilised by toxic chemicals or strong fertilisers and is often very low in organic matter (humus). Both humus and large numbers of soil organisms work to make soil porous and well-aerated, provide a good balance of soil nutrients to the growing crop, protect roots from soil-borne diseases and pests, and reduce soil erosion.
Plants that grow in good, rich soil are likely to be healthy. Healthy plants are able to resist or repel most pests and diseases, by means of various processes analogous to the way our body’s immune system protects us from diseases. And healthy plants also produce more nutritious food for animals and humans. Eating a diet of healthful, nutritious food will help keep us healthy and reduce health-care expenses. It’s a win-win system.
Benefits
* Complex and interconnected linkages between agriculture, biodiversity and ecosystem management
* Ecological risk assessment of agroecosystems under changing climatic conditions
* Integrate landscape ecology and ecosystem-based approaches that support agrobiodiversity
* Manage wetlands for sustainable agriculture and aquaculture
* Introduces resource conservation technologies (i.e. organic agriculture, low external input system agriculture (LEISA), integrated crop management (ICM) and ecological agriculture etc.) to enhance the productivity of existing farmlands and reduce the environmental trade-offs
* Popularises information technology for precision farming and sustainable management
* Encourage adaptive and climate-resilient agricultural practices to enhance food production and nutritional quality under changing climatic conditions
* Sustainable use of agro-residues for multipurpose environmental benefits
CASE STUDY
Rice–fish farming systems in Asia. Integrated agro-ecosystems with complex species interactions
Rice-fish farming systems form some of the most striking agricultural landscapes of the world. They have a variety of local designs adapted for cultural, environmental and economic attributes. Those complex and inter-dependent agro-ecosystems are using ecological services, such as biological control and N-fixation as well as landscape integration to ameliorate some persistent failures of elements of the system. Moreover, traditional and low-intensity rice-fish systems play an important role in safeguarding the global environment, notably from a biodiversity perspective. Rice-fish systems support and are in turn supported by a large diversity of cultures and their associated institution for the management of these systems.
A large diversity of agro-ecosystems
Rice is the dominant staple crop of tropical Asia. It has a long history of domestication and rich diversity of cultivated ecotypes based on three varieties of Oryza sativa: indica, japonica and javanica, which are cultivated in different agro-ecological zones for their differing growth, grain and yield characteristics. There are four basic rice agro-ecosystems each with peculiar edaphic conditions: irrigated ecosystems, upland (terraces) and lowland rainfed ecosystems, and flood-prone (very deep water) ecosystems.
Fish culture can be concurrent (mixed) or rotational with rice, at different intensities. This case considers traditional (capture) and low-intensity culture (no fertiliser, no feed) systems, as they enhance many ecological services. Moreover, those systems are less risky for the resource-poor farmers than intensive fish farming, because of their efficiency derived from synergisms, their diversity of products and their environmental soundness.
An integrated system with complex interactions
There is a combined use of habitat and resources for rice and fish. A rich variety of direct and mainly indirect beneficial effects emanate from the interactions between the different elements of the rice-fish agro-ecosystem, enhancing grain and fish production and contributing to the dynamism of the system. For example, rice provides shade for fish, organic matter produced by rice is used by fish, water oxygenation by fish and nutrient recycling benefit rice, biological inter-dependencies provide biological pest control (for example, predation on insects and pests by fish) and N-fixation by Azolla spp. for rice. Rice-fish systems are often based on and regulated by complex and highly diverse food webs of microbe, insects and their predators. However, many indirect non-beneficial effects are exacerbated by the intensification of rice-fish production.
Global importance in term of food production and environmental issues
The rice-fish systems are globally important in terms of food production. The integration of fish in rice farming systems provides invaluable protein and fatty acids, especially for subsistence farmers managing rain-fed systems. They are also important in terms of the three global environmental issues: climate change (emission of greenhouse gas in rice fields is determined by farming practices, plant metabolism and soil properties; rain-fed systems tend to contribute fewer emissions than irrigated systems), shared waters (retaining floodwaters in shared catchments and river basins) and biodiversity.
