Sustainability of Adding Cereal Grains to Crop Rotations
ScenarioA group of corporations reliant on cereal grains (e.g. wheat, barley, oats, etc.) for the supply of raw product have joined together to try to increase the U.S. domestic supply. Currently, much of the grain supply manufactured into food in the U.S. is coming from Canada or Eastern Europe. They hope to motivate growers in the U.S. to produce more cereal grains by describing the positive aspects of cereal grains on the sustainability of a typical corn-soybean rotation better. To compile the data to support this argument, cropping systems studies in the peer-reviewed literature will be used to outline the benefits of this type of diversified rotation as compared to a corn-soy or continuous corn system common in the Corn Belt. Questions asked will include: What are the benefits with respect to soil and greenhouse gas emissions (including transportation)? Are there any economic benefits to the farmers?
The status of the current marketplace is depicted in the Chart of US Grain Supply and Distribution provided by the USDA.
Currently much of the grain supply manufactured into food is imported from Canada or Eastern Europe. In order to motivate growers in the U.S. to produce more cereal grains, the benefits of crop rotations are described. The environmental metrics used in the analysis (nitrous oxide emissions, soil quality via water runoff contaminants, and carbon sequestration) are all shown to be significantly more sustainable in cereal grain-inclusive rotations than in conventional rotations. A meta-analysis of the sustainability of crop rotations which include cereal grains versus the sustainability of more widely adopted continuous corn and corn-soybean rotations finds that cereal grain-diverse rotations are strongly correlated with an increase in environmental sustainability. Economic metrics in the analysis show no significant increase in economic sustainability and show indications of a possible decrease in profitability due to government subsidies for corn. The comparison of the social sustainability of the two systems is largely contingent on government subsidies and the profitability of the rotation system. The current disparity between the economic sustainability of the two types of rotations studied plays a large role in stifling the adoption of a more environmentally sustainable, cereal grain-inclusive crop rotation.
|Chart 1: Description of the best cover crops for regional area in the United States. In the Corn Belt several various cover crops are listed (Clark 2007)..|
Crop rotation diversification is the most powerful tool that farmers have to reduce economic risk, disrupt pest cycles, increase soil resilience, and improve water quality (Teasdale et al., 2007). It has been estimated that between 50 to 70 percent of global soils are degraded (Heikkinen, 2015). Crop rotation is a system of growing different kinds of crops in a successional pattern on the same land. Within the Corn Belt, spanning the states of Iowa, Missouri, Illinois, Indiana, and Ohio, the typical crop rotation consists of a corn-soybean rotation (USDA, 2016). When corn prices increase, corn-soybean rotations are replaced with continuous corn. Corn is a heavy nitrogen feeder (Clark, 2007). As a result, corn production is heavily dependent upon the use of fossil-based energy to produce synthetic fertilizers, cultivate fields, plant and harvest crops, and transport the corn to feed mills (Ray & Shaffer, 2012). The use of fertilizer is problematic for a variety of reasons. Enhanced nitrification and denitrification rates are caused by high levels of mineral nitrogen in agricultural soils are the main anthropogenic source of nitrous oxide (Robertson & Vitousek, 2009). Currently approximately 20 percent of all acres in the Midwest Corn Belt are in continuous corn--a percentage that is likely to increase as future demand for corn grows (USDA, 2016). Over the last half century, conventional approaches to crop production have relied heavily on synthetic fertilizers and pesticides in order to increase yields, but have also degraded water quality, emitted greenhouse gases, and prevented carbon from being sequestered on agricultural land (Davis et al., 2012; Osterholz et al., 2014; King et al., 2016).
Using diversified rotations including cereal grains as either a cash crop or a cover crop can be a potential alternative to continuous corn. Diversified rotations with respect to cash crops have the potential to minimize the amount of nitrogen input and maintain species diversity (Gaudin et al., 2015; Amitava et al., 2016). Crop rotations integrating cereal grains as cash or cover crops have the potential to build soil organic matter, increase carbon sequestration, improve soil quality, minimize greenhouse gas emissions (Johnson et al., 2007; USDA, 2016). A diversity of cover crop species can be implemented into crop rotations across the United States (Chart 1). Increasing plant diversity with cover crops has been a successful strategy to augment ecosystem services from agriculture and increasing the diversity of cover crops may provide even greater benefits (Finney et al. 2016). Soil with more organic matter has been found to increase crop yields, filter water, and reduce runoff and flooding. As atmospheric CO2 increases, finding ways to sequester carbon in topsoil could be an important way of mitigating anthropogenic impacts on climate change (Robertson et al., 2000; Hutsch, 2001; Johnson et al., 2007; Heikkinen et al., 2015).
