Fertilizer Nitrogen Dynamics in Inbred Seed Corn (Zea mays L.): Yield Response, Utilization and Residual Effects in Southwestern Ontario

Abstract

Inbred seed corn (Zea mays L.) production in Southwestern Ontario benefits from favorable agro-climatic conditions but faces critical challenges in fertilizer nitrogen (FN) management. The objective of this dissertation was to establish a regional FN recommendation for inbred seed corn through accessing yield response, uptake, distribution and fate of FN in the soil-plant system using a three-study approach. The first study evaluated 46 inbreds from 2015 to 2018 across 13 site-years. Significant variability was observed, with 27 inbreds demonstrating quadratic marketable yield responses to FN, with an agronomic optimum N rate (AONR) ranging from 115 to 210 kg N ha⁻¹. When AONR data pooled by sites, regardless of responsiveness, an overall AONR was 162 kg N ha⁻¹, providing a regionally relevant benchmark recommendation for seed corn production in Southwestern Ontario (i.e. the Southwestern Ontario FN recommendation). However, applications of 180 kg N ha⁻¹ significantly increased residual soil inorganic N (70 kg N ha⁻¹), identifying a threshold for environmental risk. The second study used 15N-labeled FN in microplots on loamy sand and loam soils to track the fate of FN. Findings showed that FN uptake was more heavily influenced by soil type than inbreds, with grain N content being 22% higher in loamy sand than the loam soil. Notably, 25% of applied FN was immobilized in soil organic pool, while 12 to 30% was unaccounted for by harvest depending on soil type. The third study used residue exchange approach to assess the fate of residual FN. Results confirmed that residual FN is an insignificant N source, contributing only 1 to 3 kg N ha⁻¹ to spring wheat (Triticum aestivum L.) uptake, while up to 50 kg N ha⁻¹ was unaccounted for and presumed lost during the non-growing season. Together, these findings demonstrate that a single fixed FN rate cannot adequately account for the high variability in inbred response. To enhance both sustainability and productivity, future management should adopt the 4R Nutrient Stewardship framework to refine nitrogen applications