NC_old1195: Enhancing nitrogen utilization in corn based cropping systems to increase yield, improve profitability and minimize environmental impacts

(Multistate Research Project)

Status: Inactive/Terminating

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Issues


Designing efficient, economically sound and environmentally-friendly corn (Zea mays L.) based cropping systems is a prerequisite to remaining competitive in today’s global agricultural market place. The dilemma facing US corn producers and policy makers today is that the steady increase in corn yield realized over the past 50 years, and needed in the future, can be partially attributed to the intensive and increasing use of N fertilizer (Houlton et al., 2012). Yet, N fertilization comes with both a steep input cost and, particularly when more N is applied than the crop can effectively use, a potentially high environmental cost, such as reduced water quality (Verhoeven et al., 2006), an increase in hypoxic zones off the mouth of our major rivers (Donner and Scavia, 2007), and increased emissions of powerful greenhouse gases (GHG, i.e. nitrous oxide - N2O, Davidson, 2009; Shcherbak et al., 2014). Unfortunately, after nearly a century of research to develop precise N fertilizer recommendations and efficient N management systems, fertilizer N use efficiency (NUE) worldwide is still less than 50%.


The relationship between corn yield and N uptake by the plant is strongly correlated (Ciampitti and Vyn, 2011). As yield potential increases the plant requires more N to produce the vegetation and grain associated with higher yield. However, while the relation between increasing corn yield and N uptake is tightly correlated, the relationship between yield and fertilizer N need is not (Shapiro and Wortmann, 2006). This is due, in large part, to the varying supply of N provided by the soil to a crop each year. More specifically, this is the rate at which N is mineralized from soil organic matter in a given year, but also widely different potential for N losses from soils during the cropping season (a function of soil properties, crop management systems, as well as local climate).


Though the individual processes which compose the N cycle in soils are now well understood, much less is known about how these processes, cropping systems, climate and N fertilization practices all interact to impact NUE. Nor is there much known on how these N processes interact with carbon and other nutrient cycles. The interaction of sources of available N with soil organic matter and crop residue for example is rarely considered when making N fertilizer rate recommendations. However, fertilization is known to lead to an increase in the N mineralization (Jenkinson and others 1985), which can result in producers over-applying N fertilizer. But microbial processes can also result in immobilization or sequestering of N in soils (Booth et al., 2005), reducing NUE and crop yield in the year of application, but increasing mineralization at some latter time (otherwise known as a lag effect).


Rainfall and temperature are two important factors controlling most components of N cycling in soils (Brzostek et al., 2012) Thus a coordinated regional research effort which can look at gradients in temperature, precipitation and soil organic matter content across the Cornbelt and how they impact processes controlling both N mineralization and N losses from soils, is much more likely to arrive at a deeper understanding of N cycling and develop more efficient N management practices and increase NUE, than a series of independent, individual investigator projects conducted in the same geographical setting. Also there is a large gap in our understanding of the spatial and temporal variability of the soil processes that make N more or less available, preventing progress on predicting field-scale N requirements for corn.


The long-term general goals of this regional project are to better understand how the interactions of soil, climate, cropping system and N fertilization practices impact NUE, and develop better N rate and management recommendations for growers. If these recommendations are utilized, growers will more efficiently utilize N fertilizers to meet the needs of increasing crop yield, while minimizing any potentially adverse effects on the environment. A key specific goal of this regional project is to determine whether new knowledge and management strategies generated by this group and others, and communicated to stakeholders, can reduce N fertilizer application to corn in the US by 5% over the next five years.


Justification
Corn production in the US today uses large amounts of N fertilizers due to the crop’s large N nutritional requirement (Simons et al., 2014). Soil N mineralization provides a substantial portion of corn’s total N need in many areas (Lynch, 2013), and is supplemented as needed with inorganic fertilizer and organic manures and co-products. A key component to improved fertilizer N efficiency and reduced environmental impact is a better understanding and quantification of N mineralization. Fertilizer N efficiency is normally based on N uptake/yield of unfertilized (check) plots. An important, possibly incorrect, assumption in this approach is that release of organic soil N is unaffected by N fertilization (Jenkinson and others 1985, Castellano personal communication). Not accounting for N fertilizer’s impact on soil N release can lead to over-fertilization and increased N loss. While it is commonly accepted that N fertilizer influences soil N mineralization by “priming” processes (Jenkinson and others 1985, Castellano personal communication) little has been done to quantify these effects and incorporate this knowledge into our N management recommendations or calculations of fertilizer N use efficiency. Thus, quantifying uptake of fertilizer N by the crop and associated changes in soil N mineralization are paramount to developing sound management approaches that maintain high corn yields while minimizing N losses.


Though N cycle processes are well characterized, less is known about factors controlling N’s fate when these processes interact. The interaction of sources of available N with SOM pools is rarely considered where sufficient labile N is added as fertilizer. This often leads producers to over-apply N fertilizer. This proposal directly addresses the issue of N use efficiency in intensively managed systems. Adequate N supply is required to achieve economic, producer acceptable, yields. Since the relationship between yield and N uptake is usually tightly conserved, achieving ever-higher yields often depends on greater N uptake, which in turn requires greater amounts of available N. Fertilizer N has contributed greatly to yield maintenance and increase, in the face of SOM decline around the world. However, overuse of N fertilizer to ensure consistent crop yields has led to decreased crop system N use efficiency (Tilman and others 2002). Excessive N fertilizer use threatens environmental quality and human health. Emission of greenhouse gases, specifically N2O, is attributed to inefficient use of N fertilizers. Fertilizer N also typically accounts for approximately 50% of the fossil energy input into intensively managed crops like corn. Environmental degradation and rising energy costs have become major impediments to both the profitability and sustainability of intensively managed cropping systems.


Climate change science suggests a slight increase in overall precipitation in the US Corn Belt, with a significant increase in intensity and frequency of large rainfall events in the spring/early summer corn growing season (Kellner and Niyogi, 2015). This pattern is consistent with weather events over the past five years. These changes in precipitation patterns will drive increased loss of both mineralized and fertilizer N from soils, via denitrification and leaching. Loss directly from soils via denitrification, and in-stream denitrification of NO3- leached to surface waters, will also increase emission of N2O. Therefore, one potential indirect consequence of climate change driven precipitation changes and N loss could be increased N-based GHG production.


Mitigation of the N flux from corn fields requires improved understanding of N release from soil organic N pools to provide better N rate recommendations which can account for variation in N mineralization between years; improved N management practices to reduce N loss and better synchronize soil N availability with corn’s N demand; and an increase corn N use efficiency. Improved management practices include N rate recommendation systems, timing and placement of fertilizer N, selection of N source and additives that slow NO3- formation to reduce loss and better synchronize N supply with crop demand. Improved N management practices may also include using crop sensors or other decision tools to guide in-season application, and fertilizer products and additives that reduce loss - all of these practices will aid corn producers in adapting to climate change, provide environmental benefits, improve corn yield, and give a better economic return to N.


The ultimate success of the project – reduced N loss, efficient N fertilizer use and continued increase in corn yield - lies in the N recommendations and N management practices developed being adopted and utilized corn growers across the corn producing regions of the U.S. This will require a thorough understanding of how these practices impact N availability and yield, understanding the producer and adviser decision making process, and development of decision tools that will help people make good N fertilization decisions. Thus, a strong, transformative extension education/outreach program targeted to producers and crop advisors (in addition to extension educators, local/state/federal regulatory personnel, and policy makers), is embedded in this project.


The long-range prosperity of the U.S. agricultural and food system is increasingly tied to concerns over environmental impact including climate change. Unused N fertilizer represents a reduction in profitability, can cause environmental degradation and can impact global climate change. Over- application of fertilizer N is often the result of difficulty in predicting the amount of plant available N supplied from mineralization of soil organic N. This project will provide information to more accurately determine the contribution of organic N to corn’s N needs, and resulting fertilizer requirement. In addition, decision making tools will assist growers in determining how best that fertilizer can be applied to result in high utilization by the target crop, and minimal loss to the environment. Improved N management across the U.S. Corn Belt will make important contributions to reduced N2O emissions, reduced NO3- movement to surface and groundwater, and will still result in high levels of corn productivity.

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