ENHANCING NITROGEN UTILIZATION IN CORN BASED CROPPING SYSTEMS TO INCREASE YIELD, IMPROVE PROFITABILITY AND MINIMIZE ENVIRONMENTAL IMPACTS

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 1011656
• Multistate No.: NC-_old1195
• Project Start Date: Dec 8, 2016
• Project End Date: Sep 30, 2021
• Program Code: [(N/A)]- (N/A)

Recipient Organization
UNIVERSITY OF CALIFORNIA, DAVIS
410 MRAK HALL
DAVIS,CA 95616-8671

Performing Department
Land, Air and Water Resources

Non Technical Summary
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. 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, an increase in hypoxic zones off the mouth of our major rivers, and increased emissions of powerful greenhouse gases (GHG, i.e. nitrous oxide - N2O). 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. 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. 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, which can result in producers over-applying N fertilizer. But microbial processes can also result in immobilization or sequestering of N in soils, 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 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.

Animal Health Component

50%

Research Effort Categories

Basic

30%

Applied

50%

Developmental

20%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
102	0110	1060	100%

Knowledge Area
102 - Soil, Plant, Water, Nutrient Relationships;

Subject Of Investigation
0110 - Soil;

Field Of Science
1060 - Biology (whole systems);

Keywords

nitrogen use efficiency

corn based cropping systems

soil nitrogen mineralization

Goals / Objectives
Gain a more thorough understanding of the influence of macro- and micro-scale ecosystems and landscape properties on soil N dynamics. Develop nitrogen management decision-making tools for crop advisers and growers.

Project Methods
A wide range of methods will be used. Programs, equipment, and expertise for many committee members are mainly field-based, and for a few are mainly lab-based. An emerging area of expertise for several committee members is measurement of nitrous oxide flux under different management scenarios, contributing to objective 1.Only a few committee members get any funding associated with their membership, thus activities will mainly be based on grants that can be obtained. In some cases, a sub-group of the committee will submit a proposal together (there is one such proposal from four members that is currently in review; few if any grant opportunities are at a large enough scale to support a proposal from the entire committee). In other cases, committee members will identify places that two funded projects can dovetail to enhance the outcome of one or both.Methods that will be employed are thus dependent on which funding efforts are successful. Substantial continuity with methods previously employed by the committee and its members is expected. Likely methods include field trials of nitrogen treatments (timing, source, rate, placement, loss inhibitors), field trials of other management practices (cover crops, rotations, tillage practices), microbiological studies of soils and rhizospheres, measurement of N2O flux, measurement of soil inorganic N content/dynamics, measurement of system parameters (soil temperature and moisture, plant spectral properties) that may help to explain observed N dynamics and behavior.Related, Current and Previous WorkHere we highlight some of the work this multistate committee has been working on. All of the following activities are synergistic. For example, progress in research on Soil N dynamics would help to inform Decision tools. A search of the NIMSS website http://www.nimss.org/ using keywords corn and fertilizer retrieved 325 projects, of the active projects twelve (NCERA_Temp180, NCERA13, WERA_Temp1016, NCERA59, WERA103, NCCC211, NEERA1402, NC1178, NC1182, SERA46, W3147, NCERA103) had some relevance to this project but did not appear to duplicate our efforts. Consultation with specific groups may lead to joint meetings, symposia or other outputs where knowledge can be shared.Soil N dynamicsOptimal N fertilizer rate is known to vary widely across landscapes (Mamo et. al., 2003; Scharf et al., 2005) due to differences in soil N contribution to the crop. Microbial processes largely dictate N transformations in soil and the availability of soil N to crops. Thus it appears that microbial processes and ecosystems vary widely across landscapes in ways that are poorly understood but strongly affect how best to manage fertilizer. Our goal is to contribute to a better understanding of the fundamental processes controlling N dynamics in soil, especially mineralization and immobilization, in order to reduce N fertilizer inputs while maintaining yield and protecting the environment. Currently, several members of the committee are working on a project to quantify the mineralization potential of 32 different soils over a wide range in climatic conditions across eight Midwestern states from Missouri to North Dakota and from Indiana to Nebraska. We are highly interested in soils that show no yield response to N fertilizer, either transiently or ongoing. Additionally, understanding of the microbiology behind this would be desirable, and we have an opportunity to address this with committee member Drijber. Presentation and integration of this data across states has led to discussion of potential manuscripts and grant opportunities at our annual meeting.Several committee members are making contributions to our understanding of N2O fluxes under different management scenarios (Mitchell et al., 2013; Fernández et al., 2015a; Iqbal et al, 2015; Sutradhar et al., 2015; Zhu-Barker et al., 2015; McDaniel et al. in revision). Although nitrous oxide is a minor player in overall soil N dynamics, it is important due to its contribution to atmospheric heat-trapping. Two committee members have promising preliminary data showing that nitrous oxide flux is reduced when nitrogen fertilizer is applied later in the season. These observations formed the basis of a proposal to NIFA from four committee members to further explore this relationship.Most of the processes that control N form and flux in soil are mediated by microorganisms: mineralization-immobilization, nitrification and denitrification, the latter an important contributor to greenhouse N2O emissions. Committee member Drijber has made several recent contributions to our understanding of how arbuscular mycorrhizal fungi influence and are influenced by plant N uptake and soil N dynamics (Duan et al., 2015; Tian et al., 2013; Jeske, 2012 ). This has important implications to NUE as well as C sequestration, as fungal biomass is a significant contributor to the soil carbon pool and aggregate stabilization. Microbial N transformations are greatly influenced by addition (or removal) of organic source materials (Johnson et al., 2012; Lindsey et al., 2013; Pantoja et al., 2015) and by management- or weather-related modification of the soil environment (Pantoja et al., 2015; Roberts et al., 2015; Toosi et al., 2014, McDaniel and Grandy in revision). These references highlight recent contributions from committee members and have been the subject of much discussion at our annual meetings.

