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Abstract. Ashfall from volcanic eruptions endangers crop production and food security
while jeopardising agricultural livelihoods. As populations in the vicinity
of volcanoes continue to grow, strategies to reduce volcanic risks to and
impacts on crops are increasingly needed. Current models of crop
vulnerability to ash are limited. They also rely solely on ash thickness (or
loading) as the hazard intensity metric and fail to reproduce the complex
interplay of other volcanic and non-volcanic factors that drive impact.
Amongst these, ash retention on crop leaves affects photosynthesis and is
ultimately responsible for widespread damage to crops. In this context, we
carried out greenhouse experiments to assess how ash grain size, leaf
pubescence, and humidity conditions at leaf surfaces influence the retention
of ash (defined as the percentage of foliar cover coated with ash) in tomato
and chilli pepper plants, two crop types commonly grown in volcanic regions.
For a fixed ash mass load (∼570 g m−2), we found that
ash retention decreases exponentially with increasing grain size and is
enhanced when leaves are pubescent (such as in tomato plants) or when their surfaces are
wet. Assuming that leaf area index (LAI) diminishes with ash retention in
tomato and chilli pepper plants, we derived a new expression for predicting
potential crop yield loss after an ashfall event. We suggest that the
measurement of crop LAI in ash-affected areas may serve as an impact metric.
Our study demonstrates that quantitative insights into crop vulnerability
can be gained rapidly from controlled experiments. We advocate this approach
to broaden our understanding of ash–plant interactions and to validate the
use of remote sensing methods for assessing crop damage and recovery at
various spatial and time scales after an eruption.

This book analyzes potential yields of six major food crops - rice, wheat, maize, potato, soybean and rapeseed worldwide using both qualitative and quantitative approaches to study both Chinas and global food security under climate change. Firstly, it reviews previous studies on potential yields of rice, wheat, maize, potato, soybean and rapeseed worldwide to provide a detailed information of studying on Chinas and global food security based on the products supply and demand of these crops. Secondly, average and top (national) yields of rice, wheat, maize, potato, soybean and rapeseed since 1961 on global scale are employed to analyze their temporal and spatial variation trends and potential limits. Thirdly, the effects of global warming in climate change on both average and top yields of rice, wheat, maize, potato, soybean and rapeseed since 1961 at global level are analyzed using regression model, and their differences between average and top yields among these crops are identified and compared. Fourthly, the yields and per capita quantity of rice, wheat, maize, potato, soybean and rapeseed in major producer-countries and the world are analyzed to assess the situation and trend of international trade for the products of these crops, respectively. Fifthly, potential yields of rice, wheat, maize, potato, soybean and rapeseed worldwide by 2030 are projected using both trend-regressed models and ARIMA models to estimate the per capita quantity of these crops based on the projection of world population and assess the status of Chinese and global food security in that future. Finally, it provides policy implications and advice on food security for China and the world directing food production by 2030 under climate change.

Intro -- Acknowledgements -- Contents -- 1 Introduction -- 1.1 Background of Study -- 1.2 Literature Review -- 1.2.1 Potential Yields of Six Major Food Crops in the World -- 1.2.2 Chinese and Global Food Security -- 1.2.3 Summary of Literature Review -- 1.3 Structural Logic of Book -- References -- 2 Analyzing Average and Top (National) Yields of Six Major Food Crops in the World -- 2.1 Analyzing Average and Top (National) Yields of World Rice -- 2.1.1 Variation Trends of Average and Top (National) Yields of World Rice -- 2.1.2 Distribution of Top (National) Yields of World Rice -- 2.2 Analyzing Average and Top (National) Yields of World Wheat -- 2.2.1 Variation Trends of Average and Top (National) Yields of World Wheat -- 2.2.2 Distribution of Top (National) Yields of World Wheat -- 2.3 Analyzing Average and Top (National) Yields of World Maize -- 2.3.1 Variation Trends of Average and Top (National) Yields of World Maize -- 2.3.2 Distribution of Top (National) Yields of World Maize -- 2.4 Analyzing Average and Top (National) Yields of World Potato -- 2.4.1 Variation Trends of Average and Top (National) Yields of World Potato -- 2.4.2 Distribution of Top (National) Yields of World Potato -- 2.5 Analyzing Average and Top (National) Yields of World Soybean -- 2.5.1 Variation Trends of Average and Top (National) Yields of World Soybean -- 2.5.2 Distribution of Top (National) Yields of World Soybean -- 2.6 Analyzing Average and Top (National) Yields of World Rapeseed -- 2.6.1 Variation Trends of Average and Top (National) Yields of World Rapeseed -- 2.6.2 Distribution of Top (National) Yields of World Rapeseed -- 2.7 Summary of this Chapter -- Reference -- 3 Potential Limits of Six Major Food Crops' Yields Worldwide -- 3.1 Potential Limit of World Rice Yield.

