Quantifying soil nitrogen dynamics in manured fields

Aug 2021


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.


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.


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 Updates

Note: Project reports published on the INRC website are often revised from researchers' original reports to increase consistency.

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, included:
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.