Progress 12/08/16 to 09/30/21

Outputs
Target Audience:The target audiences were farmers, commodity groups, certified crop advisors, state and federal agency staff and scientists and non-governmental organization (Sustainable Conservation, Community Alliance of Family Farmers, Environmental Defense Fund, etc.). The primary target group was USDA Cooperative Extension, with the goal of informing the mission of the agricultural experiment station to convey the latest and most up to date results to inform policy makers and practitioners. Our goal was also to target fellow researchers to provide information on better fertilizer nitrogen management practices, and in addition, provide the basic and applied science to address soil nitrogen availability. Soil nitrogen availability remains both highly contested and least understood of sources of nitrogen for crop utilization. Presentations from my research group activities include the annual California Plant and Soil Conference, UC Davis Russell Ranch Sustainable Agriculture Facility field day, and the California Department of Food and Agriculture Fertilizer Research and Education Program annual meeting, Western Plant Health Association annual meeting and the Soil science Society of America annual meeting. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Graduate student researchers (Veronica Romez, Geoff Koch and Cole Smith) were involved in performing analyzing and writing up the results. It included the assistance of many undergraduate assistants who were involved in all aspects of the project. In addition, the project provided paid internships for 4 undergraduate students that satisfied their major degree requirements. How have the results been disseminated to communities of interest?Multiple outreach events were carried out over the course of the project period, each aimed at reaching different audiences. Project results were shared at each of there events listed. Many of these events were attended by growers and farmers, who were often the majority of the audience. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? The group's main goal was to understand and interpret science that will improve fertilizer nitrogen use in corn and other cropping systems, such as those that include soybean and other crops such as processing tomatoes. There is an urgent need to understand the soil and agronomic management factors that affect the release of plant available nitrogen (N) from soil organic fractions in order to achieve improvements in nitrogen use efficiency (NUE) and most importantly to minimize nitrogen loss to the environment via runoff and leaching. As a committee member from California, information on nitrogen availability from soil is extremely important, but as California promotes the use of soil organic amendments from green waste and food waste sources, there is a critical need to understand plant nitrogen availability from these other organic nitrogen sources. In addition, California farmers are required by state law to account for these additional nitrogen sources to protect both surface and subsurface water resources. It is imperative to precisely manage nitrogen from soil, organic amendments and fertilizer as a combined approach to ensure the maximum NUE is achieved. Nitrogen availability from organic sources are highly influenced by seasonal and site-specific conditions, making its prediction of availability challenging. The challenge is directly related to complex interactions among climate, soil biology and soil properties, organic input quality and chemistry, and type and intensity of agronomic management practices. Although in general, nitrogen can be released quickly from fertilizers, there is limited information on its effect on organic nitrogen containing sources. The inclusion of nitrogen from organic sources in fertilizer recommendations is essential to improving NUE. Underestimation of the contribution of organic nitrogen to plant-available N can result in excess nitrogen loss to the environment. Excess nitrogen fertilization often leads to increased nitrous oxide emissions as well contributing to climate change. To avoid such serious consequences of over nitrogen fertilization, a better predictive capability to predict N release from organic sources and synchrony with fertilizer nitrogen with crop N demand is needed. The use of organic amendments and fertilizers has the potential to improve agricultural sustainability, yet the nutrient availability profiles of these materials must be better understood. With strong growth in the sale of organically certified agricultural products, this understanding is also critical to farm-level profitability. Objectives were addressed: 1. Gain a more thorough understanding of the influence of macro- and micro-scale ecosystems and landscape properties on soil N dynamics. We combined data gathered from the literature, aerobic lab incubations and field trials to better understand plant available N release from organic nutrient sources. Results from the literature meta-modeling exercise showed that the commonly used single pool model may not be the most appropriate model for all organic amendments (mean sigma = 17.4). Notably, the model parameters representing turnover rates (k) did not differ by carbon to nitrogen (C/N) ratio, unlike potentially mineralizable N. After 60-days of aerobic incubation, only amendment type was significantly different in total net mineralized N (p= 5.54e-15). Data from 37 studies that reported amendment C/N ratio, with a total of 861 observations were used. The dataset was divided using C/N ratio as a grouping factor and fit to the single pool exponential kinetic model (Stanford and Smith, 1972) using Bayesian non-linear regression. Identification of unknown parameters, both representing the total percent nitrogen mineralized (N0) or the turnover rate characteristic of the mineralization process (k), were carried out. After the fitting procedure, a resampling technique using Markov Chain Monte Carlo sampling, which samples over 2000 iterations of the algorithm, was implemented. The Gelman-Rubin statistic, R-hat, of approximately 1 was used to determine model convergence. Results show that low C/N ratio material 0-5 have a mean percent nitrogen of 38.36 (CI: 23.25-51.72), next C/N ratio 5-10 had a mean value of 9.82 (CI: 7.51-12.27), middle range C/N 10-15 of 8.07 (CI: 6.27-9.90) and high C/N ratio 15-30 of 1.12 (CI: 0.23-2.04). The model fits for the single pool were generally poor and need further refinements as seen by high sigma values (mean sigma = 17.4). Composts and organic fertilizers differed significantly in potentially available N (p<0.05). Turnover rates did not significantly differ, but organic fertilizers were slightly higher (p=0.12) Full factorial aerobic laboratory incubations were completed using contrasting soil textural types (clay vs. sand) under two temperature regimes (20°C and 10°C). The results showed that both temperature and soil type have inconsistent impacts on net nitrogen release. Additionally, the results showed that across different organic amendments with varying C/N ratios, the strength of the relationship to N release is stronger for high-N containing amendments. The temperature response appeared variable across the organic amendments containing low C/N ratios. Field trials showed that both compost and pelletized chicken manure applied at a rate of 140 kg N/ha showed higher pepper (C. annuum) yield under the compost amendment treatment (4087 lbs/acre) when compared to the other organic amendments. Both compost and chicken pellets also increased NUE (p=0.002) when measured with nitrogen stable isotope techniques (15N labeled urea). Chicken manure pellets had the highest NUE which (42% of applied N) was an unexpected result. The results reinforce that the nitrogen availability from organic amendments is predominately controlled by carbon to nitrogen C/N ratios. Results showed that early in the release of N from the materials, both temperature and soil type were significant influences of net N mineralized (p= 0.028 and p= 0.029, respectively). Yet, over the entire 60-day incubation period these factors appear to become less relevant. With the amendment type being the only significantly different factor (p= 5.54e-15) by the end. Data was used to constrain the DayCent model output and compare results with COMET-Farm tool reports. Both organic amendments, compost and chicken pellets, showed increases in fertilizer use efficiencies. When calculated as an indirect, enrichment difference, fertilizer N utilization was significantly higher (p=0.002) but calculated directly no significant difference was detected. Using the indirect calculation, the A-Value or fertilizer equivalents was determined to be significantly different than the inorganic N treatment (p=0.0012). Total -15N also showed to be evenly distributed between crop components with a max 15N enrichment of 0.85 % excess. Results indicate that the high C:N ratio amendment, compost increased total pepper yield overall (mean = 32.6 kg and sd = 10.7). Organic fertilizers have diverse mineralization responses across different temperatures and soil textures. The magnitude of these impacts appears variable depending on specific conditions. Incubations show, early nitrogen release can impact dynamics of nitrogen release but over time this impact is important. This finding has significant implications for long-term agronomic planning, potentially allowing growers to reduce applications within certain soil types as well as adjust for seasonal temperature fluctuations. Additionally, if growers are attempting to time crop N uptake with N release it will be challenging to predict this release. 2) Based on our literature data collection, C/N ratio may be an appropriate single predictor for homogenous, high-N containing fertilizers, but additional factors are necessary to understand nutrient release for more complex carbon low C/N ratio amendments.