Abstract This study aimed to measure yield gaps and the potential gains in production and revenue from mitigating these gaps for the four main food crops in Brazil and worldwide (rice, maize, soybean, and wheat). Based on the concepts of potential yield, observed yield, and yield gap, and data from the 2017 Brazilian Agricultural Census, a parameter for the potential yield of each crop was defined at the microregional level, and yield gaps and potential gains in production and revenue resulting from reducing these gaps were measured. The results showed that reducing yield gaps in Brazil for the analyzed crops may lead to an expansion in supply of these food products by almost 10% of the volume achieved in 2017, or the equivalent of 19 million tons. The greatest potential gains in yield and production were found for maize, 13.2%, valued at about US$ 1.7 billion (at 2017 prices). Soybean showed the lowest potential for gains in percentage terms (5.5%), but these gains would represent US$ 1.8 billion, the highest value among the crops analyzed.

A survey data of 600 dairy farms obtained from the largest dairy cluster in Pakistan's Punjab was used to provide new evidence on the yield gap and yield improvement potential of dairy farms producing milk and meat. The yield gap was estimated by the frontier-based input distance function analysis. The results indicated that a large yield gap exists in the sample where an average dairy farm has a yield improvement potential of 55 percent. By closing the gap, an average dairy farm can increase yearly production of fat-corrected milk (FCM) by 120,036 kg and non-milking herd for meat by 25 heads. The evidence also shows that small farms (< 25 herd-size) are technically more efficient than those of medium (26 ≤ herd-size ≤ 50) and large farms (> 50 herd-size). The study finds clear evidence of an efficiency boost for keeping a higher share of non-milking to milking herd, a greater proportion of exotic cows to local breeds, and a higher farm-gate price of milk, which can all trigger efficiency gains. Policymakers hence have room to provide adequate intervention strategies that can help in enhancing efficiency.

Europe accounts for around 20% of the global cereal production and is a net exporter of ca. 15% of that production. Increasing global demand for cereals justifies questions as to where and by how much Europe's production can be increased to meet future global market demands, and how much additional nitrogen (N) crops would require. The latter is important as environmental concern and legislation are equally important as production aims in Europe. Here, we used a country-by-country, bottom-up approach to establish statistical estimates of actual grain yield, and compare these to modelled estimates of potential yields for either irrigated or rainfed conditions. In this way, we identified the yield gaps and the opportunities for increased cereal production for wheat, barley and maize, which represent 90% of the cereals grown in Europe. The combined mean annual yield gap of wheat, barley, maize was 239 Mt, or 42% of the yield potential. The national yield gaps ranged between 10 and 70%, with small gaps in many north-western European countries, and large gaps in eastern and south-western Europe. Yield gaps for rainfed and irrigated maize were consistently lower than those of wheat and barley. If the yield gaps of maize, wheat and barley would be reduced from 42% to 20% of potential yields, this would increase annual cereal production by 128 Mt (39%). Potential for higher cereal production exists predominantly in Eastern Europe, and half of Europe's potential increase is located in Ukraine, Romania and Poland. Unlocking the identified potential for production growth requires a substantial increase of the crop N uptake of 4.8 Mt. Across Europe, the average N uptake gaps, to achieve 80% of the yield potential, were 87, 77 and 43 kg N ha −1 for wheat, barley and maize, respectively. Emphasis on increasing the N use efficiency is necessary to minimize the need for additional N inputs. Whether yield gap reduction is desirable and feasible is a matter of balancing Europe's role in global food security, farm economic objectives and environmental targets.