From a biodiversity perspective, rice-fish farming systems contain:
* low to moderate rice genetic diversity due to intense varietal selection primarily for yields and secondarily for system maintenance and economic viability. Higher levels of biodiversity are found in traditional and low-intensity systems (temporal, spatial and genetic diversity resulting from farm-to-farm variations in cropping systems confers at least partial resistance to pest attack). For each agro-ecological, cultural and management system, ecotypes have been selected and developed, optimizing hydro-edaphic, vegetative, reproductive and ripening characteristics and minimizing losses to consumers, to competitors (weeds), as organic wastes and metabolites and to environmental hazards (cool temperatures, soil acidity and salinity, floods, etc.);
* moderate to high fish species’ diversity, with a low selection of varieties within species. Fish species and aquatic biodiversity appear richer in traditional and low intensity rain-fed than in high-intensity irrigated rice-fish systems.
CHARACTERISTICS OF AGROECOSYSTEMS
Agroecosystems are usually examined from a range of perspectives including energy flux, exchange of materials, nutrient budgets, and population and community dynamics. Solar energy influences agroecosystem productivity directly by providing the energy for photosynthesis and indirectly through heat energy that influences respiration, rates of water-loss, and the heat balance of plants and animals.
Nutrient uptake from soil by crop plants or weeds is primarily mediated by microbial processes. Some soil bacteria fix atmospheric nitrogen into forms that plants can assimilate. Other organisms influence soil structure and the exchange of nutrients, and still, other microorganisms may excrete ammonia and other metabolic byproducts that are useful plant nutrients.
There are many complex ways that microorganisms influence nutrient cycling and uptake by plants. Some microorganisms are plant pathogens that reduce nutrient uptake in diseased plants. Larger organisms may influence nutrient uptake indirectly by modifying soil structure or directly by damaging plants.
Although agroecosystems may be greatly simplified compared to natural ecosystems, they can still foster a rich array of population and community processes such as herbivory, predation, parasitisation, competition, and mutualism. Crop plants may compete among themselves or with weeds for sunlight, soil nutrients, or water. Cattle overstocked in a pasture may compete for forage and thereby change competitive interactions among pasture plants, resulting in selection for unpalatable or even toxic plants. Indeed, one important goal of farming is to find the optimal densities for crops and livestock.
THE SITUATION TODAY
Agroecosystems comprise 40% of the Earth’s surface, and can be defined as, “the ecosystems in which humans have exerted a deliberate selectivity on the composition of the biota i.e., the crops and the livestock maintained by the farmer, replacing to a greater or lesser degree the natural flora and fauna of the site.” Agroecosystems provide various ecosystem services, and management practices used in the agroecosystems determine the state of the global environment.
However, most agroecosystems are disturbed more frequently and with greater intensity than natural ecosystems resulting in reduced biological diversity. Poor land management practices within many agroecosystems result in reduced soil organic carbon (SOC) and crop production and increased erosion.
About 50% of the global arable land is already under mechanical and chemical-intensive agriculture, which requires high inputs of nutrient, energy, and water.
CONCLUSION
As a growing world population slowly pushes ecosystem services to new limits, the issue that more and more scientists and policymakers are trying to confront is how to value ecosystem services. Because we don’t directly support many of these services, we may undervalue them. Yet ecosystem services are very valuable to agriculture, which is why scientists and policymakers are increasingly working to understand ecosystem services and find ways to elevate our understanding of their importance and value them at the same time.
Considering the many benefits of healthy crops, good soil and a diverse ecosystem, it only makes sense for the farmer to do as much as possible (or feasible) to work with natural processes and receive the rewards of better soil, plants and animals. Higher quality crops and animals can also command higher market prices, making farming more profitable.
Some ways a farm can be made to function in a more ecologically sound manner include:
1. Treat the soil as the valuable resource it is by improving its ability to grow healthy crops. Recycle manure, crop residues and/or compost. Avoid the use of strong fertilisers and toxic chemicals.
2. Encourage nearby natural ecosystems, such as grassy fence-row vegetation, field corners, and nearby meadows, woods and marshes. Build bluebird and wren houses.
3. Plant more than one crop species at once (or consecutively). Various cover crops and interplanted crops can smother weeds and supply nutrients to other crops (as with legumes supplying nitrogen), and if tilled into the soil, cover crops can supply humus and nutrients to the soil. Crop rotations also provide similar benefits.
4. Diversify the farm by raising a variety of crops and animals. Not only can diversity protect against bad weather and volatile markets, but a variety of species is a closer approximation of a natural ecosystem than is a monoculture of one or two crops and no animals.
A wise farmer should be an applied ecologist, aware of the variety and functions of both wild and domesticated plants and animals, and especially aware of the importance of good, “healthy” soil. Don’t develop the profit-seeking, control-nature mindset that pervades high-tech agriculture. Be a steward of the land.