Publications

• Type: Journal Articles Status: Published Year Published: 2021 Citation: Ruoya Ma, Jianwen Zou, Zhaoqiang Han, Kai Yu, Shuang Wu, Zhaofu Li, Shuwei Liu, Shuli Niu, William R Horwath, Xia Zhu?Barker. 2021. Global soil-derived ammonia emissions from agricultural nitrogen fertilizer application: A refinement based on regional and crop-specific emission factors. Global Change Biology 27: 855-867.
• Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Savannah Haas, William Horwath, Xia Zhu-Barker. 2021. Compost Effects on Agroecosystem Soil C and N Cycling Dynamics. Proceeding of the California Plant and Soil Conference, Fresno, CA, February 8-9, 2021.
• Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: William R. Horwath, Xia Zhu-Barker and Cole Smith. 2021. Evaluation of Certified Organic Fertilizers for Long-Term Nutrient Planning. Proceeding of the Annual Fertilizer Research and Education Program, Sacramento, CA. October, 27-28, 2021.
• Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Cole Smith and William Horwath. Selecting Compost for Use in Agricultural Production. Presented at theThe EcoFarm Conference: Re-imagining Our Future. Presentation was virtual. January 21st, 2021.
• Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Cole Smith and William Horwath. Selecting Compost for Use in Agricultural Production. Dirt First Conversation Series: The Compost Conundrum. Virtual. May 4th, 2021.
• Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Cole Smith and William Horwath. Kinetic Modelling aof Nitrogen Mineralization from Organic Fertilizers. ASA, CSSA, SSSA 2020 Virtual Annual Meeting, Salt Lake City. November 11th, 2021.

Progress 10/01/19 to 09/30/20

Outputs
Target Audience:Target audience is comprised of farmers, commodity groups, certified crop advisors, state and federal agency staff and scientists and non-governmental organization (Sustainable Conservation, Community Alliance of Family Farmers, Environmental Defense Fund, etc.). Our goal is also to target fellow researchers to provide information on better fertilizer nitrogen management practices. Presentations from group activities include the annual California Plant and Soil Conference, UC Davis Russell Ranch Sustainable Agriculture Facility field day, and the California Department of Food and Agriculture Fertilizer Research and Education Program annual meeting, Western Plant Health Association annual meeting and the Soil science Society of America annual meeting. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Graduate student researcher (Cole Smith) was involved in performing and writing up this research. It included the assistance of many undergraduate assistants. The undergraduate assistants were involved in all aspects of the project. In addition, the project provided paid internships for 4 undergraduate students. How have the results been disseminated to communities of interest?We presented results at the annual California Department of Food and Agriculture Fertilizer Research and Education Program meeting held October 28-29 in Fresno, California. In addition the the results were presented at the 2019 Central Coast Organic Amendments Workshop, Alba, California, November 9th, 2019. What do you plan to do during the next reporting period to accomplish the goals?To date we have made significant progress on many of our objectives, with aerobic laboratory incubations, one field season and multiple outreach events. Additional tasks that need to be accomplished include more laboratory incubations, another field season, and DayCent model evaluation. Research related to this project will continue, including exploring additional factors within the literature derived dataset, aerobic incubations of more amendments at different temperature ranges, the conclusion of a buried litter bag field experiment, kinetic model fitting and DayCent model validation. Information generated by this project aims to increase grower confidence in using organic fertilizers and amendments.

