Heat Stress and Low Humidity with Climate Change will be Hard on Midwestern Corn Crops

 

by Christina Whalen and Emil Morhardt

Maize (corn) production continues to be a very important source of food, feed, and fuel all around the world, but climate change has raised the concern about being able to maintain the yield rates. A negative relationship between extremely high temperatures (above 30˚C) and yield has already been observed in various regions. Previous studies have not been able to demonstrate which mechanism causes the correlation between extreme temperatures and yield, thus it is possible that the relationship reflects the influence of another variable, such as precipitation rates. There are other possible explanations for the observed relationships. This study explores the mechanisms used in other studies that document the importance of extreme heat on rainfed maize using the process-based Agricultural Production Systems Simulator (APSIM). The study asks three main questions: can APSIM reproduce the empirical relationships—what farmers are seeing on the ground?; if so, what does APSIM imply are the key processes that give rise to these relationships?; how much are these relationships affected by changes in atmospheric CO2? Continue reading

Saving Land and Water by Cultivating Miscanthus

Due to government mandates in repsponse to climate change, ethanol production has steeply increased since 2009, and there are now for 79 billion liters of cellulosic biofuels yearly by 2022.  Cellulosic crops such as maize, switch grass, and Miscanthus have been determined to be viable biofuel sources. In order to meet the biofuel target in 2022, cellulosic crop cultivation needs to be expanded and intensified. The impact on land and water use needs to be considered as well. Zhuang et al. (2013) present a data-model assimilation analysis assuming that maize, switchgrass, and Miscanthus can be grown on available U.S. croplands.—Christina Whalen

Zhuang, Q. Qin, Z. Chen, M. 2013. Biofuel, land, and water: maize, switchgrass, or Miscanthus. Environ. Res. Lett. 8, 015020.

                  The current production levels of maize are not enough to be simultaneously used as biofuels and as a food source. The cellulosic crops switchgrass and Miscanthus have been identified as viable alternatives to maize in producing second-generation biofuel. This is staged to work especially well in temperate regions because of their higher biomass productivity and available crop-producing land. Other studies have shown that bioenergy crops have higher land and water efficiencies than food crops do, but the increasing demand of land and water to cultivate these crops hasn’t been researched using ecosystem models.  The study uses the terrestrial ecosystem model (TEM) to predict the demand of land and water for growing various biofuel crops so that enough ethanol can be produced to hit the 2022 target. The goal of the study is to analyze the demand for resources rather than to analyze the environmental impact of growing biofuel crops.
                  The TEM ecosystem model uses gross primary production (GPP) as the core algorithm, which describes the rate at which a plant produces usable chemical energy. The Net primary production (NPP) is the difference between GPP and plant respiration. In order to analyze the productivity of feedstocks and biofuels, the researchers estimated the biomass and biofuel production in terms of harvestable biomass (HBIO) and bioethanol yield. Current and future biofuel production was estimated using conversion efficiencies and currently available and potentially advanced technologies.  TEM was run several times at each site in order to achieve model equilibrium. Analyses were conducted on biomass and biofuel yield, water balance, and water use efficiency and were estimated based on simulations.
                  The results of the model demonstrate that in order to produce 79 billion liters of ethanol from maize grain, there would be a need for 190 million tons of conventional grain and 26.5 million hectares of land, which is equivalent to 20% of total US cropland. The water loss of this production would be 92 km3, but if the maize stover were also used, water would be saved. Because switchgrass has lower conversion efficiency, using this crop would result in a higher demand of biomass. More land and water would need to be used to produce the same amount of ethanol than using maize. Alternatively, Miscanthuswould only require half the amount of land and two-thirds the amount of water used for maize grain in order to produce the same amount of ethanol. Furthermore, with the advanced technologies predicted for future years, even less water and land will need to be used in converting biomass to biofuel. The model experiments demonstrate that switching from maize to Miscanthus will save land and water, but that switching from maize to switchgrass will require more land and water.

                  This study only predicts ethanol production using available croplands, but recent studies have illustrated that marginal lands could also be a source for cultivating cellulosic crops. Experiments have also shown that switchgrass may be more productive on marginal lands than on traditional croplands. The model may produce some bias because it does not consider the effects of fertilization, irrigation, rotation, and tillage. To strengthen the study, analysis of economic viability, food security, nutritional and ethical concerns, and other environmental consequences and benefits need to be conducted.

Setbacks of Using Agricultural Crops and Natural Ecosystems as Energy Sources

The currently growing concerns around the world about foreign oil dependency and growing climate change, have contributed to an increasing interest in using bio-fuels as an alternative to fossil fuels such as coal, gas, and oil. The study conducted by Graeme I. Pearman (2013) demonstrates that bio-fuels and bio-sequestration can only make a minor contribution to lowering carbon levels and minimizing net emissions of carbon into the atmosphere. This is done through examining available solar radiation and observing how efficient natural and agricultural ecosystems are in converting that energy to usable biomass. The 11 countries compared in the study are Australia, Brazil, China, Japan, Republic of Korea, New Zealand, Papua New Guinea, Singapore, Sweden, United Kingdom, and United States, with a main focus on the researcher’s homeland, Australia. The objective of the study is to answer the following question: from a biophysical perspective, can using bio-fuels or bio-sequestration of carbon significantly contribute to the future of energy and the reduction of greenhouse-gas  (GHG) emissions?—Christina Whalen

                  Pearman, G. 2013. Limits to the potential of bio-fuels and bio-sequestration of carbon. Energy Policy 59, 523-535.

