Understanding and predicting nitrogen dynamics in the Midwest United States Corn Belt

Understanding nitrogen (N) dynamics in agricultural systems is very critical for profitable corn production while minimizing the N losses from agroecosystems which cause environmental degradation and increase cost of production. The nitrogen cycle in agricultural systems is complex; it includes interactions among many pools and fluxes. These pools and fluxes are controlled by climate, soil properties and crop management. The overall objective of this research is to better understand the impacts of crop management practices on cropping systems N dynamics. Potentially mineralizable N (PMN), measures the release of plant-available N from soil organic matter, is controlled by the soil properties, climate and past crop management practices. However, the effect size and relationship with the crop yield across different conservation and conventional crop management practices remain uncertain. Using a meta-analysis approach, chapter two examined the effects of various conservation and conventional crop management practices on PMN in soil. This quantitative review suggests that, as compared with no fertilizer, cropping systems with inorganic N fertilizer had 22%, and systems with manure had 34% higher PMN. Three or more different crops in rotation had 44% higher PMN than continuous cropping systems. Cropping systems with leguminous cover crops had 211% higher PMN than systems without cover crops. Compared with till systems, no-till systems had 13% higher PMN. Although few studies reported PMN and crop yield, in those that did report both variables, conservation crop management practices consistently increased both PMN and yield. Consistent with the use of PMN as a soil health indicator, this study suggests that practices benefiting PMN also benefit yield. Uncertainties about the effects of inorganic N fertilizer on soil organic matter has led to a great debate about the long-term sustainability of fertilized continuous corn production systems in the Corn Belt. Fertilizer application enhance the primary productivity and thereby increase the soil organic matter by adding higher residue inputs. Whereas, other studies have suggested N fertilizer application enhances the microbial activity and thereby decreasing the soil organic matter. The objective of chapter three was to quantify the effects of inorganic N fertilizer on soil organic matter mineralization using a combination of field and laboratory experiments. In the field, at the onset of rapid corn N uptake, N fertilizer reduced gross ammonification rate by 12-15%. A companion laboratory experiment suggests that the negative effect of N fertilizer was due to direct effect of ammonium fertilizer addition rather than indirect effects of N on crop growth that affect gross ammonification such as soil water content and temperature (i.e., well-fertilized crops use more soil water and shade the soil). Ammonium pool was negatively associated with the gross ammonification rate. This work demonstrates that optimum rates of inorganic N fertilizer does not enhance SOM mineralization and increases crop yield and residue input to the soil and therefore, does not contribute to reducing SOM content of conventionally managed continuous corn production systems of Midwestern US Corn Belt. Careful management of N is agroecosystems require to match the N supply with crop N requirement. Late spring soil nitrate test and end of season corn nitrate test are commonly used methods to determine the N fertilizer recommendations in corn cropping systems of Midwestern US Corn belt. However, late spring soil nitrate test is an indicator of N supplying capacity of soil and the end of season test is a post hoc test which indicates the whether the N in corn was low, optimum or excessive and it cannot be used for in-season N fertilizer recommendation. Chapter four evaluated the potential for corn stalk sap nitrate concentration to make a useful tool to monitor crop N status and determine the need for supplemental N fertilizer input. Multiple N rate trials were conducted across the state of Iowa to determine the response of corn stalk sap nitrate concentration at the V7-V8 development stage to soil N availability and crop N demand. There was a positive linear or quadratic response of sap nitrate concentration to N fertilizer rate at each site. Grain yield had positive association with the sap nitrate concentration at V7-V8 developmental stage. This one-year study conducted at multiple locations suggested that 570-820 ppm N was the sap nitrate concentration sufficiency range at V7-V8 corn development stage to maximize net return from per unit of N applied per unit of land. Sap nitrate test can be used to make in-season fertilizer N recommendations based on the plant N status

Nitrogen Fertilizer Suppresses Mineralization of Soil Organic Matter in Maize Agroecosystems