Impacts
What was accomplished under these goals? The group's main goal is to understand and develop knowledge to improve fertilizer nitrogen use in cropping systems. Understanding the release of plant available nitrogen (N) from organic fertilizers is critically important in order to achieve high N use efficiency (NUE) and minimize N loss to the environment. Information on nitrogen availability from soil and organic amendments are required by growers to more precisely manage nutrients according to seasonal and site-specific conditions. The challenge of understanding net N mineralization from soil and organic fertilizers is directly related to complex interactions between climate, soil biology and physical properties, organic input quality and chemistry, and intensive management practices. Although, in general, inorganic N can be released quickly from high-N containing fertilizers, there is limited information on the degree to which biotic and abiotic factors influence characteristics of nutrient release, for example the release rate, total plant availability or the significance of short-term verses long-term immobilization processes. The inclusion of mineralized N from organic sources of N into fertilizer recommendations is essential to improving NUE and optimizing agronomic planning. Underestimation of the contribution of organic soil amendments and fertilizers to plant-available N can result in excess reactive N being released into the environment. Over fertilization has been shown to result in increased nitrous oxide emissions and the pollution of groundwater with nitrate. To avoid such serious consequences of over-fertilization, it is necessary to accurately predict N release from organic sources and sync N supply with crop N demand. The following objectives were addressed: 1. Determine seasonal N mineralization and N mineralization potential in soils repeatedly amended with organic fertilizer in CA. 2. Conduct field trials to assess and confirm lab and DayCent model results and to inform the COMET-Farm. 3. Conduct extensive engagement and outreach to inform on the value and to reassess organic fertilizer amendment rates to avoid N loss and promote healthy soils. We combined data gathered from the literature, aerobic lab incubations and field trials to better understand plant available N release from organic nutrient sources. We used the data to validate the daily time step version of the CENTURY biogeo- chemical model - DayCent. Laboratory Incubations included two full factorial 60-day aerobic Laboratory Incubations; Two full factorial 60-day aerobic laboratory incubations have been completed in contrasting soil textural types (clay vs. sand) under two temperature regimes (20°C and 10°C). Our results show that both temperature and soil type have inconsistent impacts on net N release. Kinetic model fitting is currently on going and will aid in quantifying the impact these factors have on net N release. Additionally, the results show that across different organic amendments with varying C/N ratios, the strength of the relationship to N release is stronger for high-N containing amendments. Additionally, the temperature responses appear to be heterogenous across the organic amendments with low C/N ratios. Our project results indicate 1) Organic fertilizers have diverse mineralization responses across different temperatures and soil textures. This finding has significant implications for long-term agronomic planning, potentially allowing growers to reduce applications within certain soil types as well as adjust for seasonal temperature fluctuations; 2) C/N ratio may be an appropriate single predictor for homogenous, high-N containing fertilizers, but additional factors are necessary to understand nutrient release for more complex amendments such as composts. Additional research is required to determine specifically why amendments that may have similar general characteristics mineralize N differently. Research related to this project will continue, including exploring additional factors within the literature derived dataset, aerobic incubations of more amendments at different temperature ranges, the conclusion of a buried litter bag field experiment, kinetic model fitting and DayCent model validation. Information generated by this project aims to increase grower confidence in using organic fertilizers and amendments.

Publications

• Type: Journal Articles Status: Published Year Published: 2020 Citation: M. D. McDaniel D. T. Walters L. G. Bundy X. Li R. A. Drijber J. E. Sawyer M. J. Castellano C. A. M. Laboski P. C. Scharf W. R. Horwath. 2020. Combination of biological and chemical soil tests best predict maize nitrogen response. Agronomy J. 112:1263-1278
• Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Smith, C., X. Zhu-Barker and W. R. Horwath. Evaluation of Certified Organic Fertilizers for Long-term Nutrient Planning. Proceedings of the Annual California Department of Food and Agriculture Fertilizer Research and Education Program meeting held October 28-29 in Fresno, California.
• Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Smith, C., X. Zhu-Barker and W. R. Horwath. Evaluation of Certified Organic Fertilizers for Long-term Nutrient Planning. Proceedings of the Annual California Department of Food and Agriculture Fertilizer Research and Education Program meeting held October 28-29 in Fresno, California. Pp. 14-18.
• Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Smith, C., X. Zhu-Barker and W. R. Horwath. Evaluation of Certified Organic Fertilizers for Long-term Nutrient Planning. Central Coast Organic Amendments Workshop, Alba, California, November 9th, 2019.

