The Faculty of Civil and Environmental Engineering
The Stephen and Nancy Grand Water Research Institute
The 11th Dahlia Greidinger Memorial Symposium -2013
Advanced methods for investigating nutrient dynamics in soil and ecosystems 4-7 March, 2013 Technion-IIT, Haifa, Israel
Symposium Proceedings
Organized and Supported by:
The Dahlia Greidinger Memorial Fund and
BARD, The United States – Israel Bi-national Agricultural Research and Development Fund
Edited by: Uta Cheruti, David Myrold, Avi Shaviv
The 11th Dahlia Greidinger Memorial Symposium -2013
Advanced methods for investigating nutrient dynamics in soil and ecosystems 4-7 March, 2013 Technion-IIT, Haifa, Israel
Symposium Proceedings
Organized and Supported by:
The Dahlia Greidinger Memorial Fund and
BARD, The United States – Israel Bi-national Agricultural Research and Development Fund
Edited by: Uta Cheruti, David Myrold, Avi Shaviv
The 11th Dahlia Greidinger Memorial Symposium -2013
Advanced methods for investigating nutrient dynamics in soil and ecosystems
Local Organizing Committee Chair- Dr. A. Shaviv, Technion-IIT;
Prof. Emeritus J. Hagin, Technion-IIT;
Dr. S. Avrahami, Ruppin Academic Center;
Dr. Yael Dubovski, Technion-IIT;
Dr. V. Alchanatis, ARO, Volcani Center;
Dr. A. Angert, Hebrew Uni., Jerusalem;
Dr. Paricia Imas, ICL Fertilizers.
Scientific Committee In addition to the scientists listed above, the scientific committee included: Co-Chair Dr. David Myrold, OSU, USA;
Dr. Peter Bottomley, OSU, USA;
Dr. Barbara Cade-Menun, Agriculture and Agri-Food Canada.
Symposium coordinator Dr. Uta Cherui, CEE, IIT-Technion
Symposium link - http://dgsymp13.technion.ac.il/
Dahlia Greidinger International Symposium 2013
Table of Contents Symposium Committee
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Table of contents
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Preface
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Session 1: Global Aspects of Food Security Soils and Sustainability & Approaches for Better Understating Nutrient Processes in Terrestrial Ecosystems – Overviews 3 What Will Future Food Systems Look Like? Achim Dobermann
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Future Potash and Fertilizer Consumption to Sustain Agricultural Production: Possible Trends and Characteristics Hillel Magen and Patricia Imas 6 Advances in Understanding Nitrogen Transformations in Terrestrial Ecosystems Christoph Müller and Timothy Clough
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The Potential of Metagenomic Approaches for Understanding Soil Microbial Processes David D. Myrold, Lydia H. Zeglin and Janet K. Jansson
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Session 2: Advanced Tools to Investigate N Processes in Soil
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Changes in Relative Diffusivity Explain Soil N2O Flux Dynamics Nimlesh Balaine, Tim J. Clough, Mike H. Beare, Steve M. Thomas, Esther D. Meenken, James G. Ross
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In Situ Measurement of Ammonia Content in Soil Headspace Using Mid-Infrared Photoacoustic Spectroscopy Du Changwen, Wang Jiao, Zhou Zijun, Shen Yazhen, Zhou Jianmin
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Evaluating the links among carbon and nitrogen saturation: Theories to advance nutrient cycling science Michael Castellano and Daniel Andersen 76 Real Time Monitoring of N2O Emissions from Agricultural Soils using FTIR Spectroscopy Yael Dubowski, D. Harush, A. Shaviv, L. Stone and R. Linker
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Session 3: Microsensors for Investigating Soil Processes
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In situ measurements of diffusion and mass flow of nitrogen compounds in forest soils using microdialysis Torgny Näsholm, Olusegun Ayodeji Oyewole, Erich Inselsbacher 92 Distribution of Extracellular Enzymes in Soils: Spatial Heterogeneity and Determining Factors at Various Scales Petr Baldrian 97 Effects of Organo-Modification on the Interactions Between Soil Particles and Inorganic Cations as Revealed by Wien Effect Measurements Yujun Wang, Chengbao Li, Lingxiang Wang, Dongmei Zhou, Youbin Si, Shmulik P. Friedman 98 A Novel Method Combining FTIR-ATR Spectroscopy and Stable Isotopes to Investigate the Kinetics of Nitrogen Transformations in Soils Oz Kira, Raphael Linker and Avi Shaviv