The possibility that N fertilizer increases soil organic matter (SOM) mineralization and, as a result, reduces SOM stocks has led to a great debate about the long-term sustainability of maize-based agroecosystems as well as the best method to estimate fertilizer N use efficiency (FNUE). Much of this debate is because synthetic N fertilizer can positively or negatively affect SOM mineralization via several direct and indirect pathways. Here, we test a series of hypotheses to determine the direction, magnitude, and mechanism of N fertilizer effect on SOM mineralization and discuss the implications for methods to estimate FNUE. We measured the effect of synthetic N fertilizer on SOM mineralization via gross ammonification at two long-term experiments in central and southern Iowa, USA with replicated plots of continuous maize that received one of three “historical” N fertilizer rates (zero, moderate or high) from 1999 to 2014. In 2015, prior to our measurements, we split the historical N fertilizer rate plots into two subplots that received either the site-specific agronomic optimum N rate or zero N fertilizer. At the onset of rapid maize N uptake, N fertilizer reduced gross ammonification by 13–21% (2–5 kg NH4-N ha−1 d−1). A companion laboratory experiment rejected the hypothesis that differences in net primary productivity between fertilized and unfertilized treatments explained the negative effect of N fertilizer on SOM mineralization. Moreover, the NH4+ pool size was negatively correlated with the gross ammonification rate (r2 = 0.85, p \u3c 0.001). Thus, we conclude that NH4+ -N fertilizer had a direct suppressive effect on SOM mineralization. These results demonstrate that the direct effect of N fertilizer on microbial activity can exceed the indirect effects of N fertilizer via large changes in NPP that alter organic matter inputs, soil temperature and moisture content. The magnitude of this effect and specificity to NH4+ -N has significant implications for fertilizer management as well as the measurement and modeling of agroecosystem N dynamics including FNUE

Nitrogen Fertilizer Suppresses Mineralization of Soil Organic Matter in Maize Agroecosystems

The possibility that N fertilizer increases soil organic matter (SOM) mineralization and, as a result, reduces SOM stocks has led to a great debate about the long-term sustainability of maize-based agroecosystems as well as the best method to estimate fertilizer N use efficiency (FNUE). Much of this debate is because synthetic N fertilizer can positively or negatively affect SOM mineralization via several direct and indirect pathways. Here, we test a series of hypotheses to determine the direction, magnitude, and mechanism of N fertilizer effect on SOM mineralization and discuss the implications for methods to estimate FNUE. We measured the effect of synthetic N fertilizer on SOM mineralization via gross ammonification at two long-term experiments in central and southern Iowa, USA with replicated plots of continuous maize that received one of three “historical” N fertilizer rates (zero, moderate or high) from 1999 to 2014. In 2015, prior to our measurements, we split the historical N fertilizer rate plots into two subplots that received either the site-specific agronomic optimum N rate or zero N fertilizer. At the onset of rapid maize N uptake, N fertilizer reduced gross ammonification by 13–21% (2–5 kg NH4-N ha−1 d−1). A companion laboratory experiment rejected the hypothesis that differences in net primary productivity between fertilized and unfertilized treatments explained the negative effect of N fertilizer on SOM mineralization. Moreover, the NH4+ pool size was negatively correlated with the gross ammonification rate (r2 = 0.85, p < 0.001). Thus, we conclude that NH4+-N fertilizer had a direct suppressive effect on SOM mineralization. These results demonstrate that the direct effect of N fertilizer on microbial activity can exceed the indirect effects of N fertilizer via large changes in NPP that alter organic matter inputs, soil temperature and moisture content. The magnitude of this effect and specificity to NH4+-N has significant implications for fertilizer management as well as the measurement and modeling of agroecosystem N dynamics including FNUE

Understanding and predicting nitrogen dynamics in the Midwest United States Corn Belt

