Ultimately, reducing health risks from agriculture will require a shift to a more environmentally benign form of agriculture, one that uses fewer agricultural chemicals overall, minimizes ecological disruption, and reduces agriculture’s heavy demand for water.
Managing Pests Strategically. Over the long term, IPM promises to reduce the use of pesticides greatly. This strategy encourages natural control of pest populations by anticipating problems and preventing them from reaching economically damaging levels. Techniques include enhancing natural enemies, planting pest-resistant crops, and, as a last resort, judicious use of pesticides.
In a number of cases, IPM has proven not only better for health but more economical than pest control based solely on agrochemicals. In Brazil, about 40 percent of commercial soybean farmers have switched to IPM since the 1970s, saving more than US$200 million dollars a year as the result of reduced use of insecticides, labor, machinery, and fuel. In the early 1970s, five insecticide applications per season were needed to control soybean pests; now one or two yearly applications are sufficient (76). Pesticide use has been reduced by 80 to 90 percent (77).
Although IPM use has increased steadily over the past two decades, the proportion of farmers using it remains small. Part of the difficulty is that in each case, specific techniques must be identified for local conditions. Governments often offer little support, such as funding or education, to encourage growers to invest in this new approach. In addition, pesticides continue to be attractive to most farmers and governments because their use is simple and economic returns are predictable. Promoting a switch to IPM will require more education and training at the farm level, along with continuing research. In addition, promoting IPM will require adjusting those subsidies and policies that encourage extensive pesticide use.
Reducing Fertilizer Use. Excessive fertilization of agricultural crops can damage both ecosystems and human health. Excess fertilizer can leach through soil where porosity is high, leading to nitrate contamination of groundwater, which poses a direct threat to infant health. Runoff from heavily fertilized fields is also a prime contributor to the eutrophication of surface waters and coastal estuaries–one of the most critical threats to aquatic ecosystems today and therefore to the harvest of fish and shellfish that constitute an important human food source.
Reducing the risks of fertilizer use will require a combination of better agricultural practices that raise fertilizer efficiency and increased efforts to trap agricultural runoff before it leaches into waterways. Better timing of fertilizer applications, for instance, can reduce the amount of fertilizer wasted in the field. In Hawaii, one sugar cane plantation was able to cut nitrogen fertilizer use by one third and reduce losses of nitrous oxide 10-fold by dissolving the fertilizer in irrigation water, delivering it below the soil surface, and timing multiple applications to meet the needs of the growing crop (78). Other strategies to keep excess fertilizer from contaminating local waterways include establishing vegetation buffer strips around crop and pasture lands and restoring natural wetlands. Over the long term, controlling water pollution from agriculture will require more coordination between agricultural and environmental objectives.
Rational Irrigation. Although the spread of irrigation has been a major contributor to the remarkable increases in agricultural output, current irrigation practices can cause much damage. Problems include excessive consumption of fresh water, which can contribute to local water scarcity and also indirectly undermine health by harming the agricultural resource base. Irrigation projects can also create breeding sites for mosquitoes and other vectors, increasing the transmission of these diseases. And when wastewater is used for irrigation, it can increase the risk of cholera, hepatitis, and other diseases associated with human sewage.
Even relatively simple improvements in irrigation projects and planning can bring high short-term rewards in terms of reduced water consumption and improved health. Careful scheduling of irrigation, matching crops to local climatic conditions, and modest improvements to inefficient systems can result in large water savings (79). Coordination between water development planners and health authorities could substantially lower the incidence of vector-borne diseases. If health concerns and costs are analyzed and factored into planning, controlling vectors through environmental management can be relatively inexpensive and effective, with long-term benefits–in contrast to having to implement a chemical control strategy or establish treatment centers after the disease vector has taken hold (80). Changing dam water levels at strategic times, or digging channels to ensure proper water flow, for instance, can reduce the risks of vector-borne disease.
The risks associated with using wastewater for irrigation can also be greatly reduced through simple interventions. For example, irrigation with wastewater during planting is less risky than application during the growing cycle; risks drop if wastewater irrigation ceases several weeks before the harvest. Using wastewater to irrigate cotton or animal fodder, rather than fruits and vegetables, is another good choice. (81).