Progress 10/01/18 to 09/30/19

Outputs
Target Audience:Target audience is comprised of farmers, commodity group annual meetings, certified crop advisors, state and federal agency staff and scientists and non-governmental organization (Sustainable Conservation, Community Alliance of Family Farmers, Environmental Defense Fund, etc.). The group's main efforts are targeted to fellow researchers to provide information on better fertilizer nutrient management practices. Presentations from group activities include the annual California Plant and Soil Conference, UC Davis Russell Ranch Sustainable Agriculture Facility field day, and the California Department of Food and Agriculture Fertilizer Research and Education Program annual meeting, Western Plant Health Association annual meeting and the Soil science Society of America annual meeting). Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Graduate student researcher (Cole Smith) was involved in performing and writing up this research. It included the assistance of many undergraduate assistants. The undergraduate assistants were involved in all aspects of the project. JCole Smith is transitioning from the master degree to a PhD program. How have the results been disseminated to communities of interest?We presented results at the annual California Department of Food and Agriculture Fertilizer Research and Education Program meeting held October 28-30 in Fresno, California. In addition the the results were presented at the 2019 Central Coast Organic Amendments Workshop, Alba, California, November 9th, 2019. What do you plan to do during the next reporting period to accomplish the goals?To date we have made significant progress on many of our objectives, with aerobic laboratory incubations, one field season and multiple outreach events. Additional tasks that need to be accomplished include more laboratory incubations, another field season, and DayCent model evaluation. As part of this extension we are proposing to enhance our project objectives through developing the literature review into a meta-analysis based on the data collected as well as conduct an additional organic amendments field day in Fall 2020. We plan to conduct an additional field trial using a different method that is more adaptable to our partner grower partner field operation. We anticipate completion of this trial in Fall 2020. Concerning the laboratory incubations, we are currently in our third incubation and plan to continue a fourth next year. We currently have 9 remaining amendments from our original proposed list and aim to have these completed by late Spring 2020. The modelling component of our objectives will begin once sufficient data is acquired. Our current plan is to begin this during Summer 2020 with expected completion Fall 2020. Additional tasks to be completed include finalizing the literature review analyzing the data using meta statistical procedures and hosting another public organic amendments field day in Fall 2020.

Impacts
What was accomplished under these goals? The group's main goal is to understand and develop knowledge to improve fertilizer nitrogen use in cropping systems. Nitrogen is often a limiting nutrient in all intensively managed cropping systems due to the large nitrogen requirement of modern crops. We used a combination of literature values, lab incubations and field trials to calibrate and verify the DayCent model to predict the seasonal and long-term nutrient value of organic fertilizer amendments for soil productivity improvement and nutrient management. We specifically determined nitrogen mineralization responses to predict the long-term effects of repeated annual applications of organic fertilizers on soil N availability. Key to effectively use the information on nitrogen mineralization generated in this project is the parameterization of the DayCent model, so that the model can accurately predict nitrogen mineralization rates at different soil temperatures under soil conditions in California throughout the year. Most models use default values resulting in poor prediction outcome. Our results will provide for adjustments of nutrient management guidelines depending on organic fertilizer sources, soil type, and climate data. The information generated in this research will be used by UC Extension, CCAs and farmers to reassess nitrogen management across a variety of crops. This is a three-year project and to date we have accomplished literature review and one season field trial. The laboratory incubation is on-going and a second season of field trials is being conducted. The outcome of this research will allow for adjustments of nutrient management plans to maintain and increase crop productivity, reduce the potential for N loss to groundwater, and minimize greenhouse gas emissions. The following objectives were addrtessed: 1. Determine seasonal N mineralization and N mineralization potential in soils repeatedly amended with organic fertilizer in CA. 2. Conduct field trials to assess and confirm lab and DayCent model results and to inform the COMET-Farm. 3. Conduct extensive engagement and outreach to inform on the value and to reassess organic fertilizer amendment rates to avoid N loss and promote healthy soils. We evaluated organic amendments consisting of green-waste compost and pelletized chicken manure to determine whether they can increase fertilizer nitrogen utilization compared to the control (urea only). Calculated as the fraction of total fertilizer taken up by the crop by using enrichment difference in both the crop fruit and biomass divided by the percent enrichment of the applied fertilizer, fertilizer utilization was significantly higher (p=0.0015) for organic amendments than for urea alone. The true recovery of applied 15N was calculated as a percent of labelled fertilizer directly taken up by crops and it showed no significant difference (p = 0.094) among organic amendments. However, the15N enrichment data showed that fertilizer N was evenly distributed between crop residue and fruit. In addition to field studies, multiple laboratory incubations were initiated. They were aerobic incubations of soils with a range of texture and fertilizer amendments sources lasting 60 days at standard temperature and moisture. Initial results indicate that soil texture has an influence on the rate of nitrogen mineralization for a select number of organic amendments. The nitrogen mineralization rate of soils amended with urea or the low C: N ratio amendment (i.e chicken pellets) was higher in the sandy soil than in the clay soil. However, for the high C: N ratio amendments (i.e. compost), higher N mineralization rate was found in the clay soil than in the sandy soil. A similar result was detected during the second incubation of different organic amendment, for example seabird guano and fish meal responded similarly in each soil type but feather meal and blood meal different. Statistical modelling to assess the magnitude of environmental influences is currently on-going.

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Smith, C., X. Zhu-Barker and W. R. Horwath. Evaluation of Certified Organic Fertilizers for Long-term Nutrient Planning. Proceedings of the Annual California Department of Food and Agriculture Fertilizer Research and Education Program meeting held October 28-30 in Fresno, California.
• Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Exploring Nitrogen Fertilizer Transformations Using an Indirect 15-N Field Method in California's Central Coast Vegetable Crops. C Smith, X Zhu-Barker, M de la Fuente, WR Horwath - SSSA International Soils Meeting, 2019
• Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Improving Nutrient Use and Reducing Greenhouse Gas Emissions of Dairy Manure through Hydrodynamic Cavitation and Chemical Coagulation Processes. R Ellison, X Zhu-Barker, WR Horwath - SSSA International Soils Meeting, 2019
• Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Responses of soil organic matter stability, N transformation processes and nitrous oxide production to compost application in long-term sustainable managed soils X Zhu-Barker, C Xu, Y Qiong, WR Horwath - AGU Fall Meeting 2019, 2019

