Location: Soybean and Nitrogen Fixation Research
Project Number: 6070-21220-070-083-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Oct 1, 2025
End Date: Sep 30, 2026
Objective:
This project aims to develop soybean genotypes capable of maintaining high yields under reduced fertilizer inputs, contributing to the broader goals of sustainable agriculture. Successful outcomes will lead to the identification and development of soybean lines that can thrive in low-input environments while minimizing the need for costly and environmentally impactful fertilizer applications. The project's focus will be on improving nitrogen use efficiency (NUE) and evaluating traits such as salt tolerance, petiole ureide concentration, and root growth, which influence productivity under reduced nutrient availability.
Objectives to which ARS investigator will contribute:
1. Identify soybean germplasm lines capable of maintaining high yields under reduced fertilizer input. This objective focuses on identifying soybean lines that can sustain high yields while requiring fewer fertilizer inputs. Special emphasis will be placed on lines with enhanced nitrogen use efficiency (NUE), improved nodule formation, and higher nitrogen fixation capacity, which can reduce input costs without compromising yield. This will be the foundational step in developing low-input, high-yielding soybean cultivars for future release.
2. Data on the influence of nodulation and ureide petiole concentration on yield under varying fertilizer inputs. We will collect data on growth parameters, nodulation, and ureide petiole concentration from identified germplasm lines under different fertilizer treatments in both greenhouse and field conditions. By better understanding the relationship between nitrogen fixation, nodulation, and agronomic traits, we can improve breeding strategies for developing soybeans that thrive under reduced fertilizer use, promoting sustainable agricultural practices.
Approach:
1). In 2026, we will conduct replicated field trials using lines selected based on performance in 2025 greenhouse experiments, advanced breeding lines, and commercial checks. The trials will be designed to compare yield, seed oil content, protein content, and agronomic characteristics such as plant height, disease resistance, and maturity.
Soil samples will be taken before planting and at maturity to estimate nitrogen use by each genotype. The primary objective is to evaluate how super-nodulating and intermediate super-nodulating lines perform under varying levels of fertilization, including non-fertilized, rain-fed, and irrigated conditions. These trials will include comparisons with current high-yielding commercial lines and a non-nodulating check to assess the relative contributions of nodulation capacity and fertilizer inputs on yield.
Additionally, wild soybean-derived breeding lines, which have shown improved nitrogen use efficiency (NUE) and reduced growth reduction under low nitrogen (N), will be included in the trials to evaluate their yield performance and NUE characteristics. The objective is to identify wild soybean-derived lines that not only maintain high yields under low fertilizer conditions but also exhibit enhanced resilience to environmental stress.
2). In collaboration with ongoing greenhouse trials, we will evaluate advanced breeding lines with enhanced nodulation capacity across a range of nutrient conditions. These lines, derived from crosses between super-nodulating lines and high-performance cultivars, will be tested under three levels of di-ammonium phosphate (DAP), potash, and nitrogen fertilizer (0, 135, and 270 kg/ha). Each treatment will be evenly applied by hand at planting, the second vegetative growth stage (V2), and the second reproductive growth stage (R2). Greenhouse trials will be conducted under controlled conditions to minimize variability and establish consistent treatment effects.
Nitrogen fixation will be measured via isotope analysis of leaf tissue, and changes in nodulation and root mass will be measured in comparison to commercial checks. Key variables like root mass, total root length, and root surface area will be evaluated using imaging and root washing techniques.
A critical aspect of this objective will be investigating the impact of petiole ureide concentrations, a known indicator of nitrogen fixation efficiency. We will evaluate how ureide concentrations correlate with nitrogen application rates and yield under different fertilizer regimes. This will be done using PIs with varying levels of petiole ureide concentrations (1.44 to 106.4 µmol/g). Understanding these relationships will help identify breeding lines with optimized nitrogen fixation capacity, leading to more efficient fertilizer use under low input systems.