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Session 4: Microbial Effects on Nitrogen Cycling
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Discriminating Soil Nitrification Contributions of Ammonia-Oxidizing Thaumarchaea and Bacteria using Aliphatic n-Alkynes Peter J. Bottomley, Anne E. Taylor, Andrew T. Giguere, Alix I. Gitelman and David D. Myrold 119 Determining The Contribution of Archaea to Nitrification in Acidic Soils Graeme Nicol
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Advance in Understanding the Ammonia-Oxidizing Bacteria Response to Change in Environmental Conditions Sharon Avrahami 137 Impact of Short-Term Acidification on Nitrification and Nitrifying Bacterial Community Dynamics in Soilless Cultivation Media Eddie Cytryn, Irit Levkovitch, Yael Negreanu, Scot Dowd, Sammy Frenk, and Avner Silber 154
Session 5: Factors Affecting Soil Microbial Activity
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Pore-Scale Hydrological Controls of Microbial Life in Soil Dani Or
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Microbial communities selected by agricultural management and the associated flux of greenhouse gases Thomas M. Schmidt, Vicente Gomez-Alvarez, Tracy Teal and Bjørn Østman 171
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Treated Wastewater Effect on Soil Microbial Community Ecology Sammy Frenk and Dror Minz
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Session 6: Tools to Investigate Phosphorus Reactions in Soils
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Solution 31P-NMR Spectroscopy of Soils from 2005-2013: A Review of Sample Preparation and Experimental Parameters Barbara Cade-Menun and Corey W. Liu
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Molecular Speciation of Phosphorus Present in Readily Dispersible Colloids from Agricultural Soils Jin Liu, Jianjun Yang, Xinqiang Liang, Yue Zhao, Barbara J. Cade-Menun and Yongfeng Hu 184 Phosphorus Forms in the Soil Profile Determined by 31P-NMR Spectroscopy as Influenced by Tillage Practices and P Fertilization Dalel Abdi, Barbara J. Cade-Menun, Noura Ziadi and Léon-Étienne Parent
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Phosphorus Transformations from Reclaimed Wastewater to Irrigated Soil: A 31P NMR Study Iris Zohar, Barbara Cade-Menun, Adina Paytan and Avi Shaviv 197 Oxygen Isotopes for Unraveling Phosphorus Transformations in the Soil–Plant System: A Review Federica Tamburini, Verena Pfahler, Christian von Sperber, Emmanuel Frossard and Stefano M. Bernasconi 198 Phosphate Stable Isotopes in Soils Alon Angert and Avner Gross
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Bacterially Mediated Removal of Phosphorus In a Non-Polluting Intensive Mariculture System Michael Krom, Jaap van Rijn, Arad Ben David, Ellery Ingall, Liane G. Benning, Santiago Clerici and Robert J.G. Mortimer 210
Session 7: Micro and Nano Systems to Investigate Biogeochemical
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Joining NanoSIMS and STXM/NEXAFS to visualize soil biotic and abiotic processes at the nano-scale Jennifer Pett-Ridge, Marco Keiluweit, Lydia H. Zeglin, Jeremy J. Bougoure, David D. Myrold, Markus Kleber, Peter K. Weber, and Peter S. Nico 213 Accelerated Hybridization of DNA Using Isotachophoresis and Application to Rapid Detection of Bacteria M. Bercovici, C.M. Han, J.C. Liao, J.G. Santiago 237
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Evaluating Nutrient Dynamics in Streams Using a Combination of Microelectrodes and an Online UV-Vis Spectrophotometer Shai Arnon, Arie Fox, Natalie de Falco, and Fulvio Boano 245 Sensor-Based Precision Fertilization for Field Crops Kenneth A. Sudduth, Hak-Jin Kim
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Remote Estimation of Nitrogen and Chlorophyll Contents in Maize at Leaf and Canopy Levels M. Schlemmer, A. Gitelson, J. Schepers, R. Ferguson, Y. Peng, J. Shanahan, D. Rundquist 279 Remote sensing for fertilization management in irrigated crops Victor Alchanatis
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Session 8: Carbon and C-N Interactions in Soils