Progress 10/01/17 to 09/30/18

Outputs
Target Audience:Target audience is comprised of farmers, commodity group annual meetings, certified crop advisors, state and federal agency staff and scientists and non-governmental organization (Sustainable Conservation, Community Alliance of Family Farmers, Environmental Defense Fund, etc.). The group's main efforts are targeted to fellow researchers to provide information on better fertilizer nutrient management practices. Presentations from group activities include the annual California Plant and Soil Conference, UC Davis Russell Ranch Sustainable Agriculture Facility field day, and the California Department of Food and Agriculture Fertilizer Research and Education Program annual meeting, Western Plant Health Association annual meeting and the Soil science Society of America annual meeting). Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Graduate student researchers (Jordan Wade and Hannah Waterhouse) were involved in performing and writing up this research. It included the assistance of two undergraduate assistants. The undergraduate assistants were involved in all aspects of the project. Jordan is now a PhD student at the Ohio State University. How have the results been disseminated to communities of interest?A variety of new soil tests to predict soil mineralizable nitrogen are currently being promoted for use in commercial test labs as an indicator of soil health. This project was successful at increasing the understanding of the myriad of intertwined factors that surround the prediction of nitrogen mineralization with the results now published in scientific journals. The use of SEM and soil iron fractions to predict N mineralization is a paradigm shift. Soil iron was previously thought to be more associated with the stabilization of soil carbon. However, since soil nitrogen is intimately associated with soil carbon the relationship can be taken advantage of to predict soil nitrogen mineralization and availability. Throughout presentations and interactions with industry and research, many have expressed gratitude on efforts to determine new soil tests to examine soil nitrogen and its role as a nitrogen source for crop uptake. One of the main takeaways for many growers that have been at outreach events is that their soil has an innate ability to supply a considerable amount of N to their crops that they are likely not accounting for. This study provides a new path to understand nitrogen mineralization, and provides an understanding on how to integrate soil nitrogen mineralization into current Nutrient Management Planning. With this new demonstrable method to examine soil nitrogen available growers can confidently reduce their nitrogen fertilization rates to account for in season soil nitrogen mineralization. Further study needs to be done to explore the economic viability of iron based soil tests so growers can be informed on in season soil N mineralization. Our hope is for future studies to develop more rigorous tests and economics to examine profitability in a way that is easily translatable to growers. What do you plan to do during the next reporting period to accomplish the goals?The next phase of research to meet project objectives will examine the effectiveness of organic amendments such as food-based composts to increase soil nitrogen mineralization potential. The use of organic fertilizer materials has been problematic due to its unknown nitrogen availability due to inconsistencies in its preparation. Knowledge of nitrogen availability form organic soil amendments is limited because the nutrients from these sources are gradually released into soils and may be temporally tied up in soil microorganisms or organic matter. The consistency of some of the organic based fertilizer varies considerably depending on the quality and availability of fertilizer materials, such as manures, fish by-products, food processing waste, etc. Therefore, predicting nutrient release from organic based fertilizers is challenging resulting in a dearth of information available to make consistent informed nitrogen management decisions. The nutrient value of annually applied organic fertilizer amendments should provide a more consistent nitrogen mineralization response than infrequent (3 to 5 years, business as usual) applications. However, running field experiments to determine the nitrogen mineralization response from organic soil amendments is impractical without a large study to examine different soil types and regions. This project will combine lab incubations with modeling to evaluate the use of organic fertilizer amendments applied on an annual basis. The uses of organic fertilizer amendments will also add to the potential to sequester soil carbon and improve soil productivity and healthy soil. This project is important to informing policies and management guidelines that promote productive soils. Objectives. The overarching objective is to inform nitrogen management planning with the use of organic amendments. Specific project objectives are: 1) characterize the temperature response of nitrogen mineralization of organic based amendments in soils of the major agriculture production areas; 2) use results to parameterize the DayCent model to predict long-term nitrogen availability; 3) Conduct field trials to validate DayCent model results; and 4) use outreach events to inform on the value of organic soil amendments to increase the nitrogen use efficiency of cropping systems and promote healthy and productive soils.

