Assessing Nitrogen Limitation in Inoculated Soybean in Southern Brazil

Abstract

Soybean yield did not respond to low starter fertilizer N rates in soils with high organic matter content. Nitrogen limitation tended to be greater in low compared with medium‐high yield levels. Nitrogen limitation is potentially related to lower contribution of N coming from biological nitrogen fixation (BNF) and mineralization. Overcoming potential N limitation in soybean [Glycine max (L.) Merr.] is a critical factor for sustaining plant nutrient demand and improving productivity. Following this rationale, a set of studies were executed in southern Brazil with the goals of quantifying yield response to early season fertilizer N rates (up to 40 kg ha−1), “starter N fertilization,” and to understand if soybean seed yields are limited by N (testing a non‐limiting N scenario) when grown in soils with medium to high organic matter content. The main key outcomes of this research were: (i) starter N fertilization did not increase yields compared with non‐fertilized soybean, potentially highlighting the absence of an early season N limitation; and (ii) N limitation was observed when soybean yields were compared with non‐limiting N scenario and it tended to be greater in low compared with medium‐high yield levels, potentially connected with co‐limitations on both N sources (N2 fixation and mineralization) to satisfy soybean N demand. Producing soybean in a sustainable manner implies focus on production practices to conserve and, potentially, to increase soil organic matter on a long‐term basis. Furthermore, it requires enhancing the biological N2 fixation process for satisfying the large plant N demand for achieving high soybean yields. Future research should be focused on understanding factors governing biological N2 fixation and N mineralization processes in soybean grown in soils with medium‐high organic matter content.

Soybean profitability and yield component response to nitrogen fertilizer in Iowa

“…Many soybean N fertilizer trials highlighted that N‐limitation exist in soybean fields while cultivated under standard practices (particularly no‐N fertilizer addition) in high‐yielding environments. Thus, the aim to mitigate this N‐limitation and reinforced BNF is by the addition of N fertilizer, in some cases soon after planting to avoid affecting nodule formation (Abendroth, Elmore, & Ferguson, 2006; Ambrosini et al., 2019), others guided by additions at different soybean developmental stages (Haq & Mallarino, 2000, 2005; Schmitt, Lamb, Randall, Orf & Rehm, 2001; Cafaro La Menza, Monzon, Specht, & Grassini, 2017, 2019).…”