Long-term no-till increases soil nitrogen mineralization but does not affect optimal corn nitrogen fertilization practices relative to inversion tillage

Abstract

No-till management is a proven practice for increasing soil organic matter in many environments. By increasing soil organic matter, no-till may increase soil N mineralization, potentially reducing crop demand for N fertilizer relative to inversion tillage. In this study, we hypothesized that, relative to inversion tillage (moldboard plowing), long-term no-till would: i) increase total N stocks, ii) increase mineralized N during the growing season, iii) increase grain yield and N uptake, and iv) reduce reliance of corn (Zea mays L.) on N fertilizer inputs. We tested these hypotheses in a long-term, continuous corn tillage and fertilizer N rate study located in Lexington, KY. We measured the total soil N and potentially mineralizable N after 48 years, the in situ mineralized N and N uptake during two corn seasons (2018–2019), and the corn grain yield for five seasons (2015–2019). We evaluated the effect of no-till on N fertilizer reliance in two ways – the first was by measuring the agronomic optimum N rate of corn in the two tillage systems, and the second was by measuring the corn yield response to late N fertilization timing in the two tillage systems. We found that the no-till system had 1000 kg N ha−1 greater total soil N stocks in the top 20 cm, mineralized 65 kg ha−1 more N during corn growth, and resulted in 22−71 kg N ha−1 and 780−1800 kg ha−1 greater N uptake and grain yield across N rates, respectively, than the plowed system. The agronomic optimum N rate (AONR) did not differ among tillage treatments, potentially because the no-till treatment yielded more and thus demanded more N. Although corn yield responded to the late N fertilization treatment, the response was similar in both the no-till and plowed treatments. We conclude that long-term no-till increases soil N mineralization and corn yield relative to inversion tillage, with minimal effect on the AONR or optimal timing of N fertilizer application.