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New Insights on C Cycling in Soils: Do Microbial Residues from Diverse Groups Contribute Differently to Stable Soil Carbon Maintenance and Accumulation? William R. Horwath, H. M. Throckmorton, J. A. Bird, L. Dane, M. K. Firestone 304 Relationships Between Carbon Sequestration and Nitrogen Cycling in a Semi-Arid Pine Forest Dan Yakir, Ilya Gelfand, Eyal Rotenberg 316 Using Food-Web Dynamics to Explain Variation in Carbon and Nitrogen Cycling Dror Hawlena
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Humic-like and Proteinaceous Components of Organic Matter in Aquatic and Soil Environments: Three Case Studies Analyzed With EEM+PARAFAC Methodology Mikhail Borisover, Yael Laor, Guy J. Levy 324
Session 9: Soil Organic Matter and Environmental Aspects
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Contribution of Carbonate Dissolution to CO2 Emission from Soils with Addition of Organic N Guy Tamir, Moshe Shenker, Hadar Heller, Paul Bloom, Pinchas Fine, Lilach Barsheshet, Guy Levy, Asher Bar-Tal 337 New Techniques for Nitrous Oxide Fluxes Research, Inter-Comparison, Validation, and Measurements of Nitrous Oxide Emissions from Agricultural Soils: The Role of Soil Carbon, Nitrogen, and Water Availability Ilya Gelfand, Mengdi Cui, Lei Tao, Kang Sun, Terenzio Zenone, Jim Tang, Jiquan Chen, Mark A. Zondlo and G. Philip Robertson 343
Dahlia Greidinger International Symposium 2013
Contaminants of Emerging Concern in the Agro-Environments: Fate and Processes Benny Chefetz, Rotem Navon, Adi Maoz, Daniella Harush, Tamar Mualem, Myah Goldstein and Moshe Shenker 356 Use of Stable Isotopes to Study the Fate of Organic Pollutants in Soils Anat Bernstein, Faina Gelman, Eilon Adar, Harald Lowag, Willibald Stichler, Rainer U. Meckenstock, Sharon Sagi-Ben Moshe5, Ofer Dahan3, Noam Weisbrod, and Zeev Ronen 360 Irreversible Impacts of Micro-Pollutants on Natural Soils Ishai Dror, Bruno Yaron, Brian Berkowitz
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Summary of Panel Discussion
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Summary of the Collection of Papers in Soil Science Society of America Journal 386
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Dahlia Greidinger International Symposium 2013
PREFACE The symposium on Advanced Methods for Investigating Nutrient Dynamics in Soils and Ecosystems addressed knowledge gaps and R&D priorities related to the need to quantify nutrient dynamics and reaction mechanisms, particularly those of nitrogen and phosphorus in crop/food production systems. Special emphasis was placed on interactions with organic loads/wastes and under possible global changes (warming and/or rainfall/water scarcities), and the urgent need to assure sustainable crop/food production with minimal environmental threats. There was a focus on advanced and novel tools and approaches (including those developed in other disciplines) that enable real time investigation and quantification of processes and options to observe and model changes at various scales (from nano/micro up to field scale). Tools and methods leading to improved and sustainable utilization of nutrients were discussed as well.
Four themes were explored during nine oral sessions and one poster session that were held over the course of four days: Global Aspects of Food Security, Advanced Tools/Approaches to Investigate N or P Dynamics in Soil, Soil Organic Matter Dynamics, and Advanced Sensors for Sustainable Utilization of Nutrients in Soil Systems. Presentations about the importance of sustainable soils to food security provided the foundation for the symposium and were followed by two overview presentation that introduced the three scientific and technical themes. Four sessions were devoted to new approaches for understanding N and P cycling in soils, two sessions focused on organic matter and interactions between C and N, and two sessions reported on advances in measurement methods at multiple scales. The proceedings contains reports based mainly on the symposium talks and selected posters presented at the conference. A selection of manuscripts was also be published as a special section in the Soil Science Society of America Journal (Volume 78, Issue 1, JanuaryFebruary 2014; open access). Abstracts of the manuscripts in Volume 78 of SSSAJ are placed in the proceedings book followed by a link to their open access in SSSAJ.
