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