Breakthroughs in higher yields lead to faster spread and replacement of new varieties for some crops but not others. The positive and significant signs of the Yield Frontier variables in the wheat VT equations  demonstrate that when higher yielding wheat varieties appear in their provinces farmers turn their varieties over more frequently. The correlation between a higher yield frontier and more rapid turnover may explain why wheat yields outperformed other major grains during the reform period. In contrast, higher values of Yield Frontier variables in the rice and one of the maize equations are associated with slower turnover . Such a finding is consistent with our gap analysis and may reflect the fact farmers  in the mid- to late-reform period prefer adopting higher quality rice varieties, even though higher yielding varieties are available. The impact of the materials from the CG system is mainly a story of the China’s breeders using IRRI and CIMMYT varieties for the yield enhancement of their seed stock. If it can be assumed that, when China’s breeder incorporate foreign germplasm into its varieties, the material contributes to part of the rise in productivity, then the test of the direct impact of CG material is seen in the results of the TFP equation. If technology is important in all the TFP equations, by virtue of the fact that IRRI’s material is used more frequently by China’s rice breeders, compared to that used by wheat and maize breeders, it is making the largest contribution of the CG system to China’s TFP in the reform era.It is possible, however, that foreign material may be bringing in an extra “boost” of productivity, beyond its contribution to the varieties themselves,hydroponic grow table by increasing the rate of turnover of new varieties.Such an effect would show up in the VT equations. If the coefficients of the CG variables were positive and significant, they would indicate that the presence of material from CG centers makes the varieties more attractive to farmers and contribute to technological change in China in a second way.

In fact, there is not particularly strong evidence that increases in the presence of IRRI material is important in increasing the turnover of rice varieties . If farmers are, in fact, mainly looking for characteristics that are not associated with higher yields, it could be that IRRI material is making its primary impact on yields and only a secondary impact on the other traits that have been more important in inducing adoption in the reform period. A similar cautious interpretation is called for in the case of wheat and maize  where the standard errors are large relative to the size of the coefficient in all but one case. But although the contribution of CIMMYT wheat and maize germplasm to China, according to this analysis, may be smaller, in some provinces the contribution of CIMMYT’s material has been large and may have extraordinary effects on the productivity of some of China’s poorest areas. For example, the CG genetic materials contributes more than 50 percent of Yunnan Province’s wheat varieties and more than 40 percent of Guangxi Province’s maize varieties in the late 1980s and early 1990s. Yunnan and Guangxi Provinces are both very poor provinces and some of the poorest populations in China are in the mountainous maize growing areas. Elsewhere , we have shown that the impact of CG material in poor provinces, in general, is more important than its effect in rich areas—both directly and in some cases in terms of inducing more rapid turnover. Such a pattern of findings is consistent with a story that although the focus of the CG system on tropical and subtropical wheat and maize varieties has limited its impact on China productivity as a whole, it has played a role in increasing technology in poor areas, a chronic weakness of China’s research system .Our results for the TFP equation, presented in Table 4, also generally perform well. The goodness of fit measures  range from 0.80 to 0.85, quite high for determinants of TFP equations. In other work, in India for example, the fit of the specification was only 0.17 . The signs of most of the coefficients also are as expected and many of the standard errors are relatively low.15 For example, the coefficients of the weather indices are negative and significant in the TFP equations in the rice, wheat, and maize specifications . Flood and drought events, as expected, push down TFP measures, since they often adversely affect output but not inputs.

Perhaps the most robust and important finding of our analysis is that technology has a large and positive influence on TFP. The finding holds over all crops, and all measures of technology. The positive and highly significant coefficients on both measures of the rate of varietal turnover  show that as new technology is adopted by farmers it increases TFP . Following from this, the positive contributions of China’s research system and the presence of CG material both imply that domestic investments in agricultural R & D and ties with the international agricultural research system have contributed  to a healthy agricultural sector. Further analysis is conducted to attempt overcome one possible shortcoming of using VT as a measure of technological change. It could be that an omitted variable is obscuring the true relationship between VT and TFP. As varieties age, the yield potential may deteriorate . We add a variable measuring the average age of the varieties  to isolate the age effect from the new technology effect . Although we find no apparent negative age impact on TFP in any of the equations , in a number of the regressions, the coefficient ofVT variable in the TFP equation actually rises, a finding that reinforces the basic message of the importance of technology. The role of extension is less simple. The impact of extension can occur through its effect on spreading new seed technologies  and through its provision of other services enhancing farmer productivity . The positive and significant coefficients on the extension variable in all of the VT technology equations for all crops demonstrate the importance of extension in facilitating farmer adoption . Extension, however, plays less of an independent role in increasing the yield potential of varieties that have been adopted by farmers, perhaps an unsurprising result given the reforms that have shifted the extension from an advisory body to one that is supporting itself, often through the sale of seed .The long-termsustainability of agricultural systems concerns diverse groups of people. They emphasize different aspects of sustainability, from land steward- ship and family farms, to low external-input methods and food safety. Often there are two different themes: sustainability defined primarily in terms of resource conservation and profitability, and sustainability defined in terms of pressing social problems in the food and agriculture system.