At the end of this book there is a summary of the final panel discussion highlighting several of the important findings and main points stressed in the presentations, as well as subjects that require further investigation or issues that should serve as key topics for
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future research. This is followed by a brief introduction of the selected manuscripts, which were published by SSSAJ.
The symposium generously supported by BARD and the Dahlia Greidinger Memorial Fund, which for the 11th time made this important scientific meeting possible. Thanks are also due to the Grand Water Research Institute – GWRI and the Faculty of Civil and Environmental Engineering at the Technion, ICL Fertilizers Ltd. and Fertilizers and Chemicals Ltd., who contributed time, effort and resources to support this event. Special thanks are given to members of the Scientific Committee, the staff of the Department of Environmental Engineering, Water and Agriculture, and particularly to Dr. Uta Cheruti, who efficiently coordinated all the administrative arrangements and took responsibility over editing and publishing the Calls, The Book of Abstracts, and finally these Proceedings.
In the name of the organizing committee,
Avi Shaviv and David Myrold
Dahlia Greidinger International Symposium 2013
Session 1: Global Aspects of Food Security Soils and Sustainability & Approaches for Better Understating Nutrient Processes in Terrestrial Ecosystems – Overviews
WHAT WILL FUTURE FOOD SYSTEMS LOOK LIKE? Achim Dobermann International Rice Research Institute (IRRI), Los Baños, Philippines.
The demand for food will greatly increase due to rising incomes and an additional two or three billion people to feed. Investing in agriculture is also one of the most effective strategies for achieving critical post-2015 development goals related to poverty and hunger, nutrition and health, education, economic and social growth, peace and security, and preserving the world’s environment. To achieve the new post-2015 global development goals, rising food yields must be decoupled from unsustainable utilization of water, energy, fertilizers, chemicals and land. This can only be done through a multifaceted agro-ecological intensification of agriculture and food systems. The specific policies, business models and technologies for implementing such an agro-ecological intensification depend on the social and biophysical contexts in which farmers operate. Different solutions are required for large farms with good market access and high input use, small farms with good market access and high input use, or small farms with low market access and low input use. The domestic private sector – composed of millions of farmers and other local business – is by far the biggest investor in agriculture. It must be central to any investment and policy strategy that enables the development and widespread adoption of new solutions for more efficient, sustainable food production systems. Structural transformations in the agricultural sector are already emerging that will change the way food will be grown in the future. Many of these changes are driven by
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processes such as a declining share of agriculture in gross domestic product and employment, rural to urban migration, the rise of an industrial and service economy, and demographic transitions from high rates of birth and death to low rates. Land is scarce and input costs are rising, requiring further increases in productivity as well as greater efficiency of labor, water, fertilizer and energy. This also provides an incentive for more skilful, more precise agriculture through which one can also better adapt to the environment, or even control parts of it. Traditional smallholder farm management will more and more be supplemented or replaced with outsourcing of farming operations or the formation of small and medium-size agribusiness enterprises, including contract farming. Value chains for major agricultural commodities will become more tightly integrated because processors and consumers demand more information and control over how food is being produced, with supermarket chains playing a particularly important role. Farmers will increasingly turn to the private sector as a source of new technologies and information, but also as a direct buyer of their produce, requiring agricultural raw materials with higher standards. Access to interactive, locally tailored information will be increasing, leading to much wider rural communication networks than ever before. These mega trends will provide new opportunities for the development, adaptation and adoption of technologies that could enable an ecological intensification of cropping systems, a more eco-efficient way of food production at high levels of productivity and resource use efficiency and with lower risk. Agricultural science needs to be re-oriented towards that. We need to anticipate what is needed by farmers and others in the value chain 10 or 20 years from now, and we need to take full advantage of such new opportunities for agronomic research. Increasing complexity in the demand and supply of food, feed and fuel at local, regional and global scales asks for tailor-made solutions. Agronomists must lead such efforts and thus help shaping a new image for modern agriculture. The grand challenge for agronomists lies in developing cropping systems and crop management technologies that allow operating at the upper limits of yield and resource efficiency, yet are stable in yields, sustainable and environmentally sound. We have already seen some amazing success stories for large yield and efficiency increases in recent years that demonstrate what can be achieved. Hence, agronomists should critically re-evaluate their research and extension strategies and approaches. They should look ahead and focus their efforts on new technology solutions for tactical management of crops and crop rotations at greater precision than ever before. Foresight
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is needed to avoid that the world runs into another food crisis. Hence, in addition to investing in early solutions or technologies that are likely to become available in the next 5-10 years, strategic investments in groundbreaking research are needed to potentially make quantum leaps in the performance of agricultural systems beyond that.