Europe accounts for around 20% of the global cereal production and is a net exporter of ca. 15% of that production. Increasing global demand for cereals justifies questions as to where and by how much Europe's production can be increased to meet future global market demands, and how much additional nitrogen (N) crops would require. The latter is important as environmental concern and legislation are equally important as production aims in Europe. Here, we used a country-by-country, bottom-up approach to establish statistical estimates of actual grain yield, and compare these to modelled estimates of potential yields for either irrigated or rainfed conditions. In this way, we identified the yield gaps and the opportunities for increased cereal production for wheat, barley and maize, which represent 90% of the cereals grown in Europe. The combined mean annual yield gap of wheat, barley, maize was 239 Mt, or 42% of the yield potential. The national yield gaps ranged between 10 and 70%, with small gaps in many north-western European countries, and large gaps in eastern and south-western Europe. Yield gaps for rainfed and irrigated maize were consistently lower than those of wheat and barley. If the yield gaps of maize, wheat and barley would be reduced from 42% to 20% of potential yields, this would increase annual cereal production by 128 Mt (39%). Potential for higher cereal production exists predominantly in Eastern Europe, and half of Europe's potential increase is located in Ukraine, Romania and Poland. Unlocking the identified potential for production growth requires a substantial increase of the crop N uptake of 4.8 Mt. Across Europe, the average N uptake gaps, to achieve 80% of the yield potential, were 87, 77 and 43 kg N ha −1 for wheat, barley and maize, respectively. Emphasis on increasing the N use efficiency is necessary to minimize the need for additional N inputs. Whether yield gap reduction is desirable and feasible is a matter of balancing Europe's role in global food security, farm economic objectives and environmental targets.

peer-reviewed ; Europe accounts for around 20% of the global cereal production and is a net exporter of ca. 15% of that production. Increasing global demand for cereals justifies questions as to where and by how much Europe's production can be increased to meet future global market demands, and how much additional nitrogen (N) crops would require. The latter is important as environmental concern and legislation are equally important as production aims in Europe. Here, we used a country-by-country, bottom-up approach to establish statistical estimates of actual grain yield, and compare these to modelled estimates of potential yields for either irrigated or rainfed conditions. In this way, we identified the yield gaps and the opportunities for increased cereal production for wheat, barley and maize, which represent 90% of the cereals grown in Europe. The combined mean annual yield gap of wheat, barley, maize was 239 Mt, or 42% of the yield potential. The national yield gaps ranged between 10 and 70%, with small gaps in many north-western European countries, and large gaps in eastern and south-western Europe. Yield gaps for rainfed and irrigated maize were consistently lower than those of wheat and barley. If the yield gaps of maize, wheat and barley would be reduced from 42% to 20% of potential yields, this would increase annual cereal production by 128 Mt (39%). Potential for higher cereal production exists predominantly in Eastern Europe, and half of Europe's potential increase is located in Ukraine, Romania and Poland. Unlocking the identified potential for production growth requires a substantial increase of the crop N uptake of 4.8 Mt. Across Europe, the average N uptake gaps, to achieve 80% of the yield potential, were 87, 77 and 43 kg N ha−1 for wheat, barley and maize, respectively. Emphasis on increasing the N use efficiency is necessary to minimize the need for additional N inputs. Whether yield gap reduction is desirable and feasible is a matter of balancing Europe's role in global food security, farm economic objectives and environmental targets. ; We received financial contributions from the strategic investment funds (IPOP) of Wageningen University & Research, Bill & Melinda Gates Foundation, MACSUR under EU FACCE-JPI which was funded through several national contributions, and TempAg (http://tempag.net/).

