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V. Characteristics of an improved cropping/farming system
A.
Land-use planning
B.
Watershed management
C.
Sustaining soil productivity
A truly sustainable system must (a) maintain the long-run biological and ecological integrity of natural resources, (b)) sustain a desirable level of support to a farms, community's, or regions social, political, and economic well-being, and (c) enhance quality of life. To be operational, however, sustainability must have tangible and objective criteria (e.g., soil and water conservation, productivity restoration, improvement in water quality in relation to dissolved and suspended loads, a positive thermodynamic energy balance, improvement in air quality, reduction in use of off-farm input for the same level of production and profitability, and acceptable life style as influenced by socio-political factors). All of these criteria are quantifiable but also have a time dimension. Over what period of time are these changes desired or achieved months, years, decades, or centuries? Is the system that we desire to achieve closed, static, steady state, or dynamic,! Obviously, closed or static systems, though ecologically stable, are not productive enough to meet present demands and future needs. Because the system is dynamic, what are the energy fluxes involved in terms of output/input ratio and what is the carrying capacity of such a system? It is not only the energy efficiency but also the total energy flux that is very important in sustainability. What are the indirect costs of achieving such a goal? Indirect costs are indeed important goals to be considered. For example, reducing the use of off-farm input may necessitate bringing additional land into production. The latter may be marginal, subject to severe problems of accelerated erosion and other degradative processes. Substitution of inorganic fertilizers with organic amendments of, green manure may equally endanger the quality of surface and ground water and emit radiatively active gases into the atmosphere, thereby aggravating the greenhouse effect. Will substitution of, input by management have serious social and economic implications?
Sustainability must be assessed at different levels or hierarchies (e.g., technology, sub-system, or system). Therefore, the choice of a criterion to assess sustainability would depend on the hierarchy to be evaluated. Agronomic yields and productivity are useful criteria at the level of crop or cropping system. Profit rather than production is the suitable criterion at the level of farm household or farming system. An assured supply of raw materials, off-farm income, and preserving the productive potential of land resources and environmental quality are appropriate criteria for evaluating the sustainability of a community or a region. A system sustainable at a lower level (crop or cropping system) may, however, not be sustainable at a higher level (community or nation). An ideal system would be one that is sustainable at al] levels.
Furthermore. a system that is economically viable in the short run may not be ecologically viable in the long run. Farm households or communities may adopt systems that are economically viable in the short run but are ecologically detrimental to the community or region in the long run. Typical examples of ecologically incompatible systems include resource-based agriculture with little or no input, intensive use of steep slopes and other marginal lands, uncontrolled grazing at excessive stocking rates, etc. The strategic questions to be considered are:
(i) What system or systems should be made sustainable?
(ii) What policies or incentives are needed to bring about these changes,?
(iii) Who is responsible for Implementing these policies,?
These are difficult but relevant policy questions, because in most cases the beneficiary may be a community or a region rather than the individual household. Furthermore, some of the benefits may not be strictly in economic terms. A critical appraisal of the first question is important. Should the farm household, community, or national policy makers decide which fanning systems should be made sustainable (e.g., intensive food crop production, plantation crops, or food crops)? Keeping national interests in perspective, policy makers can provide appropriate incentives to transform subsistence agriculture into intensive systems of food crop production. Once that decision is made, policy makers have several options/tools for using technologies associated with sustainable management of soil and water resources for a chosen system (e.g., conservation tillage, mulch farming, agroforestry, water harvesting, fertilizer use, cover crops, and multiple cropping). The choice of these technologies involves several considerations, including the following:
Soil degradation, a symptom of land misuse, can be curtailed if land is used for whatever it is capable of and by using methods of soil and crop management that are ecologically compatible. An important prerequisite of appropriate land-use planning is inventory and assessment of land resources (e.g., soil, hydrology, vegetation, and climate). Detailed surveys (at 1:10,000 or 1:50,000) are needed for systematic evaluation of natural resources. Site-specific use of these surveys can be made through the use of Geographic Information Systems (GIS), Global Positioning Systems (GPS), or the Digital Elevation Model (DEM). The assessment of socio-economic factors is also an important aspect of the evaluation of natural resources. While soil mapping and classification may be important, what is required is an assessment of the potential and constraints of natural resources. The nutrient capital of the soil, effective rooting depth and plant-available water reserves, soil structure and physical characteristics, including irritability, are all important factors that affect crop yield, cropping systems productivity, and household income. These properties also influence how soils are managed. The choice of an appropriate farming system for a land type also depends on its capability as determined by an evaluation of soil properties, hydrological characteristics, vegetation type, and climatic attributes.