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FUTURE POTASH AND FERTILIZER CONSUMPTION TO SUSTAIN AGRICULTURAL PRODUCTION: POSSIBLE TRENDS AND CHARACTERISTICS Hillel Magen1 and Patricia Imas2 1International 2ICL
Potash Institute (IPI), Horgen, Switzerland; Fertilizers, Beer Sheeva, Israel.
Abstract During the last 50 years, global production of oil crops, vegetables, sugarcane, fruit and cereals increased by 6.5, 4.3, 3.8, 3.5 and 2.8 times respectively, the additional production achieved mainly via intensification. Nitrogen (N), phosphorus (P2O5) and potassium (K2O), played a major role in this intensification process and their use (from 1961-2010) increased by 8.7, 3.7 and 3 times respectively. In China, increases in productivity over the last few decades have resulted primarily from increases in fertilizer use, mechanization and irrigation. By contrast, limited use of fertilizers in subSaharan Africa, (less than 10 percent of the world average), is a major cause for low yields in this region. Nutrient deficiencies are widespread. However, in some regions there is an overuse of N and P, which does not contribute to crop productivity and leads to nutrient imbalances, inefficiency and environmental damage. Mueller et al. (2012) estimate that globally, for farmers to achieve 75 percent attainable yield (current level is approximately 50 percent), consumption of N, P and K will need to be adapted by +9, -2 and +34 percent respectively. Clearly, according to this analysis, low K application is a serious limiting factor for increased productivity. Estimates of additional crop production required by 2050 vary from 50 to 110 percent. Accordingly, nutrient demand is projected to increase at the same level, yet respond to efficiency and improved management practices as well as environmental stewardship. Relatively little research has estimated how the demand for nutrients will change by 2050. While the future demand of N varies between 40 to 100 percent, that of P and K is similar to the overall nutrient demand increase, projected at about 50 percent. A more detailed analysis using partial nutrient balance (PNB) for K, show that K use is projected to increase by 47-55 percent. The continued increase in the production of
Dahlia Greidinger International Symposium 2013
vegetables, sugarcane, oil crops (e.g. soybean) and maize, will account for much of this projected increased.
Nutrient use 1960-today and levels of deficiency: Driven by population growth and improved diets, global crop production has steadily increased. Over the last 50 years (1960-today) global population has about doubled and cereal production has increased by almost three-fold. This was achieved with little increase in the arable land under cultivation, but with a doubling of land under irrigation (Fig. 1; FAOSTAT). During the same time period, fertilizer use increased: N consumption increased dramatically by more than eight-fold, while that of P and K increased by about three-fold (FAOSTAT). In addition to increased fertilizers use, the use of other agro inputs, such as irrigation water and pesticides, contributed to the marked increase in global production of food crops (Tilman et al., 2002). The link between fertilizer use and agricultural production is well established. Smil (2002) estimated that during the last 50 years N fertilizers enabled a 40 percent increase in per capita consumption. Stewart et al., (2005) estimated that the average percentage of yield attributable to fertilizer ranged from about 40 to 60 percent in the USA and UK, but tended to be even higher in the tropics. Mineral fertilizers as well as manures and leguminous crops have played a key role in increasing agricultural intensification globally (Foley et al., 2011). In China, increases in productivity have been mainly a consequence of an increase in fertilizer use (Dyson, 1999) and fertilization, mechanization and irrigation (Jingzhu Zhao et al., 2008).
Shortages of fertilizer, deficiency of N fertilizer and depletion of soil fertility have been identified as major production constraints in major farming systems in Asia and Africa (Waddington, 2010). Nutrient deficiencies which limit yield potential are widespread (The Royal Society, 2009; Mueller et al., 2012), but at the same time overuse of N and P leads to nutrient imbalances and inefficiencies in regions such as China (Mueller et al., 2012).