In addition to the beneficial impact on the environment, diversified crop rotations have been shown to be economically advantageous to farmers as well (Posner et al., 2000; Jain et al., 2010; Ray & Shaffer, 2012; Thiefelder et al., 2013). Research has shown that the incorporation of cereal grains such as wheat can increase crop yields (Gaudin et al., 2015) and minimize labor costs (Bernstein et al., 2011). However, there has been some debate regarding the economic sustainability of the incorporation of cereal grains. Similarly, there is uncertainty regarding the social sustainability of widely implementing diversified crop rotations. This study seeks to address the three pillars of sustainability as they relate to the diversification of crop rotations. Specifically, we pose the question: will diversifying crop rotations with cereal grains as cash or cover crops be more economically and environmentally sustainable than the prevalent corn-soybean rotation?
Will diversifying crop rotations with cereal grains as cash or cover crops be more economically and environmentally sustainable than the prevalent soybean-corn rotation?
When comparing conventional continuous corn and corn-soybean rotations with more diverse crop rotations which include cereal grains, a higher crop diversity will correlate with reduced negative environmental impacts (e.g. N2O concentration, carbon sequestration, water contamination, soil loss) and will net at least a profit margin comparable to conventional systems.
This meta-analysis of peer-reviewed literary sources is a compilation of data relevant to the economic and environmental sustainability of crop systems diversified by cereal grains in comparison to conventional, continuous corn and corn-soybean, low diversity systems. The individual metrics and results of each source were analyzed individually in regards to water quality, nitrous oxide, and carbon sequestration. These three areas of interest were identified as critical benefits of diversified crop rotations in relation to the typical corn-soybean rotation. The results and implications of the sources were compared and contrasted with one another in order to form a holistic understanding of how to better understand the impact of crop rotations in terms of these three areas. The resulting information was consolidated into a concise summary within the results section. The discussion portion of this meta-analysis focuses on the dissection of qualitative findings and applies the information derived from the results section in order to approach the topic of environmental, economic, and social sustainability in cereal grain-containing, crop diverse systems. From the results and discussion section, a table was provided to highlight the sustainability benefits of integrating cereal grains into the typical corn-soybean rotation. The final section of the study provides a summary and conclusion of major findings.
|Figure 01. The improvement of soil moisture in a system that contains rye as a cover crop. Till vs no till systems are also examined (Bernstein et al 2011).|
Climate patterns in the central US are expected to become increasingly variable with the changes in precipitation intensity and seasonality and changes in available soil water for crop production. Prevailing weather conditions, available water in the soil, crop species and development stage influence crop water use. As can be inferred, water is an important factor in crop production (Strock & Dalzell, 2014). King et al. (2016) evaluates the loss of nitrogen and phosphorus through tile drainage under corn and soybean production over the course of eight years in a typical corn-soybean rotation across the Corn Belt. They found the relationship between dissolved reactive phosphorus and loading to not be significantly different between crop types, but differed significantly by season. However, they found that nitrate concentration and load was dependent on the interaction between crop type and season. Overall, they found that practices such as cover crops and drainage water management should be explored as a means to decrease nitrogen and phosphorus loads. They stress the necessity for farmers to adhere to nutrient stewardship practices to minimize nutrient leaching to tile drains in a corn-soybean rotation.
In another study (Bernstein et al., 2011) the soil moisture of a soy system, integrating a rye cover crop as a no-till method was analyzed for two years. In this system, tilled systems only had the traditional rotation, while no-till systems had a rye cover crop. In both years of the study, the soil moisture for the rye-no till systems was greater than the soil moisture for the tilled traditional systems (Figure 1). This suggests that both cover-crop-based no till improves the over all quality of the soil.