The sustainable management of soil and water resources is based on judicious and scientific management of all landscape units within a watershed. Widespread and severe problems of accelerated erosion and sedimentation, perpetually devastating floods, land degradation beyond the point of no return, and pollution and eutrophication of water and environment are traceable to poor planning and mismanagement of landscape units within a watershed. The choice of an appropriate land use, exploitation of water resources for irrigation and domestic purposes and the development of an infrastructure including access roads should be done on the basis of watershed as managerial and planning unit. Some landscape units are marginal for agricultural or forestry purposes and should be lets alone under the protective cover of natural vegetation. Degraded landscape units, due to previous mismanagement, should be reverted back to planted fallows or quick growing human-made forests for restoration of their biological and ecological integrity. Grass waterways, water reservoirs, salutation dams, and engineering structures (e.g., gabions, chutes, drop structures, graded channel terraces) should be installed for safe disposal of excess water, runoff management, and erosion control. Land deemed suitable for intensive food crop production should be managed by conservation effective cropping systems with a judicious combination of on-farm and off-farm inputs.
The scientific use of a watershed for sustainable land and water development is more easily said than done. The problem is caused by the private ownership of small land holders. Farm boundaries cut across landscape units and natural waterways. The problem is aggravated by dubious land tenure systems and ownership rights. Legislation, policies, and incentives are needed to foster cooperation among farmers and promote the ecologically compatible development of natural resources.
C. Sustaining soil productivity
1. Bringing new land under cultivation
2. Managing existing lands and restoring the
productivity of degraded lands
An important factor responsible for low yields is the neglect. misuse, and mismanagement of soil resources and the resulting widespread degradation of soil and environment. The amount, frequency, and type of off-farm inputs depend on land resources and the yields desired. Substantial amounts of nutrients harvested annually must be replaced. Some highly weathered and excessively leached soils of the tropics and sub-tropics are virtually devoid of essential plant nutrients (e.g., N and P). For these soils, the addition of organic amendments may enhance soil structure, but they may not eliminate the need for balanced fertilizer because large amounts of nutrients are required in easily available forms to produce economic returns. In addition to the supply of major nutrients (N. P. K), some soils are deficient in certain micro-nutrients (Nz, Cu), while others may have toxic levels of other elements (Al, Mn, and other salts). Low or high pH may require ameliorative measures for high yields. In the human time frame, soil is a non-renewable and finite resource. A national, regional, and world soil policy is needed to advocate the judicious use of soil resources.
An Improved system must alleviate the soil-related and other biophysical constraints to intensive land use for high and sustained production. The conceptual bases of new and innovative systems are known and have been described by Okigbo (1991) with special reference to Africa, and by Beets (1990) with special reference to small land holders of the tropics. There are two approaches: one is to bring new land under cultivation and the other is to restore the productivity of degraded land (Fig. 9).
1. Bringing new land under cultivation
This is usually done by deforestation and the removal of existing vegetation cover. If deforestation is absolutely necessary, it must be done in a way to cause the least damage to soils and the environment. Sustaining the productivity of new land requires maintenance of its life-support processes by:
- minimizing disturbance in the delicate balance between hydrological cycle and energy budget. Regulating the hydrological cycle on cleared land similar to that under TRF would lead to erosion control and a favorable soil moisture regime.
- while maintaining the energy budget would regulate the soil temperature regime. maintaining regular and substantial additions of organic residues to the soil surface, as is the case of litter fall and forest floor in TRF. The application of organic residue is necessary to enhance soil structure, improve soil biodiversity and faunal activity, and maintain soil organic matter.
- replenishing nutrients harvested in crops, trees, and animals. This should be done through a judicious combination of inorganic fertilizers and organic amendments.
Fig. 9 Conceptual basis of an improved cropping/farming system for sustained productivity in the humid tropics
2. Managing existing lands and restoring the productivity of degraded lands
Because of a shortage of prime agricultural land, an increase in production in several countries will have to be achieved by more intensive cultivation of land already developed (Ruttan, 1987). Furthermore, vast areas of land previously developed from TRF have been degraded because of land misuse, adoption of productivity-mining cultural practices, and use of resource based rather than science-based production systems. It is important to restore the productive capacity of these lands so that the need for deforestation and bringing new land under cultivation can be minimized. Restoring these lands requires:
- controlling soil erosion through runoff management and ground cover establishment;
- improving soil structure through appropriate measures of soil surface management;
- establishing vegetative cover through growing an appropriate combination of aggressively growing cover crops and quick-growing perennials;
- replenishing plant nutrients lost out of the ecosystem; and preventing additional losses of water and nutrients from the ecosystem.
Once restored, the land should be managed judiciously to maintain its productive capacity, life-support systems, and environmental regulatory mechanisms.
The following chapters elaborate innovative technological options relevant to these strategies.