The stagnation of some productive cropping systems in Asia is related to unbalanced application of fertilizers, especially that of K (Ladha et al., 2003). Globally, it is estimated that in order to increase the level of yields of the major grain crops from their
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current level (approx. 50 percent of attainable yield) to reach a level of 75 percent of attainable yield potential, the application of N, P and K will need to be adapted by +9, -2 and +34 percent, respectively (Mueller et al., 2012). According to this analysis, the current low K application rate is a serious limiting factor for increased productivity, which if increased will boost yields. Increasing K applications will also improve the balance between N and K which will improve the capacity of the plant to exploit N, leading to a higher yield benefit from applied N (Milford and Johnston, 2007; The Royal Society, 2009).
Global nutrient consumption has increased from approximately 10 million mt for N, P2O5 and K2O in 1961, to more than 100, 40 and 25 million mt in 2010 (Fig. 2). This increase was disrupted severely by the fall of the Soviet Union (USSR) in the late 1980s early 1990s. Two other events have impacted the growth of nutrient consumption: the energy crises of the early 1970s and the 2008 financial crisis. Measuring the average consumption growth rates of N, P and K over 13 years (1994-2007) - a period of steady growth starting after the recovery from the fall of the USSR until the financial crisis of 2008 - offers a better entry point to understanding the growth process of the industry than measuring growth rates from 1961 to 2010. From 1994-2007, the growth rate of K consumption (3.1 percent pa) was much higher than that of N and P (2.4 and 2.1 percent, respectively). We believe that this is explained by the large increase in the production of crops, such as oil seeds (mostly soybean and oil palm) and horticultural crops (vegetables and fruits), that have a higher K demand than cereals, reflecting a shift in changing global diets. China has seen a shift in cropping patterns and a large increase in vegetable production, in Brazil soybean production has increased significantly, and growth of oil palm production has been strong in Indonesia and Malaysia. However, the increase in vegetable and fruit production in India has had a lesser impact (Magen and Imas, 2007). Gaps in crop productivity: Agricultural production varies greatly between regions. The gap between developing and developed regions is particularly large (Table 1). For example, maize production in Africa reaches only 7 percent yield potential, compared to 47 percent in the US. These gaps are mainly the result of better management practices used by farmers in developed countries.
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The gap between attainable yield - which is achieved using current technology and management techniques (Mueller et al., 2012) - and actual productivity for various crops is significant (Table 2). Mozambique, for example, achieves only 28 percent of attainable yield, while in countries with well managed systems, such as the US and Brazil, average productivity is similar to attainable yield. In countries like China, India and Ukraine, there is a large scope for improvement in productivity (Table 2) if current technologies and management techniques are more widely adopted.
Another factor affecting productivity is irrigation. Rosegrant et al. (2002) show that while total rainfed cereal production on average is about 30 percent higher than irrigated production, irrigated land is twice as productive. In China, for example, it is estimated that 30 percent of the land (which is irrigated), provides 70 percent of the food (Fusuo, personal communication). Lobell et al. (2009) have calculated the gap to yield potential in rainfed crops to be 50 percent, suggesting significant potential for improvement.
Mueller et al. (2012) identified fertilizer use, irrigation and climate as the major causes for yield variability, with high fertilizer application rates typically occurring in highincome regions as well as in some rapidly developing countries. While ‘attainable yield’ is lower than the biophysical ‘potential yield’, it has the advantage of benchmarking realistic, achievable yield goals. Improvements in productivity can be achieved through plant breeding, and improved crop management, tillage, fertilization, weed and pest control, harvesting, and water use (Borlaug, 2007). Improving soil fertility and breeding crops with better tolerance for stresses (St. Clair and Lynch, 2010) will also help. But while there are ample of ways for improvement, many of these are closely related to farmers’ knowledge. If high commodity prices prevail, providing incentive to farmers, better and more affordable agro inputs are made available and more effective extension tools are used - all these enable farmers to produce more effectively and raise productivity. Future needs for food: Estimations for the amount of additional crop production that will be required in the future vary. Dyson (1995), at a time when the impact of biofuels on cereal production was unclear, assumed that population growth would be the main determinant for cereal demand to 2020. Tilman et al. (2011) projected a 100-110 percent increase (2005-
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2050), driven mostly by the increase in GDP per capita and consequently the per capita caloric demand. This is much higher than FAO’s prediction (Alexandratos, 2009) of 70 percent for the same period, who also emphasize that any change in biofuel production may change the figure significantly.