International audience ; Europe accounts for around 20% of the global cereal production and is a net exporter of ca. 15% of that production. Increasing global demand for cereals justifies questions as to where and by how much Europe's production can be increased to meet future global market demands, and how much additional nitrogen (N) crops would require. The latter is important as environmental concern and legislation are equally important as production aims in Europe. Here, we used a country-by-country, bottom-up approach to establish statistical estimates of actual grain yield, and compare these to modelled estimates of potential yields for either irrigated or rainfed conditions. In this way, we identified the yield gaps and the opportunities for increased cereal production for wheat, barley and maize, which represent 90% of the cereals grown in Europe. The combined mean annual yield gap of wheat, barley, maize was 239 Mt, or 42% of the yield potential. The national yield gaps ranged between 10 and 70%, with small gaps in many north-western European countries, and large gaps in eastern and south-western Europe. Yield gaps for rainfed and irrigated maize were consistently lower than those of wheat and barley. If the yield gaps of maize, wheat and barley would be reduced from 42% to 20% of potential yields, this would increase annual cereal production by 128 Mt (39%). Potential for higher cereal production exists predominantly in Eastern Europe, and half of Europe's potential increase is located in Ukraine, Romania and Poland. Unlocking the identified potential for production growth requires a substantial increase of the crop N uptake of 4.8 Mt. Across Europe, the average N uptake gaps, to achieve 80% of the yield potential, were 87, 77 and 43 kg N ha(-1) for wheat, barley and maize, respectively. Emphasis on increasing the N use efficiency is necessary to minimize the need for additional N inputs. Whether yield gap reduction is desirable and feasible is a matter of balancing Europe's role in global food ...

International audience ; Europe accounts for around 20% of the global cereal production and is a net exporter of ca. 15% of that production. Increasing global demand for cereals justifies questions as to where and by how much Europe's production can be increased to meet future global market demands, and how much additional nitrogen (N) crops would require. The latter is important as environmental concern and legislation are equally important as production aims in Europe. Here, we used a country-by-country, bottom-up approach to establish statistical estimates of actual grain yield, and compare these to modelled estimates of potential yields for either irrigated or rainfed conditions. In this way, we identified the yield gaps and the opportunities for increased cereal production for wheat, barley and maize, which represent 90% of the cereals grown in Europe. The combined mean annual yield gap of wheat, barley, maize was 239 Mt, or 42% of the yield potential. The national yield gaps ranged between 10 and 70%, with small gaps in many north-western European countries, and large gaps in eastern and south-western Europe. Yield gaps for rainfed and irrigated maize were consistently lower than those of wheat and barley. If the yield gaps of maize, wheat and barley would be reduced from 42% to 20% of potential yields, this would increase annual cereal production by 128 Mt (39%). Potential for higher cereal production exists predominantly in Eastern Europe, and half of Europe's potential increase is located in Ukraine, Romania and Poland. Unlocking the identified potential for production growth requires a substantial increase of the crop N uptake of 4.8 Mt. Across Europe, the average N uptake gaps, to achieve 80% of the yield potential, were 87, 77 and 43 kg N ha(-1) for wheat, barley and maize, respectively. Emphasis on increasing the N use efficiency is necessary to minimize the need for additional N inputs. Whether yield gap reduction is desirable and feasible is a matter of balancing Europe's role in global food security, farm economic objectives and environmental targets.

International audience ; Australia's farmers are among the most efficient in the world, despite a relatively large gap between potential and achieved water-limited grain yield. With wheat yield gaps typically > 1.7 t/ha or 50% of the water-limited yield, it is important to investigate the degree to which this gap may be attributable to (rational) subprofit-maximising input levels in response to risk and risk aversion in many major grain-growing regions, particularly those with lower and more variable rainfall. Here, we use a set of 14 case study sites across the Australian wheatbelt to examine the risk-return profile of several agronomic management practices and show the extent to which the farmers' risk attitude determines their decision-making. Using a novel profit-risk-utility framework that incorporates crop simulation, probability theory, finance techniques and risk-aversion analysis, we were able to better demonstrate how farmers might select practices that manage economic risk across sites ranging from low to high rainfall. Results varied with risk preference and yield potential. However, there are real opportunities to close the yield gap by adopting non-limiting or near non-limiting nitrogen fertiliser practices and controlling fallow weeds. We show for the first time that yields associated with current best practice can be surpassed for most levels of risk aversion by adopting an emergent practice of optimising the site-specific time of sowing and matching variety to time of sowing. For some sites and risk profiles, the emerging best practice package which includes additional N fertiliser is also profitable under risk. We also propose a modified integrated framework for yield gaps. Here, we distinguish allocative input constrains due to risk aversion from those due to access to resources, and we account for an innovation gap where the current agronomic frontier is shifted upwards by growers successfully, implementing new technologies that are not yet part of current best practice.