A Systems Approach for Estimating Plant Available Nitrogen from Organic Materials and Fertilizers

A Systems Approach for Estimating Plant Available Nitrogen from Organic Materials and Fertilizers

Summary

Laboratory measurements of potentially mineralizable N expressed as % of total applied N averaged -1.3% for 11 composts, 37% for 15 poultry litters, and 50% for 25 commercial organic fertilizers. Within each group there was large variability in potentially mineralizable N, which emphasized the need for a fast method for estimating mineralizable N. Near infrared spectroscopy was used to scan the different materials and develop a calibration for mineralizable N.

Objectives/Performance Targets

Objective 1. Determine potentially mineralizable N and rates of N mineralization for 51 organic materials (manures, composts, other organic fertilizers), and determine the effect of soil texture on N mineralization rates of organic materials.

Objective 2. Calibrate NIRS/VNIRS to estimate mineralizable N and rates of N mineralization for 51 organic materials.

Objective 3. Develop a web-based calculator for potentially available N (PAN) that allows producers to calculate PAN over the growing season as a function of local weather and soil conditions.

Objective 4. Collect PAN data from plots at the UGA farm and at cooperating farms, and use the data to calibrate and validate the PAN calculator.   

Objective 5. Disseminate the N mineralization data, availability of the NIRS/VNIRS analysis for organic materials, and web-based PAN calculator to the public, farmers, and extension agents.

Accomplishments/Milestones

The accomplishments and milestones completed in the first year of this grant are on track with our proposed grant timeline.  In April 2016, the postdoctoral researcher was hired and organic materials and supplies were gathered for both the field experiment and laboratory experiments.  Progress has been made towards each of the main objectives listed above.

Objective 1. To better estimate potentially mineralizable N from a wide variety of organic certified materials, a 100-d incubation experiment was conducted from August to November 2016.  For the study, 51 different organic materials (25 commercially available fertilizers, 15 poultry litters and 11 composts) were collected.  Materials were added to a soil at a rate estimated to supply 150 lbs per acre of plant available N and N mineralization was measured over the duration of the experiment.  Samples from this experiment have been analyzed for nitrate and ammonium, which allowed for the calculation of mineralizable N available from these materials.  A similar study determining the effect of soil texture on nitrogen mineralization (objective 1) was begun January 2017 and will be completed April 2017.  This study uses five different soils collected across the state of Georgia and three materials (feather meal, Nature Safe Fertilizer, and poultry litter). 

 Objective 2.  In addition to measuring the potentially mineralizable N of these 51 organic materials, materials were analyzed for initial characteristics such as inorganic N, total N, total C, and other elements such as phosphorus, potassium, and metals.   These materials have been prepared/scanned for NIRS analysis and results are in the process of being used to calibrate NIRS for initial material characteristics.  Once the determination of the rate and pool of potentially mineralizable N is available, these data will also be calibrated and validated against NIRS scans.  In addition to NIRS scans, materials will be scanned later this year with a portable visible-NIRS scanner (VNIRS) to determine any potential calibrations with initial material characteristics and potentially mineralizable N rates and pools.

Objective 3.  Laboratory data, field data, and NIRS scans will be used for the development of the web-based PAN calculator throughout the timeline of this grant.  In preparation of the web-based PAN calculator, a mock-up of the calculator has been created online (aesl.ces.uga.edu/Calculators/Nitrogen).  The purpose of the mock-up calculator is to aid in the creation of a user-friendly interface and results.  Using the mock-up, we have been gathering feedback on the look, needed inputs, and how to best present the results for farmer use.  An informal survey was conducted at the Georgia Organics 2017 to gather information on the mock-up calculator.  Additionally, our cooperating farmers have been giving input on the development of this calculator.  Data collected on the interface will be used to better determine how to present the inputs and results of the calculator as the calculator is created. 

Objective 4.  During 2016, field trials were conducted at Emory Oxford Farm and the UGA Horticulture Farm to determine N mineralization rates under field conditions (objective 4).  Field trials were conducted for both tomatoes (summer season) and broccoli (fall season).  At the Emory Oxford Farm, the fertilizer was selected by the farmer (feather meal for tomatoes and Symphony for broccoli) and a 100-ft row was used for this experiment.  Half of the experimental row received the application of fertilizer, while the other half remained unfertilized as a control.  In-situ N mineralization cores were installed after planting and were removed approximately every two weeks (in total 13 weeks for tomatoes and 10 weeks for broccoli).  A weather station installed on-farm was used to collect soil water content, soil temperature, air temperature, precipitation, and humidity.  Plant health was measured every two weeks (height, width, flowering, and fruit) and yield was recorded by our participating farmer.  Mineralization data have been completed for the tomato season and is currently being analyzed for nitrate and ammonium for the broccoli 2016 season.