Impacts
What was accomplished under these goals? The group's main goal is to understand and develop knowledge to improve fertilizer nitrogen use in maize cropping systems. Nitrogen is often a limiting nutrient in all intensively managed cropping systems especially in maize due to the large nitrogen requirement of the crop. In previous year's effort we examined soil tests based on biological parameters associated with the soil microbial community. These tests are based on carbon mineralization and showed to be ineffective in predicting soil nitrogen mineralization. The prediction of soil nitrogen mineralization is necessary to account for soil nitrogen availability so that accurate amounts of fertilizer nitrogen can be applied while avoiding excessive application. We examined the factors affecting nitrogen that is preferentially chemically bound to organo-mineral complexes, with the notion that iron controls the protection of soil nitrogen. We examined the interactive effect of recently-incorporated cover crops, pedogenic soil iron fractions, climate, and soil physio- chemical properties on net nitrogen mineralization rates in a range of California agricultural soils. Agricultural soils from across California with and without winter cover crops were analyzed for soil physical, chemical, and mineralogical properties and incubated in the lab to determine their 28-day net N mineralization rates. Soil properties were then coupled with a structural equation modeling (SEM) approach to understand their direct and indirect effects on net N mineralization in agricultural soils. Our objectives were to: 1) use structural equation modeling to address issues of collinearity in nitrogen mineralization in soils to understand direct and indirect interactions affecting nitrogen mineralization, and 2) evaluate the effects of iron fractions on nitrogen mineralization across managements with and without cover crops, while accounting for variations in soil physiochemical and climatic properties. Specifically, we hypothesized that after accounting for variations in texture, climate, and organic matter content, the strong sorption of organic matter by pedogenic iron will control N mineralization. The inclusion of iron in describing nitrogen mineralization has not been extensively studied. For all managements and incubation intervals done in lab incubations, the inclusion of pedogenic iron fractions increased the multiple and adjusted R2 values describing nitrogen mineralization significantly. The increase in the adjusted R2 values with the inclusion of iron fractions are nearly identical to the increases in the multiple R2 values, demonstrating that the increases in explanatory power from iron offset any penalties due to overparameterization. This suggests that the inclusion of soil iron fractions is describing variance that other approaches to assess soil nitrogen mineralization do not capture. This underscores the increased modeling power associated with structural equation models and supports the application of SEM in predicting soil nitrogen mineralization. The role of soil mineralogy in nitrogen mineralization has largely gone unexamined. Here, we use structural equation modeling to illustrate that pedogenic iron fractions play a significant role in nitrogen mineralization dynamics in soils. Our results show that in addition to the widely-accepted relationship between total nitrogen and nitrogen mineralization, iron minerals and pH can also play a significant role describing nitrogen mineralization under different soil management, such as with and without cover crops. These relationships were generally stronger in cover crop treatments, although there was no difference in explained variance in SEM models. While there are several potential mechanisms for the observed relationships, further studies will be needed to explore the relationship between iron, and more generally the soil mineral fraction, and nitrogen mineralization. To this end, structural equation modeling offers increased explanatory power over traditional linear models and has considerable potential to account for covariation among multiple soil characteristics.

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Horwath, WR. How much can soil organic matter realistically be increased with cropping management in California? February 6-7, 2018, California Plant and Soil Conference, Fresno, CA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Horwath, WR. Soil tests to define soil health and productivity. Dec. 6-6, 2018, Soil Security and Planetary Health Conference, The University of Sydney, Australia.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: Wade, J, H Waterhouse, LM Roche, WR Horwath. 2018. Structural equation modeling reveals iron (hydr) oxides as a strong mediator of N mineralization in California agricultural soils. Geoderma 315: 120-129.

Progress 12/08/16 to 09/30/17

Outputs
Target Audience:Target audience includes farmers, commodity group annual meetings, certified crop advisors, state and federal agency staff and scientists and non-governmental organization (Sustainable Conservation, Community Alliance of Family Farmers, Environmental Defense Fund, etc.). Presentations on the ongoing research activities were done to these these stakeholders (i.e., at the national and local state level include the annual California Plant and Soil Conference, UC Davis Russell Ranch Sustainable Agriculture Facility field day, and the California Department of Food and Agriculture Fertilizer Research and Education Program annual meeting, Western Plant Health Association annual meeting and the Soil science Society of America annual meeting). Results were also presented to the California Air Resource Board Agriculture Technical Committee monthly meeting where stakeholders from the agriculture industry (commodity groups, regional water and air boards, etc.) hold monthly meetings. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?A graduate student researcher (Jordan Wade) is currently completing the project and is assisted by two undergraduate assistants. The undergraduate assistants were involved in all aspects of the project. Jordan is now a PhD student at the Ohio State University. How have the results been disseminated to communities of interest?Mineralizable C is currently being promoted for use in commercial test labs as an indicator of soil health. Previous studies have often focused on a narrow range of soils in a given study or have examined simple linear relationships of mineralizable C with other variables, obscuring the potential discrepancies in absolute values that can be obtained using this metric. This project was successful at increasing the understanding of the myriad of intertwined factors that surround the prediction of N mineralization with the results now published in scientific journals. The use of soil respiration to predict N mineralization has recently gained traction in both public and private sector. Throughout presentations and interactions with industry and research, many have expressed gratitude that the claims are being rigorously tested. One of the main takeaways for many growers that have been at outreach events is that their soil has an innate ability to supply a considerable amount of N to their crops that they are likely not accounting for. Additionally, this study provides information about the range of expected values for N mineralization, which can provide rough estimates to be integrated into current Nutrient Management Planning. The current study did not examine interactions that can occur between N mineralization and fertilizer application rates, but future studies can build on our current findings to integrate this vital missing information. With the integration of this final piece, growers can begin to confidently reduce their N fertilization rates to account for in season soil N mineralization, which can lead to potential increases in profitability as well as mitigating any adverse environmental effects of reactive N loss to the environment. Although the current study only begins to explore the economic viability of supplying soil tests to growers to assess in season soil N mineralization, our hope is to provide a basis for future studies to develop more rigorous tests and economics to examine profitability in a way that is easily translatable to growers' needs. What do you plan to do during the next reporting period to accomplish the goals?The next phase of research to meet project objectives will examine the contribution of organic amendments to increase soil nitrogen (N) mineralization potential. The use of organic fertilizer materials with a certified nutrient analysis for crop production is problematic due to inconsistencies in nutrient availability, especially N. Knowledge of nutrient values of these organic soil amendments is limited because the nutrients from these sources are gradually released into soils in plant available forms and may be temporally tied up in soil microorganisms or organic matter. The consistency of some of the organic based fertilizer varies annually depending on the quality and availability of fertilizer materials, such as manures, fish by-products, food processing waste, etc. Therefore, predicting nutrient release from organic based fertilizers is challenging resulting in a dearth of information available to make consistent informed nutrient management decisions. Organic based fertilizers, with lower carbon to nitrogen ratios, likely have higher nutrient value than high C to N materials such as greenwaste composts. However, relying on C to N ratio alone has shown inconsistent result. Composts for example have low C to N ratios but low N availability. There is a general lack of reliable predictions of nutrient release from organic sources in California's soils and climate. The nutrient value of annually applied organic fertilizer amendments likely provides a more consistent nitrogen mineralization response than sporadic applications. However, running field experiments to determine the accumulative nitrogen mineralization response from annual application of organic soil amendments across different cropping systems and soils is impractical without a large study that first incorporates the response of organic fertilizer amendments and soils from various regions. This project proposes to combine lab incubation with predictive modeling to evaluate the use of organic fertilizer amendments applied on an annual basis to provide guidelines for reassessing nitrogen fertilizer inputs across a variety of crops. The information is necessary to avoid over loading of N that can lead to N losses through greenhouse gas emissions and leaching to groundwater. The uses of organic fertilizer amendments also add to potential soil carbon sequestration and thereby likely improve soil productivity and healthy soil. Therefore, this project is important to informing policies and management guidelines that promote and embody the intent of the Healthy Soils Initiative. Objectives. The overarching objective is to provide baseline data to inform nitrogen management plans where organic amendments are used in agricultural production areas. Specific project objectives are: 1) Conduct an extensive literature review on soil N and organic N fertilizers; 2) characterize the temperature response of N mineralization of organic based fertilizers in soils of the major agriculture production areas; 3) incorporate temperature response and N mineralization kinetics and turnover rates in the the DayCent model to predict long-term N availability; 4) Conduct field trials to confirm lab and DayCent model results and to inform the Comet-Farm modeling tools; and 5) conduct extensive engagement and outreach to inform on the value and to reassess organic fertilizer amendment rates to avoid N loss and promote healthy soils.

