High nitrogen rates do not increase canola yield and may affect soil bacterial functioning

A - Papers appearing in refereed journals

Becker, F., MacLaren, C., Brink, C., Jabobs,K., le Roux, M. R. and Swanepoel, P. A. 2019. High nitrogen rates do not increase canola yield and may affect soil bacterial functioning. Agronomy Journal.

AuthorsBecker, F., MacLaren, C., Brink, C., Jabobs,K., le Roux, M. R. and Swanepoel, P. A.
Abstract

Nitrogen fertilization has a fundamental role in agricultural productivity. However, injudicious N applications to crops are common. It is important to ensure the minimum N required for satisfactory crop growth is applied but that excess amounts are avoided due to potential impacts on agroecosystem functioning. Nitrogen at 0, 60, and 150 kg ha-1 was applied as limestone ammonium nitrate to plots arranged in a randomized complete block design, on three farms to determine the impact of rate and temporal distribution of fertilizer on canola (Brassica napus L.) production in South Africa, and the effect of N fertilizer application on the composition and diversity of soil bacterial communities. The amount and distribution of N had only minor effects on canola growth (P < 0.05) and no effects on yield or harvest index. Splitting fertilizer into two or three applications throughout the season resulted in more mineral N available in the soil later in the season. Increasing the N rate from 60 to 150 kg ha-1 had a significant impact on bacterial community composition. The lower rate favored bacteria that are more able to break down N-containing carbon sources. No effects of fertilizer amount or distribution were observed on either N fixation potential (number of nifH gene copies) or bacterial community diversity. Overall, a low rate of N fertilizer split into multiple applications is recommended for canola production, as higher rates do not increase yield and may have a detrimental impact on soil carbon and nitrogen cycling.

Year of Publication2019
JournalAgronomy Journal
Digital Object Identifier (DOI)doi:0.2134/agronj2019.05.0359
Web address (URL)https://dl.sciencesocieties.org/publications/aj/first-look/pdf/agronj2019.05.0359.pdf
Open accessPublished as green open access
Accepted author manuscript
Copyright license
CC BY
Output statusE-publication ahead of print
Publication dates
Online03 Oct 2019
Publication process dates
Accepted01 Oct 2019
PublisherAmerican Society of Agronomy (ASA)
ISSN0002-1962

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