A similar but larger scale experiment was conducted simultaneously at the University of Georgia Horticulture Farm in 2016.  For this experiment, nine treatments (feather meal, blood meal, fish meal, Symphony, Perdue Microstart, poultry litter, compost, sodium nitrate, and no fertilizer) were applied in a randomized complete block design with three replications to plots 50 ft x 65 ft and tomatoes and broccoli were grown.  In-situ N mineralization cores were installed in each plot, collected every two weeks, and an onsite weather station collected local weather conditions as listed above.  In addition to plant health characteristics being measuring every two weeks, chlorophyll and the plant canopy (Crop Circle) were measured.  Each harvest (9 for tomatoes and 5 for broccoli) was measured by plot and marketability and yield were determined.  Additionally fruit and vegetable characteristics (size, dry matter, and quality) were determined.  In-situ N mineralization data have been analyzed for the tomatoes and are in in the process of being analyzed for broccoli.  These studies will be repeated for both tomato and broccoli in 2017 on the Emory at Oxford Farm and the UGA Horticulture farm.  Additionally, the other cooperating farms will be added to 2017 to determine N mineralization rates with farmer chosen fertilizers for tomato and broccoli crops.  Data from these studies are currently being analyzed and prepared for the development of the model and publications.   

Objective 5.  Dissemination of the data and information about the creation of the calculator (objective 5) has occurred throughout the study.  Additionally, we have used our cooperating farmer team to ensure that the experiments conducted reflect materials and practices commonly used in the Southeast for certified organic vegetable farming.  During on-farm meetings with cooperating farmers (October/November 2015 and June 2016), input was gathered on the 51 materials used in the laboratory study, irrigation and fertilizer practices, and common cultivars of broccoli and tomatoes used.  As stated above, cooperating farmer input has been used for the creation of calculator interface and results.  During the next two years of this project, cooperating farmer meetings will continue.  Both Emory at Oxford Farms and Cedar Grove Farm have been visited this year (Feb 2017) and have given input on data collected and the creation of the calculator.  Future meetings for suggestions on the calculator are scheduled with Dayspring Farm and Front Field Farm  

Impacts and Contributions/Outcomes

The purpose of this project is to develop a web-based plant available nitrogen (PAN) calculator to predict field-available N from the addition of organic materials used in organic vegetable production. The availability of such a tool will help organic farmers address better N management, aid in synchronizing PAN release with plant uptake, reduce farmer costs and environmental degradation, and lead to increased sustainability in these systems. This project will address the need for a rapid estimation of PAN from organic materials available in the Southeastern United States, will create a user-friendly PAN calculator, and will conduct outreach activities to improve this calculator and ensure its use by producers.

Preliminary results from our 100-d laboratory study, has shown both immobilization of soil N and mineralization after application of 51 different materials.  Potentially mineralizable N measured in 11 different composts averaged -1.3% of the total N applied, showing that N immobilization occurred with many of the applied composts.   In contrast, potentially mineralizable N averaged 37% of the total N applied for 15 poultry litters, and 50% for commercially available organic fertilizers.  The range of N mineralization found in this laboratory study demonstrates the need for rapid estimations of potentially mineralizable N.  The use of NIRS/VISNIRS in this project will help with the rapid estimation N supplied from organic materials.  On farm experiments showed the amount of N mineralized from different materials under field conditions and that N mineralization from the soil organic matter may contribute significant N in organically managed soils (which are often intensively cover cropped).  Further analysis and the continuation of on-farm experiments will allow for the calibration and validation of the PAN calculator which will be made available to the public. 

Preliminary results, experimental design, and information about the creation of the calculator have been shared with the public.    The field experiment was highlighted at the UGA Research Farm Twilight Farm Tour (July 2017) where the public was invited to tour the tomato research plots and the tour was described by the Athens Banner Herald (http://onlineathens.com/mobile/2016-07-17/uga-opens-oconee-farm-organic-tour).  Additionally, a handout was created to explain the need for the calculator.  Work collected at the Emory at Oxford farm summer project was presented as a poster by the undergraduate student worker at the Georgia Organics Conference.  Contacts were made with other farmers to get additional input on the calculator prior to launch and to spread the word about the calculator creation.  A brief handout was also made available at the UGA Sustainability Expo table at Georgia Organics to highlight the creation of the calculator and present preliminary laboratory results.  Progress of this project has been shared on the UGA Sustainability Facebook Page.  Sharing this information with farmers will continue as a major goal for this project.  Information will continue to be shared through on-farm tours, conferences, through farmer interaction, and the development of extension and scientific publications.

Collaborators: