86 | North America and Europe (NAE) Report

of insects, farmers will often also treat with pesticides to control other insect pests. The primary concern is that in­sect resistant crops may have toxic effects on non-target or beneficial organisms (Sears et al., 2001, Dively et al., 2004). Another concern is the persistence of insecticidal proteins in the soil ecosystems, particularly over cold winter periods, although no negative impacts on non-target soil organisms have been found so far (Stotzky, 2004). As IR crops have been in use since 1996, there has been significant experience with their use. A significant reduction in total pesticide use has been found for IR crops relative to comparable non-IR varieties, especially in cotton (Brookes and Barfoot, 2005; Fernandez-Cornejo et al., 2006). Different pesticides have very different toxicities and persistence, so the total amount of pesticide used is a rather poor measure of environmental impact. A more direct measure of effect is on non-target populations. Non-target insects are generally more abun­dant in Bt fields than in non-transgenic maize and cotton fields managed with insecticides, although not as abundant as in pesticide free fields (Marvier et al., 2007). Concern re­mains about non-target effects, e.g., indications that pollen from Bt corn can affect aquatic Lepidoptera (Rosi-Marshall et al., 2007).
     The planting of herbicide tolerant (HT) crops allows the farmer to control weeds by treating with a broad-spectrum herbicide because the crop will not be affected. As HT crops are intended to be used with herbicides, there is little or no reduction chemical use. However, the herbicides used in HT crops tend to be less persistent and toxic than the herbicides they have replaced (e.g., Fernandez-Cornejo and McBride, 2002; Brimner et al., 2005). HT crops can facilitate the use of conservation tillage, which provides a number of environ­mental benefits. A major environmental concern with HT crops is the potential development of herbicide tolerant per­sistent weed species through cross-pollination of transgenic crops to wild relatives or to other (non GE) varieties of the crop. The risk of gene-flow to wild relatives needs to be as­sessed for each new GE event and the particular geographical region, before release. Where the risk of cross-pollination to wild relatives is considered too high, restrictions have been applied. Also, it has been predicted that continued herbicide use, associated with HT crops, could lead to a reduction in the broad-leaf weed flora (Heard et al. 2003) and could potentially have toxic effects on ecosystems, including soil microflora (Lerat et al., 2005).
     There is considerably less experience of potential envi­ronmental effects with the other traits that may come into use. One exception is virus resistant papaya, which was approved for use in 1996 in the US and now represents over 50% of the Hawaii papaya plantings. There is prob­ably little environmental cause for concern in a reduction of transmission of a disease virus specific to papaya. This may also be true for bacterial and fungal diseases, provided the method of protection does not introduce properties det­rimental to non-target organisms. Alteration of agronomic traits, to increase salinity and drought tolerance, which de­termine the conditions under which a plant can survive and grow, have greater potential for creation of varieties that could become feral and a problem either directly, or through cross breeding.
     It is anticipated that, as is the case with conventional in-


secticides and herbicides, that insects will develop resistance to the transgenic toxin proteins and that weeds will develop resistance to the herbicides used in combination with trans­genic HT crops. Weed resistance to Roundup (glyphosate) is now a serious concern in the US and other places where Roundup Ready crops are grown on a large scale (Baucom and Mauricio, 2004; Roy, 2004; Vitta et al., 2004). The development of weeds resistant to the herbicides used for transgenic crops will require farmers to switch (return) to other herbicides, potentially with consequent environmental changes.
     If insects were to develop resistance to the toxic proteins used in IR crops this would cause the loss of effectiveness of the IR crops but also pose a threat to cultivation of organic crops on which the same insects are controlled by topical applications of Bt protein. The Bt protein itself and certain formulations of it, being natural products, are permitted as treatments on organic crops. As Bt is one of a very few such treatments available to organic growers, the loss of effec­tiveness of Bt would be a serious loss in such instances. Ac­cordingly, growers of IR crops are required to create no-IR refuges in order to decrease the chances of development of resistant insects.
     The evidence for the presence of direct environmen­tal impacts arising from the current genetically engineered (GE) crops grown on a large scale, compared with conven­tional agriculture, remains controversial. Conclusions that the production of GE crops in N. America have not led to adverse environmental effects are not accepted by some stakeholders. Environmental consequences of increased mechanization
The introduction of powerful engine driven plows opened up areas for crop production that were previously difficult to work due to less tractable soil conditions. One consequence has been large-scale removal of hedges to create larger fields to assist maneuverability of the large machinery (Wilson and King, 2003). Deep plowing can increase soil erosion, but mechanization has also increased the potential for less environmentally damaging minimum tillage soil cultivation practices. The ability to spread more fertilizers or pesticides because of increased mechanization may pose dangers of runoff into streams and rivers resulting in water and air pol­lution beyond the farm gate. However, the greater precision of modern machines has tended to reduce some environ­mental hazards (e.g., reduced spray drift, more precise fer­tilizer application). Frequent passes of heavy machinery in fields causes damaging soil compaction which is exacerbated when the crop is harvested in the winter months on wet ground, as can be the case in Northern Europe (Culshaw and Stokes, 1995). Thus, increased mechanization can have both positive and negative effects on the environment.
     Agriculture, is a contributor to global CO2 emissions from the burning of fossil fuels used in farm machinery, en­ergy use for irrigation pumps, temperature control in indoor and glasshouse units, the burning of agricultural waste and drying of agricultural crops for storage. Since the mid 1960s the primary direct energy use on US farms has shifted from gasoline (petrol) to diesel powered engines. Farm energy use in the USA has been estimated to be 9.2 and 3.5 Tg