Understanding nitrogen (N) dynamics in agricultural systems is very critical for profitable corn production while minimizing the N losses from agroecosystems which cause environmental degradation and increase cost of production. The nitrogen cycle in agricultural systems is complex; it includes interactions among many pools and fluxes. These pools and fluxes are controlled by climate, soil properties and crop management. The overall objective of this research is to better understand the impacts of crop management practices on cropping systems N dynamics. Potentially mineralizable N (PMN), measures the release of plant-available N from soil organic matter, is controlled by the soil properties, climate and past crop management practices. However, the effect size and relationship with the crop yield across different conservation and conventional crop management practices remain uncertain. Using a meta-analysis approach, chapter two examined the effects of various conservation and conventional crop management practices on PMN in soil. This quantitative review suggests that, as compared with no fertilizer, cropping systems with inorganic N fertilizer had 22%, and systems with manure had 34% higher PMN. Three or more different crops in rotation had 44% higher PMN than continuous cropping systems. Cropping systems with leguminous cover crops had 211% higher PMN than systems without cover crops. Compared with till systems, no-till systems had 13% higher PMN. Although few studies reported PMN and crop yield, in those that did report both variables, conservation crop management practices consistently increased both PMN and yield. Consistent with the use of PMN as a soil health indicator, this study suggests that practices benefiting PMN also benefit yield. Uncertainties about the effects of inorganic N fertilizer on soil organic matter has led to a great debate about the long-term sustainability of fertilized continuous corn production systems in the Corn Belt. Fertilizer application enhance the primary productivity and thereby increase the soil organic matter by adding higher residue inputs. Whereas, other studies have suggested N fertilizer application enhances the microbial activity and thereby decreasing the soil organic matter. The objective of chapter three was to quantify the effects of inorganic N fertilizer on soil organic matter mineralization using a combination of field and laboratory experiments. In the field, at the onset of rapid corn N uptake, N fertilizer reduced gross ammonification rate by 12-15%. A companion laboratory experiment suggests that the negative effect of N fertilizer was due to direct effect of ammonium fertilizer addition rather than indirect effects of N on crop growth that affect gross ammonification such as soil water content and temperature (i.e., well-fertilized crops use more soil water and shade the soil). Ammonium pool was negatively associated with the gross ammonification rate. This work demonstrates that optimum rates of inorganic N fertilizer does not enhance SOM mineralization and increases crop yield and residue input to the soil and therefore, does not contribute to reducing SOM content of conventionally managed continuous corn production systems of Midwestern US Corn Belt. Careful management of N is agroecosystems require to match the N supply with crop N requirement. Late spring soil nitrate test and end of season corn nitrate test are commonly used methods to determine the N fertilizer recommendations in corn cropping systems of Midwestern US Corn belt. However, late spring soil nitrate test is an indicator of N supplying capacity of soil and the end of season test is a post hoc test which indicates the whether the N in corn was low, optimum or excessive and it cannot be used for in-season N fertilizer recommendation. Chapter four evaluated the potential for corn stalk sap nitrate concentration to make a useful tool to monitor crop N status and determine the need for supplemental N fertilizer input. Multiple N rate trials were conducted across the state of Iowa to determine the response of corn stalk sap nitrate concentration at the V7-V8 development stage to soil N availability and crop N demand. There was a positive linear or quadratic response of sap nitrate concentration to N fertilizer rate at each site. Grain yield had positive association with the sap nitrate concentration at V7-V8 developmental stage. This one-year study conducted at multiple locations suggested that 570-820 ppm N was the sap nitrate concentration sufficiency range at V7-V8 corn development stage to maximize net return from per unit of N applied per unit of land. Sap nitrate test can be used to make in-season fertilizer N recommendations based on the plant N status.</p

Conservation Agriculture Practices Increase Potentially Mineralizable Nitrogen: A Meta-Analysis

Potentially mineralizable nitrogen (PMN) is considered an important indicator of soil health. Cropping systems management can affect PMN. However, the effect size and relationship with crop yield across specific management practices remain uncertain. We conducted a quantitative review to understand how conservation agriculture management practices affect PMN including N fertilizer application, cropping system diversity, and tillage system as well as the relationship of crop yield with PMN. Data were extracted from 43 studies published in peer-reviewed journals, providing 494 paired comparisons of PMN and 26 paired comparisons of PMN and yield across selected crop management practices. In our meta-analysis, the effect size for each management practice was expressed as a response ratio, calculated as PMN or yield for the fertilizer application, high crop diversity, and no-till system to the no-fertilizer, less diverse crop system, and tillage system. On average, N-fertilized cropping systems had greater PMN: compared to no N fertilizer, inorganic N fertilizer had 22%, and manure had 34% higher PMN. Diverse cropping systems also had greater PMN: three or more different crops in rotation had 44% greater PMN than continuous cropping systems; cropping systems with a leguminous cover crop had 211% greater PMN than systems without cover crops. Compared to till systems, no-till systems had 13% higher PMN. Overall, conservation practices consistently increased both PMN and yield; however, the increase in PMN and yield were not correlated. Consistent with the use of PMN as a soil health indicator, this synthesis demonstrates that practices benefiting PMN also benefit yield.This is a manuscript of an article published as Mahal, Navreet K., Michael J. Castellano, and Fernando E. Miguez. "Conservation Agriculture Practices Increase Potentially Mineralizable Nitrogen: A Meta-Analysis." Soil Science Society of America Journal (2018). doi: 10.2136/sssaj2017.07.0245. Posted with permission.</p

Role of sulfur mineralization and fertilizer source in corn and soybean production systems

