Peter M. Vitousek

Integrated reactive nitrogen budgets and future trends in China

Significance China is the world’s largest producer of reactive nitrogen (Nr), and Nr in the form of synthetic fertilizer has contributed substantially to increased food production there. However, Nr losses from overuse and misuse of fertilizer, combined with industrial emissions, represent a serious and growing cause of air and water pollution. This paper presents a substantially complete and coherent Nr budget for China and for 14 subsystems within China from 1980 to 2010, evaluates human health/longevity and environmental consequences of excess Nr, and explores several scenarios for Nr in China in 2050. These scenarios suggest that reasonable pathways exist whereby excess Nr could be reduced substantially, while at the same time benefitting human well-being and environmental health. Reactive nitrogen (Nr) plays a central role in food production, and at the same time it can be an important pollutant with substantial effects on air and water quality, biological diversity, and human health. China now creates far more Nr than any other country. We developed a budget for Nr in China in 1980 and 2010, in which we evaluated the natural and anthropogenic creation of Nr, losses of Nr, and transfers among 14 subsystems within China. Our analyses demonstrated that a tripling of anthropogenic Nr creation was associated with an even more rapid increase in Nr fluxes to the atmosphere and hydrosphere, contributing to intense and increasing threats to human health, the sustainability of croplands, and the environment of China and its environs. Under a business as usual scenario, anthropogenic Nr creation in 2050 would more than double compared with 2010 levels, whereas a scenario that combined reasonable changes in diet, N use efficiency, and N recycling could reduce N losses and anthropogenic Nr creation in 2050 to 52% and 64% of 2010 levels, respectively. Achieving reductions in Nr creation (while simultaneously increasing food production and offsetting imports of animal feed) will require much more in addition to good science, but it is useful to know that there are pathways by which both food security and health/environmental protection could be enhanced simultaneously.

Evidence for a Historic Change Occurring in China

Xuejun Liu,*,† Peter Vitousek,‡ Yunhua Chang, Weifeng Zhang,† Pamela Matson, and Fusuo Zhang† †College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China ‡Department of Biology, Stanford University, Stanford, California, 94016, United States Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China School of Earth, Energy and Environment, Stanford University, Stanford, California 94305, United States

Variation in Rapa Nui (Easter Island) land use indicates production and population peaks prior to European contact

Significance Our paper evaluates a long-standing debate and examines whether the prehistoric population of Rapa Nui experienced a significant demographic collapse prior to European contact in AD 1722. We have used dates from hydrated obsidian artifacts recovered from habitation sites as a proxy for land use over time. The analysis suggests region-specific dynamics that include the abandonment of leeward and interior locations. These temporal land-use patterns correlate with rainfall variation and soil quality. This analysis demonstrates that the concept of “collapse” is a misleading characterization of prehistoric human population dynamics. As a result, we see our approach as useful in the study of other prehistoric societies for which a sudden demographic collapse has been proposed in prehistory. Many researchers believe that prehistoric Rapa Nui society collapsed because of centuries of unchecked population growth within a fragile environment. Recently, the notion of societal collapse has been questioned with the suggestion that extreme societal and demographic change occurred only after European contact in AD 1722. Establishing the veracity of demographic dynamics has been hindered by the lack of empirical evidence and the inability to establish a precise chronological framework. We use chronometric dates from hydrated obsidian artifacts recovered from habitation sites in regional study areas to evaluate regional land-use within Rapa Nui. The analysis suggests region-specific dynamics including precontact land use decline in some near-coastal and upland areas and postcontact increases and subsequent declines in other coastal locations. These temporal land-use patterns correlate with rainfall variation and soil quality, with poorer environmental locations declining earlier. This analysis confirms that the intensity of land use decreased substantially in some areas of the island before European contact.

