Evaluation of nitrogen release of enhanced fertilizers in two different soil types through laboratory incubation and leaching studies

Authors: NAGARJU, VIDYA - Purdue University; CHATTERJEE, RYAN - Purdue University; GRAEF, RHONDA - Purdue University; Penn, Chad; WASSGREN, CARL - Purdue University; AMBROSE, KINGSLY - Purdue University

Submitted to: Journal of Agriculture and Food Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2025
Publication Date: 12/20/2025
Citation: Nagaraju, V., Chatterjee, R., Graef, R., Penn, C.J., Wassgren, C., Ambrose, K. 2025. Evaluation of nitrogen release of enhanced fertilizers in two different soil types through laboratory incubation and leaching studies. Journal of Agriculture and Food Research. https://doi.org/10.1016/j.jafr.2025.102602.
DOI: https://doi.org/10.1016/j.jafr.2025.102602

Interpretive Summary: Plants require more nitrogen (N) than any other nutrient. Crop yields are directly connected to N uptake. However, N does not stick to the soil very well and a significant portion of applied fertilizer N is lost through leaching. This loss of N spells trouble for both crop health and water quality, which impacts the health of people. Too much N in groundwater can cause the death of unborn and young babies by "blue baby syndrome". Too much N in surface waters also makes lakes and rivers turn green with algae blooms, like in Lake Erie, ruins fishing and tourism. All these problems cost the taxpayer and farmers money. As an alternative, a slow-release N fertilizer can slowly dole out the N as the plant needs it, which is like spoon feeding without having to stand there and actually feed it yourself. We formulated two different slow-release N fertilizers and tested how good and how fast they can release N. We started with regular urea N fertilizer and coated it with either a special organic gum compound, or with calcium sulfate (a naturally occurring mineral that promotes plant health). Both of the coated N fertilizers released N more slowly to the soil compared to the regular non-coated N fertilizer, but the one coated with calcium sulfate was better. This fertilizer shows strong promise to help cut some of the fertilizer costs on grain and vegetable farms, which increases income and prosperity of rural communities.

Technical Abstract: Nitrogen (N) release performance and leaching studies were performed on four urea-based fertilizer formulations: market urea, technical urea, a mixture of urea and gums, and a urea-gypsum cocrystal (URCASU). The urea/gums and URCASU fertilizer formulations were developed in an attempt to reduce the rapid dissolution of urea, thereby controlling nitrate leaching into groundwater and mitigating eutrophication issues. All fertilizer formulations were evaluated for N release performance in clay loam and silty loam soils. Nitrogen release was assessed through a 56-day laboratory soil incubation experiment, with measurements taken on days 1, 4, 7, 14, 28, and 56. On each sampling day, both organic and inorganic forms of N were measured. Two fertilizer placement methods were used: surface application and incorporation into the soil. In addition to N release experiments, flow-cell leaching studies were conducted on samples collected on day 14. The results from the soil incubation studies showed that both urea+gums and URCASU released N significantly more slowly than market urea. Pairwise comparison results indicated that URCASU released significantly less N than market urea in the clay loam fertilizer incorporated, silt loam fertilizer incorporated, and silty loam fertilizer placed on surface. Additionally, the urea+gums formulation performed significantly better than market urea in silt loam (incorporated). However, no significant difference in N release was observed between URCASU and the urea+gums treatment across both soil types and placement methods. In summary, the leaching studies demonstrate the slow release behavior of the enhanced urea formulations in both soil types tested in this study.