|Figure X. Response of yield for corn in various levels of nitrogen concentration (Guadin et. al., 2015).|
Nitrous oxide can be a product from the addition of nitrogen based fertilizers into the soil. The amount of fertilizer that is applied to a system greatly impacts the amount of nitrous oxide that is released into a system (Osterholz et al., 2014). One study found that application of N fertilizer increases exponentially when the N application is 300 N / kg N ha-1 (Van Groenigen et. al., 2010). These nitrogen base fertilizers are often used in corn systems because corn is a heavy nitrogen feeder (Clark, 2007). Crop rotations can minimize the amount N fertilizer needed to have a high amount of corn yield. Gaudin et. al. demonstrates that rotations that include wheat crops and red clover improve the overall yield of corn (Figure X). This is an alternative method to continuous corn with high N fertilizer inputs to increase corn yields. Ultimately the decrease in nitrogen based fertilizers will decrease the N2O in the environment. Additional studies have also found that there is a reduction in synthetic N put into soil when there is a more diversified crop system. Posner et al. (2000) found a 63% reduction in synthetic N inputs on corn in the 3-crop rotation compared to the 2-crop rotation. Osterholz et al. (2014) found that extended and diversified cropping systems could reduce area-scaled nitrous oxide emissions from agriculture but none of the systems studied significantly reduced yield-scaled nitrous oxide emissions.
As atmosphere carbon dioxide increases, finding ways to direct more of that carbon into the topsoil could be an important way to help mitigate human-caused climate change (Varvel, 2006; Heikkinen, 2015). Carbon sequestration in soils is a slow and dynamic process (Varvel, 2006). Research has shown that nonlegume cover crops have a higher carbon to nitrogen ratio than legume cover crops. Because of their high carbon content, grasses break down more slowly than legumes, resulting in longer-lasting residue (Clark 2007). Nonlegume cover crops can produce a lot of residue, which contributes to their ability to prevent erosion and suppress weeds while they are growing or when left on the soil surface as a mulch (Clark 2007). Soil organic matter conservation is affected by the composition of cultivated plant species and input of dry matter and nitrogen into the system (Raphael et al., 2016). Short term experiments analyzed in Cates et al. (2016) found that perennialization and reducing soil tillage have increased soil organic matter in both aggregate and particulate organic matter in a variety of agricultural cropping systems. Small changes in soil management practices have significantly change the soil organic carbon dynamics in the soil (Varvel, 2006).
|Figure X. Corn yield was heavily dependent on the weather of the year. In particularly dry years, an increase in corn yield was seen (Gaudin et al., 2015).|
Inclusion of cover crops, although they might not be considered cash crops, can improve economic benefits to the farmers. In Gaudin et al. (2015) it as shown that both corn and soybean yields can be improved by the addition of cover crops. For corn, yield was heavily dependent on year. However, in a dry year, the inclusion of winter wheat increased maize yields by 18.8% (Figure X). As suggested in a previous study (Bernstein et al., 2011) the diverse crop rotation systems could have an increased soil moisture which could help produce a higher yield of corn. In this study it was seen that two of the years, 2010 and 2013, that the corn yield was lower in the corn-corn and corn-soy rotations. The study also concluded that on average, winter wheat improved maize performance by 16.6% and 18.8% . This increase in overall productivity could potentially increase profitability for farmers.
|Figure X. Soybean yield was increased in systems with higher crop diversity (Gaudin et al., 2015).|
Gaudin et. al. (2015) also concluded that soybean yields were improved in systems that included wheat as a cover crop (Figure X). The inclusion of wheat in a maize-soybean (MS) or soybean-soybean (SS) rotations significantly increased soybean yields by an average of 0.47 Mg ha−1 across tillage systems. Higher soybean yields may be attributed to the benefits of small grain cereal on soil structure. This increased yield could mean increased profits from the soybean production. However, in a different study (Bernstein et. al., 2011) it was concluded that there was a 24% less soybean yield and 25% less economic return when a cover crop such as rye was included. This suggests that yield/economic return could be highly variable.
Hedtcke et al. (2006) also concluded that there was no difference in profitability between the system of continuous corn, a corn-soy and a corn-soybean-winter wheat/red clover system. Although it is noted in their multiple year study that input costs were lower for the corn-soybean-winter wheat/red clover system than the other two systems. The reduction in profitability from the corn-soybean-winter wheat/red clover system could be attributed to government aid provided for corn growers, as mentioned in the paper.