                  The first part of the study focuses on comparing annual rates of solar radiation and respective energy consumption for each country. The results group countries into 3 groups. Group 1, Japan, Korea, and Singapore had energy consumption around 1 en dash 10% of incident (surface) radiation. Group 2, China, U.K., and U.S. had energy consumption around 0.1% and Group 3, Australia, Brazil, New Zealand, Papua New Guinea, and Sweden had energy consumption around 0.1 en dash 0.001% of incident radiation. These comparisons demonstrate the limits that deriving energy from the sun has on meeting national expectations for energy consumption. We can consume much more energy than the sun could ever provide us.
                  Photosynthetic efficiency is another limit to the use of bio-fuels or bio-sequestration. The pigments in the chloroplast are only activated by certain parts of the solar spectrum, leaving much of the solar radiation unutilized. In addition, more than 50% of photosynthetic products (sugars) are lost through photorespiration. The whole process is only 3.3% efficient in C3 plants and 6.7% in C4 plants.
 The study then continues to examine the limitations of bio-fuels regarding energy efficiency captured from natural vegetation and from global crops. Net primary production (NPP) is how much carbon (or energy in this case) remains after the photosynthetic organism has used it for growth and other metabolic functions. In natural environments, a large portion of captured solar energy is used within the community and is vital for a functioning and healthy ecosystem. Thus, human use of this energy will no doubt have negative impacts on preexisting ecosystems. Agricultural ecosystems are constructed for the purpose of providing biomass for human consumption. The main difference between the two types of ecosystems is that a cultivated system inputs fossil fuels, which needs to be considered when accounting for the net production of energy. Comparisons within each of the countries were then made between energy captured annually as net primary production and the national solar radiation and energy consumption rates. The comparison demonstrates the inefficiency of the biochemistry involved in photosynthesis and is also influenced by temperature and water availability. The comparisons also conclude that modifying the NPP of the biosphere could be possible when global scale changes occur to temperature, rainfall, and carbon dioxide concentrations.
Photosynthesis can be more efficient in agricultural crops when there is plenty of water and fertilizer and crop management is most favorable during the peak growth rates. In the study, multiple samples were taken from various countries and locations in order to accurately compare the relative efficiencies of different cropping systems. This is called “tradable production” because the net production is calculated after discarding the roots, leaves, and stems of plants. Sugar cane and wheat crops have the potential to contribute significantly the nation’s energy demand, but have some economic and political setbacks that are not discussed in detail in the paper.
Though natural and agricultural biomass have the potential to provide energy for human use and to offset carbon emissions from fossil fuels, this study demonstrates that there are major limiting factors to this solution including the availability of solar radiation and the efficiency of photosynthesis needed to convert the energy into feedstock. Another limitation is how efficiently biomass can be converted into fuels that are appropriate for existing feedstocks, conversion systems, and applications. Solar radiation on land accounts for 1700 times the amount of energy consumed by humans, but the radiation and the energy demands are not evenly distributed geographically, so this process depends on the redistribution of energy. It also depends on how efficiently solar energy can be converted to meet the demands of humans, which is where photosynthesis becomes a limiting factor. In comparison, agricultural crops may be more efficient at converting solar radiation to a more usable form of energy, but the study demonstrates that wheat, rice, and corn crops have low efficiency rates that are similar to those of natural ecosystems. The only crop that shows a decent amount of efficiency is sugar cane.
                  The analysis conducted in this study is not meant to completely reject the idea of using crops and natural ecosystems as bio-fuel and bio-sequestration of carbon, but  is meant to illustrate that this would require a huge amount of increase in land utilization and/or altering existing crops. Investors in these types of activities and governments seeking policy implementation need to be aware of these so-called “attractive” energy efficiency solutions.
                  The paper summarizes 12 criteria of assessments of issues raised by the possibility of using bio-fuels as a future energy source and for the bio-sequestration of carbon. The first issue that needs to be examined is the potential for agricultural and forestry capacity to deliver to energy demands and emissions reduction. Another one is evaluating the co-benefits or dis-benefits of developing policies about bio-fuels such as soil productivity, job creation, economic opportunities, international balance of trade, security of energy supply and so on. There also has to be enough net energy to cultivate crops for fuels, to produce fertilizer, transform the energy into chemical energy, and for transporting the subsequent fuel.  Another issue to keep in mind is the continuously changing climate and its affect on which bio-fuels are appropriate. Other issues include timing, production location, strategic carbon & nitrogen budgeting, human capacity to convert the energy, competing use of land, costs of production, and social and political realities.
                  The conclusion of the paper does little to provide the answers to the various questions raised throughout the study, but rather implies that “we” have the knowledge to develop a system to produce bio-fuels and bio-sequestration of carbon from agricultural crops and natural ecosystems, but now we need more efficient biomass that will provide us with the tools we need to power that process.