Rotational Effects of Legumes and Non‐Legumes on Hybrid Canola and Malting Barley

Abstract

High costs of fertilizer in western Canada have generated interest in alternative N sources. Legumes produce N through fixation, and may increase soil residual and mineralizable N, thus reducing the need for fertilizer N in subsequent crops. Hybrid canola (Brassica napus L.) has a high N requirement for optimum yield, but knowledge of rotational effects of legumes on canola is limited. The objective was to determine the effects of legume and non-legume preceding crops on yield and quality of canola grown the following year and malting barley (Hordeum vulgare L.) grown after canola. Field pea (Pisum sativum L.), lentil (Lens culinaris Medik.), faba bean (Vicia faba L.), canola, and wheat (Triticum aestivum L.) harvested for grain, and faba bean grown as a green manure were direct-seeded at seven locations in 2009. Canola was seeded in 2010 and barley in 2011, with fertilizer N applied at 0, 30, 60, 90, and 120 kg ha -1 . On average, all legumes, except faba bean for seed, produced higher canola and barley yields than when wheat was the preceding crop. Faba bean green manure produced the highest yields, while canola on canola produced the lowest canola yield. The legumes had little negative effect on canola oil or barley protein concentration. Yields of both crops increased with increasing N rate, but canola oil concentration decreased, and barley protein increased. The results indicate that growing legumes for seed before hybrid canola can improve canola and subsequent barley yield without negatively affecting canola oil or malting barley protein.

Canola cultivar mixtures and rotations do not mitigate the negative impacts of continuous canola

“…In general, our study confirms other reports of greater canola yields when canola follows other crops (Harker et al , 2015Kutcher et al 2013;O'Donovan et al 2014). Although field peas are capable of providing nitrogen benefits to crops 2 yr after their growth , it is not likely that the observed rotation benefit in the current study was nitrogen-related since our peaÁwheatÁcanola rotation (trt.…”

“…In addition, canola is likely to be grown in high-frequency rotations. From a yield reduction and pest infestation standpoint, the agronomic risks of growing canola in high-frequency rotations can be considerable (Krupinsky et al 2002;Johnston et al 2005;Dosdall et al 2012;Harker et al 2012Harker et al , 2015Khakbazan et al 2014;O'Donovan et al 2014).…”

Canola rotation frequency impacts canola yield and associated pest species

“…These results are consistent with many other studies suggesting canola yield improvements with increased rotational diversity (Christen and Sieling 1995;Sieling et al 1997;Krupinsky et al 2002;Guo et al 2005;Johnston et al 2005;Dosdall et al 2012;Harker et al 2012;Manitoba Management Plus Program 2014;O'Donovan et al 2014). However, results from other studies were not always definitive as the years between canola crops increased.…”

“…Interestingly, in short-term studies, where only the year prior to canola is considered, the consistent result is that canola yields are always better when they are preceded by a crop other than canola (Johnston et al 2005;Harker et al 2012;Manitoba Management Plus Program 2014;O'Donovan et al 2014). In longer-term studies, the effect is similar, but less consistent.…”

“…Furthermore, canola is likely to be grown in rotations at higher frequencies than ever before. From a yield reduction and pest infestation standpoint, the agronomic risks of growing canola in short crop rotations can be considerable (Krupinsky et al 2002;Johnston et al 2005;Dosdall et al 2012;Harker et al 2012;O'Donovan et al 2014).…”