Posner et al. (2000), found that corn yields were not affected significantly by the 3-crop, more diverse rotation system. However, soybean yields were significantly increased in these 3-crop rotation systems that included a cereal grain. Plant counts on 3-crop averaged 181,500 plants/acre while the 2-crop system averaged 161,610 plants/acre (Posner et al., 2000).
|Chart 2. Environmental Benefits of Various Cereal Cover Crops (Clark, 2007).|
Research has shown diversified crop rotations that include cereal grains use less nitrogen fertilizer, sequester more carbon, retain organic matter, and emit fewer greenhouse gases in comparison to continuous corn farming typical to the Corn Belt (Hutsch, 2001; Davis et al., 2012; Cates et al., 2016; Finney et al., 2016). Reduction of nitrogen input decreases nitrous oxide outputs. This finding emphasizes the importance of land use. The crop residue present in the soil affects methane oxidation differently depending on the carbon to nitrogen ratio (Hutsch et al., 2001).
When a farmer selects a cover crop they need to take into consideration what crops will provide them with the best benefits. Different cereal crops have different environmental qualities as shown in Chart 2 (completely dark circles means the best at that certain quality, whereas white circles mean the worst). For example, if farmers wish to reduce their nitrogen based fertilizers into the soil, they could choose cover crops such as sorghum or rye which are very good nitrogen scavengers.
As stated in the results, yields and profits were highly variable among the different systems (continuous corn, corn-soy, corn-soy-wheat, etc). Potentially the reason for continuous corn to have such a high profit margin is because of the government subsidies that encourage corn production as an input for manufacturing biofuel (Jain et al., 2010). In Figure X, the profit from the different rotation systems is shown. A primary reason that continuous corn has an increased profit is because of relatively high government subsides. If the government support for continuous corn was removed, the more diverse systems would have an increased profit margin over continuous corn. Government subsidizes in the United States encourage corn and soybean production over more diversified crop rotations. It would be beneficial if the government considering incentivizing diversified cropping systems in order to grow the domestic supply of grain for food production, simultaneously increasing environmental sustainability.
|Figure X. Profit margins in different rotation systems. Chemlite refers to the corn-soybean-wheat-red clover rotation (Hedcke et al., 2006).|
However, with the current government programs in place, the diverse crop rotation might not be economically sustainable. However, Posner et. al (2000) states that there are instances in which cereal grains are being supported by large groups economically. A farm group in North Dakota has attracted 250 oat growers for a project called Oat Technologies. The group forecasts it will have a revenue of $25 million and wants to pay farmers up to $2.20/bushel. Groups like these could make the growing of cereal grains much more economically sustainable as these farmers would have support from these groups.
Additionally, profitability depends on whether or not there is a market for the crops that are being put into rotation (Thierfelder et al. 2013). If there is an assumed market for cereal grains than the rotation systems that include cereal grains could be profitable. If there is not a market for these however, then the system will not be profitable. Posner et. al (2000) stated the existence of a market for these cereal crops that could be used for milling and malting, matching the prices of foreign competitors. Therefore, if there is a market for the cereal grains as Posner et. al. predict, then the crop rotation system with these cereal grains could be economically sustainable.
|Figure X. Corn Belt Yield and Opportunity Cost (2003-2007).|
The economic sustainability of diversified crop rotations is promising. Research has supported that diversified crop rotations were just as profitable as the standard corn-soybean rotation common to the Corn Belt (Davis et al., 2012). Sustainable agriculture will require drawing definitive boundaries to minimize externalities. In order for the system to be economically sustainable, it is necessary to take these externalities into account. If the producer isn't paying for the degraded ecosystem services, the consumer will.
Social sustainability is a critical element of this topic. The ultimate question of production is: how can agriculture meet the food demands of a rapidly growing population? Davis et al. writes that “One of the key challenges of the 21st century is developing ways of producing sufficient amounts of food while protecting both environmental quality and the economic well-being of rural communities.” However, within the environmental and economic considerations lie the social factors influencing these decisions. Agricultural decisions are made as the result of established norms and are influenced by policy-makers.
Another impact on social sustainability is the profit-driven state of agriculture in the United States. Because farming is largely a competitive practice of refining efficiency and steadily increasing profits, social adoption of a change in crop diversity must at the very least prove to be economically beneficial to the farmer. With the hopes of increasing the domestic grain supply, the market would be less dependent on foreign imports. This decreased dependency would increase the job security of US grain farmers while also increasing the domestic supply of cereal grains. Currently, government subsidies and incentives promote the production of corn which makes it difficult for systems which include additional crops to the rotation to compete economically. Without the inclusion of government-provided benefits to corn production, cereal grain-inclusive systems would prove to be much more economically competitive due to the reduced need for nitrogen inputs into the soil. By altering government programs and incentives, the resulting increase in the economic sustainability of cereal grain-inclusive rotations would likely also increase the social sustainability of the rotation as well due to the strong correlation between the two. By educating farmers about the prospective environmental and economical benefits to a more diverse crop rotation, the adoption and social acceptance of such a system would be very likely to increase.