Each of these perspec- tives has been illustrated by William Lockeretz1 and Miguel Altieri.2 In his review article on sustainability, Lockeretz documented primarily production-oriented components of sustainability. Altieri, on the other hand, has pointed out that concentration on only the technological aspects of sustainability results in, among other things, failure to distill the root causes of nonsustainability in agriculture. While sustainability efforts need to address both social and technical issues, they frequently overemphasize the technical, a problem we see originating in the way sustainability is often defined. Our purpose in this paper is to discuss concerns about current sustainability definitions and suggest a definition based upon a broader perspective.Among those working in sustainability there is often a feeling that we need to devote less time to talking about the meaning of sustainable agriculture and more time to implementing it. While this is an understandable position, especially for those directly involved in production agriculture, it also expresses a contradiction. How can we form an improved agricul- tural system if it has not yet been clearly conceptual- ized? Lockeretz1 queries, “Isn’t something backwards here?” and shows that, although there is a surge of interest in agricultural sustainability, “even its most basic ideas remain to be worked out.” There is no generally accepted set of goals for sustainable agricul- ture, and little agreement even on what and who it is we intend to sustain.3 Is it possible, for example, to both sustain production levels and preserve the natural environment? Who should we work to sustain – farmers, consumers, future generations – or should all of them be our priorities? Can we truly sustain one group without considering others? Without clarifying these goals the necessary changes in cultural, infra- structural, technological, and political arenas are difficult to negotiate. If we want sustainable agricul- ture to pursue a path differentiable from that of conventional agriculture, we need to explicitly state and gain some consensus on these goals. A clear, comprehensive definition of sustainability forms the necessary theoretical foundation for articulating sustainability goals and objectives.The emergence of agricultural sustainability reflects many people’s dissatisfaction with conventional agricultural priorities, especially the extent to which short-term economic goals have been emphasized over environmental and social goals. In response, a number of agricultural sustainability concepts have been developed under the terms “alternative,” “regen-erative,” “organic,” “low-input,” and “sustainable.” In this paper we refer to those definitions most com- monly espoused in the agricultural research commu- nity, definitions which are predominant in the literature and are used as the basis of sustainability programs.

We examine what priorities these defini- tions embody, how these priorities relate to those expressed in conventional agriculture,flood tray and how developing sustainability would benefit by broadening these priorities. Althoughsustainability definitions include a range of environmental, economic, and social characteris- tics, most focus somewhat narrowly on environment, resource conservation, productivity, and farm- and firm-level profitability. Charles Francis4 defines sustainable agriculture as a “management strategy” whose goal is to reduce input costs, minimize envi- ronmental damage, and provide production and profit over time. The National Research Council5 defines alternative agriculture as food or fiber production which employs ecological production strategies to reduce inputs and environmental damage while promoting profitable, efficient, long-term production. For Richard Harwood6 the three principles for sus- tainable agriculture are: “the interrelatedness of all parts of a farming system, including the farmer and his family; the importance of the many biological balances in the system; the need to maximize use of material and practices that disrupt those relation- ships.” According to Vernon Ruttan7 enhanced productivity must be a key factor in any sustainability definition. Rod MacRae, Stuart Hill, John Henning, and Guy Mehuys8 adopt a sustainability definition which emphasizes environmentally sound production practices. They note that sustainable agriculture today is characterized mainly by products and practices which minimize environmental degradation, although they also point out the potential to move beyond this restrictive application. In his review of sustainable agriculture definitions, Lockeretz1 stresses agronomic considerations although he does note the connection between changing production practices and associated socioeconomic transformations. Sustainabilitydefinitions such as the above focus on environmental conservation which is to be achieved through changing farm production practices without reducing farmers’ profits. They challenge some but not all of the assumptions that underlie agriculture’s nonsustainable aspects, generally neglecting questions of equity or social justice, or devoting little specific language to it. Altieri,2 for one, has challenged the narrowness of these approaches and their implicit assumption that taking care of the environmental, production, and economic aspects of sustainability automatically takes care of social aspects: “Intrinsic to these [agroecology] projects is the conviction that, as long as the proposed systems benefit the environment and are profitable, sustainability will eventually be achieved and all people will benefit.” Altieri has noted that without intervention on policy, research, and other levels, the more appropriate technology devel- oping in the name of sustainability will merely perpetuate and enhance the current differentiation between those members of society who benefit from agriculture and those who do not. Furthermore, the technology itself will not be developed and used unless we address the cultural, infrastructural, and political factors which shape how it is designed and implemented. These factors include scientific para- digms, fiscal policy, international trade, domestic commodity programs, and consumer preferences.Pursuing the dialogue on sustainability is essential in order to make visible the often invisible assump- tions and priorities which have governed agricultural research, policy, and business decisions leading to nonsustainable systems.