Quantifying soil nitrogen dynamics in manured fields
- Sotirios Archontoulis
- Marshall McDaniel
- Peter Kyveryga
- Scott Nelson
Issue
Improved understanding of soil nitrogen dynamics in manured cropping systems is imperative in developing better recommendation systems that maximize productivity while protecting natural resources. Today there is large uncertainty in estimating manure N availability for crop N uptake.
Objective
The goal of this project is to enhance our understanding on soil N dynamics in manured fields via field experimentation and simulation modeling. Our objectives are:
1. Quantify soil N temporal dynamics in 30 manured fields across Iowa over two years (via field sampling) and subsequent years (via APSIM modeling).
2. Determine soil N immobilization/mineralization patterns and crop N availability from different manure sources and application timings.
Approach
Researchers will use the Agricultural Production Systems sIMulator (APSIM), a well-calibrated cropping systems model for Iowa, to perform a regional scale systems analysis (4,000 fields). The model will be driven by weather, soil and management databases that include tile drainage in the landscape, synthetic and organic N fertilizer by county and by year, annual changes in planting densities, cultivars and planting dates.
Specifically : Manure and soil samples will be collected from 15 farmers’ fields per year in November, March, April, June, July, August and immediately after harvest. The fields will be selected from a pool of Iowa Soybean Association (ISA) farmer participants and will cover different geographies within Iowa and capture different production practices and manure types. Additionally, at the ISU Boone Agronomy Farm, a series of manure N mineralization experiments will be established. These experiments will use in-situ, buried PVC cores that simulate field conditions but have benefits of a controlled laboratory experiment
Project Update
October 2025
During this reporting period, we finalized analysis of the lab incubation study and developed a master's thesis. We found significant and complex interactions between manure source, application rate and soil on net N mineralization. Across all three N forms (NH4+-N, NO3- -N and TIN), manure source and rate were the most influential factors, with additional significant two-way (source x rate, source x soil and rate x soil) and three-way (source x rate x soil) interactions. These findings highlight that N mineralization was not uniform across soils, and treatment effects depended on context.
In both soils, ammonium (NH4+-N) concentrations following beef manure application remained relatively low compared to other manure types. Total Inorganic N (TIN [NH4+-N + NO3—N]) concentrations in the beef manure treatments were consistently the lowest among all manure types. In both soils used, ammonium (NH4+-N) concentrations in the swine manure treatments showed moderate increases early in the incubation. Total Inorganic N (TIN) trends reflected the combined effects of NH4+-N and NO3- -N, with high swine-producing sustained increases in both soil. Ammonium (NH4+-N) concentrations in the turkey manure treatments showed the most pronounced increases of all manure types. In the loamy sand, the high turkey treatment peaked sharply around 424 mg kg-1 in the first 7 days before gradually declining to under 100 mg kg-1 by day 35. Nitrate (NO3--N) dynamics in the turkey treatments showed a delayed accumulation following NH4+-N peaks, especially at high application rates. Total Inorganic N (TIN) was highest in the turkey manure treatments, particularly at the high application rate. These findings highlight that turkey manure, especially at high application rates, drives the strongest net N mineralization response in both soils.
Related Activities and Accomplishments
2 presentations
1 MS Thesis: Nitrogen Mineralization from Manure: Insights from Laboratory Incubation and Field Studies, by Michael Lee Cook
July 2024
In this reporting period, we initiated the lab incubation experiment. We used two soils, a Clarion clay loam (mesic Typic Hapludoll) and a Sparta loamy sand (mesic Entic Hapludoll). We used manure from three animal operations: turkey litter, beef pack manure and liquid swine manure. The manures were collected from local livestock operations and were stored at 4°C in sealed containers.
For the incubation experiment, 10.00 g (±0.01 g) of each soil type was weighed into 150-mL clear Nalgene bottles. A control treatment was established for each soil with no manure added. For each manure, a low and a high application rate were established to simulate typical field application rates, with a control group having no manure to serve as a baseline. The turkey litter manure was applied to each soil at a rate equivalent to 12 Mg ha⁻¹ for the low rate and 47.4Mg ha⁻¹ for the high rate. The liquid swine manure was applied at a rate of 22.8 Mg ha⁻¹ and 96.6 Mg ha⁻¹ for the low and high rates, respectively. The beef pack manure was used at a rate of 5.4 Mg ha⁻¹ at the low rate and 22.8 Mg ha⁻¹ at the high rate. Each treatment had four replicates, resulting in 28 samples per soil per time point. The incubation timeline established included nine sampling points: days 0, 7, 14, 21, 35, 49, 63, 77, and 91. At each time point, the replicate samples for all of the seven treatments were destructively sampled for salt-extractable inorganic nitrogen.
Related Activities and Accomplishments
1 presentation
December 2023
Researchers continued collecting soil samples from the field research site throughout the growing season. The soils were extracted for nitrogen content allowing a time-series representation of mineralization patterns over the growing season. This was partnered with data collected from commercial growers and a similar time-series was created using nitrogen content readings to present mineralization patterns.
The team carried out a laboratory incubation testing manure nitrogen mineralization.
Related Activities and Accomplishments
1 Field day: Presented the information at a field-day tour of the research site in Boone County.
2 Presentations, including presented information regarding the overall goals of the project along with preliminary field mineralization data at the Tri-Societies conference in St. Louis in the fall.
1 Workshop
December 2022
During July-Dec., 2022, data collection continued from the on-farm experiments (with and without manure) spread across the state of Iowa and also from the Layers experiment. Project meetings were held to review the initial results from the on-farm experiments and discuss plans for the “mineralization” experiments. This is particularly important as the N supply capacity of different manure types will be estimated. The lab incubation experiment will be initiated (nearly 1,000 cores) to measure mineralization from different manure types.
Other activities included one field day.
June 2022
During Jan to June, 2022, researchers collected soil samples for nitrate analysis from on-farm experiments (with and without manure) spread across the state of Iowa. Also, the team identified a nearby to ISU campus field experiment (Layers) with different types of manure and drainage infrastructure and in this location, were able to take biweekly soil samples for nitrate analysis and also plant samples to estimate the crop N uptake as affected by manure treatments.