Potential Benefits for Farmers
Improve soil and water quality
Decrease nitrogen run-off
Increased carbon sequestration
Decrease nitrogen input
Increase crop yields
Decrease labor costs
Increase domestic grain supply
Increase job security of grain farmers
LimitationsIn terms of assessing environmental impacts, it is important to have studies which analyze similar systems. Similar systems will have similar soil types and employ similar crop rotations. It is also important to compare studies that were conducted over comparable lengths of time. The length of the study can impact the overall findings, as short-term results may not apply over the long term. Our study was limited in regards to these two important considerations because we attempted to compare research that covered many different rotations and were conducted over varying lengths of time. Some studies, such as Bernstein et. al (2011), were conducted over the course of two years. From these short-term studies, it is difficult to draw overarching conclusions in regards to sustainability. The Brundtland Report (1987) defines sustainability as “development that meets the needs of the present without compromising the ability for future generations to meet their own needs." According to its definition, assessing sustainability requires consider how current crop rotations will impact future generations, projecting tens of years into the future. In terms of economic and social sustainability, we found it would be important to change government subsidizes and implement incentives for including cereal grains into crop rotations. Governmental change, however, takes place over long periods of time and requires extensive research to support new implementations. Thus, the practical implementation of our study would require more research supporting our findings as well as time in which the new policies could be put into place. It is also of note that we were limited to six months in order to conduct our meta-analysis. Our own time constraint limited our ability to delve deeper in our literature review and find studies that were more comparable.
Summary and Conclusions
When comparing the sustainability of cereal grain-inclusive crop rotations against continuous corn and corn-soybean rotations, the inclusion of cereal grains produces an overall increase in environmental sustainability. Water quality and soil moisture show a positive correlation with the introduction of cereal grains such as rye into crop rotations. In addition, cereal grain inclusion has shown to greatly decrease the need for the addition of synthetic nitrogen additives to the soil by up to as much as 63% and have been shown to improve crop yield and decrease nitrous oxide emissions. Cereal grain-inclusive systems also show an increase in carbon sequestration by the soil due to the increased amount of crop residue left by non-legume crops. The comparison of the economic sustainability of the two systems favors conventional systems due to the increased profitability of corn and soybean as crops and the difficulty for farmers to find a market for cereal grains. The social sustainability comparison of the two systems largely reflects the economic sustainability of each system due to the nature of the profit- and efficiency-driven agricultural system in the United States.
After conducting the meta-analysis, we revisited our hypothesis and concluded that while higher crop diversity correlated with reduced negative environmental impacts, the profit margin of cereal grain-systems cannot be considered comparable to conventional systems. The increase in environmental sustainability in cereal grain-inclusive rotations, however, we believe outweighs the slight decrease in profitability and have ascertained that the disparity in profitability is largely, if not completely, due to government subsidies for farmers growing corn. The first step toward an increase in environmental sustainability via a greater crop diversity may be to revise these government subsidies or to provide incentives for farmers to diversify their crop rotations. According to this analysis, a change in the profitability of cereal grain-inclusive rotations is likely to increase the economic and social sustainability of such systems when compared to conventional corn and corn-soybean rotations.
As a whole, diversification of crop rotations to include cereal grains presents a promising future for increasing sustainability in the agricultural sector. Grain companies should consider the environmental and economic benefits to increasing the domestic supply of cereal grains. Crop rotations with cereal grains could help restore soil and water quality and combat anthropogenic impacts on the climate. In lessening the inputs of nitrogen while still increasing crop yield, grain farmers will benefit economically while bettering the environment.
Further research which is needed to understand the dynamics of the economic and social sustainability of cereal grain-inclusive systems should include social surveys to farmers across the United States in order to better understand the social rives and incentives they would require before they consider adding cereal grains to their current rotations. Research on government subsidies on agricultural crops and successful government initiatives on changing farming practices would prove beneficial to changing regulations. Lastly, projections of long-term impacts of cereal-grain rotations in the United States, including environmental benefits and estimated impacts on the markets for cereal grains would provide a foundation for organizing change in an effort to widely increase crop diversity.
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