Sulfur (S) is an important nutrient for plant growth and crop yield. In the northern US Corn Belt, a decrease in atmospheric S deposition and an increase in grain harvest have increased the frequency of S deficiency in corn and soybean. Nevertheless, S deficiency remains difficult to predict owing to complex interactions between the production of plant-available sulfate-S from soil organic matter (SOM) mineralization and sulfate-S losses to leaching. Our objective was to measure corn and soybean yield response to four S fertilizers (ammonium sulfate, elemental S, gypsum, and polyhalite) in the first year following fertilizer application and in the second (residual) year following fertilizer application in Iowa, USA. Across four site-years, none of the S fertilizer products increased soybean yield. Across 12 site-years in the first year following application, sulfate-S based fertilizers increased corn yield in four site-years while elemental S had no effect. Across six site-years in the second residual year following application, elemental S, polyhalite, and gypsum increased corn yield in one siteyear while ammonium sulfate had no effect. Laboratory incubations confirmed that there was slower production of plant-available S from elemental compared to sulfate-based fertilizers, potentially explaining the lack of elemental S effect in the first year following application. In contrast to our expectations, there was a weak, but positive relationship between corn yield response to S fertilizer and SOM concentration. Overall, the kinetics of S fertilizer mineralization and solubility appear to affect the magnitude and timing of crop response to S fertilizer.This is the peer reviewed version of the following article: Mahal, Navreet, John Sawyer, Javed Iqbal, Aaron M. Sassman, Renuka Mathur, and Mike Castellano. "Role of sulfur mineralization and fertilizer source in corn and soybean production systems." Soil Science Society of America Journal (2022), which has been published in final form at doi:10.1002/saj2.20417. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited

Soil Labile Carbon and Nitrogen Fractions after Eleven Years of Manure and Mineral Fertilizer Applications

Manure nutrient management can affect soil carbon (C) and nitrogen (N) fractions. The objective of this study was to determine the effects of long- term manure and mineral fertilizer applications on C and N fractions. This study was conducted for 11 years under corn and soybean rotation. The study rates included low manure (LM (4,194 kg ha−1), based on the crop’s phosphorus (P) requirement), medium manure (MM (8,081 kg ha−1), based on the crop’s N requirement), high manure (HM (16,162 kg ha−1), two times the rate of MM), medium fertilizer (MF (204 kg N ha−1), recom-mended), high fertilizer (HF (224 kg N ha−1), high), and control. Soil samples were collected to measure C and N fractions. HM recorded higher particulate C (8%) at 0–10 cm and higher dissolved C (26%) at 10–20 cm compared to LM. All manure rates had higher permanganate oxidizable C compared to mineral fertilizer rates. Carbon management index was higher under MM compared to the HF (17%) and MF (33%). This study suggests that manure application (16,162 kg ha−1 rate and even 8,081 kg ha−1 and 4,194 kg ha−1 rates in some cases) can enhance C and N pools compared to mineral fertilizer application

Agricultural Management Affects the Active Rhizosphere Bacterial Community Composition and Nitrification

Cropping system diversity provides yield benefits that may result from shifts in the composition of root-associated bacterial and fungal communities, which either enhance nutrient availability or limit nutrient loss. We investigated whether temporal diversity of annual cropping systems (four versus two crops in rotation) influences the composition and metabolic activities of root-associated microbial communities in maize at a developmental stage when the peak rate of nitrogen uptake occurs. We monitored total (DNA-based) and potentially active (RNA-based) bacterial communities and total (DNA-based) fungal communities in the soil, rhizosphere, and endosphere. Cropping system diversity strongly influenced the composition of the soil microbial communities, which influenced the recruitment of the resident microbial communities and, in particular, the potentially active rhizosphere and endosphere bacterial communities. The diversified cropping system rhizosphere recruited a more diverse bacterial community (species richness), even though there was little difference in soil species richness between the two cropping systems. In contrast, fungal species richness was greater in the conventional rhizosphere, which was enriched in fungal pathogens; the diversified rhizosphere, however, was enriched in Glomeromycetes. While cropping system influenced endosphere community composition, greater correspondence between DNA- and RNA-based profiles suggests a higher representation of active bacterial populations. Cropping system diversity influenced the composition of ammonia oxidizers, which coincided with diminished potential nitrification activity and gross nitrate production rates, particularly in the rhizosphere. The results of our study suggest that diversified cropping systems shift the composition of the rhizosphere’s active bacterial and total fungal communities, resulting in tighter coupling between plants and microbial processes that influence nitrogen acquisition and retention.This article is published as Bay G, Lee C, Chen C, Mahal NK, Castellano MJ, Hofmockel KS, Halverson LJ. 2021. Agricultural management affects the active rhizosphere bacterial community composition and nitrification. mSystems 6: e00651-21. https://doi.org/10.1128/mSystems.00651-21. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International license

