Agricultural practices that lead to soil erosion, use pesticides exclusively to achieve insect, weed, and disease control, and depend on inexpensive fertilizers to maintain soil fertility are not sustainable ecologically (or economically, for that matter). Such systems degrade or destroy the resource base on which future productivity depends.
On the other hand, agricultural systems that fail to produce sufficient food to meet the demands of the population are not viable and won't be widely adopted. Maintaining productivity will require developing systems that both (1) provide crops with adequate resources and (2) use these resources in efficient ways.
A first step in trying to move agriculture in the direction of more sustainable systems is to try to understand why agricultural systems today are the way they are.
A too commonly held belief in agroecology is that technology per se poses a major threat to sustainability. Technological change can either detract from sustainability (for example, insecticides) or enhance sustainability (for example, conservation tillage, IPM).
At the global scale, technological change is driven by two kinds of pressures: demographic and socioeconomic (Giampietro et al., 1999):
An additional factor that drives technological change is "environmental loading"-the negative ecological impacts of farming practices, including soil erosion, ground water depletion, pollution, and loss of biodiversity. Giampietro et al. (1999) suggest that the ratio of food energy production/fossil fuel input is a good measure of environmental loading. Countries with both high DP and SEP also have the highest environmental loading from agriculture-Japan and the European Union.
Agricultural practices are influenced not just by markets but also by policy-laws and regulations developed to obtain certain societal goals. In the past 50 years those goals have mainly been to achieve food production while minimizing the allocation of labor to agriculture (at least in the developed countries). Minimizing environmental loading has not been a priority, and that has contributed in a major way to the widespread employment of unsustainable practices.
Strategies for making agriculture more sustainable are of three general types, successively involving greater changes in the design and management of agroecosystems:
What degree of change is needed to make agriculture more sustainable is an area of considerable debate. Agroecologists (such as Altieri and Gliessman) argue that only system redesign can achieve long-term sustainability. And the key process to system redesign is usually increased diversification.
Miguel Altieri argues that monocultures are fundamentally flawed for the following reasons:
Organic agriculture is the best current example of system redesign. Legally-defined organic systems use no pesticides or fertilizers. Generally organic and "conventional" systems can be contrasted with respect to their goals and practices:
| Conventional Agriculture | Organic Agriculture |
| Emphasis on yield | Emphasis on sustainability |
| Nitrogen supplied by fertilizers | Nitrogen supplied by BNF, amendments |
| Insect control by insecticides | Insect control by natural enemies |
| Weed control by herbicides | Weed control by rotation, cultivation |
| Monoculture or short-rotation | Diversified long rotations |
A major assertion of advocates of organic agriculture (and many other alternate systems) is that ecological processes in the soil can be managed to greatly increase nutrient availability and nutrient-use efficiency. Management practices that seek to eliminate erosion and increase SOM are favored.
For example, (Wall & Moore, 1999) state: "... historically, a common result of conventional agriculture has been to disrupt this cycle [of mineralization and uptake] by shifting nutrient dynamics from the fungal pathway to the bacterial pathway, accelerating decomposition so that nitrogen mineralization occurs soon after the crop has been harvested .... If conventional agriculture were more finely tuned to the natural cycles of soil biotic interactions, nitrogen retention would be maximized, and more nitrogen would be available to plants."
The conventional view (exemplified, for instance, by Loomis and Connor, 1992) is that the yields achievable in organic agricultural are equivalent to pre-World War II yields-about 50% or less of yields today. Evidence from paired farms does not support this view:
Organic farms in the USA often have lower yields, but costs are also lower and the products can be sold in higher-value markets. Thus such systems can be profitable if there is access to such markets.
Many studies of organic systems have demonstrated beneficial long-term effects on soil properties, including higher SOM, higher soil microbial activity, and reduced erosion.
It is certainly premature to equate organic agriculture with sustainable agriculture. It may be true that diversification-rather than strict elimination of agrichemical inputs-is the key to the improved performance of organic systems. Systems incorporating diversification with reduced input use may well have the same long-term sustainability as organic systems.
One way in which sustainable agriculture may be more similar to agriculture in the first half of the 20th Century is in a return to mixed crop-livestock operations.
The trend in agriculture in this country has been the separation of crop production and animal production enterprises. Reintegrating crop and livestock production could have several advantages:
Agroecologists have suggested that several agroecosystem attributes can serve as "indicators of sustainability". Such indicators are often variables that are correlated with many other variables, many of which may be hard to measure. Bookstaller et al. (1997) recommend the following list:
Agricultural policy is the means by which governments influence agricultural practices to achieve societal goals. Mechanisms used to achieve policy goals include foreign exchange rates, trade policies, food and fiber output pricing, input price controls, and subsidies to growers. The later may include guaranteed prices, input subsidies, deficiency payments, low-interest loans, disaster relief, and crop insurance. The withholding of subsidies can be an effective sanction to discourage certain practices.
The original goals of US agricultural policy were to (1) maintain farm income; and (2) discourage overproduction. Aspects of US agricultural policy included, until recently:
Program crops included all major cereal grains and cotton. 70% of US croplands were planted to program crops; 88% of eligible acreage was enrolled.
Bradshaw and Smit (1997) argue that the effect of these support systems has been to promote "an industrial mode of agriculture", that is, achieving economic efficiency through economies of scale, specialization, and capital investment. Most national policies have failed to achieve their goals, since the production sector of agriculture is still characterized by unstable markets, low rates of return on capital, low farm income, and a high rate of farm failures.
Effects of farm policies-intended and unintended-include:
US agricultural policy is spelled out in the "Farm Bill", which is revised every five years. 1995 Farm Bill was called the "Freedom to Farm" bill because it removed most base acreage and cross-compliance restrictions. It did not, as incorrectly reported in the national media, phase out subsidies. Government payments in the US still constitute a major fraction of farm income.
Agricultural policy will need to be completely overhauled to achieve sustainability goals at the national level. While policy can be an important tool in achieving sustainability, it requires a national consensus on the problems and solutions regarding sustainability, and such a consensus does not yet exist.
URL: http://ag.arizona.edu/~spmcl/lecturenotes/sustainablesystems.htm
17 April 2003