Strengthening Agronomy Research for Food Security and Environmental Quality

A faces great challenges to ensure global food security by increasing yields while reducing environmental costs. This linked production/environment challenge is particularly stark in rapidly developing economies, such as China and India; it is here that the potential yields of agriculture must be raised close to their biophysical potential, here that gaps between potential and realized yields must be minimized, and here that already-intolerable levels of environmental degradation must be reduced. China has 124 million ha of farmland with which to feed over 1.37 billion people (versus 165 million ha and 311 million people in the U.S.), and its air and water are so polluted by industry and agriculture that China now experiences 750 000 premature pollution-caused deaths per year. Increasing crop yields toward limits of feasibility while at the same time saving many lives represents an immediate, compelling scientific challenge as well as an extraordinary contribution to human well-being. Possible solutions to global agricultural challenges have been discussed widely in the scientific community; they include crop breeding through biotechnology and high-technology precision agriculture−which together have made substantial contributions to the high-yielding and relatively resource-efficient cropping systems of North America and Western Europe. Can these relatively efficient agricultural systems provide a path toward similar successes in rapidly developing economies? Recent agricultural research in developed countries has focused upon agricultural biotechnology, much of it in the private sector. This approach has contributed to the high yield ceiling in U.S. maize (Figure, 1A); here the yield ceiling is defined as yields achieved under optimum management in wellcontrolled experimental systems). China too has supported crop breeding, including a recent focus on newer methods in biotechnology. The similarity in maize yield ceiling between the U.S. and China illustrates the long-term success of this approach. Maize cropping systems in the U.S. have a relatively narrow yield gap (the difference between yield ceiling and the actual yield achieved by farmers), contributing to their high overall yields (Figure 1B). The yield gap in China is much larger (Figure 1C), and increased agronomic inputs cannot close this gap, because China already has gone past a point of diminishing returns in the case of fertilizer applications in particular (Figure 1D,E). Chinese systems now yield only 35 kg of grain per kg of N (versus 67 kg kg−1 in the U.S.); they lose much more N to the environment, with substantial and growing environmental costs (621 versus 231 kg CO2 eq per Mg grain for China and U.S., respectively) (Figure 1F). Can China and other rapidly developing countries increase yields (as they must) by following paths similar to the U.S. and Europe? U.S. agriculture has benefited from relatively high, long-term agricultural research and development (R&D) investment. Agricultural R&D intensities have long remained >2%, expressed as the percentage of agriculture R&D spending (public and private) to agricultural gross domestic product. In the past this investment supported basic agronomy research on regional scales including crop physiology, soil biogeochemistry, and integrated crop-soil management−in addition to crop biotechnology. This investment has led to crops resistant to various biotic and abiotic stresses, which become more serious under changing climate, managed with high-technology precision agriculture. In turn these developments, together with large-scale farms and well educated farmers, drive the narrow yield gaps and relatively efficient nutrient use characteristic of US agriculture. In contrast to the U.S., agriculture in China and India is managed by more than one hundred million small-holder farmers, often with low levels of education a situation that contributes to substantial variation in both crop yield and fertilizer use among farmers. Under these circumstances, many promising crop varieties fail to increase yields in practice. For

Restoring people and productivity to Puanui: challenges and opportunities in the restoration of an intensive rain-fed Hawaiian field system

Prior to European contact, Hawaiian cultivators developed and sustained large rain-fed field systems based on sweet potato (Ipomoea batatas) and other crops. However, these intensive systems largely were abandoned in the 19th century, and there is little knowledge of how they functioned. Since 2008, we have worked to restore people and production to one such rain-fed field system at Puanui in leeward Kohala on the Island of Hawai’i using traditional knowledge, local knowledge, and experiments to understand how such systems functioned and to provide an educational and cultural resource to local communities. We encountered both climatic and biotic challenges to using traditional knowledge for restoring agricultural production. Climatically, there has been a recent drying trend and a severe 6-yr drought. Biotically, a wide range of weeds, pests, and diseases have been introduced to Hawaii since European contact. Experimental studies of cultivation practices demonstrated that rock mulching, a traditional practice, led to significantly greater yields of sweet potato than did alternative methods. More than 3000 students and community members have participated in the restoration effort and have contributed local and traditional knowledge in the process.

Combining spectroscopic and isotopic techniques gives a dynamic view of phosphorus cycling in soil

Current understanding of phosphorus (P) cycling in soils can be enhanced by integrating previously discrete findings concerning P speciation, exchange kinetics, and the underlying biological and geochemical processes. Here, we combine sequential extraction with P K-edge X-ray absorption spectroscopy and isotopic methods (33P and 18O in phosphate) to characterize P cycling on a climatic gradient in Hawaii. We link P pools to P species and estimate the turnover times for commonly considered P pools. Dissolved P turned over in seconds, resin-extractable P in minutes, NaOH-extractable inorganic P in weeks to months, and HCl-extractable P in years to millennia. Furthermore, we show that in arid-zone soils, some primary mineral P remains even after 150 ky of soil development, whereas in humid-zone soils of the same age, all P in all pools has been biologically cycled. The integrative information we provide makes possible a more dynamic, process-oriented conceptual model of P cycling in soils.Our understanding of phosphorus (P) cycling in soils, a basis for many ecosystem services, has been limited by the complexity of P forms and processes. Here the authors use spectroscopic and isotopic techniques to estimate turnover times of P pools and tease apart biologically-driven and geochemically-driven P fluxes.

Grassland ecology: Complexity of nutrient constraints

Grasslands account for as much as one-third of the net primary production on land. Results from a network of experiments carried out on five continents suggest that two or more nutrients often constrain the productivity of these globally significant ecosystems.