Nitrogen Fertilizer Suppresses Mineralization of Soil Organic Matter in Maize Agroecosystems

The possibility that N fertilizer increases soil organic matter (SOM) mineralization and, as a result, reduces SOM stocks has led to a great debate about the long-term sustainability of maize-based agroecosystems as well as the best method to estimate fertilizer N use efficiency (FNUE). Much of this debate is because synthetic N fertilizer can positively or negatively affect SOM mineralization via several direct and indirect pathways. Here, we test a series of hypotheses to determine the direction, magnitude, and mechanism of N fertilizer effect on SOM mineralization and discuss the implications for methods to estimate FNUE.Wemeasured the effect of synthetic N fertilizer on SOMmineralization via gross ammonification at two long-term experiments in central and southern Iowa, USA with replicated plots of continuous maize that received one of three “historical” N fertilizer rates (zero, moderate or high) from 1999 to 2014. In 2015, prior to our measurements, we split the historical N fertilizer rate plots into two subplots that received either the site-specific agronomic optimum N rate or zero N fertilizer. At the onset of rapid maize N uptake, N fertilizer reduced gross ammonification by 13–21% (2–5 kg NH4-N ha−1 d−1). A companion laboratory experiment rejected the hypothesis that differences in net primary productivity between fertilized and unfertilized treatments explained the negative effect of N fertilizer on SOM mineralization. Moreover, the NH+ 4 pool size was negatively correlated with the gross ammonification rate (r2 = 0.85, p This article is published as Mahal, Navreet Kaur, William R. Osterholz, Fernando E. Miguez, Hanna Poffenbarger, John E. Sawyer, Daniel C. Olk, Sotirios Archontoulis, and Michael J. Castellano. "Nitrogen fertilizer suppresses mineralization of soil organic matter in maize agroecosystems." Frontiers in Ecology and Evolution 7 (2019): 59. doi: 10.3389/fevo.2019.00059.</p

Continuous Monitoring of Soil Nitrate Using a Miniature Sensor with Poly(3-octyl-thiophene) and Molybdenum Disulfide Nanocomposite

There is an unmet need for improved fertilizer management in agriculture. Continuous monitoring of soil nitrate would address this need. This paper reports an all-solid-state miniature potentiometric soil sensor that works in direct contact with soils to monitor nitrate-nitrogen (NO3--N) in soil solution with parts-per-million (ppm) resolution. A working electrode is formed from a novel nanocomposite of poly(3-octyl-thiophene) and molybdenum disulfide (POT–MoS2) coated on a patterned Au electrode and covered with a nitrate-selective membrane using a robotic dispenser. The POT–MoS2 layer acts as an ion-to-electron transducing layer with high hydrophobicity and redox properties. The modification of the POT chain with MoS2 increases both conductivity and anion exchange, while minimizing the formation of a thin water layer at the interface between the Au electrode and the ion-selective membrane, which is notorious for solid-state potentiometric ion sensors. Therefore, the use of POT–MoS2 results in an improved sensitivity and selectivity of the working electrode. The reference electrode comprises a screen-printed silver/silver chloride (Ag/AgCl) electrode covered by a protonated Nafion layer to prevent chloride (Cl-) leaching in long-term measurements. This sensor was calibrated using both standard and extracted soil solutions, exhibiting a dynamic range that includes all concentrations relevant for agricultural applications (1–1500 ppm NO3--N). With the POT–MoS2 nanocomposite, the sensor offers a sensitivity of 64 mV/decade for nitrate detection, compared to 48 and 38 mV/decade for POT and MoS2 alone, respectively. The sensor was embedded into soil slurries where it accurately monitored nitrate for a duration of 27 days.This is a manuscript of an article publsihed as Ali, Md Azahar, Xinran Wang, Yuncong Chen, Yueyi Jiao, Navreet K. Mahal, Satyanarayana Moru, Michael J. Castellano, James C. Schnable, Patrick Schnable, and Liang Dong. "Continuous Monitoring of Soil Nitrate Using a Miniature Sensor with Poly (3-octyl-thiophene) and Molybdenum Disulfide Nanocomposite." ACS Applied Materials & Interfaces (2019). doi: 10.1021/acsami.9b07120. Posted with permission.</p