the last 60 years, there is evidence of little increase in yields since 2000, suggesting that farmers may have reached eco­nomically optimal yield achievable with the cultivars avail­able at the present time and in the current economic and policy atmosphere. Similar responses can be identified for other major arable crops.
     As well as the direct contribution of science and tech­nology to increases in yields, the establishment of effective technology transfer systems to ensure that the "new" advice was conveyed to the farmer users was also of great impor­tance. Such advisory systems have sometimes involved the public sector (government sponsored advice) and sometimes the private sector. In the US, development of an extensive public knowledge transfer system through the cooperative extension  service   of land-grant   universities  contributed greatly to agricultural productivity (Hildreth and Armbrust-er, 1981). However, today there is a transition from publicly supported technology transfer systems to private technology transfer systems (see Chapter 4). The former tended to be more holistic in approach while the latter has primarily been associated with commercially viable products, whether new agrochemicals or new cultivars (c.f. Fuglie et al., 1996).

2.4.3 Increasing cropping systems productivity through inputs
As noted above, changes in outputs of cropping systems across the NAE reflect changes in production and manage­ment systems that utilize inputs such as mechanization, labor, seeds, genetics, nutrients and irrigation, in new and different ways.

2.4.3.1 Mechanization
The last half of the 20th century saw dramatic changes in farming operations because of increased mechanization. The introduction of the diesel engine, compact combine harvest­ers and sophisticated hydraulic and transmission equipment has reduced labor requirements in weeding, harvesting and threshing (Park et al., 2005).
     Improved efficiency and increase in machine scale may explain some of the decline in the number of harvesters and threshers observed in the USA in the 1960s, which has main­tained a plateau since the mid-1970s. In contrast, data for Europe showed a large increase in uptake during the 1960s and 1970s showing a continued investment in this machin­ery and reaching a peak in the number of machines during the mid-1980s.
     New developments in mechanization also relate to pre­cision agriculture, which seeks to improve performance by mapping the specific nutrient needs or levels of pest damage to growing crops in such a way that differing treatments may be provided within the same field (e.g., McBratney et al., 2005). By providing precise information about variable field conditions, precision agriculture can substitute knowledge for chemical inputs such as fertilizer and pesticides (Bon-giovanni and Lowenberg-DeBoer, 2005), while improving management techniques for environmental and economic goals. It is often—but not necessarily, associated with the incorporation of new technologies (e.g., global positioning service or electronic sensors) into varying agricultural ma­chinery (McBratney et al., 2005). Precision agriculture can benefit the environment by reducing excess applications of

inputs and reducing losses due to nutrient imbalances or pest damage, but the necessary technology is at present best suited to relatively large farms so that the capital cost of investment can be spread over a large output, primarily in places like the United States and Canada (Natural Resources Canada, 2006).
     In some CEE countries, the collectivization of agricul­ture tried to exploit economies of scale, particularly in the fields of mechanization and in the use of agrichemicals. In the Soviet Union, productivity advances were largely achieved by government-mandated and government-spon­sored industrialization of agriculture. Thus, between 1950 and 1974 the production of plough-tractors increased by 79% to 218,000 units per year and the production of cereal harvesters increased by 91% to 88,400 units per year. How­ever, investment in machinery was limited by lack of state resources for collectivized farms and lack of access to credit for private landowners (Kovách, 1999).
     Another agricultural sector that has seen significant mechanization advances is glasshouse production, which is used for high value crops such as tomatoes and ornamen­tals. The use of glasshouses and other structures enable horticultural crops to be protected from frost, irrigated as required, protected from pests and disease and brought to market out of normal season in first class conditions. Since 1950 growing sophistication resulting from the use of au­tomatic temperature, humidity and ventilation controls has improved performance and reduced the labor requirement. However, as transport becomes cheaper, protected crops face growing competition from imports grown in climates that are more favorable. One response has been to devise cheaper ways of protecting crops, notably the use of plastic and polytunnels.
     Mechanization of agriculture allows more timely com­pletion of tasks and reduces labor requirements, thereby increasing productivity, avoiding labor shortages and elimi­nating unpleasant jobs. It also allows cropping of lands pre­viously too difficult to cultivate. But mechanization also has disadvantages; including loss of jobs, costs of maintenance and fuel as well as elimination of hedges and expanded field size to accommodate larger equipment (Wilson and King, 2003).
     The main drivers of mechanization have been the de­sire for greater productivity in the 1950-60s (EEA, 2003), the reduction of the labor leading to an increased quality of life and increased economic needs. Moreover, AKST has provided mechanisms for the achievement of engineering improvements for agricultural and forestry equipment and more sophisticated handling of milking, as well as allow­ing for the development of computer management in animal feeding. Thus, mechanization is correlated with field size across NAE, changed management systems and increased flexibility of land use and management. All of these changes have had very important economic, environmental and so­cial implications.

2.4.3.2 Plant breeding, seeds and genetics
A key contributor to productivity increases in crops has been the major advances in crop breeding since the late 1930s, including the development of hybrid crops, cell fu­sion, embryo rescue and genetic engineering. Many of these