Impacts
What was accomplished under these goals? Mineralizable carbon (C) is respired upon the rewetting of dried soil, and has been proposed as a metric of soil health, but the metric still lacks a standardized protocol and validation. A standardized protocol is an essential first step in quality control needed for a robust soil test. The development of commercially viable soil health testing focused on biological properties is needed for improving the sustainability of our agricultural production systems. The burst of respiration on rewetting of air-dried soil, commonly referred to as "the Birch effect", hereafter referred to as 'mineralizable C', is a potentially valuable tool in helping growers better understand the role of soil microbial biomass in their soils. Mineralizable C has been proposed as an important metric of overall health and quality of a soil. We examined numerous sources of laboratory variability associated with mineralizable C, with the overall goal of understanding the influence of each source variability to determine whether this test is robust enough for adoption by the soil test industry. Our analysis included soil from eight studies on 72 agricultural cropland sites from across the United States. In addition to traditional soil measurements, mineralizable C was measured using permutations of soil processing and rewetting protocols (n = 1142 individual observations) to determine the sources of variation associated with these procedures (sieve size, water content, direction of rewetting). Additionally, selected studies were used to determine the analytical and inter-laboratory variability associated with measurements of mineralizable C. Similar to other soil measurements, mineralizable C has multiple sources of variability: spatial, temporal and analytical. Mineralizable C had a twofold to 20-fold greater inter-laboratory variability than other commonly used soil tests, leading to a high degree of uncertainty associated with the interpretation of results. Procedural differences--such as sieve size and the method of rewetting--significantly influenced measurements of mineralizable C and underscore the need for the development of a standardized and universally adopted protocol. Capillary rewetting consistently suppressed mineralizable C relative to rewetting with a specific amount of water and is therefore is not a recommended approach. However, the sensitivity of mineralizable C to changes in management did not differ among incubation intervals of 6, 24, and 72 h. However, our findings show these sources of variability are soil-specific and may be a substantial hurdle to a repeatable measurement of mineralizable C and to its utility as a robust soil health metric. We used a conservative Type II ANOVA to determine effect sizes, suggesting that the potentially confounding effects are even greater when more liberal analyses are performed. Several in situ studies of respiration have found that samples sizes of up to 75 separate samples are needed to achieve 95% confidence in values ±10% of a population mean to account for these multiple sources of variability. In our study, the analytical variability is exemplified in the lack of statistical differences at the 95% confidence level between the means of 25% WHC (284.0 mg CO2-C kg−1 soil) and 50% WHC (444.2 mg CO2-C kg−1 soil) in soils sampled from one site, despite a 56% increase in mean mineralizable C measured. While these procedural effects may influence inter-laboratory variability, there was also a considerable amount of analytical variability associated with mineralizable C measurements within a laboratory that is highly dependent on soil type. In a commercial setting, this analytical variability can result in unreliable and/or inconsistent recommendations when using a single measurement. If additional analytical replicates were to be suggested, this would increase the cost of analysis and may serve as a financial barrier for growers.

Publications

• Type: Journal Articles Status: Published Year Published: 2017 Citation: Burger, Martin, Matthew R Dumlao, Juan Wang, Barzin A Moradi, William R Horwath, Wendy K Silk. 2017. Cover Crop Development Related to Nitrate Uptake and Cumulative Temperature. Crop Science doi:10.2135/cropsci2016.09.0741.
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Wade, J., W. R. Horwath, M. B. Burger. 2016. Integrating Soil Biological and Chemical Indices to Predict Net Nitrogen Mineralization across California Agricultural Systems. Soil Science Society of America Journal. 80: 1675-1687.
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Wade, J., S. W. Culman, T. T. Hurisso, R. O. Miller, L. Baker, W. R. Horwath. 2017. Sources of Variability that Compromise Mineralizable Carbon as a Soil Health Indicator. Soil Science Society of America Journal. doi:10.2136/sssaj2017.03.0105