4.6. Chemical Loading of Soil and Ground/Surface Water

An important potential impact from bioenergy feedstock production is the introduction of agricultural inputs into the environment. Inputs such as fertilisers and pesticides (including herbicides, fungicides, insecticides, and nematicides) are likely to be used for growing perennial bioenergy feedstocks, although to a lesser extent than for annual row crops (Table 4.3). Fertilisers can lead to nutrient overloading of surface waters and accelerate the growth of algae, while inhibiting the growth of other aquatic species. Persistent toxins in pesticides can bio-accumulate and poison wildlife, workers, and communities, with human impacts ranging from cancer to immune disorders to hormone disruption. Resistance to these same chemicals can appear in pests, making them all the more difficult to control. Globally, at least 450 species of insects and mites, 100 species of plant pathogens, and 48 species of weeds have become resistant to one or more pesticide products. (See Thrupp, 1996, as a main reference for the material in this section.)

As they have come to recognise the environmental and health impacts of agricultural chemicals, farmers and agronomists have developed a range of management practices to minimise the need for such inputs. These practices should be applied to bioenergy crops, even though they already have lower chemical input requirements. One example is integrated pest management (IPM), which relies less on chemical inputs and more on nature’s species diversity, adaptability, and nutrient cycling capability (Thrupp, 1996). Farmers in many places are demonstrating that IPM is an ecological and cost-effective alternative to conventional chemical-intensive practices for a wide array of crops and regions - contrary to the expectations of some conventional farmers and researchers. In many cases, IPM has proven to be more profitable, although farmers sometimes bear the costs of a transition period of one or two years (Thrupp, 1996).

Farmers in many places are demonstrating that [integrated pest management] IPM is an ecological and cost-effective alternative to conventional chemical-intensive practices for a wide array of crops and regions - contrary to the expectations of some conventional farmers and researchers.

Several steps can be taken to reduce reliance on fertilisers. Using nitrogen-fixing species and using green manure (including crop residues and compost) can maintain or enhance soil fertility without the use of fertilisers. Rotation of crops can slow or prevent the depletion of nutrients, as well as the spread of diseases and pests. Intercropping (growing two or more crops simultaneously), cover crops (crops that cover and protect the soil during periods when it would otherwise be bare), crop residue management, and changes in tillage practices can improve soil quality and enhance nutrient availability.

Similarly, many options are available for eliminating or reducing the use of pesticides. Where labor is readily available, farmers can employ labor-intensive methods of applying inputs and controlling weeds that use inputs more efficiently than methods typically used in highly mechanised agriculture. Very effective non-chemical traps have been developed for many insects. For example, a program in Kenya reduced tsetse flies populations by more than 95 percent with non-chemical traps, greatly reducing the incidence of trypanosomiasis infections in cattle (Ssennyonga, 1996). Steps can be taken to increase the diversity of beneficial insects and to restore the natural predator-prey interactions in crops. For example, if some portion of the land is set aside and preserved in its natural state, it can function as a habitat for predators that reduce the need for pesticides on adjacent cropland. Traditional plant breeding can also be used to develop more pest-resistant strains.

Bioenergy crops can also help mitigate the impacts of chemical use from agricultural cropland. Well-planned siting of bioenergy crops can help to filter agricultural chemicals in runoff from annual row crops.

A number of policy changes can help encourage use of IPM approaches. Such policy measures include:

· removing incentives and subsidies for pesticides, including credit policies tied to chemicals,

· tightening and enforcing regulations on pesticide import and use,

· providing public funds and political support to IPM programs or educational processes, and

· involving stakeholders, farmers groups, and NGOs in policy decisions concerning plant protection, pesticide laws, and production issues.