The agricultural sector will be required to produce more food for more people, which will require food production to double within 40 years to meet this demand. If the global population was to remain at approximately 9 billion people, and a reasonable per capita calorie intake was achieved by 2050, the period until 2050 would likely be the last period that dramatic food production increases were seen. However, the next phase of growth will need to increase sustainable crop and animal production practices (including land, water and nutrient use efficiency), maintain and restore soil fertility, and provide ecosystem services (Tilman et al., 2002).
With limited land expansions forecast (from 1.592 billion ha in 2005/07 to 1.661 billion ha in 2050; Alexandratos and Bruinsma, 2012), increased crop productivity will have to emerge from increases in production in regions with low yields and where there is ample scope for improvements. Mueller et al. (2012) revealed that on average world productivity in 2008 (data of Monfreda et al., 2008) for many crops is only 50 percent of attainable yield (Table 3). The authors refer to ‘attainable yields’ as those that can be achieved using ‘current technology and management techniques’, thus comparing these with regions that have a similar climate may provide a more accurate estimate of achievable yield increases. When comparing FAO projections for 2050 production levels (Alexandratos and Bruinsma, 2012), and attainable yield (Mueller et al., 2012) of various crops (Table 3), it appears that in most cases reaching 50 to 100 percent attainable yield will meet the target. This suggests that a significant portion of future demand of food can be met by simply adopting better management practices in low productivity regions.
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Future nutrient demand: Assessments Estimations of future nutrient demand have been assessed by various researchers, with reference to meeting population and crop demand (Tenkorang and Lowenberg-DeBoer, 2009; Alexandratos and Bruinsma, 2012), to efficiency and improved management practices (Dobermann and Cassman, 2005; Tilman et al., 2011) and environmental stewardship (Tilman et al., 2001). In these assessments, N captures most of the attention, for a few reasons: 1) N is the yield builder of food crops, especially of crops that provide protein (excluding leguminous crops), and insufficient amounts will jeopardize plant performance, and consequently food security; 2) when not efficiently used, the effect of reactive N on the environment is negative; and 3) properly managed N application at farm level offers a significant improvement in efficiency of use, as compared to the application management of P and K, where the degrees of efficiency that can be improved is less.
Current (2012) and future nutrient consumption is summarized in Table 4. The various projections differ significantly from each other: according to Alexandratos and Bruinsma (2012), the increase in N consumption by 2050 will be ~40 percent, while others (Tilman et al., 2001; 2011) project an increase of ~100 percent (Table 4). Alexandratos and Bruinsma (2012) project that by 2050 P and K consumption will increase by ~40 percent while the total amount of N+P2O5+K2O being used will be 262.9 million mt, representing an increase by 2050 of 47.5 percent over 2012 consumption levels. Tenkorang and Lowenberg-DeBoer (2009), in their assessment for 2030, however, project a lower amount of 223.1 million mt, which represents a 25 percent increase over 2012 levels. Clearly, the basis for these calculations is different, and hence results deviate significantly. Potassium partial nutrient balance (PNBK) Nutrient balance or audit calculations are commonly used to assess nutrient requirement and fertilization rates (Sheldrick et al., 2002 and 2003; Roy et al., 2003; Buresh et al., 2010; Spiess, 2011) as well as its effect on sustainability and impact on the environment (Eltun et al., 2002; Vitousek et al., 2009). Nutrient balance is another way to look at future requirements of nutrients, by assessing the ‘takeoff’ of nutrients through the removal of the harvested part from the field and adjusting fertilizer rates accordingly
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(Witt et al., 2007). Partial nutrient balance (PNB) only takes into account easily measured inputs and outputs, for example mineral and organic fertilizers as inputs, and harvested products and crop residues as outputs (Roy et al., 2003). In this manner, PNB = 1 is when offtake is fully compensated by nutrient input, and PNB
