The Root of the Matter – Are Changes in Corn Root Morphology Responsible for Improved Yield and Higher Nitrogen Use Efficiency in Diversified Cropping Systems?

Date: 
Aug 2019

Issue

There is an important need to develop sustainable alternatives to the corn-soybean cropping system that dominates the upper Midwest, as evidenced by recurring problems with water quality, susceptibility to weather extremes and low profitability. Many of the shortcomings of the existing corn-soybean system are due to its sole reliance on short-season annual crops and the exclusion of deep-rooted perennial crops like alfalfa that provide long periods of living cover. The Iowa Nutrient Reduction Strategy noted that "extended rotations" can reduce both applications of nitrogen (N) inputs and undesired N discharges to the environment.

Objective

Researchers will investigate mechanisms whereby extending a corn-soybean rotation with small grain and legume forage crops can simultaneously increase corn yield and N-use efficiency. We expect that soil resistance to corn root penetration will be lower, corn root systems will be larger and deeper, and the rate of potential N mineralization from soil organic matter will be greater for corn following alfalfa than following soybean. Empirical data from these research plots will be used within the Agricultural Production Systems Simulator model (APSIM), which can assess the impact of various soil, climate and crop management factors on crop productivity, nitrate leaching and nitrous oxide emissions to the atmosphere. Insights from this project will inform strategies promoting higher agronomic productivity, greater N use efficiency and lower potential for N discharges to water and air. This project will use findings to parameterize a widely used crop growth model, the Agricultural Production Systems sIMulator (APSIM).

Approach

We will measure soil physical properties, corn root architecture, soil N dynamics, and corn performance in a long-term experiment in Boone County, Iowa, that includes a two-year corn-soybean rotation and a four-year corn-soybean-oat/alfalfa-alfalfa rotation. Data will be analyzed with linear mixed-effects models and non-linear regression techniques to evaluate the effects of rotation system and time since planting on corn shoot mass, N uptake and root mass and depth of soil penetration. Root front velocity, maximum root depth, root mass and specific root length (root length per unit of root mass) will be used in the APSIM model to evaluate corn growth and yield, and N discharges from soil, in the contrasting rotation systems.

We will produce scientific publications and conduct outreach activities to share information about the effects of extended rotations on corn root growth, yield and water quality.